Efficacy and safety of green-lipped mussel powder supplementation in adults with knee osteoarthritis: a randomized, double-blind, placebo-controlled trial

Abstract

Background

Knee osteoarthritis (OA) is a prevalent degenerative joint disease associated with pain, functional limitation, and reduced quality of life. Although nonsteroidal anti-inflammatory drugs are widely prescribed, long-term use is limited by safety concerns. Green-lipped mussel powder (GLMP) has demonstrated anti-inflammatory and chondroprotective effects in preclinical studies. This trial evaluated the efficacy and safety of GLMP supplementation in adults with knee OA.

Methods

Adults aged 40–75 years with symptomatic radiographic knee OA were randomly assigned (1:1) to receive GLMP (1,000 mg/day) or placebo for 12 weeks. Assessments occurred at baseline, week 6, and week 12. The primary endpoint was change in the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) total score. Secondary endpoints were WOMAC subscales (pain, stiffness, physical function), visual analog scale (VAS) pain, and inflammatory biomarkers (C-reactive protein [CRP], erythrocyte sedimentation rate [ESR]). The per-protocol (PP) set included 93 participants (GLMP, 47; placebo, 46); the intention-to-treat (ITT) set included 100.

Results

A total of 100 participants were randomized and included in the ITT population, and 93 completed the study and were included in the PP population. In the PP analysis, GLMP resulted in greater improvement in WOMAC total score at week 12 than placebo (between-group difference − 3.66; 95% CI − 6.87 to − 0.45; p = 0.032). Significant between-group differences were also observed for WOMAC pain (p = 0.026), WOMAC physical function (p = 0.027), and VAS pain (between-group difference − 19.93 mm; 95% CI − 25.31 to − 14.55; p < 0.001). In the ITT analysis, the overall pattern of results was consistent with that observed in the PP analysis. WOMAC physical function (p = 0.042) and VAS pain (p < 0.001) remained significantly improved with GLMP, whereas WOMAC total score showed a non-significant trend favoring GLMP (p = 0.061). No significant between-group differences were observed in CRP or ESR levels. No clinically meaningful safety concerns were identified.

Conclusions

Twelve-week supplementation with GLMP was associated with improvements in pain and physical function in adults with mild-to-moderate knee OA. Improvements in pain-related outcomes were observed consistently across PP and ITT analyses, although the primary WOMAC total outcome reached statistical significance only in the PP population. GLMP was well tolerated and may have potential as a complementary nutritional intervention for symptom management in individuals with knee OA.

Trial registration

The study was registered with the Clinical Research Information Service (CRIS; registration number KCT0008821) on September 22, 2023, and the full study protocol is available on the CRIS website (https://cris.nih.go.kr).

Supplementary Information

The online version contains supplementary material available at 10.1186/s12906-026-05465-5.

Introduction

Knee osteoarthritis (OA) is one of the most common musculoskeletal disorders and a leading cause of pain and disability worldwide. A recent population-based study estimated that approximately 654 million individuals aged 40 years and older are affected by knee OA globally, corresponding to a prevalence of 22.9% in this age group. As life expectancy increases and populations continue to age, the burden of knee OA is expected to grow substantially [1].

Non-pharmacological and adjunctive approaches have attracted increasing attention for managing knee OA because long-term pharmacological treatment may be associated with adverse effects. Among these approaches, dietary supplements containing bioactive compounds have been widely investigated. Although supplements such as glucosamine, chondroitin, and curcumin have been widely studied, their efficacy remains controversial and guideline recommendations are inconsistent [2–6]. In contrast, green-lipped mussel (GLM; Perna canaliculus) has attracted interest as a potential complementary intervention because of its unique profile of marine-derived bioactive lipids, including omega-3 fatty acids and eicosatetraenoic acid (ETA) [7–9]. Unlike many conventional dietary supplements, GLM may exert broader anti-inflammatory effects through modulation of multiple inflammatory pathways, providing a biological basis for further clinical investigation in knee OA.

Experimental studies provide biological plausibility for the potential role of GLM in OA. Bioactive compounds derived from GLM have been shown to modulate inflammatory signaling pathways, including suppression of NF-κB activation and downstream pro-inflammatory cytokine production [10]. In vitro studies have demonstrated that lipid extracts from GLM suppress TNF-α, IL-1β, and cyclooxygenase-2 (COX-2) expression in cultured chondrocytes and macrophages while inhibiting NF-κB activation [7, 8, 11]. GLM-derived lipid fractions have also been shown to inhibit both cyclooxygenase (COX) and lipoxygenase (LOX) pathways, reducing the synthesis of pro-inflammatory eicosanoids such as prostaglandin E₂ and leukotriene B₄ [7, 12]. In addition, reductions in matrix metalloproteinase activity have been observed in chondrocyte models, suggesting a potential role in limiting cartilage matrix degradation [13].

