Scientists from the Chinese Medical University studied how a person's weight over the course of life is linked to the risk of depression and anxiety disorder. The work was published in the Journal of Affective Disorders. The main conclusion: if a child was heavier or thinner than peers, but by adulthood their weight returned to normal, the elevated risk of mental health problems disappears.
The study involved 368,756 people from UK Biobank, a British database of long-term medical data. These were adults aged 40-69 who had not been diagnosed with depression or anxiety at the start of observation. Participants recalled what their weight was at age 10 compared with peers: thinner, like everyone else, or heavier. The researchers also measured their current body mass index (BMI), an indicator calculated by dividing weight in kilograms by the square of height in meters. BMI is used to assess underweight, normal weight, overweight or obesity.
Participants were followed for an average of just over 13 years. During this time, 11,546 new cases of depression and 15,780 cases of anxiety were recorded. It turned out that among those who were thinner than peers in childhood, the risk of depression was 9% higher, and the risk of anxiety 13% higher. Among those who were heavier in childhood, the risks were 19% and 11% higher, respectively.
Weight in adulthood was more strongly linked to mental health. The relationship had a U-shape: the lowest risk was at a BMI of about 23-24, that is, within the normal range, while deviations in either direction raised it. In people with overweight, the risk of depression was 18% higher than with normal weight. With obesity, the risk of depression rose by 52%, and of anxiety by 15%.
The most revealing results came from combining data on weight in childhood and adulthood. Participants were divided into nine groups depending on how their weight changed. The highest risk was among those who went from being a thin child to an adult with obesity: they faced depression 73% more often and anxiety 33% more often than those who always had average and normal weight.
Statistical analysis showed that adult BMI explains about 45% of the link between childhood heaviness and depression in adults and about 31% of the link with anxiety. This suggests that part of the risk associated with childhood weight may be explained by excess weight persisting or increasing with age.
However, childhood heaviness did not mean a lifelong increase in risk. Those who were heavier in childhood but had normal weight by adulthood did not show a statistically significant increase in the risk of depression or anxiety. Their indicators were comparable to those who always remained within the normal range. This suggests that the psychological risk associated with childhood weight is potentially reversible if weight returns to normal by adulthood.
The study relied on participants' recollections of their weight at age 10, which was decades ago. Memory is imperfect, so recall error is possible. The categories "thinner," "like everyone else" and "heavier" are subjective. In addition, this is an observational study: it does not prove that weight directly causes depression or anxiety. It concerns a statistical association, which by itself does not confirm a cause-and-effect relationship. Other unaccounted biological, social or environmental factors could also have had an influence.
The authors also note limitations: UK Biobank consists mainly of volunteers of European origin, which reduces the applicability of the findings to other populations. Participants in such studies are often healthier than the population as a whole. In addition, depression and anxiety were counted using combined medical codes, without separating disorder subtypes.