I do not like the study because the authors recognise that it does not allow causal relationships to be established, but they repeat the message of association as if it were causal, inducing a certain consumption that would only make sense if the relationship were causal. The press release merely repeats the same thing, only shorter. Moreover:

1. They repeat the obsolete term ‘significant’, associated with the much discussed P<0.05.
2. If they are interested in non-causal association, they should quantify its predictive value with measures of the ability to anticipate the future, such as R2 [coefficient of determination] or ROC [ Receiver Operating Characteristic].
3. They insist on a measure, relative risk, which only makes sense for causal associations. But they do not facilitate its practical interpretation. For example, how long will individuals remain free of the complication [diabetes]?
4. The analysis of their weaknesses is poor, not useful for learning.
5. Can we believe that they have no conflict of interest simply because of public funding? We have no guarantee that the analysis was designed impartially, in the so-called ‘original position’, before the results were known.

This is a first very large-scale analysis of an association of chocolate intake and self-reported Type 2 diabetes across three prospective cohort studies in the US. The distinctiveness of this research is that they specifically assessed which type of chocolate was linked to diabetes risk.

As dark chocolate has a much higher cocoa content, this means that bioactive compounds in cocoa, and in dark chocolate, such as flavanols, may contribute to the lowering of diabetes risk, possibly by increasing insulin sensitivity. However, if and how flavanols on their own reduce diabetes risk remains to be established – a recent large scale randomized controlled trial (the COSMOS study) found that cocoa flavanol supplements did not affect the risk of type 2 diabetes.

The authors found that milk chocolate consumption was associated with weight gain, whereas dark chocolate intake was not. Weight gain is an important risk factor for type 2 diabetes development, so it is important to control for this in the analysis, which is something the authors did.

Interestingly, the inverse association between eating dark chocolate and the risk of type 2 diabetes was mostly observed in those that were younger than 70 years old, and the association was stronger in men than in postmenopausal elderly women. Other studies have found that chocolate consumption lowers the risk of type 2 diabetes in men but not in women, and in one of our own studies we found that eating dark chocolate improved platelet function in men but not in women. It is unlikely that sex differences in absorption or metabolism of the cocoa flavanols are responsible for the differences in observed effects between men and women. It is more likely that sex hormones may differentially modify the association between chocolate consumption and the risk of type 2 diabetes, or platelet function.