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Research · Food and drink

Dark chocolate

Cocoa products lowered blood pressure about 1.8 mmHg in a Cochrane review, more in people with hypertension, and improved blood vessel function and insulin resistance in trials. A 21,442-person trial of cocoa flavanol extract did not significantly cut cardiovascular events. Cohorts link moderate chocolate to less heart disease. Many dark chocolates contained lead or cadmium above California limits.

Add to Bio HackChecked 2026-11-13
Status
A food, not a regulated health product. In 2023 the FDA found "very limited credible evidence" for cocoa flavanols in high flavanol cocoa powder and reduced risk of cardiovascular disease, and limited its qualified claim to cocoa powder because the credible studies did not test dark chocolate [1].
Also called
cocoa, cacao, cocoa powder, cocoa flavanols, flavan-3-ols, high-flavanol cocoa, dark chocolate 70%, chocolate, hot cocoa, cacao nibs
Studied for
blood pressure, heart health, stroke, blood vessel function, insulin sensitivity, mood, depression, focus, memory, brain health, antioxidants

Strong several reviews agree · Moderate one review or consistent trials · Limited one or a few small studies · Untested no study in people, listed with what it rests on

Shown to help4

Reported risks3

What it was studied for, and what was found

Shown to help4

Strong

Blood pressure

Shown to lower blood pressure by about 1.8 mmHg with flavanol-rich cocoa products in short trials, by about 4 mmHg systolic in people with hypertension.

Compared with flavanol-free products or low-flavanol cocoa powder [2]; control conditions the abstract does not describe [3]

The numbers and sources
Effect
Across 40 comparisons, flavanol-rich cocoa products lowered systolic pressure by 1.76 mmHg (95% CI 0.43 to 3.09) and diastolic by 1.76 mmHg (95% CI 0.94 to 2.57) over 2 to 18 weeks. Systolic pressure fell 4 mmHg in people with hypertension and did not change significantly in people with normal blood pressure. Removing trials with authors employed by industry sponsors made the effect slightly smaller [2]. A second meta-analysis found diastolic pressure fell 1.60 mmHg (95% CI 0.43 to 2.77), with larger effects above 50 mg of epicatechin a day [3].
Population
1,804 mainly healthy adults in 35 trials [2]. 1,297 participants in 42 trials of up to 18 weeks [3].
Sources
[2], [3]
Caveats
Unexplained heterogeneity lowered the Cochrane rating to moderate quality, and unblinded trials tended to show larger effects [2]. Many trials used cocoa drinks or extracts rather than chocolate bars.
Moderate

Blood vessel function and insulin resistance

Shown to improve blood vessel widening and lower insulin resistance in short trials of chocolate or cocoa, in one meta-analysis rated low to moderate quality.

Compared with control conditions the abstract does not describe [3]

The numbers and sources
Effect
Flow-mediated dilation rose 1.34% (95% CI 1.00 to 1.68) with regular intake and 3.19% after a single dose. HOMA-IR fell 0.67 (95% CI 0.36 to 0.98) through lower serum insulin. Changes in LDL cholesterol (-0.07 mmol/L, 95% CI -0.13 to 0.00) and HDL cholesterol were of borderline significance [3].
Population
1,297 participants in 42 trials of up to 18 weeks [3].
Sources
[3]
Caveats
The authors rated the evidence low to moderate quality and called for larger, longer, independently funded trials [3].
Limited

Heart disease and stroke, in cohorts

Linked to slightly lower heart disease and stroke in cohort meta-analyses, with the lowest risk near 45 g a week, rated low credibility.

Compared with people eating 20 g a week less [4]; people eating 10 g a day less [5]

The numbers and sources
Effect
Each 20 g a week more chocolate was linked to 1.8% lower cardiovascular disease (RR 0.982, 95% CI 0.972 to 0.992) and 4.4% lower stroke. Risk was lowest at about 45 g a week (RR 0.890), and the authors suggest higher intakes may lose the link [4]. Per 10 g a day, coronary heart disease (RR 0.96, 95% CI 0.93 to 0.99) and stroke (RR 0.90, 95% CI 0.82 to 0.98) were slightly lower, while heart failure and type 2 diabetes were not linked [5].
Population
405,304 participants with 35,093 cases in 23 studies [4]. 27 cohort analyses [5].
Sources
[4], [5]
Caveats
Observational. Most studies measured all chocolate, not dark chocolate. The credibility of the evidence was rated low to very low [5].
Moderate

Mood and anxiety

Shown to ease depressive and anxiety symptoms in the short term, in one meta-analysis of 9 small studies of cocoa-rich products.

Compared with control conditions the abstract does not describe [7]

The numbers and sources
Effect
Cocoa-rich products lowered depressive symptoms (Hedges' g -0.42, 95% CI -0.67 to -0.17) and anxiety symptoms (g -0.49), and improved positive (g 0.41) and negative affect (g -0.47) [7].
Population
9 studies, 5 of a single dose, 2 of 3 days and 2 of more than a week [7].
Sources
[7]
Caveats
Few participants and short studies, so the results do not cover regular intake over months [7].

