Does dark chocolate lower blood pressure?
Cocoa flavanol preparations have produced small average reductions in blood pressure in short trials, and the effect is real, modest and measured over weeks. Whether eating chocolate delivers it is a separate question the trials mostly do not answer.
Emerging research
Real human studies exist and point somewhere, but the body of evidence is small, mixed, short-term or heavily industry-funded.
What the evidence shows
This is among the better-studied questions in the area. Randomised trials of cocoa or cocoa flavanol preparations against a control have been synthesised in systematic reviews, and the pooled result has been a small average reduction in blood pressure, of a magnitude measured in a small number of millimetres of mercury.
The proposed mechanism is reasonably well characterised and consistent with the vascular findings covered separately: flavanols appear to increase nitric oxide availability, which relaxes the vessel wall and reduces peripheral resistance.
Effects have tended to be larger in people with raised blood pressure at baseline than in people with normal readings, which is a common pattern and makes physiological sense.
What it does not show
It does not show that chocolate reduces cardiovascular events. Blood pressure is a marker, the trials are short — typically weeks — and no trial in this literature has run long enough or large enough to measure heart attacks or strokes. A reduction in a marker is a reason to keep investigating, not a demonstrated health outcome.
It does not show that the effect persists. Most trials are brief, and whether a small reduction is maintained over months or years is not established.
It does not show that eating chocolate produces the result. The trials overwhelmingly use cocoa preparations or standardised flavanol doses rather than retail chocolate, and the flavanol content of a bar is variable, undeclared and substantially reduced by ordinary processing.
And the average conceals wide variation between trials, several of which found no significant effect. Industry funding is common in this literature and is not a reason to dismiss it, but is a reason to weigh the pooled estimate cautiously.
The amount the finding rests on
Trials in this area have generally administered cocoa flavanols in daily amounts of a few hundred milligrams, delivered as a cocoa drink, a standardised extract or a high-flavanol cocoa product, over periods of weeks.
The dose is stated in flavanols rather than in grams of chocolate, because that is how the trials were designed. ChocolateHQ describes the range approximately rather than quoting a figure, because the relevant passages have not been re-read against the published reviews.
In practice: There is no reliable way to know how many flavanols a given bar contains. Content varies with genetics, fermentation, drying, roasting and — most sharply — alkalisation, none of which is declared. Reaching a trial-level intake by eating ordinary dark chocolate would also mean consuming a substantial quantity of sugar and fat, which the same evidence base says nothing favourable about.
How good is the evidence
The trials are randomised and the syntheses are systematic, which puts this among the strongest cocoa health claims. The weaknesses are consistent across the literature and are not minor: short durations, small samples, considerable heterogeneity between trials, frequent industry funding, difficulty in blinding a cocoa intervention convincingly, and the use of preparations rather than food. The tier reflects that combination — real human evidence pointing somewhere, in a body that is short-term and mixed.
Who this may not apply to
- Effects have generally been larger in people with elevated blood pressure than in those with normal readings, so a finding reported as an average does not describe everyone.
- Anyone taking antihypertensive medication should not treat this as a reason to alter it, and should speak to a clinician.
- Trials have typically recruited healthy adults or adults with mild hypertension; the findings do not transfer automatically to other groups.
- Anyone managing a health condition, taking medication, or making decisions about their diet should speak to a clinician rather than treat this as guidance.
Related claims
“Dark chocolate is a health food — the darker the better.”
Research on cocoa flavanols and short-term measures of vascular function is real, and a narrowly scoped EU health claim exists on that basis. It concerns a specified daily intake of flavanol compounds, not chocolate. Flavanol content is not indicated by cocoa percentage, is substantially reduced by ordinary processing, and is not declared on mainstream products. Meanwhile the non-cacao mass of a dark bar is overwhelmingly sugar.
The kernel of truth: The underlying research exists and is not junk. A regulatory body assessed a claim in this area and authorised one, which very few food claims achieve. The overreach is in the distance between 'a specified flavanol intake affects a measure of vessel dilation' and 'chocolate is good for you'.
Where it comes from: Traceable in large part to industry-funded research programmes and the press coverage built on them. The Cochrane review of cocoa and blood pressure notes industry funding across a substantial share of the trials it includes.
Related
Health topics
- Cocoa flavanols and blood vessel functionRead alongside Cocoa and blood pressure. There is real evidence that cocoa flavanols affect a specific measure of blood vessel function, and a large gap between that finding and 'chocolate is good for your heart'.
- Cocoa and antioxidantsRead alongside Cocoa and blood pressure. Cocoa is measurably high in polyphenols in the laboratory. What that means inside a person is a separate question, and a less settled one.
- Cocoa products are not interchangeableRead alongside Cocoa and blood pressure. No, and the difference is the single largest source of error in chocolate health writing. Most favourable cocoa findings come from defatted, flavanol-standardised cocoa preparations, and are then reported as though they were about a bar of chocolate.
- Cocoa and cognitionRead alongside Cocoa and blood pressure. There are short-term studies reporting small effects on some cognitive measures, a plausible mechanism through blood flow, and a great deal of overstatement. It is a much weaker evidence base than the blood-pressure work and is frequently reported as though it were stronger.
Covered in
- Is dark chocolate good for you?What the meta-analyses actually found, and how small small is.
Health topics covering this
- Chocolate, insulin sensitivity and metabolic markersRead alongside Chocolate, insulin sensitivity and metabolic markers. Cocoa flavanol preparations have produced small average reductions in blood pressure in short trials, and the effect is real, modest and measured over weeks. Whether eating chocolate delivers it is a separate question the trials mostly do not answer.
- Chocolate, cholesterol and blood lipidsRead alongside Chocolate, cholesterol and blood lipids. Cocoa flavanol preparations have produced small average reductions in blood pressure in short trials, and the effect is real, modest and measured over weeks. Whether eating chocolate delivers it is a separate question the trials mostly do not answer.
Sources
- Effect of cocoa on blood pressure — Cochrane Database of Systematic Reviews, 2017(citation identity confirmed; passage not re-read)
- Scientific Opinion on the substantiation of a health claim related to cocoa flavanols and maintenance of normal endothelium-dependent vasodilation — EFSA Panel on Dietetic Products, Nutrition and Allergies (NDA), 2012(citation identity confirmed; passage not re-read)
- FoodData Central — United States Department of Agriculture, Agricultural Research Service(citation identity confirmed; passage not re-read)
Nothing on this page is health advice or dietary advice. See the editorial policy.