Depressive symptoms are more common in teenage girls than in their male peers. However, boys' mental health appears to be affected more if they suffer from obesity. Irrespective of gender, bullying is a considerably greater risk factor than being overweight for developing depressive symptoms. These conclusions are drawn by researchers at Uppsala University who monitored adolescents for six years in a questionnaire study, now published in the Journal of Public Health.

Peer-review/observational study/people

"The purpose of our study was to investigate the connection between body mass index (BMI) and depressive symptoms, and to take a close look at whether being subjected to bullying affects this relationship over time. We also wanted to investigate whether any gender differences existed," says Sofia Kanders, a PhD student at Uppsala University's Department of Neuroscience.

In the study, young people born in Västmanland County, replied to questions about their height, weight and depressive symptoms on three separate occasions (2012, 2015 and 2018). The respondents' mean age was 14.4 years on the first occasion and 19.9 years on the last.

Based on BMI, the adolescents were divided into three groups: Those with normal weight, those who were overweight and those with obesity respectively. They were also grouped according to the extent of their depressive symptoms.

Overall, regardless of their weight, the girls stated more frequently that they had depressive symptoms. In 2012, 17% of the girls and 6% of the boys did so. By 2015, the proportions of adolescents with these symptoms had risen to 32% for the girls and 13% for the boys. The corresponding figures for 2018 were 34 and 19% respectively.

A higher BMI did not, as far as the researchers could see, affect the girls' mental well-being to any great extent. Among the boys, however, the pattern observed was entirely different.

"When we analyzed girls and boys separately, we saw that for boys with obesity in 2012, the risk for having depressive symptoms in 2015 was, statistically, five times higher than for normal-weight boys. In the girls we found no such connection," Kanders says.

The study has been unable to answer the question of what causes this gender difference, and the researchers think more research is needed in this area.

The young respondents were also asked about bullying—for example, to state whether, in the past year, they had been physically exposed to blows and kicks, teased or excluded, subjected to cyberbullying (abusive texting or other electronic or web bullying), or bullied by an adult at school.

In every analysis, exposure to bullying was associated with a higher risk of depressive symptoms. This connection was also evident six years later, especially in overweight boys. The researchers believe that these results seem to indicate a gender difference in how BMI and bullying together drive development of future depressive symptoms.

"One key conclusion and take-home message from our study is that bullying can affect mental illness for a long time to come, which therefore makes preventive measures against bullying in schools extremely important," Kanders says.