These mechanistic observations are supported by in vivo studies, strengthening the translational relevance of GLM for OA management. In rodent models of surgically or chemically induced osteoarthritis, GLM supplementation has been associated with attenuation of cartilage destruction, decreased synovial inflammation, and improvements in pain-related behavioral outcomes [7, 14]. Collectively, these preclinical data provide a mechanistic and translational rationale for evaluating green-lipped mussel preparations in human clinical trials for knee OA.

Although several randomized controlled trials have evaluated GLM preparations in patients with OA, important limitations remain, including small sample sizes, heterogeneous formulations (lipid extracts versus whole-powder products), variable dosages, and inconsistent outcome measures. Consequently, the clinical efficacy of standardized GLM powder supplementation remains insufficiently established [11, 15–17]. Consequently, a randomized, double-blind, placebo-controlled clinical trial is warranted to determine whether the mechanistic and preclinical effects translate into improvements in pain and physical function. Therefore, the present trial was conducted to evaluate the efficacy and safety of standardized green-lipped mussel powder supplementation in adults with mild-to-moderate radiographic knee OA. Given the variability of previous findings, this study sought to further evaluate the potential efficacy and safety of GLMP supplementation in this population.

Materials and methods

Study design

This study employed a randomized, double-blind (subject and investigator), placebo-controlled, parallel-group design. Eligible participants were randomly assigned in a 1:1 ratio to the GLMP or placebo group using block randomization with a fixed block size of four.

Participants received either the GLMP or placebo product along with an intake diary. They were instructed to consume one dose daily according to the provided guidelines and record adherence. Efficacy and safety assessments were conducted at baseline (Day 0), week 6 (Day 42), and week 12 (Day 84). The trial was conducted at Pusan National University Korean Medicine Hospital, Yangsan, Republic of Korea. Patients and the public were not involved in the design, conduct, reporting, or dissemination plans of this trial. This trial was reported in accordance with the CONSORT 2010 statement and checklist.

Participants

The inclusion criteria were as follows: (1) age: 40–75 years, (2) knee pain intensity of ≥ 30 mm on a 100-mm visual analog scale (VAS), (3) radiographic evidence of Kellgren–Lawrence (KL) Grade 1 or 2 OA in both knees. KL grades were assessed during screening by a licensed Korean Medicine Doctor with formal training in musculoskeletal radiographic interpretation based on standard knee radiographs. Only participants with KL grade 1–2 OA were eligible for enrollment. (4) discontinuation of OA medications or supplements for at least 4 weeks before screening (washout period), and (5) the ability to perform normal physical activities and provide written informed consent.

The exclusion criteria were as follows: (1) history of fracture within the past year; (2) moderate arthritis with osteophytes, irregular joint surfaces, or subchondral bone cysts; (3) currently being treated for thyroid disease; (4) kidney disease or serum creatinine ≥ 1.4 mg/dL; (5) proteinuria ≥ 2+; (6) liver disease (excluding fatty liver) or aminotransferase (aspartate/alanine aminotransferase) levels ≥ 100 IU/L; (7) uncontrolled hypertension or heart disease (e.g., angina pectoris or myocardial infarction); (8) use of psychiatric medications (excluding intermittent use for sleep disorders); (9) use of herbal or prescription medications within 2 months before screening; (10) participation in other clinical trials or use of investigational drugs within 4 weeks prior; (11) ongoing use of medications likely to affect study outcomes; (12) history of gastrointestinal resection (except cecum); (13) pregnancy or lactation; (14) alcohol abuse; (15) hypersensitivity to GLMP or its ingredients; (16) Individuals who were unable or unwilling to comply with study procedures, attend scheduled visits, complete study assessments, or adhere to the study protocol, as determined by the investigator. (17) diagnosis of inflammatory, autoimmune, infectious, crystal-induced, or other non-degenerative forms of arthritis (e.g., rheumatoid arthritis, gout, psoriatic arthritis, ankylosing spondylitis, or septic arthritis), based on medical history and clinical evaluation by the investigator. Participants were recruited through advertisements posted at Pusan National University Korean Medicine Hospital and in local community settings. Individuals who expressed interest in participating were screened by a clinical research coordinator according to predefined inclusion and exclusion criteria before enrollment.

Ethical approval and trial registration

This human clinical trial was conducted in accordance with the Declaration of Helsinki and complied with the Korean Good Clinical Practice (KGCP) guidelines. This clinical trial was approved by the Institutional Review Board of the Pusan National University Korean Medicine Hospital (PNUKHIRB 2023-04-001). The trial was prospectively registered with the Clinical Research Information Service (CRIS; registration number KCT0008821) on September 22, 2023.

