Evaluation of curcumin intake in reducing exercise-induced muscle damage in athletes: a systematic review

ABSTRACT

Background

Sports practice, particularly eccentric exercises, induces significant muscular changes, including muscle fiber injuries, strength loss, pain, and increased permeability of the muscle membrane. The duration of muscle recovery depends on factors such as exercise intensity and the specific muscle groups engaged. The inflammatory response plays a crucial role in muscle regeneration, involving various cell types. Curcumin, especially when its stability is enhanced through encapsulation, exhibits potent antioxidant and anti-inflammatory properties. Supplementing with curcumin can reduce muscle damage and inflammation caused by eccentric exercise, making it a potential remedy for athletes.

Objective

The objective of this systematic review is to assess the scientific evidence supporting the efficacy of curcumin in reducing muscle damage caused by sports.

Methods

A structured search in SCOPUS, Medline, and Web of Science databases was conducted in March 2023, including all available articles. The strategy involved selecting English articles without time constraints, using the search terms “curcumin” AND “Exercise-Induced Muscle Damage” (ALL(curcumin AND “Exercise-Induced Muscle Damage”)). Titles and abstracts were screened to assess eligibility. Studies were chosen based on PICOS criteria, and quality was evaluated using the reliable PEDro scale. The eligibility criteria included adults without any diagnosed diseases who regularly exercise (at least three times per week) and follow a consistent pattern of curcumin intake before, during, or after exercise.

Results

The comprehensive search identified 11 relevant studies investigating the effects of curcumin supplementation in sport-simulated interventions. These studies suggest that curcumin intake may help reduce muscle symptoms associated with eccentric exercises, thereby improving pain perception. Effective use of curcumin depends on factors such as dosage, bioavailability, and timing, with post-exercise ingestion appearing to be more beneficial.

Conclusions

Curcumin demonstrates a significant potential to relieve muscle-related symptoms, especially delayed-onset muscle soreness (DOMS) that arises from eccentric exercises, thus potentially improving the well-being of those who are trained. It also appears to have the capability to lower biomarkers associated with inflammation and boost antioxidant levels. Nevertheless, for future studies, the bioavailability of curcumin must be considered, as it is a key factor in its efficacy.

1. Introduction

1.1. Structural and functional changes during exercise

During exercise, myocytes undergo temporary structural changes that lead to diminished muscle strength and power, delayed onset muscle soreness, inflammation, restricted range of motion, and an extracellular (blood) increase in the levels of enzymes and myocellular proteins like creatine kinase (CK) or myoglobin [1–3]. The duration of muscle recovery relies on the severity of muscle damage and is influenced by various factors, including exercise intensity and duration, joint angle and muscle length, as well as the specific muscle groups engaged in the exercise [2,4,5].

The inflammatory response plays a crucial role in muscle recovery and regeneration following exercise [1]. It was revealed the involvement of various cell types, including neutrophils, macrophages, mast cells, eosinophils, CD8 regulatory lymphocytes, and T lymphocytes, in the process of muscle tissue regeneration [5]. Exercise, particularly eccentric exercises, induces significant muscular changes such as muscle fiber injuries, strength loss, pain, and increased permeability of the muscle membrane [6]. Two studies revealed alterations in the Z line after exercise completion and are primarily associated with eccentric muscle contractions [7,8].

A different research study demonstrates that the intensity of the inflammatory response can be influenced by various factors, including the novelty of the stimulus, the specific muscle group targeted, the mode of muscle activation, and individual differences [9]. In this study, instead of analyzing the vastus lateralis muscle, the focus was on the biceps brachii muscle since eccentric movements are less commonly performed in the upper extremities. As a result, the differences in the susceptibility to muscle damage might be associated with the use of muscles in daily activities [10]. The findings from this study revealed more pronounced alterations in the upper extremities, suggesting a potentially heightened inflammatory response in these muscles.

1.2. Muscle damage, pain, and adaptation

Minor alterations in muscle structure trigger an adaptive response mediated by cell signaling, whereas intense eccentric exercises have been found to increase the likelihood of a more severe inflammatory response in the muscles [6,11]. This statement is supported by the study carried out by Hamer et al [12]. Decreased muscle strength in the days following eccentric exercise is considered a reliable indicator of exercise-induced muscle damage [13]. In contrast, markers such as pain, creatine kinase concentration, or inflammation do not consistently correlate with evidence of muscle injury [14].

Moreover, the degree of strength loss serves as an indicator of the extent of histological damage [5,15]. Following eccentric exercise, muscle strength can decline up to 62% [16]. The severity of strength loss and the duration of recovery are generally influenced by the intensity and novelty of the stimulus [17]. Insights from animal models have shed light on certain molecular mechanisms underlying the decline in muscle mass. During eccentric movements, the tension exerted stretches the sarcomeres beyond the point of filament overlap, leading to their disruption [18]. Consequently, disrupted sarcomeres directly contribute to reduced force production, as well as an overload of membrane structures and T-tubules. This disruption triggers the opening of stretch-activated channels, resulting in increased membrane permeability and dysfunction in excitation-contraction coupling [19]. The subsequent entry of extracellular calcium through channels activated by stretch and membrane permeability, favors the decrease in muscle strength, because the degradation of contractile proteins or excitation-contraction coupling proteins is promoted by means of calcium-activated calpains [20].

