I love it when we get research that says ‘chocolate is good for you’, though the reality is generally much more complicated than that. But let’s be glad of any good news we can get and today’s good news comes from high quality evidence, a new Cochrane review, published today, which found that cocoa compounds may help to reduce blood pressure. This has been suggested in earlier meta-analyses (in which data from multiple trials are combined) but recent trials have had conflicting results.
So what’s it all about? Well cocoa contains flavanols, compounds which are thought to be responsible for the formation of nitric oxide in the body. Nitric oxide causes blood vessel walls to relax and open wider, reducing blood pressure.
The Cochrane team conducted the usual extensive and systematic searches and found 20 randomised controlled trials (RCTs) suitable for inclusion. They were interested in the effects of flavanol-rich chocolate or cocoa products on blood pressure in people with normal or high blood pressure; most of the 856 participants were healthy.
Intervention group participants were given 30-1080mg of flavanols in 3-105g of chocolate each day. Control group participants had either low-flavanol or flavanol-free products. (Good advert for participation in medical research; many participants got to eat chocolate every day. Lucky, lucky people!) Results were combined in a meta-analysis.
Here’s what they found:
- A small but statistically significant blood pressure reducing effect of flavanol-rich cocoa products compared to control. Mean difference systolic blood pressure (95% confidence interval [CI]): -2.77 (-4.72, -0.82) mm Hg, p=0.005. Mean difference diastolic blood pressure (95% CI): -2.20 (-3.46, -0.93) mm Hg, p=0.006
- Trials were short, ranging from two to eight weeks, apart from one trial of 18 weeks. Significant blood pressure lowering effects were found only in the nine trials of two weeks, not the longer trials
- Chocolate/cocoa compared to flavanol-free products showed greater beneficial effects (3-4 mm Hg) but no beneficial effects when compared with low-flavanol products. The reviewers note that these results may have been influenced by trial length and by participants knowing their allocated group
- Adverse effects including digestive complaints and distaste of the trial product were reported by 5% of intervention group participants and 1% from the control groups
The authors concluded:
Flavanol-rich chocolate and cocoa products may have a small but statistically significant effect in lowering blood pressure by 2-3 mm Hg in the short term.
So are these changes in blood pressure clinically significant? Lead author Karin Ried commented:
We’ll also need to see long term trials, including the effects on the risk of stroke and cardiovascular disease, before we can come to conclusions regarding clinical outcomes and potential side effects of long-term consumption.
So, not surprisingly, the good news is limited, but let’s not knock it. Time for a little flavanol-rich something, I think.
Ried K, Sullivan TR, Fakier P, Frank OR, Stocks NP. Effect of cocoa on blood pressure. Cochrane Database of Systematic Reviews 2012, Issue 8. Art. No. CD008893. DOI: 10.1002/14651858.CD008893.pub2.
Cochrane summary and podcast of this review.