Analysis populations and compliance

Efficacy was evaluated using both per-protocol (PP) and Intent-to-Treat (ITT) populations. The PP population included 93 participants (47 in the GLMP group and 46 in the placebo group, with a dropout rate of 7%), after excluding those who withdrew from or were excluded from the blinded review. The ITT population consisted of 100 randomized participants with 50 allocated to each group (Fig. 1).

Fig. 1.

CONSORT flow diagram of participant disposition. Of 108 individuals screened, 100 were randomized to the GLMP group (n = 50) or placebo group (n = 50). Three participants in each group discontinued for various reasons. A total of 47 participants in the GLMP group and 46 in the placebo group completed the study and were included in the per-protocol analysis. Abbreviations: ITT, intent-to-treat; PP, per-protocol; GLMP, green-lipped mussel powder

The participants were instructed to consume the study product daily from the date of prescription to the day before each follow-up visit. Both the PP and ITT populations achieved compliance rates exceeding 80%, with no statistically significant differences between the groups at any visit (Table S1).

Randomization and blinding

To ensure methodological rigor, the participants were randomly assigned using a block randomization procedure without stratification. Each participant was assigned a unique three-digit identification code upon enrollment according to the randomization sequence. The GLMP and placebo products were pre-packaged and labeled by code before being distributed to the participants. Once assigned, the randomization codes were not reused, even for participants who withdrew from the study. The randomization table was generated by an independent third party and provided to the sponsor, who enclosed each assignment in sealed opaque envelopes for secure transfer to the principal investigator. Personnel responsible for participant enrollment and assignment did not have access to the random allocation sequence.

Intervention

The investigational product used in this human clinical trial was manufactured by US Pharmatech, Inc. (Las Vegas, NV, USA), labeled by US Pharmatech Korea Co., Ltd. (Busan, Republic of Korea), and subsequently supplied to the study institution. The GLMP and placebo groups were designed to be indistinguishable in appearance, with minimal differences in weight. The placebo consisted of maltodextrin (479 mg), caramel coloring (14 mg), and gardenia yellow coloring (7 mg), and was manufactured to be indistinguishable from the active product in appearance, color, weight, and packaging. Placebos are inert substances with no pharmacological activity. Accordingly, the study was rigorously conducted to ensure that both the practitioners and participants remained blind throughout the trial period.

The daily dose of 1,000 mg was selected based on human-equivalent dose calculations and consideration of safety and feasibility. These doses were converted to human-equivalent doses using a standard body surface area conversion factor of 0.16, resulting in effective human doses of 960 and 2,880 mg/day, respectively. For this clinical trial, a daily dosage of 1,000 mg was selected according to the balance between efficacy, safety, and manufacturing feasibility. Participants were instructed to take two 500-mg capsules once daily for 12 weeks [18].

Outcomes

The primary efficacy endpoint was the change in the total score on the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) questionnaire from baseline to weeks 6 and 12. The WOMAC questionnaire assesses functional impairment across three domains: pain, stiffness, and physical function [19–21].

Secondary endpoints included changes in the WOMAC subscale scores (pain, joint stiffness, and physical function); visual analog scale (VAS) scores assessed at baseline, week 6, and week 12; and changes in inflammatory biomarkers (C-reactive protein [CRP] and erythrocyte sedimentation rate [ESR]) measured at baseline and week 12. Participants rated their current knee pain on a 100-mm visual analog scale (VAS), with anchors of 0 mm indicating “no pain” and 100 mm indicating “worst imaginable pain” [22, 23]. CRP is a sensitive systemic biomarker of inflammation, synthesized by the liver in response to pro-inflammatory cytokines. The ESR is a commonly used indicator of inflammation based on the settling rate of red blood cells. CRP level and ESR are commonly used inflammatory markers that reflect systemic inflammatory activity. No changes were observed in the pre-specified outcomes after trial initiation.

Safety outcomes

An adverse event (AE) was defined as any illness, injury, or incident that occurred during the observation period that could compromise participant safety. Safety evaluations were conducted for all the randomized participants. Safety assessments were conducted by designated study personnel, whereas medical judgments were made exclusively by licensed physicians.

The assessments included monitoring for AEs, changes in clinical laboratory parameters (hematology and blood chemistry), vital signs (temperature, pulse, and blood pressure), and abnormalities reported during medical interviews. The AEs were classified according to their causal relationship with the investigational product, as summarized in Table 1. The underlying causes of AEs were examined. In cases in which AEs related to liver function were observed, discontinuation of the investigational product was planned. Regarding causality assessment, all reported AEs were evaluated and categorized as unrelated to treatment assignment.