The peak of pain occurs 24–72 hours post-exercise and typically subsides within 5–7 days. Delayed-onset muscle soreness does not consistently align with biopsy findings, exhibiting significant inter-individual variability in response to the same stimulus. Stated by Yu et al. [3] and Yoon et al. [21], muscle pain after exercise is caused by structural damage to muscles, disruptions in calcium homeostasis [22], and the sensitization of nerve endings. Research on mice has shown that muscle nociception (pain transmission) is facilitated by thin muscle afferent fibers (Aδ and C-fibers). Following eccentric exercise, these fibers exhibit increased sensitivity to mechanical stimulation, forming the neural foundation for mechanical hyperalgesia post-exercise. This heightened sensitivity in the nociceptive system indicates nerve sensitization, as noted by Mizumura K., et al. [23]. This concept is grounded in the study by Taguchi T., et al [24] who argued that unusual and strenuous exercise, particularly eccentric muscle actions, often leads to muscle tenderness, a form of mechanical hyperalgesia. Engaging in eccentric exercises promotes an elevation in muscle membrane permeability and the release of muscle-specific proteins into the bloodstream [6,25]. While various specific proteins have been identified as surrogate markers of muscle damage after eccentric exercise, such as creatine kinase, myoglobin, troponin, and myosin heavy chain, creatine kinase has gained the most prominence in scientific literature due to its ease of identification compared to other proteins and its low cost of assays to quantify it [26]. The magnitude and response of peak serum creatine kinase concentration can vary based on exercise type and the specific muscles involved. The prevailing hypothesis attributing the rise in membrane permeability implicates the activation of sodium and calcium channels, which are stimulated by stretching as evidenced by increased ion concentrations following eccentric exercise [6,19].

1.3. Chemical composition and properties of curcumin

Curcumin, derived from the turmeric plant (Curcuma longa L.), is a crystalline compound with a distinctive yellow-orange color. It was first isolated in 1815 and belongs to the diarylheptanoid chemical class. Structurally, it consists of two aromatic rings with two hydroxyl groups and two methoxy groups, as well as an unsaturated aliphatic carbon chain featuring carbonyl groups at C-3 and C-5 [27]. This hydrophobic and polyphenolic compound exhibits very limited solubility in water (11.0 ng/ml), undergoes significant metabolic transformation, and demonstrates poor gastrointestinal absorption, resulting in low bioavailability [28]. When administered orally, curcumin undergoes hydrogenation in the intestine, converting to tetrahydrocurcumin. After distribution throughout the bloodstream and tissues, it is primarily excreted through bile [29].

Curcumin exhibits stability at acidic pH levels, but it is notably unstable under alkaline conditions. Various encapsulation methods are employed to enhance its stability [30]. Furthermore, piperine, derived from black pepper, is utilized to significantly increase the bioavailability of curcumin by up to 2000% [27]. Curcumin possesses antioxidant and anti-inflammatory properties, which are attributed to the actions of enzymes like catalase, superoxide dismutase, and glutathione peroxidase. Notably, its antioxidant activity surpasses that of vitamin E by tenfold, owing to the presence of the 1,3-diketone system and the phenyl ring with the methoxy group, which impedes the generation of free radicals [31]. The phenolic composition of curcumin primarily accounts for its antioxidant efficacy, facilitating the elimination of hydroxyl and superoxide radicals.

In a study conducted by Davis et al., it was found that supplementation with curcumin significantly reduced muscle damage induced by eccentric exercise in mice [1]. This effect can be attributed to the ability of curcumin to stimulate the activation of nuclear erythroid factor 2-related factor 2 (Nrf2), which enhances its antioxidant action [32]. The anti-inflammatory properties of curcumin are attributed to its ability to suppress the production of proinflammatory cytokines such as tumor necrosis factor alpha (TNF-α), interleukin-6 (IL-6), and interleukin-8 (IL-8). Moreover, curcumin has been observed to reduce the concentration of highly sensitive C-reactive protein, an acute phase protein associated with inflammation. Other studies suggest that the anti-inflammatory activity of curcumin may involve modulation of the NF-kB and mitogen-activated protein kinase pathways, as well as the regulation of redox and epigenetic activity [32].

This systematic review examines the association between curcumin consumption and its impact on muscle damage in trained individuals. The primary aim of this review was to assess the existing scientific evidence supporting the use of curcumin to reduce exercise-induced muscle damage. Furthermore, it sought to evaluate whether curcumin intake alleviates muscular symptoms commonly associated with exercise, as delayed onset muscle soreness (DOMS). Additionally, the review aimed to investigate whether curcumin intake leads to a reduction in markers of muscle injury and to assess its potential benefits in reducing delayed onset muscle soreness.

Previous reviews, such as the one conducted by Fernández Lázaro et al. [33], have examined the effectiveness of curcumin supplementation in individuals experiencing exercise-induced muscle damage (EIMD) and have explored its impact on inflammatory and oxidative markers within a physically active population. Similarly, research by Fang et al. [34], has delved into indirect markers of muscle damage, including creatine kinase (CK) levels and muscle soreness, among both untrained and trained healthy adults of both genders, with a focus on reported clinical trials. In the systematic review carried out by Beba et al. [35], the emphasis was placed on assessing the effects of curcumin supplementation on various aspects of delayed onset muscle soreness (DOMS). Finally, Ayubi et al. [36], concentrated on evaluating available information from clinical studies regarding the effects of curcumin specifically on exercise-induced muscle damage (EIMD). Therefore, in this systematic review, an analysis has been conducted on study participants who are healthy adults, aged over 18, and without diagnosed diseases. Specifically, the focus is on individuals engaging in regular exercises (a minimum of 3 times per week) who ingest curcumin before, during, or after exercise. Unlike previous reviews, studies have been excluded if they involve the use of curcumin in combination with other compounds, lack a specified protocol for curcumin intake, lack a control group, or if participants have a diagnosed disease. In this systematic review, the inclusion criteria encompass experimental trials such as randomized blinded trials or randomized double-blind trials. Lastly, a departure from earlier reviews involves considering the analysis of exercise-induced muscle damage (EIMD), delayed onset muscle soreness (DOMS), markers of inflammation, oxidative stress, and pain perception after exercise specifically in trained individuals (minimum 3 times per week).

