Comparative effects of regular, bloomed or white chocolate on cardiovascular and antioxidant markers in healthy adults

Abstract

Background

Cardiovascular diseases (CVDs) remain the leading cause of mortality worldwide, highlighting the need for effective dietary strategies to mitigate risk. Cocoa-rich dark chocolate contains bioactive compounds with reported cardioprotective effects; however, evidence regarding the impact of fat-bloomed chocolate in humans is limited. This study evaluated the effects of 15-day consumption of isocaloric portions (316 kcal/day; ∼50 g) of regular dark chocolate (70% cocoa), bloomed dark chocolate (70% cocoa), and white chocolate (0% cocoa) on cardiovascular and antioxidant markers in healthy adults.

Methods

Thirty-six participants (27 females, 9 males) completed the intervention. Outcome measures included blood pressure, skin blood flow, lipid profile, fasting glucose, inflammatory markers, and total antioxidant capacity. The study also assessed whether fat blooming alters the functional properties of dark chocolate.

Results

Neither regular nor bloomed dark chocolate significantly affected blood pressure or skin blood flow. In contrast, white chocolate significantly reduced skin blood flow (P = 0.015). Both dark chocolate groups demonstrated non-significant changes toward lower fasting glucose (P = 0.090) and higher high-density lipoprotein (HDL) cholesterol (P = 0.088), changes not observed in the white chocolate group. Total antioxidant capacity increased significantly following both dark chocolate interventions (P < 0.05), with no change in the white chocolate group.

Conclusion

Bloomed dark chocolate retained comparable antioxidant and cardiometabolic effects to regular dark chocolate. These findings suggest that fat blooming does not diminish the functional properties of dark chocolate. Larger, longer-term studies are needed to confirm these findings and inform recommendations for chocolate consumption in CVD prevention.

1. Introduction

Cardiovascular diseases (CVDs) represent a major global health challenge, accounting for approximately 700,000 deaths annually in the United States [1] and an estimated 18 million deaths worldwide [2]. Increasing attention has been directed toward nutritional interventions as a strategy to reduce CVD risk, particularly through the consumption of foods rich in antioxidants and polyphenols, such as flavonoids [[3], [4], [5], [6], [7]]. Dark chocolate, a widely consumed food product, is a notable source of flavonoids, including catechins and epicatechins, which exhibit both antioxidant and anti-inflammatory properties [[6], [7], [8], [9], [10], [11], [12], [13]].

Experimental and clinical studies have demonstrated that dark chocolate consumption may enhance endothelial function [[14], [15], [16], [17], [18]], reduce oxidative stress [19], and support blood pressure regulation [17,[20], [21], [22], [23]], effects largely attributed to its bioactive constituents. In addition to flavonoids, dark chocolate contains methylxanthines such as theobromine and caffeine, which may promote vasodilation, improve lipid metabolism, and inhibit low-density lipoprotein (LDL) oxidation [[6], [7], [8], [9], [10], [11], [12], [13],19,24,25]. Systematic reviews and meta-analyses have reported that regular dark chocolate intake can reduce LDL cholesterol, increase high-density lipoprotein (HDL) cholesterol, and enhance glucose metabolism [[6], [7], [8], [9], [10], [11], [12], [13],25,26], suggesting its potential utility in managing Type 2 diabetes and metabolic disorders [[25], [26], [27]]. Collectively, these findings support the classification of dark chocolate as a functional food with cardioprotective potential.

However, chocolate is highly sensitive to environmental conditions such as temperature and humidity. Improper storage, transport, or repeated heating and cooling can result in a visible white or grayish coating on the surface known as “bloom” [28,29]. Blooming occurs when fats or sugars migrate to the surface and recrystallize, altering the chocolate's visual and textural qualities—producing a dull, spotted, waxy, or greasy appearance [28,29]. While bloomed chocolate remains safe for consumption and may retain certain health benefits such as lipid-lowering effects, its antioxidant capacity may be compromised [12,29].

