Chocolate Nudges Down BP in New Meta-Analysis

Marlene Busko

August 16, 2012

August 16, 2012 (Melbourne, Australia)— Indulging in flavanol-rich chocolate or cocoa every day may result in a small decrease in blood pressure, a review of 20 short-term studies by Dr Karin Ried (University of Melbourne, Australia) and colleagues suggests [1].

The research, which is published August 14, 2012, in the Cochrane Database of Systematic Reviews, updates previous meta-analyses of five trials [2], 10 trials [3], and 15 trials [4], shetold heartwire in an email.

In the current review, in almost 900 mainly healthy individuals, those who consumed as much as about 100 g of chocolate or cocoa every day saw an average 2.77-mm-Hg drop in systolic blood pressure and an average 2.20-mm-Hg decrease in diastolic pressure compared with control subjects.

The effect of ingesting "flavanol-rich cocoa products [was] somewhat comparable to [results from] other lifestyle modifications, such as diet and exercise--a 3- to 5-mm-Hg reduction--and may serve as a complementary treatment option," according to Ried.

This is important, since epidemiological studies have linked even small reductions in blood pressure with beneficial effects on cardiovascular health, she noted. However, longer trials are needed to better elucidate the benefits of chocolate, determine optimal dosages, and examine outcomes such as stroke and cardiovascular disease, she says.

Flavanol Effect

Kuna Indians in Central America consistently have a healthy blood pressure and drink about four cups of cocoa a day, leading researchers to hypothesize that the flavanols in cocoa are probably what cause its blood-pressure–lowering effect. Flavanols increase the formation of nitric oxide, which promotes vasodilation and thus blood-pressure reduction.

The current team analyzed data from randomized trials examining blood-pressure changes with daily consumption of either commercial chocolate bars (nine trials) or flavanol-rich cocoa powder (11 trials) vs control products.

The trials were very heterogeneous.

Nine trials followed participants for two weeks, 10 trials lasted two to eight weeks, and one trial was 18 weeks long.

Participants in the active treatment arms received 3.6 to 105 g of dark chocolate (6 g is equal to one piece of a 100-g dark-chocolate bar) containing 50% to 90% cocoa, milk-chocolate–based confectionary (105 g of <10% cocoa), or flavanol-enriched cocoa powder containing a dosage of 30 to 1080 mg (mean=545.5 mg) of flavanols per day.

Participants in the control arms received daily flavanol-free white chocolate, milk, or single pills (in 12 studies) or cocoa powder with a low level of flavanols (in eight studies).

In the studies comparing cocoa or chocolate vs flavanol-free placebos, treated participants had a mean decrease in systolic blood pressure of 3.70 mm Hg and a mean decrease in diastolic blood pressure of 2.71 mm Hg, compared with those in the control arms.

In contrast, there was no significant decrease in BP between treatment and control groups in the trials that used control products with low levels of flavanols--suggesting that the flavanols in these controls might have been obscuring results.

Blood pressure fell slightly more in patients who were younger than 50 or consumed chocolate with a low-sugar content (which was mostly dark chocolate), which needs to be further examined, the authors say.

"Disappointing" Impact on BP, Possible Benefit for Cognition

The analysis was "thorough but shows a disappointingly small effect of chocolate consumption on blood pressure," says Dr Franz H Messerli (Columbia University, New York), who was not involved in this research.

Nevertheless consuming small quantities of chocolate or cocoa every day may confer other health benefits, he noted, referring to another new study showing regular consumption of cocoa flavanols might improve cognitive function in elderly patients with mild cognitive impairment [5]. "These are certainly very provocative findings and deserve to be explored in depth," Messerli told heartwire in an email.

The authors in the cognition study observed a much greater fall in blood pressure than in the current study--decreases of 10 mm Hg systolic blood pressure and 4.3 mm Hg diastolic blood pressure in the group with the highest flavanol consumption. And insulin resistance, total cholesterol, LDL cholesterol, and triglycerides all moved in the "right" direction.

"Thus, the health benefits of chocolate, similar to those of red wine, may be multifactorial, and we shouldn’t be concerned about the disappointing blood-pressure effect in this Cochrane analysis," Messerli added. "Clearly, chocolate's potential benefits should be explored in an outcome study looking at dementia, heart attack, stroke, and death."

Ried and two other authors--Dr Oliver R Frank (University of Adelaide, Australia) and Dr Nigel P Stocks (University of Adelaide)--were investigators on one randomized controlled trial included in this review. Messerli had no conflicts of interest to declare.