Diabetes - should I cocoa?

“An ingredient found naturally in cocoa could help diabetics ward off the threat of heart disease”, the Daily Mail reported today. It said that a study has found that giving diabetics cocoa with higher than normal levels of flavanols, a type of antioxidant, improved blood flow through the arteries by 30%. The Daily Express also covered the story and said “patients with type 2 diabetes who drank three cups a day of the cocoa saw their blood vessel function return to normal within a month”.

This small study looked at the effects of flavonol-enriched cocoa drinks on the function of the main artery in the upper arm. However, even if the cocoa does have an effect on the function of this artery, it’s unclear whether this would have any actual effect on cardiovascular risk.

The type of cocoa used in this study is not available to buy. Food that contains cocoa, such as chocolate, is often also high in levels of fat and sugar, meaning that it’s not ideal for diabetics. Flavanols are also found in fruit and vegetables, and it would be better to increase intake of these foods rather than eating chocolate or drinking cocoa beverages in an attempt to reduce cardiovascular risk.

Where did the story come from?

Dr Jan Balzer and colleagues from University Hospital RWTH Aachen, University of California, and Mars Symbioscience carried out the research. The study was funded by Mars Inc., who also provided the cocoa drinks used in the study. The study was published in the peer-reviewed: Journal of the American College of Cardiology .

What kind of scientific study was this?

This double blind randomised controlled trial investigated the possibility of using flavanol-enriched cocoa as a daily dietary intervention for improving vascular function in diabetics.

The researchers enrolled people aged 50 to 80 with type 2 diabetes and who had been on stable medication for at least five years. They excluded anyone with congestive heart failure, malignant cancer, chronic kidney disease, severe heart rhythm abnormalities, inflammation, or who smoked currently or had smoked in the last five years.

In the first part of the study, 10 participants were asked not to eat or drink foods with high flavanol content, such as tea, red wine, specific vegetables, and cocoa products. They were given three cocoa drinks, one with a low dose of flavanols (control), one with a medium dose, and one with a high dose, in a randomly assigned order on three different occasions.

Before each drink, and at one, two, three, four, and six hours after each drink, the researchers measured the diameter of the main artery of the upper arm (the brachial artery) before and after blocking off blood supply to the arm using a type of tourniquet for 5 minutes, and calculating the change in diameter. This measurement (the flow-mediated dilation, or FMD) indicates how well the cells lining the artery are functioning; poor functioning of these cells can lead to the development of atherosclerosis, and a lower FMD has been linked to a greater risk of cardiovascular events (such as heart attacks). The researchers also monitored patients for any adverse effects.

In the second part of their study, the researchers randomly assigned 41 participants to drink either a flavanol rich cocoa drink, or a control cocoa drink with low levels of flavanol, three times a day for 30 days. The participants continued their normal diets and lifestyle during the study. The researchers measured the FMD of the brachial artery before the study, and at eight and 30 days into the study, and compared the changes in these measures between the flavanol rich cocoa and control groups.

What were the results of the study?

The medium and high dose flavanol cocoa drinks increased FMD of the brachial artery two hours after consumption, and the control (low dose flavanol) cocoa drink did not. The FMD returned to normal by about six hours after the drinks. In the 30-day trial, flavanol rich cocoa increased FMD compared to the control drink at eight and 30 days. The cocoa drinks were not associated with any adverse effects.

What interpretations did the researchers draw from these results?

The researchers concluded, “diets rich in flavanols reverse vascular dysfunction in diabetes”. They said this highlighted the possibility that cocoa could be used as a treatment to reduce the risk of cardiovascular disease.

What does the NHS Knowledge Service make of this study?

This was a relatively small study that used FMD in the brachial artery as a proxy measure for cardiovascular risk. However, it’s unclear what effect, if any, the changes in brachial artery FMD seen with flavanol rich cocoa in this study would have on a person’s cardiovascular risk. It’s also unclear whether long term cocoa use has any adverse effects.

Although it’s possible that the flavanols in cocoa may reduce cardiovascular risk, if they are to be used medically they are likely to be extracted and given in pill form, and would need to be regulated as a medicine.

Food that contains cocoa, such as chocolate, is often also high in levels of fat and sugar, meaning it’s not ideal for diabetics. People who wanted to increase their intake of flavanols would be better off eating fruit and vegetables that also have high levels of the antioxidants, rather than increasing their intake of chocolate or cocoa drinks. Diabetics should not start eating chocolate to try to reduce their cardiovascular risk.

Sir Muir Gray adds...

Favanol looks promising but one swallow does not a summer make; there is however, enough promise for more research studies and then for a systematic review of all research studies to be prepared.