Despite the widespread occurrence of blooming in consumer chocolate products, limited research has examined how this physical alteration affects the cardioprotective properties of dark chocolate in humans. The present study aims to evaluate the effects of daily consumption of isocaloric (316 kcal; ∼50 g) portions of regular dark chocolate, bloomed dark chocolate, and white chocolate (control) on key cardiovascular health markers. These include blood pressure, skin blood flow, fasting glucose, lipid profile, inflammation, and both antioxidant enzyme activity and total antioxidant capacity. Additionally, this study explores the differential antioxidant potential among the three chocolate types.

2. Methods

2.1. Participants

Thirty-nine adults from Southern California were recruited through flyers and word-of-mouth for the study. Of these, 36 participants (n = 27 females, n = 9 males) completed the study (Fig. 1), while three were excluded due to non-compliance. Inclusion criteria required participants to be healthy adults aged 18–50 years. Exclusion criteria included individuals taking prescription medications affecting blood pressure or lipid levels, those with allergies to cocoa or ingredients in the chocolate bars, and those with diabetes, or who were pregnant or lactating. Participants were instructed to maintain their usual diets and physical activity. The study was approved by the Institutional Review Board for Human Subjects at San Diego State University, and written informed consent was obtained from all participants prior to the study. The study is registered at clinicaltrials.gov (NCT06808282).

Fig. 1.

CONSORT flow diagram of participant selection.

2.2. Study design

A 15-day randomized, parallel-arm, controlled trial with three isocaloric intervention groups of white chocolate (control), regular dark chocolate and bloomed dark chocolate was conducted. Due to the distinct visual differences among the chocolate types, this study was conducted as an open-label trial, and participants were aware of the type of chocolate they received. Participants were randomly assigned to different groups using a drawing-based randomization process. The randomization sequence was prepared in sealed opaque envelopes, which were opened only after participant enrollment to ensure allocation concealment. This procedure ensured that researchers enrolling participants were unaware of the next group assignment. Prior to the study, participants were instructed to refrain from consuming any chocolates and dietary supplements for one week. Participants were instructed to consume approximately 50 g of their assigned chocolate each day for 15 consecutive days. All participants were provided with 15-day supply of their assigned chocolate during the baseline visit. The white chocolate group was provided with Lindt Excellence White Coconut (0% cocoa) (54g serving, 316.3 kcal, 29.8g carbohydrate, 18.6g fat, 29.8g sugar, 3.7g protein), while the dark chocolate group received Lindt Excellence Smooth Dark 70% cocoa (50g serving, 317 kcal, 21.7g carbohydrate, 23.3g fat, 15g sugar, 3.3g protein), (Lindt & Sprungli Inc., Stratham, NH). Bloomed dark chocolate was generated by subjecting Lindt Excellence Smooth Dark 70% cocoa chocolate bars to seven thermal cycles at 42 °C for 16 h, followed by cooling at room temperature for 8 h [30,31]. Bloom formation was assessed through visual inspection, and more than 80% of the chocolate surface exhibited visible bloom prior to the intervention.

Participants attended two visits, one at baseline and another 15 days post-intervention, arriving in a fast state for a minimum of 10 h prior to each visit. During each visit, fasting blood samples were collected and centrifuged at 1200×g for 10 min at 4 °C. The serum samples were then stored at −80 °C until analysis.

2.3. Anthropometric measurements

Anthropometric measurements, including height, weight, body mass index (BMI), and body fat percentage, were collected on days 1 (baseline) and 15 of the experiment. Height and weight were measured using a beam scale (Detecto 439 Eye-level Weight Beam Physician Scale, Webb City, MO). BMI was calculated using the formula, BMI = body weight (Kg)/height (m²). Body fat percentage was assessed via Bioelectrical Impedance Analysis (BIA) using a handheld device (Omron Healthcare Inc., Bannockburn, IL).

2.4. Dietary intake

Written 24-h dietary recalls were collected at baseline and day 15 of the study. The dietary data were analyzed using Food Processor software (ESHA Research, Salem, OR). The study considered each subject's height, weight, gender, age, and activity levels to calculate individual Dietary Reference Intakes (DRI). The dietary components assessed included total kilocalories, kilocalories from saturated fat, protein, carbohydrates, dietary fiber, total fat, saturated fat, monounsaturated fat, polyunsaturated fat, cholesterol, calcium, iron, and vitamins A, C, D, and E.

