Dark Chocolate

What it is

Chocolate and cocoa products are rich in polyphenols such as catechins, anthocyanidins and pro-anthocyanidins [1]. A 2024 meta-analysis included cocoa extract or dark chocolate of at least 70% cocoa [2].

How it might work

Proposed: flavanols in cocoa may increase nitric oxide in the lining of blood vessels, which relaxes them [3].

What the research says

Blood pressure: a Cochrane review of 35 trials (1,804 mostly healthy people) found systolic and diastolic pressure each about 1.76 mmHg lower than with control products [3]. A 2024 meta-analysis of 31 trials found drops of 2.52 mmHg systolic and 1.58 mmHg diastolic [2]. A 2020 meta-analysis of middle-aged and older adults could not show a benefit in people with normal or elevated readings [4].

Blood vessel function: a 2019 meta-analysis of 15 trials found flow-mediated dilation rose by 1.17% [5].

Cholesterol: a 2024 meta-analysis found lower total and LDL cholesterol, with no change in HDL or triglycerides [2]. A 2021 systematic review found no significant difference on lipid measures except triglycerides, which improved [1].

Weight: a 2019 meta-analysis of 35 trials found no significant change in body weight, BMI or waist size [6].

Doses used in studies

Trials gave 30 to 1,218 mg of flavanols a day, mean 670 mg, in 1.4 to 105 g of cocoa products daily, for two to 18 weeks [3]. A dose-response analysis of endothelial trials peaked near 710 mg of total flavanols [5]. These are research doses, not recommendations.

Safety and interactions

Side effects: stomach upset and nausea were reported by 1% of people eating cocoa products and 0.4% of controls [3].

Heavy metals: in 72 dark chocolate and cocoa products tested from 2014 to 2022, lead exceeded California's Proposition 65 limit in 43% and cadmium in 35%; none exceeded it for arsenic. Organic products were more likely to have higher cadmium and lead [7].

Blood pressure: in 17 healthy volunteers, a single large dose of 70% dark chocolate raised systolic pressure from 115 to 122 mmHg in people who rarely ate chocolate, but not in people eating more than 50 g a week [8].

Not covered by the studies cited: interactions with blood pressure medicines, pregnancy and breastfeeding, upper limits, and caffeine. Kidney disease was not studied; the kidney study was in healthy volunteers [8]. People on blood pressure medicine should ask a doctor first.

Caveats and open questions

Results vary widely between trials and the variation is not explained by blinding, flavanol content, age or duration [3]. Most trials last weeks, and the Cochrane authors say long-term trials of cardiovascular events are still needed [3]. Two authors of the Cochrane review had run included trials; excluding industry-linked trials reduced the effect [3]. Ongoing research on chocolate and cardiovascular function is listed below.