Therefore, in this systematic review, an analysis has been conducted on study participants who are healthy adults, aged over 18, and without diagnosed diseases. Specifically, the focus is on individuals engaging in regular exercises (a minimum of 3 times per week) who ingest curcumin before, during, or after exercise. Unlike previous reviews, studies have been excluded if they involve the use of curcumin in combination with other compounds, lack a specified protocol for curcumin intake, lack a control group, or if participants have a diagnosed disease. In this systematic review, the inclusion criteria encompass experimental trials such as randomized blinded trials or randomized double-blind trials. Lastly, a departure from earlier reviews involves considering the analysis of exercise-induced muscle damage (EIMD), delayed onset muscle soreness (DOMS), markers of inflammation, oxidative stress, and pain perception after exercise specifically in trained individuals (minimum 3 times per week).

The related evidence on how curcumin may reduce muscle damage could influence the structuring of exercise regimens to optimize performance and minimize the risk of injuries. Depending on the level of evidence, the consideration of curcumin supplements in specific cases may be warranted, always under appropriate supervision and guidance. This could be particularly relevant in situations with intensive training or during periods of intense competition.

2. Materials and methods

2.1. Search strategy

A comprehensive search was conducted in March 2023 across multiple databases: SCOPUS, Medline (PubMed), and Web of Science. Due to a more extensive search result scope, only SCOPUS results were ultimately considered.

The search strategy that has been used in this systematic review consisted in the selection of articles, in English, without time restriction, which included the terms ”curcumin‘ AND ’Exercise-Induced Muscle Damage.” The following combination of search terms was used: “ALL(curcumin AND ‘exercise-induced muscle damage’).”

2.2. Selection criteria

All titles and abstracts were screened to evaluate eligibility for inclusion. Studies were selected by applying the following Population-Intervention-Comparator-Outcome-Study design (PICOS) and they were included if they met the eligibility criteria described in Table 1.

Table 1.

Eligibility criteria.

Variable	Characteristics
Population	Healthy adults participating in sports regularly, without diagnosed diseases.
Intervention	Regular curcumin intake before, during, or after exercise.
Comparator	Sports participants not ingesting curcumin.
Outcomes	Improvement in muscle injuries such as fiber injuries, strength loss, pain, and muscle membrane permeability.
Study design	Randomized controlled clinical trials (RCTs).

2.3. Screening process

The screening process followed this structure:

1. Initial Screening: Title and abstract review using Abstrackr.

2. Full-Text Review: Detailed evaluation based on inclusion and exclusion criteria.

3. Final Selection: Articles meeting all criteria included for analysis.

The screening process utilized the Abstrackr program in its Beta version for initial title and abstract screening. Two authors independently applied the eligibility criteria described in Table 1, with a third author resolving any disagreements.

The full-text review was conducted according to the inclusion and exclusion criteria.

Inclusion Criteria:

• Population: Healthy adults over 18 years old who regularly participate in sports (minimum three times per week).

• Intervention: Regular intake of curcumin before, during, or after exercise.

• Comparators: Adults participating in sports regularly without curcumin intake.

• Outcomes: Improvement of muscle injuries (muscle fiber injuries, strength loss, pain, muscle membrane permeability).

• Study Designs: Randomized controlled trials (RCTs).

Exclusion Criteria:

• Studies involving curcumin in combination with other compounds.

• No standardized protocol for curcumin intake.

• Absence of a control group.

• Participants with diagnosed diseases.

The full-text review focused on participants who regularly consume curcumin before, during, or after sports activities, observing its effects on muscle injuries related to sports, such as muscle fiber injuries, strength loss, pain, and muscle membrane permeability. Only randomized controlled trials were considered to ensure the selection of high-quality and relevant research.

Studies combining curcumin with other compounds were excluded to accurately assess the effects of curcumin alone. Additionally, studies lacking a standardized protocol for curcumin intake were omitted, as consistent dosing and timing are essential for reliable results. Studies without a control group were excluded because control groups are necessary to establish the intervention’s efficacy. Lastly, studies involving participants with diagnosed diseases were excluded to focus on the effects of curcumin in a healthy population, particularly concerning muscle recovery in sports.

The inclusion and exclusion criteria are detailed in Table 2.

Table 2.

Inclusion and exclusion criteria.

Evaluation of curcumin intake to reduce sports-induced muscle damage in athletes
INFORMATION			YES	NO
Study participants are healthy adults. They must be over 18 years old and have no diagnosed disease.			X
Participants practice sports regularly (minimum 3 times per week).			X
Participants ingest curcumin before, during, or after exercise.			X
Use of curcumin in combination with other compounds.				X
There is no set protocol for curcumin intake.				X
There is no control group in the study.				X
The sample studied is small and not significant.				X
There is a diagnosed disease.				X
DESIGN			YES	NO
Human studies	Meta-analysis			X
	Systematic reviews			X
	Observational Studies	Report and case series		X
		Transversal		X
		Population		X
		Case and controls		X
		Cohorts		X
	Experimental Trials	Randomized, blinded trials	X
		Randomized, double-blind trials	X
		Non-randomized		X
Animal studies (laboratory)				X
“In vitro” studies				X

2.4. Quality assessment

The quality of included studies was assessed using the PEDro scale [37–39]. The PEDro scale includes 11 items, although the first item (eligibility criteria) is not scored but is necessary for contextual understanding. The criteria ensure methodological robustness, including aspects such as random allocation, blinding, and intention-to-treat analysis.