2.5. Blood pressure

Blood pressure (BP) was measured in a seated position after a 10-min rest using an automatic monitor (Omron Healthcare Inc., Bannockburn, IL). Participants chose either the right or left arm for measurement, and the same arm was used for all subsequent readings. Systolic and diastolic BP were recorded right before chocolate ingestion, 30 min after, and 1 h after, both at baseline and on day 15. The average of two readings was recorded for each time point.

2.6. Forearm skin blood flow

Skin blood flow was measured using Laser Doppler Flowmetry (TSI Laserflo, St. Paul, MN) while participants sat with their forearm resting on their lap and fingers relaxed and extended. The laser probe was secured approximately two inches below the elbow, positioned over a prominent blood vessel. Measurements were taken before chocolate ingestion, 30 min after, and 1 h at baseline and on day 15 of the study, following a modified protocol from Muller et al. [32]. Once the flow readings stabilized (less than 0.2 ml/100 ml/min/10 s variation), flow rates were recorded every 10 s for 1 min, and the average of the six recordings was calculated for each testing period.

2.7. Biochemical analysis

2.7.1. Albumin and glucose

Serum albumin and glucose concentrations were measured using the Albumin Liquicolor assay and Glucose Liquicolor assay, respectively (Stanbio Laboratory, Boerne, TX). Serum samples were combined with the assay reagent, leading to immediate color development. Absorbance was subsequently recorded at 550 nm and 500 nm, respectively.

2.7.2. Lipid profile

Serum levels of total cholesterol, triglycerides, and high-density lipoprotein (HDL) cholesterol were measured using the Stanbio assay kits (Boerne, TX). Low-density lipoprotein (LDL) cholesterol levels were calculated using the Friedewald equation: LDL cholesterol = total cholesterol – HDL cholesterol – (TG/5) [33].

2.7.3. C-Reactive Protein (CRP)

Serum C-reactive protein (CRP) levels were determined using a CRP ELISA kit from Immunodiagnostik, Inc. (Manchester, NH). The assay employed a peroxidase-labeled detection antibody, followed by the addition of a TMB substrate. After the reaction was stopped with an acidic solution, the absorbance was measured at 450 nm.

2.7.4. Serum antioxidant capacity

The serum antioxidant capacity was measured using an antioxidant assay kit from Sigma (St. Louis, MO, USA). This assay operated on the principle that a ferryl myoglobin radical, generated from the reaction between myoglobin and hydrogen peroxide, oxidizes 2,2′-azino-bis (3-ethylbenzthiazoline-6-sulfonic acid) (ABTS), resulting in the formation of the radical cation ABTS+. Trolox, a water-soluble analog of vitamin E, was employed as the antioxidant standard for the assay [34].

2.7.5. Antioxidant enzyme activities

Serum levels of superoxide dismutase (SOD), catalase (CAT), glutathione S-transferase (GST) and glutathione peroxidase (GPx) were measured using Cayman assay kits (Ann Arbor, MI). SOD activity was determined by adding xanthine oxidase and hypoxanthine to generate superoxide radicals, with absorbance read at 450 nm. CAT activity was assessed by monitoring the reaction between the enzyme and methanol in the presence of H₂O₂, with absorbance read at 540 nm. GST activity was determined by measuring the conjugation of 1-chloro-2,4-dinitrobenzene with reduced glutathione, with absorbance changes reflecting GST activity. GPx activity was quantified via a coupled reaction with GR, where the oxidation of NADPH indicated GPx activity. Absorbance for GST and GPx was recorded at 340 nm. All assays were performed according to the manufacturer's protocols.

2.7.6. Oxygen Radical Absorbance Capacity (ORAC)

The total antioxidant capacity of the white chocolate, dark chocolate, and bloomed dark chocolate was assessed using the ORAC assay, conducted by Brunswick Laboratory (Southborough, MA), following the methods outlined by Prior et al. [35]. Hydrophilic, lipophilic, and total antioxidant values were measured.

2.8. Statistical analysis

An a priori power calculation was conducted based on outcomes reported in previous short-term dark chocolate intervention studies [36,37]. Using changes in total cholesterol and antioxidant capacity as reference outcomes, we estimated that a sample size of 12 participants per group would provide 80% power to detect significant differences between groups.

