BMC Medicine has an interesting meta-analysis on the effect of chocolate on blood pressure. Does chocolate reduce blood pressure? A meta-analysis
The short answer is Yes.
Food containing cocoa (especially dark chocolate) has flavanols that lead to a production of nitric oxide which dilates blood vessels thereby reducing blood pressure.
The investigators pooled data from 13 studies (15 trial arms) done between 1955 to 2009. They found that the average systolic BP of hypertensive individuals decreased by 5mm Hg (±3) and diastolic BP by 2.7mm Hg (±2.2). Blood pressure was not significantly reduced in people with normal BP neither was the BP reduced to normal levels in hypertensive people.
"The relatively modest but significant blood pressure-lowering effect of cocoa in the hypertensive subgroup is clinically relevant: a decline of 5 mmHg in systolic blood pressure may reduce the risk of a cardiovascular event by about 20% over 5 years."
There are multiple flaws in the study and the result must be interpreted with caution. For example, there was a single study in the meta-analysis which showed a huge reduction in BP that could have influenced the final results.
Now the mandatory warning by the authors:
"While regular consumption of flavanol-rich cocoa products may have a beneficial short-term effect in reducing blood pressure in hypertensive individuals, the practicability of chocolate or cocoa drinks as long-term treatment is questionable.
A recent small study by our team investigating the acceptability of commercially available chocolate bars as an alternative treatment to capsules concluded that daily chocolate consumption for blood pressure may not be an acceptable and practical treatment option."
My take: Keep up with a healthy lifestyle, take your BP medications and enjoy dark chocolates.