June 15, 2015

chocolate consumption and risk of cardiovascular disease

A number of types of food have been suggested to have beneficial effects on health, and a team publishing in the journal Heart have investigated an association between chocolate consumption and cardiovascular disease. Based on a meta-analysis, the researchers report that higher intake of chocolate was associated with a lower risk of future cardiovascular events. Roundup comments accompanied this analysis.

Title, Date of Publication & Journal

Habitual chocolate consumption and risk of cardiovascular disease among healthy men and women, 15 June 2015, Heart

Study’s main claims – and are they supported by the data

The paper provides limited, weak evidence to support a reduction in cardiovascular disease for people who eat more chocolate.

Observational studies like this cannot show a causal affect. The association seen here could have an alternative explanation (some explanations are suggested by the authors).

The top line of the press release could lead people to infer that chocolate has a protective effect against CVD, and the paper does not show this.

Strengths/Limitations

The paper shows that people in Norfolk who admitted to consuming more chocolate squares, bars or hot chocolate in a questionnaire administered once in the 1990s were, according to their answers to that questionnaire, younger with lower BMI and blood pressure and less likely to have diabetes or to be physically active and more likely to smoke. During follow-up until 2008, they were also less likely to die from cardiovascular disease (although not less likely to suffer cardiovascular disease).

It is hard to know if the lower risk comes from chocolate or those other factors. The authors have tried to account for these as far as possible, but the nature of the study means that it is not possible to do that perfectly. Therefore, it is possible that the protective effect might be because of something else – not chocolate.

The study is well conducted observational research, but the limitations of the study design mean that the study can only generate hypotheses for evaluation in further research. The discussion is clear about these limitations (as is the body of the press release):

• The measurement of chocolate exposure in a questionnaire can be undermined by shy chocolate eaters who underreport their consumption
• Sometimes people at higher risk cut their consumption of “risky” food – so it could be that people more likely to get CVD are deliberately eating less chocolate, not the other way round
• It is hard to account for other risk factors (e.g. physical activity) when each is measured only once in a questionnaire. People misreport exercise, just like chocolate consumption, and even an accurate, single answer would not capture activity over the full study period (e.g. 1997-2008). Therefore it is not possible to account perfectly for these risk factors.

The authors were not able to evaluate publication bias.

Glossary

Publication bias: over-reporting of an association due to statistically significant findings being published and non-significant findings never being submitted or accepted for publication.

Any specific expertise relevant to studied paper (beyond statistical)?

No

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