Table 1.

Summary of adverse events by causality

	Green-lipped mussel powder (n = 50)	Placebo (n = 50)
	F (%)	F (%)
Definitely related	0 (0.00)	0 (0.00)
Probably related	0 (0.00)	0 (0.00)
Possibly related	0 (0.00)	0 (0.00)
Probably not related	0 (0.00)	0 (0.00)
Definitely not related	5 (100.00)	10 (100.00)
Unknown	0 (0.00)	0 (0.00)
Total	5 (100.00)	10 (100.00)

F Frequency

Statistical analysis

As no previous human clinical studies have been conducted on the investigational ingredients used in this trial, we referred to previous studies that assessed the anti-arthritic effects of anti-inflammatory factors (AIFs) contained in natural water-soluble extracts of three herbs: Panax notoginseng (Sanqi), Rehmannia glutinosa (Jihwang), and Eleutherococcus senticosus (Gasiogapi) [24]. In the referenced study, the mean ± standard deviation of the WOMAC score was 11.41 ± 14.44 in the intervention group and 3.39 ± 10.16 in the placebo group, resulting in a between-group difference of 8.02. Although the reference study utilized herbal medicinal ingredients and the present study involved a food-derived product, the 12-week intervention period was expected to offset the smaller effect size. Based on the reference study, the expected difference in the WOMAC score was assumed to be 8.02, and a pooled standard deviation of 12.613, calculated from the same source, was applied. Using G*Power, version 3.1.9.2 (Heinrich Heine University Düsseldorf, Düsseldorf, Germany) [25, 26], the minimum sample size required to detect a statistically significant difference was determined to be 40 participants per group. Assuming a dropout rate of 20%, 100 participants (50 per group) were enrolled.

The PP analysis set included participants from the ITT group who completed the study without major protocol violations.

According to the Statistical Analysis Plan, the ITT population was defined as all randomized participants who received at least one dose of study product and provided post-baseline efficacy data. Because all randomized participants met these criteria, the ITT population was identical to the randomized population (n = 100). Missing data in the ITT analysis were imputed using the last observation carried forward (LOCF) method.

The PP set served as the primary analysis population, whereas ITT analyses were conducted as supplementary references. This approach was prespecified in the Statistical Analysis Plan before database lock. Statistical analyses were performed by an independent statistician, using SPSS software (version 26.0, IBM Corp., Armonk, NY, USA). All significance tests were conducted at a two-sided 5% significance level. Interim analyses or stopping rules were not planned or implemented.

Baseline demographic characteristics were summarized by group. Between-group comparisons of continuous variables were conducted using the independent t-test or Wilcoxon rank-sum test, and categorical variables were analyzed using the chi-squared test or Fisher’s exact test. For within-group comparisons, the paired t-test was used for normally distributed variables, whereas the Wilcoxon signed-rank test was used for non-normal data. Normality was assessed using the Shapiro–Wilk test. For the ITT analysis, missing values were imputed using the last observation carried forward method. In the case of baseline heterogeneity, analysis of covariance (ANCOVA) was used to adjust for potential confounding effects.

Results

Baseline characteristics

Baseline characteristics were compared between the groups before GLMP intake. No statistically significant differences were observed, confirming the baseline homogeneity (Table S2). Changes in primary and secondary efficacy variables from baseline are summarized for the per-protocol and intention-to-treat populations in Tables 2 and 3, respectively.

Table 2.

Changes in primary and secondary efficacy outcomes from baseline to Week 12 in the per-protocol population

Outcome	GLMP (n = 47) Baseline	GLMP Change at Week 12	Placebo (n = 46) Baseline	Placebo Change at Week 12	Between-group Difference (95% CI)	p-value	Adjusted p-value†
WOMAC Total	19.47 ± 10.31	-9.36 ± 9.19	20.33 ± 12.76	-5.70 ± 10.53	−3.66 (− 6.87, − 0.45)	0.032	0.036 / 0.034‡
WOMAC Pain	4.06 ± 2.62	-2.06 ± 2.21	3.98 ± 2.54	-1.24 ± 2.37	-0.82 (-1.55, -0.09)	0.026	0.028 / 0.042‡
WOMAC Stiffness	1.89 ± 1.18	-0.57 ± 1.36	2.15 ± 1.58	-0.61 ± 1.67	-0.03 (-0.72, 0.66)	0.503	0.693 / 0.550‡
WOMAC Function	13.51 ± 7.38	-6.72 ± 6.71	14.20 ± 9.32	-3.85 ± 7.62	-2.87 (-5.21, -0.53)	0.027	0.028 / 0.028‡
VAS (mm)	45.06 ± 9.47	-23.18 ± 13.40	43.93 ± 10.21	-3.25 ± 11.19	-19.93 (-25.31, -14.55)	< 0.001	< 0.001 / <0.001‡
CRP (mg/dL)	0.10 ± 0.22	-0.01 ± 0.27	0.11 ± 0.20	0.01 ± 0.29	0.02 (-0.09, 0.14)	0.835	0.974 / 0.858‡
ESR (mm/h)	4.00 ± 3.79	0.32 ± 4.49	5.26 ± 4.97	0.22 ± 5.01	0.10 (-2.06, 1.86)	0.997	0.991 / 0.724‡

