Researchers examined the results from 20 trials in which more than 850 people regularly ate dark chocolate or cocoa powder.
The study found that participants' blood pressure was slightly reduced – on average by 2-3mmHG.
The report, published by the Cochrane Group, suggested that chemicals in cocoa – chocolate's main ingredient – relaxed blood vessels.
“Cocoa contains compounds called flavanols, thought to be responsible for the formation of nitric oxide in the body. Nitric oxide causes blood vessel walls to relax and open wider, thereby reducing blood pressure,” according to the report.
Lead researcher Karin Ried, of the National Institute of Integrative Medicine in Melbourne, Australia, said: “Although we don’t yet have evidence for any sustained decrease in blood pressure, the small reduction we saw over the short term might complement other treatment options and might contribute to reducing the risk of cardiovascular disease.”
Ried said long-term trials, including effects on the risk of stroke and cardiovascular disease, were necessary before conclusions about clinical outcomes and potential side-effects of long-term consumption could be drawn.
But Victoria Taylor, senior dietitian with the British Heart Foundation (BHF), said the results should be treated with caution. “Although this review showed a small reduction in blood pressure, the findings are hampered by a lack of consistency between the studies.
“It’s difficult to tell exactly what sort of quantities of flavanol-rich cocoa would be needed to observe a beneficial effect and the best way for people to obtain it.”
With most of the studies carried out over a short period of time, it’s impossible to know whether the benefits could be sustained in the long term, she added.
The 100g of chocolate that had to be consumed daily in a number of the studies would also come with 500 calories. That’s a quarter of a woman’s recommended daily intake.
“Beans, apricots, blackberries and apples also contain flavanols and, while containing lower amounts than cocoa, they won’t come with the unhealthy extras found in chocolate,” she said.
Chocolate also contains significant amounts of fat and sugar.
Meanwhile, worldwide high blood pressure has been linked to 54% of strokes and 47% of cases of coronary heart disease.
The BHF said an adult’s blood pressure should be below 140/85mmHg. If you have heart or circulatory disease, including coronary heart disease or angina or suffer diabetes or kidney disease, it is usually recommended that your blood pressure should be below 130/80mmHg, it advised.
The study was published in The Cochrane Library.