BACKGROUND:Chocolate stocks build up in many homes over Christmas. Keeping it around may not fit with new year's resolutions.
However, recent research has suggested that some daily chocolate might have some beneficial health effects. The key ingredient for the reported beneficial cardiac effects is cocoa. Dark chocolate contains at least 35 per cent cocoa solids, milk chocolate 25 per cent, and white chocolate none. Cocoa contains many polyphenols (a large range of compounds found in many fruits and vegetables which are responsible for many of their beneficial effects). Cocoa is rich in polyphenols called flavanoids.
EVIDENCE FROM STUDIES
Flavanoids extracted from cocoa and tested in lab studies were found to increase the production of nitric oxide in blood vessels. This causes blood vessels to dilate and has other beneficial effects on blood cells and vessels. Cocoa contains numerous other compounds that could impact on cardiac health, such as caffeine, tryptophan and minerals. Chocolate also contains plenty of sugar and fat that should be taken into account in any evaluation of its health effects.
A systematic review was published in 2010 examining the impact of chocolate or cocoa on blood pressure. Such reviews search for all the relevant research on a topic and attempt to combine the results to give an overview of the current situation. Fifteen randomised controlled trials were located and the combined results found a significant beneficial effect for dark chocolate compared to placebo or chocolate lower in cocoa.
In general, a reduction in systolic pressure of 5mm of mercury (or mm Hg) is believed to reduce the risk of cardiac problems by about 20 per cent over five years. This is viewed as a substantial reduction in risk, and is comparable to the benefits of moderate physical activity on a daily basis.
In combining results from different studies, systematic reviews have to avoid combining “apples” and “oranges”. The chocolate review found that all 15 studies varied considerably from one another, which is a limitation in combining their results. To compensate for this, the reviewers divided the studies into those involving people with high blood pressure and those with normal blood pressure. For those with normal blood pressure, chocolate or cocoa products led to no changes. Those who started the studies with high blood pressure had, on average, a reduction in systolic blood pressure of 5 mm Hg and in diastolic blood pressure of 3 mm Hg. These benefits arose from products high in cocoa (such as dark chocolate), but not from those low in cocoa (such as white chocolate).
PROBLEMATIC ASPECTS
Chocolate itself is not a problem. However, in one study where people were asked to eat 50 grams of dark chocolate per day, half the people found this difficult and 20 per cent considered it unacceptable. People said they had problems with dark chocolate’s taste, were worried about the amount of fat it contained, and several developed headaches and constipation.
RECOMMENDATIONS
For people with high blood pressure, dark chocolate can reduce blood pressure to an important degree. However, dark chocolate is not the easiest to consume regularly. Milk chocolate contains fewer flavanoids, and much more sugar and fat. Weight gain would more than counteract any direct benefits from cocoa flavanoids.
Another limitation with the studies to date is that most have only lasted for a few weeks. Blood pressure management is a long-term process, and this has not been tested with chocolate.
Isolating the active ingredients in cocoa and making them available as a food supplement would be preferable to eating them along with the sugar and fat in chocolate. If chocolate is to be your preferred source of flavanoids, remember to decrease your other sources of fats, sugars and calories.
Dónal OMathúna has a PhD in pharmacy, researching herbal remedies, and an MA in bioethics, and is a Senior Lecturer in the School of Nursing, Dublin City University. If you would like to see a herb or food supplement reviewed here, send your suggestion to healthsupplement@irishtimes.com