Data are presented as mean ± SD. Negative values indicate improvement for WOMAC and VAS scores. Between-group differences were calculated using change scores from baseline to Week 12

CRP C-reactive protein, ESR Erythrocyte sedimentation rate, VAS Visual analogue scale

^†Ranked ANCOVA

^‡Covariates: baseline diastolic blood pressure and change in total bilirubin

Table 3.

Changes in primary and secondary efficacy outcomes from baseline to Week 12 in the intention-to-treat population

Outcome	GLMP (n = 50) Baseline	GLMP Change at Week 12	Placebo (n = 50) Baseline	Placebo Change at Week 12	Between-group Difference (95% CI)	p-value	Adjusted p-value†
WOMAC Total	19.34 ± 10.15	-8.90 ± 9.11	20.70 ± 12.58	-5.82 ± 10.20	-3.08 (-6.31, 0.15)	0.061	0.066
WOMAC Pain	4.10 ± 2.57	-1.98 ± 2.18	3.98 ± 2.51	-1.24 ± 2.18	-0.72 (-1.61, 0.17)	0.040	0.068
WOMAC Stiffness	1.92 ± 1.19	-0.56 ± 1.33	2.26 ± 1.59	-0.70 ± 1.66	-0.14 (-1.02, 0.74)	0.819	0.844
WOMAC Function	13.32 ± 7.28	-6.36 ± 6.66	14.46 ± 9.19	-3.86 ± 7.36	-2.50 (-5.29, 0.29)	0.042	0.043
VAS (mm)	45.16 ± 9.53	-22.27 ± 13.78	44.35 ± 10.37	-3.10 ± 10.85	-19.17 (-24.09, -14.25)	< 0.001	< 0.001
CRP (mg/dL)	0.10 ± 0.19	-0.01 ± 0.26	0.10 ± 0.19	0.02 ± 0.28	0.03 (-0.08, 0.13)	0.920	0.903
ESR (mm/h)	3.96 ± 3.69	0.30 ± 4.35	5.04 ± 4.84	0.20 ± 4.80	0.10 (-1.92, 1.72)	0.982	0.699

Data are presented as mean ± SD. Negative values indicate improvement for WOMAC and VAS scores. Between-group differences were calculated using change scores from baseline to Week 12

CRP C-reactive protein, ESR Erythrocyte sedimentation rate, VAS Visual analogue scale

^†Ranked ANCOVA adjusted for change in total bilirubin

Primary outcomes

In the ITT population, the WOMAC total score decreased significantly at week 6 in both the GLMP (–6.44 ± 8.61, p < 0.001) and placebo groups (–4.22 ± 12.69, p = 0.003), with no significant between-group difference. At week 12, the GLMP group improved by − 8.90 (95% CI: − 11.65 to − 6.15, p < 0.001) compared with − 5.82 (95% CI: − 8.89 to − 2.75, p < 0.001) in the placebo group, yielding a between-group difference of − 3.08 (95% CI: − 6.31 to 0.15, p = 0.061).

In the PP analysis, the WOMAC total score decreased by − 9.36 (95% CI: − 12.01 to − 6.71, p < 0.001) in the GLMP group and − 5.70 (95% CI: − 8.96 to − 2.44, p = 0.001) in the placebo group, with a between-group difference of − 3.66 (95% CI: − 6.87 to − 0.45, p = 0.032). This result remained significant after adjustment for diastolic blood pressure and total bilirubin (p = 0.036 and 0.034, respectively) (Fig. 2).

Fig. 2.

Changes in total WOMAC scores at weeks 6 and 12. Data are presented as the mean change from baseline ± standard deviation. Between- group comparisons were analyzed using the independent t- test or Wilcoxon rank sum test depending on the results of the Shapiro–Wilk test (* p < 0.05, ** p < 0.01). WOMAC, Western Ontario and McMaster University osteoarthritis index

Secondary outcomes

WOMAC pain

In the ITT population, the WOMAC pain score decreased at week 12 by − 1.98 ± 2.18 (p < 0.001) in the GLMP group versus − 1.26 ± 2.29 ( p < 0.001) in the placebo group, with a between-group difference of − 0.72 (p = 0.040). After adjustment, the difference attenuated (–0.72, p = 0.068).

