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Children between the ages of 12 and 16 with a high BMI are at an increased risk of depression compared to children of the same age who are of a healthy weight, according to new research published in Psychological Medicine.
The association of high BMI and depression was weaker between the ages of 16 and 21, suggesting that preventative methods should be introduced early to have the biggest benefit.
Participants were asked about their mental health at the ages of 12, 16 and 21
The authors of the study analysed data from 10,433 twin pairs in the Twins Early Development Study and UK Adult Twist Registry.
The authors then analysed whether there was a correlation between BMI and other weight indicators and depressive symptoms.
Depressive symptoms included low mood, loneliness, isolation and exhaustion. These symptoms were self-reported in twins born between 1994 and 1996 at the ages of 12, 16 and 21.
In both samples, structural equation modelling of twin data investigated genetic and environmental influences between weight indicators and depression.
A stronger association for children with a higher BMI at an early age
Within the Twins Early Development Study, which included 7,658 pairs of twins, the relationship was found to be bidirectional between the ages of 12 and 16, with a stronger influence of earlier BMI on later depression.
However, the associations were unidirectional thereafter, with depression at 16 influencing BMI at 21.
Small genetic correlations were also found between BMI and depression at ages 16 and 21, but not at 12.
Contrastingly, in the TwinsUK study, which included 2,775 twin pairs, depression was only weakly correlated with weight indicators, and it was therefore not possible to generate precise estimates of genetic or environmental correlations.
Findings suggest that the relationship between BMI and depression is environmentally mediated
The authors of the research say the findings suggest that the directionality of the relationship between BMI and depression may be developmentally sensitive.
However, further research with larger genetically informative samples is needed to estimate the aetiological influence on these associations.
First author Dr Ellen Thompson told King’s College London that the findings should inform care approaches, with early intervention most likely to result in meaningful benefit.
She said: “Understanding the relationship between mental ill-health and weight in adolescence is vital to provide timely support where needed. This study shows a stronger association between having a higher BMI at age 12 years and subsequent depression symptoms at age 16 years than the reverse.
“This indicates that this relationship is environmentally mediated and could be due to several factors that adolescents may experience. Our study did not ask questions around the reasons why this effect was seen, but previous research has suggested body dissatisfaction and weight related stigma from external sources could be a factor. This study identifies a crucial point where intervention might be beneficial.”