To ensure inter-rater reliability during the screening and quality assessment processes, the authors implemented a structured approach, with this section overseen and standardized by a third author. First, each study included in the review was independently assessed by at least two reviewers using eligibility criteria and quality assessment scores to ensure uniformity and accuracy in evaluations.

To maximize consistency in judgments and minimize potential individual biases, the authors organized regular consensus meetings. These meetings allowed reviewers to discuss studies where significant differences in opinion arose, reviewing and comparing the reasoning behind their decisions. In cases where discrepancies persisted, a third reviewer (appointed to maintain impartiality) examined the decisions and provided a final judgment.

2.5. Eligibility criteria and quality assessment scores

• Items Scored (1 point each if met):

1. Eligibility criteria were specified.

2. Subjects were randomly allocated to groups.

3. Allocation was concealed.

4. Groups were similar at baseline regarding prognostic indicators.

5. Subjects were blinded.

6. Therapists administering the therapy were blinded

7. Assessors who measured at least one key outcome were blinded.

8. Measures of at least one key outcome were obtained from more than 85% of the subjects initially allocated to groups.

9. All subjects for whom outcome measures were available received the treatment or control condition as allocated or, where this was not the case, data for at least one key outcome was analyzed by “intention to treat.”

10. The results of between-group statistical comparisons are reported for at least one key outcome.

11. The study provides both point measures and measures of variability.

3. Results

Figure 1 shows the process in the selection of articles for this review. Of the 468 results obtained from the Scopus database, a total of 428 articles did not meet the eligibility criteria and were excluded during the initial screening. Subsequently, the full texts of the remaining 40 articles underwent thorough examination, and relevant data were extracted.

Figure 1.

Full search strategy carried out in this systematic review.

During this process, an additional 29 articles were excluded based on the inclusion and exclusion criteria specified in Table 2. Twelve articles were excluded because they involved the combined use of curcumin with other compounds [40–51], eight articles focused on untrained participants and were excluded [52–59], two articles involved participants under the age of 18 and were excluded [60,61], two articles involved experimental animals and were excluded [1,62], and one article involved participants diagnosed with diseases and was excluded. [63]

Consequently, 11 articles were included for data extraction in the systematic review.

The quality of 11 of these articles was evaluated using the PEDro scale, indicating that all of them were of high quality (Table 3).

Table 3.

Quality analysis of the articles according to PEDro scale. For every criterion met the study receives a score of 1 or 0 when the criterion is not met.

Reference	Criteria 1	Criteria 2	Criteria 3	Criteria 4	Criteria 5	Criteria 6	Criteria 7	Criteria 8	Criteria 9	Criteria 10	Criteria 11	PEDro Score
Takahashi et al. (2014) [64]	0	1	1	1	1	0	0	1	1	1	1	8
Drobnic et al. (2014) [65]	0	1	1	1	1	0	0	1	1	1	1	8
Sciberras et al. (2015) [66]	0	1	1	1	1	1	0	1	1	1	1	9
Nicol et al. (2015) [67]	0	1	1	1	1	1	1	1	1	1	1	10
McFarlin et al. (2016) [68]	0	1	1	1	1	1	0	1	1	1	1	9
Roohi et al. (2017) [69]	0	1	1	1	1	1	0	1	1	1	1	9
Tanabe et al. (2019) [70]	0	1	1	1	1	0	0	1	1	1	1	8
Tanabe et al. (2019) [71]	0	1	1	1	1	1	0	1	1	1	1	9
Hillman et al. (2020) [72]	0	1	1	1	1	1	0	1	1	1	1	9
Kisiolek et al. (2022) [73]	0	1	1	1	1	1	0	1	1	1	1	9
Ghojazadeh et al. (2022) [74]	0	1	1	1	1	1	1	1	1	1	1	10

3.1. Curcumin and oxidative stress

In 2014, Takahashi et al. [64] conducted a randomized trial with 10 male participants to investigate curcumin’s impact on exercise-induced oxidative stress. They divided the participants into three groups: a control group (placebo), group 1 (curcumin before exercise), and group 2 (curcumin before and after exercise). Each participant received either a placebo or 90 mg of curcumin two hours before exercise (group 1) or two hours before and immediately after exercise (group 2). The exercise involved walking or running on a treadmill at 65% of their maximum oxygen capacity. Blood samples were collected before exercise, immediately after exercise, and 2 hours later. The results showed that reactive oxygen species (ROS) levels in the serum immediately after exercise were significantly higher in the placebo group compared to pre-exercise values.

This increase was not observed in the curcumin-receiving groups. Additionally, the concentrations of antioxidant metabolites determined immediately after exercise were significantly higher in groups 1 and 2 compared to pre-exercise values and the placebo group. These findings suggest that curcumin supplementation may mitigate exercise-induced oxidative stress by enhancing the blood’s antioxidant capacity.

3.2. Curcumin and delayed onset muscle damage (DOMS)

In 2014, Drobnic et al. [65] aimed to alleviate delayed onset muscle soreness (DOMS) resulting from physical exercise through a randomized placebo-controlled trial using Meriva®, a novel curcumin delivery system that enhances bioavailability.