In the PP population, WOMAC pain decreased by − 2.06 (95% CI: − 2.73 to − 1.39, p < 0.001) in the GLMP group and − 1.24 (95% CI: − 1.94 to − 0.54, p = 0.001) in the placebo group. The between-group difference was − 0.82 (95% CI: − 1.55 to − 0.09, p = 0.026), which remained significant after adjustment (p = 0.028 and p = 0.042) (Fig. 3).

Fig. 3.

Changes in WOMAC pain scores at weeks 6 and 12. Data are presented as the mean change from baseline ± standard deviation. Between- group comparisons were analyzed using the independent t- test or Wilcoxon rank sum test depending on the result of the Shapiro- Wilk test (* p < 0.05, ** p < 0.01). WOMAC, Western Ontario and McMaster University osteoarthritis index

WOMAC stiffness

In both the ITT and PP analyses, stiffness scores decreased significantly at weeks 6 and 12 in both groups, but no between-group differences were observed (ITT week 12: GLMP − 0.56 ± 1.33 vs. placebo − 0.70 ± 1.66; PP week 12: GLMP − 0.57 ± 1.36 vs. placebo − 0.61 ± 1.67).

WOMAC function

In the ITT analysis, the WOMAC function score decreased by − 6.36 ± 6.66 (p < 0.001) in the GLMP group versus − 3.86 ± 7.36 (p < 0.001) in the placebo group at week 12, with a between-group difference of − 2.50 (p = 0.042), which remained significant after adjustment (p = 0.043).

In the PP analysis, function scores decreased by − 6.72 (95% CI: − 8.45 to − 5.00, p < 0.001) in the GLMP group and − 3.85 (95% CI: − 5.86 to − 1.84, p = 0.001) in the placebo group, with a between-group difference of − 2.87 (95% CI: − 5.21 to − 0.53, p = 0.027) (Fig. 4).

Fig. 4.

Changes in WOMAC physical function scores at weeks 6 and 12. Data are presented as the mean change from baseline ± standard deviation. Between- group comparisons were analyzed using the independent t- test or Wilcoxon rank sum test depending on the results of the Shapiro- Wilk test (* p < 0.05, ** p < 0.01). WOMAC, Western Ontario and McMaster University osteoarthritis index

VAS for pain

In the ITT population, VAS pain decreased by − 22.27 ± 13.78 (p < 0.001) in the GLMP group versus − 3.10 ± 10.85 (p = NS) in the placebo group at week 12, with a significant between-group difference (p < 0.001), which remained significant after adjustment (p < 0.001).

In the PP analysis, VAS pain decreased by − 23.18 (95% CI: − 27.12 to − 19.24, p < 0.001) in the GLMP group versus − 3.25 (95% CI: − 6.95 to 0.45, p = 0.218) in the placebo group. The between-group difference was − 19.93 (95% CI: − 25.31 to − 14.55, p < 0.001) (Fig. 5).

Fig. 5.

Changes in VAS scores at weeks 6 and 12. Data are presented as the mean change from baseline ± standard deviation. Between- group comparisons were analyzed using the independent t- test or Wilcoxon rank sum test, depending on the results of the Shapiro- Wilk test (* p < 0.05, ** p < 0.01). VAS, Visual Analog Scale

Effect size analysis

At week 12, the WOMAC total score decreased by − 9.36 (95% CI: − 12.01 to − 6.71, p < 0.001) in the GLMP group and − 5.70 (95% CI: − 8.96 to − 2.44, p = 0.001) in the placebo group, with a between-group difference of − 3.66 (95% CI: − 6.87 to − 0.45, p = 0.032). This result remained significant after adjustment for diastolic blood pressure and total bilirubin. At week 12, Cohen’s d was 0.38 in the PP population and 0.31 in the ITT population for WOMAC total score. For VAS pain, Cohen’s d was 0.95 in the PP population.

Ancillary analyses

This clinical trial considered potential confounding variables such as total caloric intake, physical activity, and use of concomitant medications.

Total caloric intake and physical activity

Total caloric intake was assessed using the 24-hour dietary recall method, and physical activity was evaluated using the International Physical Activity Questionnaire at visits 2 and 4. No significant differences were observed between groups in total energy intake or physical activity levels throughout the study. No statistically significant differences were observed between the groups at any visit in either the PP or ITT analysis. Therefore, these factors were excluded from the final analysis.

Concomitant medication use

The evaluation of concomitant medication use revealed no significant differences between the PP and ITT groups. Apart from a few participants who withdrew because of non-steroidal anti-inflammatory drug (NSAID) use, no cases of medication use that were likely to affect the study outcomes were identified.