Data were analyzed using a 3 (group) × 2 (time) mixed-design ANOVA with repeated measures in SPSS Statistics 29 (IBM, Armonk, NY, USA) to assess the impact of bloomed dark chocolate, regular dark chocolate, and white chocolate consumption on all variables. Bonferroni tests were conducted for follow-up post hoc analyses. In addition, paired t-tests were utilized for within-group comparisons and independent t-tests for between-group comparisons. Baseline differences across trials were evaluated using t-tests. When significant differences were observed, a repeated measures ANCOVA with baseline as a covariate was applied for between-group adjustments, followed by t-test post hoc analyses. Results were reported as means ± standard deviations (SDs), with statistical significance set at P < 0.05.

3. Results

3.1. Anthropometric measurements

A total of 36 participants were analyzed in this study, divided into three groups: the white chocolate (control) group with 10 participants (4 males, 6 females), the regular dark chocolate group with 13 participants (3 males, 10 females), and the bloomed dark chocolate group with 13 participants (2 males, 11 females) (Fig. 1). The mean age, BMI, and body fat percentage for the white chocolate group were 27.6 years, 23.97 kg/m², and 22.03%, respectively (Table 1). For the regular dark chocolate group, these values were 27.6 years, 23.96 kg/m², and 22.43%. The bloomed dark chocolate group had corresponding values of 27.7 years, 23.41 kg/m², and 22.40%. No significant differences in age, body weight, BMI, or body fat percentage were observed between groups at baseline or post-intervention. Additionally, no significant changes in anthropometric measurements, including BMI and body fat percentage, were detected within groups over time (baseline vs day 15).

Table 1.

Anthropometric measurements, blood pressure and skin blood flow measurements.

Variable	White Chocolate		Regular Dark Chocolate		Bloomed Dark Chocolate
	Day 1 (Baseline)	Day 15	Day 1 (Baseline)	Day 15	Day 1 (Baseline)	Day 15
Weight (kg)	71.73 ± 16.03	71.95 ± 16.23	66.45 ± 17.91	66.11 ± 17.30	63.06 ± 13.17	62.95 ± 13.54
BMI (kg/m2)	23.97 ± 2.92	24.04 ± 2.98	23.96 ± 4.56	23.83 ± 4.21	23.41 ± 3.69	23.36 ± 3.81
Body fat (%)	22.03 ± 7.72	22.20 ± 7.12	22.43 ± 6.10	22.13 ± 5.76	22.40 ± 4.47	22.10 ± 4.67
SBP (mmHg)	116.90 ± 12.44	118.90 ± 13.36	118.23 ± 12.94	118.38 ± 16.20	112.81 ± 8.60	113.50 ± 8.99
DBP (mmHg)	67.75 ± 6.04	68.90 ± 7.43	74.62 ± 7.30	75.15 ± 6.42	70.38 ± 8.70	70.42 ± 6.95
SBF (ml/100 ml/min)	1.35 ± 0.44	0.73 ± 0.41∗	1.01 ± 0.42	0.91 ± 0.45	1.22 ± 0.68	1.03 ± 0.65

Data are expressed as means ± SDs. N = 36. Data Indicated with an ∗ are statistically significant (P < 0.05). BMI: Body mass index; SBP: Systolic blood pressure; DBP: Diastolic blood pressure; SBF: Skin blood flow.

3.2. Blood pressure and skin blood flow

Blood pressure measurements, including systolic (SBP) and diastolic (DBP), showed no significant differences between groups during the acute phase or overtime (Table 1). In the white chocolate group, skin blood flow showed a non-significant decrease during the acute-phase changes from baseline to 60 min (P = 0.07; white chocolate 0.68 ml/100 ml/min, regular dark chocolate 1.03 ml/100 ml/min, and bloomed dark chocolate 1.14 ml/100 ml/min) and decreased significantly over the treatment period (P = 0.015). In contrast, no significant changes in skin blood flow were observed in the regular or bloomed dark chocolate groups during the acute phase or the treatment period.

