How bullying and obesity can affect girls' and boys' mental health

"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, overweight and 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 per cent of the girls and 6 per cent of the boys did so. By 2015, the proportions of adolescents with these symptoms had risen to 32 per cent for the girls and 13 per cent for the boys. The corresponding figures for 2018 were 34 and 19 per cent 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 analysed 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.

Facts about the study

This study is a sub-project in the much larger SALVe (Survey of Adolescent Life in Vestmanland) study. In SALVe, teenagers born in 1997 and 1999, and residing in Västmanland County (to the west of Uppsala), were asked in 2012 to answer questions about various ailments, well-being, sleep, computer habits, gaming, enjoyment of school and other aspects of their lives. The purpose is to follow this cohort for 20 years in order to gain knowledge of how inheritance and environment affect mental and physical health.

In this sub-project, 1,729 adolescents (962 girls and 767 boys) replied to the researchers' questions on the first occasion, in 2012. In 2015 there were 1,481 respondents, and in 2018 1,111. This decrease in numbers over time was due to drop-out, with slightly more boys than girls leaving the study.

The adolescents were grouped on the basis of their BMI and prevalence of depressive symptoms. Every answer to a question about the extent of their subjection to bullying was given a point score from 0 to 3. The researchers then compared the various groups' total scores; that is, they did not explore the results at individual level.