Safety outcomes

Fifteen AEs, including two serious adverse events (SAEs), occurred in 13 participants: 10.0% (5/50, 5 cases) in the GLMP group and 16.0% (8/50, 10 cases) in the placebo group. Both SAEs (thyroid cancer diagnosis and myalgia after a traffic accident) occurred exclusively in the placebo group and were unrelated to the investigational product (Table S3).

Four participants discontinued the study because of AEs, and two because of SAEs. Most AEs resolved without complications, and all events were reported to the Institutional Review Board in accordance with regulatory requirements. Safety monitoring, including vital signs, physical examinations, and laboratory tests, revealed no clinically significant abnormalities. Although total bilirubin levels differed between the groups (p = 0.014), all values remained within the normal range, and no liver-related complications attributed to GLMP were observed. Overall, 12-week GLMP supplementation at 1,000 mg/day was well tolerated, with no safety concerns identified.

Discussion

OA is a common degenerative joint disease that imposes a substantial burden on quality of life and functional mobility, particularly among older adults [2]. Although pharmacological treatments, such as nonsteroidal anti-inflammatory drugs (NSAIDs) and cyclooxygenase (COX)-2 inhibitors, are widely used [27–30], their prolonged administration may be associated with adverse effects involving the gastrointestinal, cardiovascular, renal, and immune systems [31–34]. Consequently, interest in non-pharmacological approaches, including exercise, dietary interventions, and dietary supplementation, has increased as part of comprehensive OA management strategies [35–38].

The present findings suggest that GLMP supplementation was associated with improvements in pain and physical function in adults with mild-to-moderate knee OA. Participants receiving GLMP demonstrated greater improvements in WOMAC total score, WOMAC pain, WOMAC physical function, and VAS pain than those receiving placebo. Although the magnitude of treatment effects was modest, consistent improvements across multiple patient-reported outcomes support the potential role of GLMP supplementation in symptom management for knee OA.

Experimental studies have suggested that GLM-derived compounds possess anti-inflammatory properties. Preclinical studies have reported modulation of inflammatory signaling pathways and suppression of mediators implicated in OA pathophysiology [12, 39–43]. Such mechanisms have been proposed as potential explanations for symptom improvement in OA; however, the present study was not designed to directly evaluate these pathways, and the absence of significant changes in CRP and ESR limits mechanistic interpretation. Therefore, the biological mechanisms underlying the observed symptomatic improvements remain uncertain and require further investigation in studies incorporating more sensitive mechanistic biomarkers.

Importantly, the improvements observed in WOMAC and VAS outcomes represent changes in patient-reported symptoms and physical function, which are directly relevant to daily living and quality of life. However, these outcomes do not provide evidence of structural modification of osteoarthritis, and no conclusions regarding cartilage preservation or disease progression can be drawn from the present study.

The baseline WOMAC total score in our study was relatively lower than that reported in several previous OA trials. This likely reflects the inclusion of participants with mild-to-moderate radiographic OA (Kellgren–Lawrence grade 1–2) and a minimum pain threshold of 30 mm on the VAS, resulting in a study population with relatively mild symptoms and less severe functional impairment. Consequently, the potential for measurable improvement may have been more limited than in studies enrolling patients with more advanced disease. Nevertheless, statistically significant improvements in pain and physical function were observed following GLMP supplementation.

The results of the present study are generally consistent with previous clinical studies evaluating GLM-based interventions for OA. Several studies have reported improvements in pain and physical function following supplementation with GLM preparations, although the magnitude of benefit has varied across studies [8, 44, 45]. Such variability may be attributable to differences in participant characteristics, baseline disease severity, intervention formulations, dosages, treatment duration, and outcome measures.

Similar heterogeneity has also been reported for other nutritional supplements commonly used in OA management, including glucosamine and chondroitin [3, 38, 46]. A network meta-analysis by Wandel et al. [3] concluded that glucosamine and chondroitin were associated with limited and inconsistent benefits compared with placebo. In the present study, GLMP supplementation demonstrated a generally consistent pattern of improvement across both the primary outcome (WOMAC total score) and multiple secondary outcomes, including WOMAC pain, WOMAC physical function, and VAS pain. Although direct comparisons between studies should be interpreted cautiously, the consistency of treatment effects across several patient-reported outcomes may support the potential role of GLMP as a complementary intervention for symptom management in knee OA.

Furthermore, while the GAIT trial conducted by Clegg et al. [46] primarily emphasized pain-related outcomes, the present study demonstrated improvements not only in pain measures but also in WOMAC physical function. Because physical function represents a clinically important outcome in individuals with knee OA, these findings may suggest potential benefits of GLMP supplementation beyond pain reduction alone.

