Chocolate for cardiovascular health?

As this is restaurant week in Durham, NC, I thought it would be fitting to blog about the health benefits of food, in particular the delicacy that is 'dark chocolate'. This is not a new idea in the cardiovascular literature, but I recently came across a brief review in Hypertension by Egan et al. on the anti-hypertensive effects of dark chocolate. Although, I doubt this topic will be tested on the nephrology boards, it will likely be consumed in large quantities while studying for them.

As reported by McCullough et al. the Kuna Indians of Panama consume large quantities of cocoa, and, despite a high sodium intake, have a low prevalence of hypertension. However, Kuna Indians who migrate to Panama have a higher prevalence of hypertension than Islanders. Kuna Islanders consume 10 times more cocoa than those in Panama and have 80% less cardiovascular disease. This, and other evidence, has led some researchers to postulate that certain flavanols (specifically epicatechin) found in cocoa can lower BP and improve vascular function, insulin sensitivity and reduce platelet reactivity.

• In vitro data has suggested that flavanols can inhibit angiotensin converting enzyme activity. However, this is at much higher doses than would be achieved in vivo.
  
• Animal data has suggested that epicatechin can activate nitric oxide synthase causing vasodilation.

Chocolate has remained an important part of many cultures. The Spanish brought cocoa to Europe where sugar was added to sweeten the taste. The Dutch developed cocoa powder, the Belgians defined pralines, and the Swiss created a smoother texture to the chocolate by a method called conching. Milk chocolate reins supreme in the US and dark chocolate has taken a back seat unfortunately (as far as possible health benefits are concerned).

The effect of dark chocolate on blood pressure has been studied in 13 reports that were of enough quality to include in this brief review. Of these, only 6 were double-blinded controlled trials. Most of these studies only included 20-90 total subjects and the effects of dark chocolate were only measured for 4 days to 6 weeks. I would hardly call any of these studies "rigorous". In the 13 reports, 6 or the 7 open-labeled studies lowered BP (only modestly, 3-12 mmHg), while only 1 of the 6 randomized studies lowered BP (3 mmHg). This has put into question whether dark chocolate consumption actually lowers BP. It is unclear if the open labeled studies only showed the placebo effect in lowering BP or if this was truly an effect of the dark chocolate. As indicated earlier, several flaws were seen in the design of these trials. Most notable was the difference in brand of cocoa that was used in each study. Ritter dark chocolate being used in the open label studies primarily and Mars/Dove being used in the randomised studies.

For now, there is not enough data to firmly answer the question as to the blood pressure lowering effects of dark chocolate. However, further research into the potential benefits of certain naturally occurring chemicals in chocolate, such as epicatechin, could produce novel antihypertensive agents. So, a firm recommendation for daily chocolate consumption is likely not happening any time soon.