Mixed results1

Moderate

Focus and thinking

Mixed results: two meta-analyses found better scores on some attention and executive tasks, while a 3-year trial of cocoa extract found no change in overall thinking.

Compared with control conditions the abstract does not describe [8]; control groups [9]; placebo [10]

The numbers and sources
Effect
Regular dark chocolate or cocoa improved Trail Making Test part A (WMD -4.51) and part B (WMD -13.1) and verbal fluency (WMD 3.15), with larger effects at 500 mg of flavanols a day or more and 8 weeks or longer. Memory results were inconsistent and Mini-Mental State scores did not improve [8]. In 7 trials in healthy adults, executive function time fell (WMD -11.77, 95% CI -22.49 to -1.05) [9]. In 2,262 older adults, 3 years of cocoa extract with 500 mg of flavanols did not change global cognition (mean z 0.03, 95% CI -0.02 to 0.08) [10].
Population
2,847 participants in 16 trials [8]. Healthy adults in 7 trials [9]. 2,262 adults with mean age 73 [10].
Sources
[8], [9], [10]
Caveats
The two meta-analyses share trials. The large trial tested an extract by telephone assessments in older adults [10].

Not shown to help1

Limited

Cardiovascular events, cocoa flavanol extract

One trial of a cocoa flavanol extract did not significantly lower total cardiovascular events in 21,442 older adults. Cardiovascular death, a secondary outcome, fell 27%.

Compared with placebo [6]

The numbers and sources
Effect
Over a median 3.6 years, total cardiovascular events occurred in 410 people taking cocoa extract and 456 taking placebo (HR 0.90, 95% CI 0.78 to 1.02). Cardiovascular death was lower (HR 0.73, 95% CI 0.54 to 0.98), and death from any cause did not differ significantly (HR 0.89, 95% CI 0.77 to 1.03). The authors reported no safety concerns [6].
Population
21,442 US women aged 65 and older and men aged 60 and older without major cardiovascular disease [6].
Sources
[6]
Caveats
This tested a capsule of cocoa extract with 500 mg of flavanols, not chocolate. Secondary outcomes do not carry the weight of the primary one.
Why limited
This rests on one trial, of 21,442 people. Strength counts independent studies that agree, so one trial is limited at any size.

Amounts studied

Blood pressure trials gave 30 to 1,218 mg of flavanols a day (mean 670 mg) in 1.4 to 105 g of cocoa products, for 2 to 18 weeks [2]. The extract trial used 500 mg of cocoa flavanols a day, including 80 mg of epicatechin, for a median 3.6 years [6][10]. Cognitive benefits were larger at 500 mg of flavanols a day or more [8]. Cohorts measured chocolate in grams a week or a day, with the lowest cardiovascular risk near 45 g a week [4]. The weight cohort counted 1 oz (about 28 g) servings of chocolate candy [11].

Risks

Reported risks3

LimitedHow often is not known

Lead and cadmium in dark chocolate

One analysis of 72 US cocoa products found 43% exceeded California's daily limit for lead and 35% for cadmium per serving. Nearly all were under FDA lead reference levels.

The numbers and sources
How common
How often is not known: the sources give no rate.
Effect
Of 72 dark chocolate and cocoa products bought from 2014 to 2022, 43% exceeded California Proposition 65 maximum allowable dose levels for lead and 35% for cadmium, and none for arsenic. 97.2% (70 of 72) fell below FDA interim reference levels for lead. Median levels were below the Proposition 65 limits, and organic products were more likely to have higher lead and cadmium [12].
Population
72 consumer products [12].
Sources
[12]
Caveats
A product analysis, not a study of blood levels in people. Several authors work for ConsumerLab.com, a commercial product testing company [12].
LimitedStudied in womenHow often is not known

Weight gain with chocolate candy

Linked to more weight gain over 3 years in a cohort of 107,243 postmenopausal women, 0.92 kg more per extra daily ounce of chocolate candy.

The numbers and sources
How common
How often is not known: the sources give no rate.
Effect
Against women eating a 1 oz serving less than once a month, those eating it 3 or more times a week gained 1.40 kg more over 3 years (95% CI 1.27 to 1.53). Each extra ounce a day was linked to 0.92 kg more gain [11].
Population
107,243 US postmenopausal women aged 50 to 79 [11].
Sources
[11]
Caveats
Observational, and chocolate candy was not separated by cocoa content. Confounding is possible.
LimitedHow often is not known

Blood pressure reactions with MAOI antidepressants

The label of the MAOI antidepressant phenelzine warns that excessive amounts of chocolate and caffeine may cause hypertensive reactions.