3.3. Albumin, glucose and lipid profile

Table 2 summarized albumin, glucose, and lipid profile data. Albumin levels remained stable across all groups over time. A non-significant change toward a group-by-time interaction for glucose was observed (P = 0.090), with decreases in glucose levels in both the regular and bloomed dark chocolate groups, but no change in the white chocolate group. Similarly, HDL cholesterol showed a non-significant increase in the regular and bloomed dark chocolate groups (P = 0.088), with no such change in the white chocolate group. Triglycerides (TG), total cholesterol (TC), and LDL cholesterol (LDL) showed no significant differences within groups over time.

Table 2.

Biochemical measurements of albumin, glucose, lipids.

Variable	White Chocolate		Regular Dark Chocolate		Bloomed Dark Chocolate
	Day 1 (Baseline)	Day 15	Day 1 (Baseline)	Day 15	Day 1 (Baseline)	Day 15
Albumin (g/dL)	4.62 ± 0.30	4.87 ± 0.36	4.83 ± 0.32	4.74 ± 0.36	4.76 ± 0.34	4.87 ± 0.33
Glucose (mmol/L)	4.79 ± 0.47	4.80 ± 0.53	4.89 ± 0.44	4.56 ± 0.28	4.70 ± 0.37	4.45 ± 0.29
TG (mmol/L)	0.77 ± 0.43	0.79 ± 0.30	0.78 ± 0.31	0.83 ± 0.36	0.80 ± 0.29	0.81 ± 0.42
TC (mmol/L)	4.38 ± 0.66	4.56 ± 0.47	4.43 ± 0.63	4.25 ± 0.52	4.40 ± 1.14	4.29 ± 0.76
HDL (mmol/L)	1.17 ± 0.22	1.12 ± 0.25	1.20 ± 0.28	1.27 ± 0.16	1.21 ± 0.32	1.30 ± 0.27
LDL (mmol/L)	2.86 ± 0.63	3.09 ± 0.48	2.86 ± 0.65	2.60 ± 0.52	2.82 ± 1.12	2.62 ± 0.69

Data are expressed as means ± SDs. N = 36. TG: Triglycerides; TC: Total cholesterol; HDL: High-density lipoprotein cholesterol; LDL: Low-density lipoprotein cholesterol.

3.4. CRP, antioxidant capacity and antioxidant enzyme activities

A significant group-by-time interaction was observed for total antioxidant capacity (P = 0.024; Table 3), with increases noted in both the regular and bloomed dark chocolate groups, but no change with white chocolate consumption. No significant differences were detected in C-reactive protein (CRP) or antioxidant enzymes SOD, CAT, GST, and GPx within or among groups.

Table 3.

Measurements of CRP, TEAC and antioxidant enzymes.

Variable	White Chocolate		Regular Dark Chocolate		Bloomed Dark Chocolate
	Day 1 (Baseline)	Day 15	Day 1 (Baseline)	Day 15	Day 1 (Baseline)	Day 15
CRP (μg/mL)	2.60 ± 1.99	2.59 ± 1.60	2.77 ± 1.73	2.49 ± 2.05	3.00 ± 2.06	2.83 ± 2.05
TEAC (mmol/L)	0.34 ± 0.06	0.30 ± 0.10	0.32 ± 0.05	0.37 ± 0.03∗	0.32 ± 0.05	0.38 ± 0.05∗
SOD (U/mL)	12.92 ± 2.05	14.83 ± 2.29	13.24 ± 3.06	14.69 ± 2.48	14.03 ± 4.01	13.29 ± 3.29
CAT (nmol/[min∗mL])	9.69 ± 6.96	8.26 ± 6.71	10.14 ± 4.65	9.38 ± 9.31	9.54 ± 8.50	10.59 ± 8.86
GST (nmol/[min∗mL])	1.22 ± 0.39	1.11 ± 0.53	1.24 ± 1.24	1.27 ± 1.20	1.26 ± 1.34	1.28 ± 1.06
GPx (nmol/[min∗mL])	2.72 ± 0.56	2.23 ± 1.04	2.30 ± 0.84	2.30 ± 0.97	2.40 ± 1.09	2.29 ± 1.08

Data are expressed as means ± SDs. N = 36. Data Indicated with an ∗ are statistically significant (P < 0.05). CRP: C-reactive protein; TEAC: Trolox equivalent antioxidant capacity; SOD: Superoxide dismutase; CAT: Catalase; GST: Glutathione S-transferase; GPx: Glutathione peroxidase.

