Closing the circle of high-sugar diets and depression
A recent study by the EU-funded MOODFOOD project has thrown up an interesting result – men who consumed more than 67g of sugar a day (equivalent to two cans of Coke) were 23 per cent more likely to have a common mental disorder (CMD) five years later, compared to those who had below-average consumption. The twist in the tale is that the same did not hold true for women in the study. The authors contend in the report, recently published in the journal Scientific Reports, that while links have been made between higher rates of sugar consumption and depression, it is not an area which has been investigated comprehensively. This, despite the fact that depression is predicted to become the leading cause of disability in high income countries by 2030. Exploring reverse causation in the link between sugar and mood The MOODFOOD researchers examined for the first time the role of ‘reverse causation’ in the observed association between the consumption of sugars, soft drinks, juices and pastries and depression. That is to say the hypothesis that people with a poor mental health increase their sugar intake, rather than increased intake playing a causal role in the risks of both incident and recurrent depression and CMD. For this bidirectional approach, the researchers analysed repeated measures (23 245 person-observations) from the UK’s Whitehall II cohort. This cohort comprises over 10 000 participants originally recruited from UK Civil Service staff from 1985 to 1988 and who have undergone subsequent follow-ups. The cohort had been set up to identify reasons for social inequalities in health. The MOODFOOD study used random effects regression, with diet assessed using food frequency questionnaires and mood using validated questionnaires. The study was however able to exclude potential ‘reverse causation’ as the reason for the observed link between high sugar intake and low mood, finding that neither CMD nor depression predicted intake changes. However, the research did confirm an adverse effect of sugar intake on long-term psychological health. Referring to the aforementioned sex difference in the results, the team suggested they may be explained by the study’s sampling, chance or due to actual differences in depression pathways by sex and type of depressive symptomatology. Developing evidence based prevention strategies Depression is one of the most prevalent, severe and disabling disorders in the EU with around 6 % of the population meeting the criteria for a major depressive disorder at any time, placing a heavy burden on individuals, their families and health services. A number of plausible biological explanations have been offered for an association between sugar intake and the longer-term risk of depression. There are indications that sugar contributes to low levels of the protein BDNF (‘brain derived neurotrophic factor’), facilitating hippocampal atrophy. There is also evidence that carbohydrates increase circulating inflammatory markers, possibly depressing mood. High sugar diets could also provoke an exaggerated insulin response inducing hypoglycaemia and influencing hormone levels, also linked to mood. MOODFOOD was set up to bring together expertise in nutrition, consumer behaviour, psychiatry and preventive psychology to improve food-related behaviour. The project combines existing longitudinal data from European cohort studies with new data from surveys, short-term experiments and a long-term preventive intervention study. The ensuing knowledge will be used to develop evidence driven nutritional strategies and to guide preventative policies. For more information, please see: project website
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