The numbers and sources
How common
How often is not known: the sources give no rate.
Effect
Among foods and drinks to avoid during phenelzine treatment and for two weeks after, the label lists excessive amounts of chocolate and caffeine, and states they may cause hypertensive reactions [13].
Population
People taking phenelzine [13].
Sources
[13]
Caveats
A label warning that sets no amount and gives no rate.

Claims tested and not found

  1. That chocolate triggers headaches or migraine. In a double-blind study of 63 women with chronic headache, chocolate did not trigger headaches more often than carob (p = 0.83) [14]. In an earlier double-blind study, only 13 headaches followed chocolate in 80 sessions among people who believed it triggered theirs [15].
  2. That cocoa flavanols protect thinking in older adults. Three years of cocoa extract did not change global cognition in 2,262 older adults [10].
  3. That cocoa lowers blood pressure in people whose blood pressure is normal. In the Cochrane review, systolic pressure did not fall significantly in people with normal blood pressure [2].

Related

Epicatechin

Sources

  1. U.S. Food and Drug Administration. Petition for a Qualified Health Claim for Cocoa Flavanols in High Flavanol Cocoa Powder and Reduced Risk of Cardiovascular Disease. Letter of Enforcement Discretion. 2023. https://www.fda.gov/media/165090/download
  2. Ried K, Fakler P, Stocks NP. Effect of cocoa on blood pressure. Cochrane Database of Systematic Reviews. 2017. https://doi.org/10.1002/14651858.cd008893.pub3
  3. Hooper L, Kay C, Abdelhamid A, et al. Effects of chocolate, cocoa, and flavan-3-ols on cardiovascular health: a systematic review and meta-analysis of randomized trials. The American Journal of Clinical Nutrition. 2012. https://doi.org/10.3945/ajcn.111.023457
  4. Ren Y, Liu Y, Sun XZ, et al. Chocolate consumption and risk of cardiovascular diseases: a meta-analysis of prospective studies. Heart. 2019. https://doi.org/10.1136/heartjnl-2018-313131
  5. Morze J, Schwedhelm C, Bencic A, et al. Chocolate and risk of chronic disease: a systematic review and dose-response meta-analysis. European Journal of Nutrition. 2020. https://doi.org/10.1007/s00394-019-01914-9
  6. Sesso HD, Manson JE, Aragaki AK, et al. Effect of cocoa flavanol supplementation for the prevention of cardiovascular disease events: the COcoa Supplement and Multivitamin Outcomes Study (COSMOS) randomized clinical trial. The American Journal of Clinical Nutrition. 2022. https://doi.org/10.1093/ajcn/nqac055
  7. Fusar-Poli L, Gabbiadini A, Ciancio A, et al. The effect of cocoa-rich products on depression, anxiety, and mood: A systematic review and meta-analysis. Critical Reviews in Food Science and Nutrition. 2022. https://doi.org/10.1080/10408398.2021.1920570
  8. Arabpour Z, Arabpour Z, Jazayeri S. Effect of Chronic Dark Chocolate or Cocoa Intake on Cognitive Function: A Grading of Recommendations Assessment, Development, and Evaluation (GRADE)-Assessed Systematic Review and Meta-Analysis of Randomized Controlled Trials. Nutrition Reviews. 2026. https://doi.org/10.1093/nutrit/nuaf286
  9. Shateri Z, Kooshki A, Hormoznejad R, et al. Effects of chocolate on cognitive function in healthy adults: A systematic review and meta-analysis on clinical trials. Phytotherapy Research. 2023. https://doi.org/10.1002/ptr.7896
  10. Baker LD, Manson JE, Rapp SR, et al. Effects of cocoa extract and a multivitamin on cognitive function: A randomized clinical trial. Alzheimer's & Dementia. 2023. https://doi.org/10.1002/alz.12767
  11. Greenberg JA, Manson JE, Buijsse B, et al. Chocolate-candy consumption and 3-year weight gain among postmenopausal U.S. women. Obesity. 2015. https://doi.org/10.1002/oby.20983
  12. Hands JM, Anderson ML, Cooperman T, et al. A multi-year heavy metal analysis of 72 dark chocolate and cocoa products in the USA. Frontiers in Nutrition. 2024. https://doi.org/10.3389/fnut.2024.1366231
  13. Parke-Davis Div of Pfizer Inc. NARDIL (phenelzine sulfate) tablets. Prescribing information. DailyMed. 2026. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=513a41d0-37d4-4355-8a6d-a2c643bce6fa
  14. Marcus DA, Scharff L, Turk D, Gourley LM. A double-blind provocative study of chocolate as a trigger of headache. Cephalalgia. 1997. https://doi.org/10.1046/j.1468-2982.1997.1708855.x
  15. Moffett AM, Swash M, Scott DF. Effect of chocolate in migraine: a double-blind study. Journal of Neurology, Neurosurgery & Psychiatry. 1974. https://doi.org/10.1136/jnnp.37.4.445

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