3.5. Chocolate ORAC

Differences across ORAC categories were observed (Fig. 2). The hydrophilic ORAC capacity was significantly higher in the regular and bloomed dark chocolate groups compared to the white chocolate group (P < 0.001). A similar pattern was observed for total ORAC capacity (P < 0.001). A non-significant change in lipophilic ORAC capacity was also found, with higher values in the regular and bloomed dark chocolate groups compared to the white chocolate group (P = 0.078). No significant differences were identified between the regular and bloomed dark chocolate groups across the three ORAC capacities tested.

Fig. 2.

ORAC hydrophilic, lipophilic and total antioxidant capacity of white chocolate, regular dark chocolate, and bloomed dark chocolate. Data are presented as means ± SDs. ∗: statistically significant at P < 0.05 compared to white chocolate. ORAC: Oxygen radical absorbance capacity.

3.6. Dietary intake

Daily consumption of 300 kcal of the assigned chocolate intervention did not significantly impact overall caloric intake in any of the groups. No significant changes were observed in the intake of carbohydrates, protein, fats, fiber, or vitamins A, C, and E within or among groups. Dietary intake results were detailed in Table 4.

Table 4.

Energy and nutrient intake at baseline and day 15 of the chocolate treatment groups.

Variable	White Chocolate		Regular Dark Chocolate		Bloomed Dark Chocolate
	Day 1 (Baseline)	Day 15	Day 1 (Baseline)	Day 15	Day 1 (Baseline)	Day 15
Energy (Kcal/d)	1830.7 ± 809.2	1993.8 ± 870.4	1824.7 ± 432.4	2011.5 ± 692.8	1731.4 ± 659.0	1888.5 ± 741.4
CHO (g/d)	246.14 ± 84.38	265.34 ± 126.53	273.80 ± 213.76	256.32 ± 92.91	210.49 ± 114.40	253.75 ± 110.37
Protein (g/d)	64.57 ± 2.37	73.22 ± 29.07	83.17 ± 23.44	78.36 ± 29.64	73.98 ± 29.15	83.61 ± 33.57
Fat (g/d)	69.14 ± 47.36	72.50 ± 40.80	71.98 ± 44.65	77.58 ± 34.91	61.84 ± 31.96	64.30 ± 25.61
SFA (g/d)	17.20 ± 10.50	23.11 ± 10.17	24.29 ± 24.19	29.89 ± 19.34	17.97 ± 11.22	23.53 ± 9.20
MUFA (g/d)	20.50 ± 22.85	14.08 ± 14.78	14.83 ± 11.85	17.11 ± 10.77	13.33 ± 8.93	17.43 ± 9.83
PUFA (g/d)	10.21 ± 13.52	4.49 ± 2.04	8.27 ± 7.14	7.30 ± 5.55	6.62 ± 5.55	6.84 ± 4.93
Cholesterol (g/d)	109.39 ± 167.83	168.56 ± 208.39	227.26 ± 253.06	214.89 ± 240.44	179.10 ± 167.13	156.21 ± 89.47
Vitamin A (μg/d)	556.99 ± 702.90	276.28 ± 454.70	416.17 ± 454.26	321.10 ± 334.75	526.07 ± 740.56	506.87 ± 364.50
Vitamin C (mg/d)	135.39 ± 78.64	99.84 ± 45.44	137.84 ± 109.53	111.76 ± 75.38	87.82 ± 44.54	84.74 ± 41.60
Vitamin D (μg/d)	3.77 ± 4.29	2.81 ± 4.25	5.11 ± 7.84	4.90 ± 6.97	7.80 ± 17.72	2.82 ± 4.72
Vitamin E (mg/d)	10.20 ± 14.68	6.05 ± 7.02	6.99 ± 8.85	8.63 ± 10.72	6.93 ± 10.09	6.30 ± 9.50
Fiber (g/d)	23.80 ± 14.18	28.79 ± 15.18	27.21 ± 13.11	28.83 ± 13.61	28.80 ± 25.78	29.07 ± 17.72
Ca (mg/d)	787.22 ± 399.84	550.28 ± 291.07	743.01 ± 352.22	673.10 ± 439.14	654.26 ± 272.28	760.14 ± 427.16
Fe (μg/d)	18.62 ± 12.51	16.00 ± 11.22	15.74 ± 5.93	20.31 ± 10.89	14.99 ± 11.11	18.94 ± 10.57

