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An association between sugar and mental health
A diet high in sugar found in sweet foods and beverages may be associated with an increased likelihood of common mental disorders (such as anxiety and depression) in men according to a study in Scientific Reports. The authors note that their findings should be replicated in other groups.
Higher levels of sugar consumption have been linked to a higher prevalence of depression in several studies. However, the possibility that a mental health disorder may lead to a higher sugar intake, so that the diet-mental health association is wholly or partly the result of poor mental health, has not been examined.
Anika Knüppel and colleagues analysed repeated data from 8,087 men and women aged between 39 and 83 collected over a 22 year period from the Whitehall II study. Based on information about diet and mental health compiled from questionnaires, the authors found that higher levels of sugar intake had an adverse effect on mental health and in follow up five years later. They also found that men in the top third of the sample for sugar intake had a 23% increased chance of incident common mental disorders after five years, independent of health behaviours, socio-demographic and diet-related factors, adiposity and other diseases. The authors found no support for the hypothesis that those susceptible to depression tend to increase their sugar intake and argue that their findings show an adverse effect of sugar intake from sweet foods and beverages on long-term psychological health
Expert Reaction
These comments have been collated by the Science Media Centre to provide a variety of expert perspectives on this issue. Feel free to use these quotes in your stories. Views expressed are the personal opinions of the experts named. They do not represent the views of the SMC or any other organisation unless specifically stated.
Dr Anna Kokavec is an experienced biological researcher, currently working as a psychologist in private practice and as a research consultant at Victoria University
This is a very well-written paper. The results section is very complicated and sounds impressive, but even though I am not a fan of sugar, I am not convinced because in my view there is little in the findings to confirm that sugar ‘causes’ depression.
The science confirms that sucrose can significantly increase insulin level, which subsequently can affect the uptake of tryptophan and alter the synthesis of serotonin. Thus, the preference for refined sugar in depression is assumed to be linked to low serotonin, which is a key factor in depression.
Before any study can conclude that sugar actually ‘causes’ depression, it would need to investigate the biological factors associated with depression. However, this is a self-report study that has not looked at biological factors. It is purely reporting questionnaire data.
Self-report data is difficult to interpret because it can be influenced by things such as poor memory and, more importantly, social desirability responding.
The introduction makes mention of biological connections that have little bearing on what is to be examined in the study. Furthermore, in the discussion the authors attempt to link the findings, which are basic at best, to biological factors that have not been assessed.
This is a common problem with questionnaire data; we are still trying to recover from the questionnaire studies claiming red wine is good for health, something the biochemistry now is failing to support, especially if we assess the effect of red wine on the body as a whole.
Professor Mark L Wahlqvist AO is Emeritus Professor and Head of Medicine at Monash University and Monash Medical Centre. He is also Past President of the International Union of Nutritional Sciences
Whether causal or not, the Whitehall II study illustrates what is generally known: that a varied nutritious dietary pattern is associated with healthier brain function, including that to do with mood. The sugar story may be simply the flip-side of this association.
This finding has practical relevance, since having less added sugar allows more space in the diet for nutritious foods - even those which have sugar naturally such as intact fruit (mainly fructose) and milk (where it is lactose).
Dose will also matter: indiscretion should be of a little, not a lot. The background data also indicate, as do other studies, that physical activity is a crucial aspect of mental health and allows more healthy food to be consumed with less risk of being over-fat, itself a risk for poor mental health.
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