Nineteen moderately active male volunteers participated in a four-day trial, receiving 200 mg of curcumin or a placebo twice daily. Curcumin supplementation started 48 hours pre-exercise and continued 24 hours post-exercise. The intervention group exhibited fewer indications of injury in the posterior thigh compartment on MRI scans.

Although curcumin recipients reported lower pain levels, it did not reach statistical significance. Notably, IL-8 levels were significantly lower in the intervention group at the 2-hour mark post-intervention. These findings suggest that curcumin supplementation with Meriva® may attenuate muscle soreness and reduce certain markers of inflammation following exercise-induced stress.

3.3. Curcumin and inflammatory markers

In 2015, Sciberras et al. [66] investigated curcumin’s (Meriva®) effects on pro-inflammatory cytokine levels, markers of inflammation, and oxidative stress following 2 hours of cycling at 95% of lactate threshold. The study involved 10 moderately active males who engaged in regular aerobic exercises of at least 3 hours per week. They participated in three randomized trials: curcumin supplementation, placebo, and control.

Participants received either 500 mg of curcumin Meriva® or a placebo for three days leading up to the test and on the test day. Two days before the test, they underwent a one-hour interval training session to deplete muscle glycogen stores. Their diet consisted of specific amounts of carbohydrates, lipids, and protein to minimize carbohydrate replenishment after training. Blood samples measured interleukin levels, cortisol, and C-reactive protein. Results showed a non-significant IL-6 reduction post-exercise in the curcumin group. No significant differences were observed in other markers, but the curcumin group reported significantly lower stress perception.

Nicol et al. [67] investigated curcumin’s effects on muscle damage, inflammation, and DOMS in 17 individuals. In a double-blind trial, participants received 2.5 grams of curcumin or a placebo twice daily for five days, starting two days before eccentric leg press exercises. Measurements included pain, muscular inflammation, jump performance, and serum markers. Curcumin led to moderate to large pain reductions in various activities at 24- and 48-hours post-exercise, a slight decrease in creatine kinase at 24 hours, and elevated immediate and 48-hour IL-6 levels. Pain reduction correlated with improved single-leg jump performance.

3.4. Curcumin’s broad impact on exercise-induced stress

In 2016, McFarlin et al. [68] explored curcumin’s effects on muscle pain, creatine kinase, and pro-inflammatory cytokines after intense leg presses. The randomized trial with 28 subjects revealed that curcumin significantly reduced creatine kinase, TNF-α, and IL-8 levels post-exercise compared to the placebo.

Roohi et al. [69] examined curcumin’s effects on antioxidant capacity, glutathione, and lipid peroxidation. The curcumin group exhibited increased antioxidant capacity, lower malondialdehyde levels, and elevated glutathione post-exercise, indicating potential antioxidant benefits.

3.5. Timing and dosage of curcumin intake

Tanabe et al. [70,71] investigated the timing of curcumin ingestion’s impact on muscle damage markers post-eccentric exercise. In one experiment, the post-exercise group showed greater range of motion and lower muscle soreness post-exercise compared to the control group, while the pre-exercise group exhibited no significant differences in serum creatine kinase activity. In a second experiment, the post-exercise group exhibited improved range of motion, maximal voluntary contraction, and lower muscle soreness and creatine kinase activity post-exercise.

Hillman et al. [72] evaluated curcumin’s impact on DOMS and muscle power following plyometric exercises. The curcumin group experienced significantly lower pain levels at 48- and 72-hours post-exercise, maintained stable vertical jump performance, but showed no notable difference in creatine kinase levels.

Kisiolek et al. [73] explored 1 g/day of Longvida® during a 14-day high-intensity interval training (HIIT). While a non-significant performance improvement was noted in all groups, further research is needed to clarify curcumin’s potential benefits in conjunction with HIIT on exercise performance and physiological markers.

In a placebo-controlled trial by Ghojazadeh et al. [74], 18 male taekwondo athletes received either 2 grams of curcumin twice daily or a placebo. Initially, no significant creatine kinase differences existed. However, as the study progressed, the curcumin group showed lower serum concentrations. Specifically, post-competition, curcumin significantly reduced creatine kinase and lactate dehydrogenase levels at 24 and 48 hours. Moreover, the curcumin group exhibited significantly higher total antioxidant capacity and a reduction in serum malondialdehyde levels post-competition compared to the placebo group.

Table 4 includes information about the author/s and year of publication, the type of study, the sample investigated, the duration of the intervention, the curcumin intake in every intervention, the variables considered in every study and the results obtained and main conclusions.

Table 4.

Main characteristics of the studies/articles included in the review. Where appropriate; VO2 max: maximal oxygen consumption; IL-1-RA: interleukin-1-receptor antagonist; IL-2: interleukin-2; IL-6: interleukin-6; IL-8: interleukin-8; IL-10: interleukin-10; INF: interferon; tnf-α: tumor necrosis factor - α; HIIT: high-intensity interval training; MDA: malondialdehyde; GSH: glutathione; RM: maximum repetition.