Data are expressed as means ± SDs. N = 36. CHO: Carbohydrates; SFA: Saturated fatty acids; MUFA: Monounsaturated fatty acids; PUFA: Polyunsaturated fatty; Ca: Calcium; Fe: Iron.

4. Discussion

The aim of the present study was to compare the effects of daily consumption of isocaloric amounts of bloomed and regular dark chocolate with white chocolate (used as a control) on cardiovascular health markers. Additionally, the study assessed whether the blooming process alters the cardioprotective or antioxidant capacity of dark chocolate.

No significant changes in systolic or diastolic blood pressure (SBP/DBP) were observed in any of the groups over the 15-day intervention. These findings align with previous short-term studies, including those by Christen et al. [38], who reported no change in resting SBP following two weeks of 50 g/day dark chocolate consumption, and Garcia-Yu et al. [39], who observed no significant blood pressure changes in postmenopausal women after six months of 10 g/day of 99% cocoa dark chocolate. However, reductions in SBP and DBP have been reported in populations with existing cardiometabolic conditions. Rostami et al. [23] observed significant blood pressure improvements in individuals with type 2 diabetes and hypertension after eight weeks of 25 g/day 83% dark chocolate, consistent with findings by Grassi et al. [21,22] using 100 g/day over 15 days.

The antihypertensive effects of dark chocolate are thought to result from flavonoid-mediated upregulation of endothelial nitric oxide synthase (eNOS), enhancing nitric oxide (NO) bioavailability and promoting vasodilation [13]. Additionally, dark chocolate flavonoids may inhibit angiotensin-converting enzyme (ACE), reducing vasoconstriction via decreased angiotensin II levels [13]. Nevertheless, the lack of standardized cocoa content, dose, and intervention duration across studies contributes to inconsistent findings. Furthermore, variability in flavonoid content due to differences in cocoa processing—from fermentation and roasting to final production—may impact the efficacy of chocolate-based interventions [28,40].

This study observed a significant reduction in skin blood flow in the white chocolate group. Similar findings were reported by Grassi et al. [15], where consumption of 100 g/day of 0% cocoa chocolate for three days resulted in decreased flow-mediated dilation, increased arterial stiffness, elevated oxidative stress, and raised levels of endothelin-1, a potent vasoconstrictor. These effects are attributed to the absence of flavanols and reduced NO bioavailability. White chocolate, primarily composed of cocoa butter and sugar [9], which may stimulate insulin secretion and sympathetic nervous system activity, promoting vasoconstriction and reducing peripheral blood flow [13,26,[41], [42], [43]].

A non-significant reduction in fasting blood glucose was observed in both dark chocolate groups, consistent with the findings by Leyva-Soto et al. [19], who reported significant reductions in fasting glucose and HOMA-IR among young individuals with metabolic risk following six months of 2 g/day 70% cocoa intake. Rostami et al. [23] also noted improvements in glucose and HbA1c levels in individuals with type 2 diabetes after consuming 25 g/day of 83% dark chocolate for eight weeks. These effects are supported by a meta-analysis by Chen et al. [26], indicating significant reductions in fasting glucose with long-term dark chocolate consumption.

The hypoglycemic effects of dark chocolate are attributed to its flavonoid content—especially catechins and epicatechins—which enhance insulin sensitivity, support pancreatic β-cell function, and inhibit α-amylase and α-glucosidase activity to moderate postprandial glucose responses [24,27,36,44]. Polyphenols also increase GLUT4 translocation and reduce oxidative stress, further improving insulin signaling [24,45].

