The findings suggest that cocoa extract has "a potential role in early prevention rather than treatment of elevated blood pressure," wrote researchers at Harvard Medical School and other institutions in the United States and China in the journal Hypertension.
The COSMOS (Cocoa Supplement and Multivitamin Outcomes Study) is a large-scale, long-term randomized controlled trial evaluating the health benefits of a cocoa extract and a multivitamin among 21,442 older participants.
Previous reports on the trial's findings have suggested that the supplements' benefits include supporting cognitive decline and brain health.
The current analysis evaluated 8,905 participants in the United States without hypertension, with a mean age of 71.1. They took a cocoa extract supplement supplied by Mars Edge, containing 500 mg/d of cocoa flavanols, including 80 mg/d epicatechin and a multivitamin-multimineral (MVM) supplement provided by Pfizer Consumer Healthcare (now Haleon) and marketed as Centrum Silver or placebo.
The researchers ascertained incident hypertension (the new development of high blood pressure) through self-reported yearly questionnaires over a median follow-up of 3.4 years.
"We did not find an overall effect of cocoa extract in reducing incident hypertension over 3.4 years," the researchers reported.
"However, the preventive effect of cocoa extract was pronounced among participants with baseline SBP <120 mmHg, with additional ≈0.7 months free from hypertension during the 4-year follow-up on average," they added, noting no robust effect on diastolic blood pressure.
The study also highlighted a potential synergistic effect with cocoa extract and the MVM supplement; "cocoa supplementation appeared beneficial only among participants assigned to the active MVM arm but not in the placebo group."
Cocoa flavanols are natural compounds in cocoa beans that are part of the flavonoid family of phytonutrients. Flavanols, such as epicatechin in cocoa, can stimulate the production of nitric oxide and inhibit angiotensin-converting enzyme (ACE) activity, which can help lower blood pressure.
The researchers noted that taking cocoa extract with an MVM supplement may enhance nitric oxide-mediated vasodilation through multiple nutrients, for example, magnesium, which may help regulate blood pressure.
In addition, the high safety profile of dietary flavanols and their presence in everyday foods make them a good candidate for public health recommendations and precision nutrition, the study noted.
However, the researchers acknowledged the overall nonsignificant results of the antihypertensive effects of cocoa and recommend future studies to determine if cocoa flavanols have a role in the primary prevention of high blood pressure.
"The effect's delayed onset and subgroup specificity highlight a need for further targeted prevention trials," they wrote.