Monday, 7 July 2014

Dark Chocolate - Does it Really Help Peripheral Artery Disease?

Melted chocolate; public domain photo by Petr Kratochvil
Recent news headlines on the Internet announced that dark chocolate helps PAD, or peripheral artery disease. The news is a little misleading. A research project that's just been performed did indeed show that dark chocolate helped the small number of people in the study, but the benefit seems to be fairly minor.

Peripheral artery disease is a condition in which plaque builds up in the walls of arteries, narrowing the passage for blood flow. The arteries involved are usually (but not always) ones in the limbs, especially the legs. Plaque is a deposit made of fat, cholesterol, calcium and other substances. It can also collect in an artery in the heart, which can lead to a heart attack, or in one going to the brain, which can cause a stroke.

Plaque eventually hardens, reducing the amount of blood that can travel beyond the blockage. Symptoms of the disorder in the legs include pain, numbness and tiredness. In addition, wounds in the area may heal slowly.

The research into the effect of dark chocolate on PAD was performed at Sapienza University in Rome. The study involved 20 people - 14 men and 6 women - with an average age in the late sixties. This is a very small sample size. Most clinical trials involving humans involve hundreds or even thousands of people.

The people in the trial first walked on a motorized treadmill for as long as they could. The treadmill was inclined at a 12% angle and was moving at 2.2 miles an hour. After the walk, the subjects were randomly assigned to eat either a 1.4 ounce bar of dark chocolate or a similarly sized bar of milk chocolate. The dark chocolate contained 85% cocoa while the milk chocolate contained less than 30% cocoa. Two hours after eating the chocolate, the people took the treadmill test again.

The people who had eaten dark chocolate were able to walk about 39 feet further and for about 17 seconds longer than the people who had eaten milk chocolate. However, they were almost certainly able to identify the type of chocolate that they were given by its taste, so the placebo effect may have played a role in the results. Another benefit was observed that is harder to explain by the placebo effect, though. The level of nitric acid - a chemical known to help arteries dilate and blood to flow - was higher in the people who ate dark chocolate.

Cocoa beans; public domain photo by Lucy Toner
Nutrient-rich cocoa is an important component of chocolate and has been shown to improve blood flow in other experiments. Scientists think that chemicals called polyphenols are responsible for cocoa's beneficial effects.

The results of the Sapienza University experiment are encouraging, but questions have been raised about their value in everyday life. Additional experiments involving more subjects need to be performed to confirm the results and to answer more questions, including the following ones.

Chocolate bars contain fat, sugar and lots of calories. Would adding these to the daily diet of people with PAD cause weight gain and negate any benefit from the chocolate? Could eating a smaller amount of chocolate or drinking cocoa have the same benefits as eating a whole chocolate bar? How long do the beneficial chemicals that appear after eating dark chocolate stay in the blood? Would eating cocoa or dark chocolate every day over a longer time period be more beneficial? Hopefully these questions will be answered in future research projects.