Author Year	Type of Study	Population (n) Sex Age (years)	Training status	Intervention (Duration)	Curcumin intake	Variables	Results
Takahashi et al. (2014) [64]	Randomized Controlled Trial	n = 10 Males (26.8 ±2.0)	Moderately active males	Each participant walked or ran at 65% of VO2max on a treadmill (60 min).	90 mg 2h before exercising and immediately after exercise.	Blood samples (biomarkers).	Curcumin supplementation can attenuate exercise-induced oxidative stress by increasing blood antioxidant capacity.
Drobnic et al. (2014) [65]	Randomized, placebo -controlled, single-blind pilot trial.	n = 20 Males (38.1 ± 11.1)	Moderately active males (at least 4 hours per week).	Downhill running test (45 min).	200 mg of curcumin twice a day (at breakfast and dinner). Four days in total: 48 hours prior to the test and up to 24 hours after.	Magnetic resonance imaging, blood samples (biomarkers), histological analysis, and pain intensity.	Curcumin supplementation can attenuate pain in the lower limb (right and left anterior thighs) and muscle injury in the posterior or medial compartment of both thighs. Reduced levels of IL-8. No differences in markers of oxidative stress and muscle histology were observed.
Sciberras et al. (2015) [66]	Double blind trial.	n = 11 Males (35.5 ± 5.7)	Recreationally active males (at least 3 hours per week).	Endurance cycling (120 min).	A single dose of 500 mg of Meriva curcumin for three days and 500 mg of Meriva curcumin just before exercise.	Blood samples (biomarkers), and subjective evaluation of training stress.	A rise in IL-6 and IL-1-RA were observed but these results were not statistically significant when compared to placebo and control. A positive correlation between absolute exercise intensity and 1h post-exercise of IL-6 levels were observed. Participants reported “better than usual” scores in the subjective assessment of psychological stress.
Nicol et al. (2015) [67]	Double blind randomized controlled crossover trial.	n = 17 Males (33.8 ± 5.4)	Moderate regular physical active males. Endurance training 2.5 ± 2.2 h week−1, team training 1.1 ± 1.6 h week−1	Single-leg press exercise (Seven sets of ten eccentric single-leg press repetitions on a leg machine).	2.5 g twice daily: 2 days before to 3 days after exercise.	Limb pain, muscle inflammation, single leg jump height, blood biomarkers, and muscle damage.	At 24 and 48h post-exercise reduction in pain and in creatine kinase activity were observed. IL-6 levels were increased at 0h and 48h post-exercise, but decreased at 24h post-exercise.
McFarlin et al. (2016) [68]	Double blind trial.	n = 28 Females (n = 18) and males (n = 10) (20 ± 1)	Moderately active females and males.	Dual-leg press exercise at 110% of the 1RM (60 repetitions: 6 sets of 10 repetitions).	400 mg of Longvida curcumin: 2 days prior to exercise and continuing to 3 days after exercise.	Blood samples (biomarkers).	Reduced levels of creatine kinase, IL-8 and TNF -α have been observed for up to 4 days after exercise.
Roohi et al. (2017) [69]	Double blind, randomized, placebo controlled trial.	n = 20 Males (25.6 ± 2.7)	Active healthy males	Running (14 km).	90 mg of curcumin for 7 days before exercise.	Blood samples (biomarkers).	An increase in total antioxidant capacity after supplementation and immediately after exercise. MDA levels were lower in the curcumin group immediately after exercise. GSH was increased immediately, 24h and 48h after exercise.
Tanabe et al. (2019) [70]	Single-blind randomized trial	n = 24 Males (28.8 ± 3.6)	Active males	Eccentric exercise of the elbow flexors on a BIODEX dynamometer (30 maximal eccentric contractions of the elbow).	90 mg twice daily (after breakfast and dinner): 180 mg/day of curcumin 7 days before exercise and 4 days after exercise.	Muscle pain, and blood samples (biomarkers).	Elbow joint range of motion and muscle soreness were improved with curcumin ingestion 4 days after exercise.
Tanabe et al. (2019) [71]	Double-blind crossover trial	n = 20 Males (Two groups: 28.5 ± 3.4 29.0 ± 3.9)	Active males	Eccentric exercise of the elbow flexors on a BIODEX dynamometer (30 maximal eccentric contractions of the elbow).	First group: 90 mg twice daily (after breakfast and dinner): 180 mg/day of curcumin 7 days before exercise. Second group: 90 mg twice daily (after breakfast and dinner): 180 mg/day of curcumin 7 days after exercise.	Elbow range of motion, muscle pain, and blood samples (biomarkers).	Levels of IL-8 were reduced 12h after exercise when curcumin was ingested before exercise. Muscle soreness and creatine kinase activity were lower 3–6 days and 5–7 days after exercise, respectively.
Hillman et al. (2022) [72]	Double-blind placebo-controlled trial.	n = 22 Females (n = 5) and males (n = 17) (22 ± 1)	Recreationally trained females and males (at least 3 days per week).	Drop jumps (5 x 20 drop jumps).	500 mg of curcumin twice daily for 10 days (6 days pre-exercise and 3 days post-exercise).	Blood samples (biomarkers), recovery test, and pain perception.	Curcumin may reduce soreness and maintain muscular power.
Kisiolek et al. (2022) [73]	Double-blinded, randomized, placebo-controlled trial.	n = 36 Females (n = 20) and males (n = 16) (24.6 ± 4.2)	At least 150 min of moderate intensity exercise per week.	Cycling (HIIT) (16.1 km).	1 g of curcumin for 14 days.	Physical performance, lactate levels, and well-being perception.	The results obtained were not statistically significant.
Ghojazadeh et al. (2022) [74]	Double-blinded, randomized, placebo-controlled trial.	n = 18 Males (22.27 ± 0.94)	Taekwondo athletes	Taekwondo competition (3 rounds each 2 minutes and 1 minute break between rounds).	4 g of curcumin (2 g twice a day: after breakfast and bedtime) for 5 days (3 days before exercise and 2 days after).	Pain perception and blood samples (biomarkers).	Creatine Kinase activity, Lactate Dehydrogenase and MDA levels were lower in the curcumin group. Total Antioxidant Capacity was increased in the curcumin group.