Taken together, the present findings contribute additional evidence regarding GLMP supplementation as a complementary approach for symptom management in individuals with mild-to-moderate knee OA. The inclusion of a Korean cohort also contributes data from a relatively underrepresented population and may help expand the evidence base across different ethnic and dietary backgrounds. Although further large-scale studies are needed to confirm these findings, the observed improvements in pain and physical function together with the favorable safety profile suggest that GLMP may represent a promising complementary option for symptom management within multimodal and non-pharmacological approaches to OA management.

Limitations

This study has several limitations. First, the intervention period was limited to 12 weeks, which may be insufficient to evaluate the long-term efficacy and safety of GLMP supplementation. Second, participants were restricted to individuals with mild-to-moderate knee OA (Kellgren–Lawrence grade 1–2), which may limit the generalizability of the findings to patients with more advanced disease. Third, no significant changes were observed in CRP or ESR levels. Because these biomarkers are nonspecific measures of systemic inflammation and may not adequately reflect local joint inflammation, the biological mechanisms underlying the observed symptomatic improvements remain unclear. Future studies incorporating more sensitive mechanistic biomarkers or imaging assessments are warranted. Finally, although PP analysis was prespecified as the primary efficacy analysis according to the Statistical Analysis Plan, PP analyses may overestimate treatment effects because participants with protocol deviations or inadequate adherence are excluded. In the present study, the primary endpoint achieved statistical significance only in the PP population, whereas the ITT analysis demonstrated a similar trend without reaching statistical significance. Therefore, the efficacy findings should be interpreted with caution. Confirmation in larger trials with longer follow-up periods is warranted.

Conclusion

Twelve-week supplementation with 1,000 mg of green-lipped mussel powder was associated with improvements in knee pain and physical function and was well tolerated in adults with mild-to-moderate osteoarthritis. These findings suggest that GLMP may have potential as a complementary dietary supplement for symptom management in individuals with knee OA. Further studies are warranted to confirm these findings, evaluate their long-term sustainability, and assess structural outcomes separately before any conclusions regarding disease modification can be made.

Abbreviations

AE

Adverse event

ANCOVA

Analysis of covariance

AIF

Anti-inflammatory factor

CI

Confidence interval

CONSORT

Consolidated Standards of Reporting Trials

COX

Cyclooxygenase

CRP

C-reactive protein

ESR

Erythrocyte sedimentation rate

ETA

Eicosatetraenoic acid

GLM

Green-lipped mussel

GLMP

Green-lipped mussel powder

ITT

Intention-to-treat

KGCP

Korean Good Clinical Practice

KL

Kellgren–Lawrence

LOCF

Last observation carried forward

LOX

Lipoxygenase

NF-κB

Nuclear factor kappa B

NSAID

Nonsteroidal anti-inflammatory drug

OA

Osteoarthritis

PP

Per-protocol

SAE

Serious adverse event

SD

Standard deviation

VAS

Visual analog scale

WOMAC

Western Ontario and McMaster Universities Osteoarthritis Index

Authors’ contributions

IH, HTK, and DJL: Conceptualization. BJS, HJP, and YWL: Data curation.HTK and BJS: Formal analysis. DJL: Funding acquisition. BCS, IH, HTK, EHW, MSH, and SYP: Methodology. IH and DJL: Project administration. HTK, SYP, and IH: Software analysis. IH and BCS: Supervision and co-corresponding author. HTK, BCS, and IH: Writing – original draft. HTK, BCS, IH, EHW, MSH, and SYP: Writing – review & editing. All authors contributed to the article and approved the submitted version.

Funding

This study was supported by a research grant from Nutrix Global Co., Ltd. The funding source had no role in the study design; collection, analysis, or interpretation of data; writing of the manuscript; or the decision to submit the manuscript for publication.

Data availability

The data that support the findings of this clinical trial are available from the corresponding author upon reasonable request. Owing to patient privacy and ethical restrictions, individual participant data cannot be made publicly available. This trial was registered with the Clinical Research Information Service under the identifier KCT0008821.

Declarations

Ethics approval and consent to participate

This clinical trial was approved by the Institutional Review Board of Pusan National University Korean Medicine Hospital (approval number: PNUKHIRB 2023-04-001). The study was conducted in accordance with the Declaration of Helsinki and the Korean Good Clinical Practice (KGCP) guidelines. Written informed consent was obtained from all participants prior to enrollment. Participant enrollment began on October 31, 2023, and the final study visit was completed on June 27, 2024.

Consent for publication

Not applicable. This manuscript does not contain any individual person’s identifiable data.

Competing interests

The authors declare no competing interests.