A non-significant increase in HDL cholesterol was also observed in both dark chocolate groups, consistent with previous experimental studies [19,25,29] and systematic reviews [9,11,26,44]. For instance, Miller et al. [25] reported significantly elevated HDL levels after eight weeks of 45 g/day of 85% dark chocolate in individuals with type 2 diabetes. This effect is attributed to flavonoid-driven enhancement of reverse cholesterol transport via upregulation of ATP-binding cassette transporter A1 (ABCA1) and inhibition of lipid peroxidation, preserving HDL functionality [10,12,13]. Additionally, theobromine in dark chocolate may stimulate hepatic apoA-I production, a key apolipoprotein in HDL formation [8,10,45].

The results of the current study showed significant increases in total antioxidant capacity, consistent with prior research demonstrating the antioxidant potential of cocoa polyphenols and flavonoids [[3], [4], [5],7,8,11,19,22,44]. These bioactive compounds neutralize reactive oxygen species (ROS), stimulate endogenous antioxidant production (e.g., glutathione), and mitigate oxidative damage [12,15,17,19,21,22,44]. While no significant changes in C-reactive protein (CRP) were found, other studies have observed reductions in inflammatory markers with longer-duration or higher-dose chocolate interventions [9,15,26,46].

ORAC testing in this study revealed no significant difference in antioxidant capacity between bloomed and regular dark chocolate, suggesting that blooming does not compromise the core antioxidant properties of dark chocolate. These findings contrast with those of Shadwell et al. [29], who reported reduced ORAC values in bloomed chocolate. However, even in their study, bloomed chocolate retained lipid-lowering effects. This discrepancy may be due to variations in blooming conditions or testing protocols. Reviews suggest that although blooming affects the chocolate's appearance and surface properties, key flavonoids remain stable and effective [7,11,29].

This study has several limitations. Although the sample size was sufficient to detect significant changes in primary outcomes such as antioxidant capacity, it may have been underpowered to detect smaller effects in other outcomes. While the 15-day duration was supported by prior studies showing changes in antioxidant markers within 2 weeks [36], longer interventions (≥4 weeks) are typically required for stable changes in lipid profiles and blood pressure [47]. Participants were predominantly female and consisted exclusively of young, healthy adults with normal baseline parameters. Consequently, the findings may not be directly generalizable to older individuals or those with pre-existing cardiovascular risk factors. Caution should be exercised when extrapolating these results to clinical populations. The open-label design, due to visible differences in chocolate type, may have influenced subjective outcomes (e.g., taste, satiety), but is unlikely to have affected objective measures such as blood pressure, lipid profile, and antioxidant capacity. Future studies with larger, more diverse cohorts of varying ages and health statuses, and longer intervention durations, are needed to confirm sustained metabolic effects and refine consumption guidelines for dark chocolate as a cardioprotective functional food. Finally, the primary method for confirming fat bloom was visual inspection, which is less precise than analytical techniques such as colorimetry, microscopy, or texture analysis. Future studies should incorporate objective measures to more rigorously verify bloom formation and assess its potential impact on chocolate properties.

In conclusion, this study demonstrates that bloomed dark chocolate produces effects comparable to those of regular dark chocolate on cardiovascular and antioxidant markers, including significant increases in antioxidant capacity and non-significant changes in fasting glucose and HDL cholesterol. In contrast, white chocolate showed significantly lower antioxidant capacity and reduced skin blood flow, highlighting the potential cardioprotective benefits of dark chocolate. These findings suggest that bloomed dark chocolate may remain a viable dietary option for supporting cardiovascular health, although further research is needed before making broader recommendations over white chocolate.

CRediT authorship contribution statement

Louise Chatagnier: Writing – original draft, Visualization, Data curation. Christina Orsa: Investigation, Data curation. Deva Plumlee: Project administration, Investigation, Data curation. Alely Wright: Investigation. Mee Young Hong: Writing – review & editing, Writing – original draft, Supervision, Resources, Project administration, Methodology, Investigation, Funding acquisition, Formal analysis, Data curation, Conceptualization.

Data availability statement

Data will be available from the principal corresponding author upon reasonable request.

Funding

This study was funded by San Diego State University Grant Program (UGP) and Nutrition 302L class. The study is registered at clinicaltrials.gov (NCT06808282).

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.