4. Discussion

The main objective of this review was to determine if there is scientific evidence confirming that the consumption of curcumin can reduce muscular injuries caused by sports.

Curcumin, a compound found in turmeric, has garnered significant interest in the context of muscle injuries induced by sports due to its potential anti-inflammatory and antioxidant properties [30,31]. These characteristics make it a promising candidate for alleviating muscle damage and pain that often result from intense physical activities.

The interest in curcumin stems from its ability to potentially mitigate inflammation and oxidative stress, which are common responses of the body to the muscle micro-tears and strain caused by sports and exercise. Inflammation and oxidative stress can lead to muscle soreness, known as delayed-onset muscle soreness (DOMS), which can hinder athletic performance and recovery [1,4,5].

The main findings of the reviewed studies suggest that curcumin can promote a reduction in muscle injuries derived from sports practice. This is particularly relevant for athletes and individuals engaged in regular physical activity, as it implies that curcumin could enhance recovery times and improve overall athletic performance [66,70–73].

These findings highlight the potential of curcumin as a beneficial supplement in sports and exercise contexts but also underscore the need for further research to optimize its use, considering factors like bioavailability and the specific demands of various types of physical activities [65,72].

4.1. Reduction of muscle injury and pain

Drobnic et al. [65] observed a decrease in muscle injury in the posterior and medial compartments of the thighs through magnetic resonance imaging. This reduction in muscle injury led to a decreased perception of pain in the lower extremities. Similarly, Nicol et al. [67] found that curcumin supplementation before and after eccentric exercises reduced delayed-onset muscle soreness. Hillman et al. [72] demonstrated that curcumin supplementation resulted in lower self-reported pain during squats and after vertical jump exercises compared to a placebo group.

4.2. Effects of curcumin on muscle pain and range of motion

Tanabe et al. [70,71] analyzed the effects of curcumin intake before and after performing eccentric exercises. They discovered improvements in elbow range of motion and a decrease in muscle pain, attributing the enhancement in range of motion to a reduction in muscle soreness. Notably, these results were significant when curcumin was taken after the eccentric exercises. The study also found that the concentration of curcumin in plasma varied depending on the timing of intake. When curcumin was consumed before exercise, the plasma concentration was approximately 40.0 ng/ml during exercise and nearly 0.0 ng/ml two days after. However, concentrations remained around 40–50 ng/ml for four days when curcumin was taken after exercise.

4.3. Timing of curcumin intake

Based on these findings, it is plausible to suggest that consuming curcumin prior to exercise may help alleviate early inflammation, while taking it after eccentric sports activities may promote faster recovery. Nevertheless, interpreting whether curcumin facilitates pain reduction from sports practice is complex. Scientific evidence indicates that improvements have predominantly been observed in sports activities involving eccentric exercises, which are known to induce substantial muscle damage [75,76].

Contrary findings are evident in the articles published by Sciberras et al. [66] and Kisiolek et al. [73]. These studies examined the effects of curcumin in individuals engaged in cycling, a sport characterized by the absence of eccentric contractions or impact loading. Despite this, a statistically significant improvement in stress perception was observed, with the group that consumed curcumin reporting lower levels of stress, thereby enhancing the overall well-being of the participants [66].

4.4. Creatine kinase levels

Drobnic et al. [65] found no differences in the concentration of creatine kinase levels despite the reduction in muscle damage. In contrast, Nicol et al. [67] and McFarlin et al. [68] reported improvements in this parameter. These variations might be due to the formulation, dosage, or timing of curcumin administration, emphasizing the importance of plasma curcumin concentration and the timing of its peak levels. For instance, Sciberras et al. [66] reported a plasma curcumin concentration of 80.0 ng/ml, with no significant differences in the concentration of analyzed biomarkers. However, another study with a concentration of 100 ng/ml [64] observed statistically significant differences. Tanabe et al. [70,71] reported lower plasma concentrations (40–50 ng/ml) but observed improvements in two biomarkers (creatine kinase and IL-8).

4.5. Inflammation biomarkers and muscle pain

McFarlin et al. [68] showed that lower concentrations of some inflammation biomarkers did not translate into a reduction of muscle pain. This may be due to different pathways involved in generating inflammation. The study observed a sustained reduction in IL-8 and TNF-α (2 and 4 days, respectively). It is also possible that the reduction in muscle pain, irrespective of inflammation biomarkers, may be due to an unevaluated psychological component related to curcumin intake [77].

4.6. Antioxidant capacity

The trial carried out by Roohi et al [69], shows an increase of total plasma antioxidant capacity parameter in all groups 48 hours after exercise, lasting up to 7 days in the group that has ingested curcumin. The increase in the concentration of enzymes with antioxidant capacity such as superoxide dismutase or glutathione peroxidase may be related to the improvement of this parameter [78]. Tanabe et al [70] have also observed a significantly lower plasma concentration of IL-8, 12 hours after sport-simulated intervention in the group that ingested curcumin before exercise. Similarly, creatine kinase concentration has peaked 4–5 days after exercise. However, in the group in which curcumin was supplied, the value of this parameter was significantly lower, and its concentration decreased faster than in the control group, after 5 days of exercise. Furthermore, Thaloor et al. [79] reported that curcumin demonstrates anti-inflammatory properties by reducing the expression of NF-κB which intervenes in the inflammatory process.

4.7. Limitations

4.7.1. Small number of participants and sport variability

This systematic review identified that the small number of participants in the reviewed studies limits the ability to broadly apply the results to larger populations. Additionally, the wide variety of sports covered in these studies introduces variability, as different sports may have varying impacts on muscle injuries and recovery. This variability potentially affects curcumin’s effectiveness and should be considered when designing future research.

