Clinical trials needed to confirm, say experts

Eating five servings of dark chocolate a week is associated with a reduction in the risk of type 2 diabetes, according to a long-term US study published by The BMJ.

Global rates of type 2 diabetes are set to rise to 700 million by 2045. Chocolate contains high levels of flavanols (a natural compound found in fruits and vegetables) which have been shown to promote heart health and reduce the risk of type 2 diabetes. But the link between chocolate consumption and the risk of type 2 diabetes remains controversial due to inconsistent results.

In addition, most previous studies have not looked at whether eating dark and milk chocolate—which have different cocoa, milk and sugar content—might have different impacts on the risk of type 2 diabetes.

To explore this further, researchers combined data from three long-term US observational studies of female nurses and male health care professionals with no history of diabetes, heart disease or cancer when they were recruited.

Using food frequency questionnaires completed every four years, they analyzed associations between type 2 diabetes and total chocolate consumption for 192,208 participants, and chocolate subtype (dark and milk) consumption for 111,654 participants over an average monitoring period of 25 years.

As changes in bodyweight strongly predict risks of type 2 diabetes, the authors also used these food questionnaires to assess participants’ total energy intake.

In the analyses for total chocolate, 18,862 people developed type 2 diabetes. After adjusting for personal, lifestyle, and dietary risk factors, the authors found that people who ate at least five servings a week of any type of chocolate (where one serving is equal to a standard chocolate bar/pack or 1 oz) showed a significant 10% lower rate of type 2 diabetes compared with those who rarely or never ate chocolate.

In analyses by chocolate subtypes, 4,771 people developed type 2 diabetes. After adjusting for the same risk factors, people who ate at least five servings a week of dark chocolate showed a significant 21% lower risk of type 2 diabetes, but no significant associations were found for milk chocolate intake.

The researchers also found a 3% reduced risk of type 2 diabetes for each additional weekly serving of dark chocolate (a dose-response effect). Increased consumption of milk, but not dark, chocolate was associated with long term weight gain.

Although dark chocolate has similar levels of energy and saturated fat to milk chocolate, the authors explain that the high levels of flavanols in dark chocolate might offset the effects of saturated fat and sugar on weight gain and the risk of other cardiometabolic diseases such as diabetes.

The authors acknowledge that the observational nature of this study prevents firm conclusions from being drawn about causality and, although they took account of lifestyle and dietary factors linked to type 2 diabetes, other unknown factors may have affected the results. Most participants were non-Hispanic older white adults, so the findings may not apply to other groups, they add.

However, they point out that results remained largely unchanged after adjusting for additional factors, suggesting that they are robust.

As such, they conclude, “Increased consumption of dark, but not milk, chocolate was associated with lower risk of type 2 diabetes. Increased consumption of milk, but not dark, chocolate was associated with long-term weight gain. Further randomized controlled trials are needed to replicate these findings and further explore the mechanisms.”