4.7.2. Heterogeneity in curcumin formulations

The significant variation in curcumin formulations used across studies presents a limitation [65,66,68,73]. This heterogeneity makes it challenging to draw definitive conclusions about the most effective type or dosage of curcumin for sports-related muscle injuries. Furthermore, the insufficient analysis of curcumin’s bioavailability in the reviewed studies is noteworthy.

The significant variation in curcumin formulations across studies presents a notable limitation, especially when comparing the mechanisms of two popular formulations: Meriva® [65,66] and Longvida® [68,73]. This heterogeneity complicates efforts to draw definitive conclusions about the most effective type or dosage of curcumin for treating sports-related muscle injuries.

Meriva® and Longvida® differ significantly in their delivery mechanisms and bioavailability, each tailored to enhance curcumin absorption in distinct ways. Meriva® combines curcumin with phospholipids to create a phytosome complex, which enhances absorption through cell membranes and increases the body’s uptake [65,66]. This formulation capitalizes on curcumin’s fat-solubility, promoting a more direct delivery to tissues and thereby potentially amplifying its anti-inflammatory effects in muscle repair.

On the other hand, Longvida® utilizes a Solid Lipid Curcumin Particle (SLCP) technology, which encapsulates curcumin within a lipid matrix to protect it from premature breakdown in the digestive tract [68,73]. This allows Longvida® to achieve prolonged release and more stable plasma levels, which could be beneficial for sustained anti-inflammatory action. This delivery method is especially relevant for athletes, as it ensures that curcumin remains available over an extended period, possibly aligning with the recovery phases post-exercise.

The lack of head-to-head comparisons between these two formulations in the reviewed studies adds to the difficulty in determining which might be more effective for muscle injury recovery. Additionally, the studies often overlook an in-depth analysis of bioavailability, a key factor influencing the effectiveness of any curcumin formulation. Without precise measures of how each formulation is absorbed and utilized by the body, it remains uncertain whether the full potential of curcumin has been realized in these applications.

Ultimately, this variability in curcumin formulations and the limited investigation into their bioavailability underline a critical gap in the current literature. Bioavailability plays a crucial role in the effectiveness of any supplement, and the lack of detailed examination means that the true potential of curcumin may not have been fully explored [80,81].

These limitations align with those identified in the systematic reviews by Fernández-Lázaro et al. [33], Fang et al. [34], Beba et al. [35], and Ayubi et al. [36]. Addressing these issues in future research will provide a better understanding of curcumin’s role in sports-related muscle recovery and its potential benefits for athletes and physically active individuals.

4.8. Recommendations for future research

Future research on curcumin’s effects on muscle recovery and performance should consider examining its impact across various types of athletes and sports contexts, focusing on the differing physical demands of endurance and power sports. This approach could provide valuable insights into how curcumin’s anti-inflammatory and recovery-promoting properties might benefit athletes with distinct physiological and performance needs.

4.8.1. Evaluation in female participants

Future studies should evaluate the effects of curcumin specifically in women. According to Beba et al. [35], estrogen hormones may confer muscle protection, suggesting that the results obtained in these studies may not be representative for both sexes [82,83]. Including female participants will ensure comprehensive and applicable findings for both genders.

4.8.2. Pharmacokinetics and bioavailability

Researchers should analyze and consider the pharmacokinetics and bioavailability of curcumin, along with the various available release mechanisms [77]. These factors can significantly influence the outcomes observed in different trials and should be standardized to draw more definitive conclusions [81]. The distinct pharmacokinetic profiles of Meriva® [65,66] and Longvida® [68,73] raise important questions about how each formulation might best serve different aspects of muscle recovery. For instance, Meriva’s quicker absorption might be more suitable for acute, immediate post-exercise recovery, while Longvida’s extended release could offer ongoing support throughout the later stages of recovery, where sustained anti-inflammatory action might be beneficial. Understanding these aspects will help optimize curcumin’s use for muscle recovery.

4.8.3. Molecular mechanisms

Further investigation is necessary to understand the precise molecular mechanisms underlying curcumin’s efficacy in preventing or reducing muscle pain associated with sports practice. This will help clarify whether the pain-alleviating effect is due to its anti-inflammatory activity [1]. Additionally, it is important to assess whether curcumin’s anti-inflammatory activity might adversely affect adaptations resulting from sports practice, like non-steroidal anti-inflammatory drugs (NSAIDs).

5. Conclusions

Curcumin demonstrates a significant potential to alleviate muscular symptoms, especially delayed-onset muscle soreness (DOMS) resulting from eccentric exercises. This indicates that curcumin could substantially enhance the well-being of individuals engaged in regular physical training. Moreover, curcumin may play a role in reducing biomarkers associated with inflammation and enhancing antioxidant capacity, suggesting broader health benefits. However, it is crucial to recognize the limitations of the current studies that underpin these conclusions. Many of these studies are characterized by small sample sizes and variable design, which undermine the generalizability of their findings. These methodological limitations underscore the necessity for further research. Specifically, controlled trials with larger and more diverse participant groups are required, to rigorously validate and extend these preliminary findings.

Funding Statement

The author(s) reported there is no funding associated with the work featured in this article.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Author contributions

Conceptualization, M.-L.P.; writing original draft preparation, P-R, DV., and M.-L.P.; writing review and editing, P-R, DV. and M.-L.P., supervision, M.-S.M., M.-L.P., E, L. All authors have read and agreed to the published version of the manuscript.