Studies have clearly established that in addition to impacting physical health, overweight and obesity in children and adolescents can also affect their current and future mental health. The nature of this link has until now only been explored by studies of limited scope. An English team therefore ventured further by studying this association at different times within a large cohort of adolescents in different countries in Europe and North America.
Exploring the link between BMI and mental health using data from over a million adolescents
A cross-sectional study was carried out using the study data Health Behavior in School-aged Children (HBSC) carried out every 4 years between 2002 and 2018. Remember that this study included more than a million adolescents aged 11 to 15 whose psychosomatic difficulties had been assessed on an 8-item scale (decreased morale , irritability, nervousness, sleepiness, dizziness, headache, stomach pain and back pain). Adolescents were asked to rate these difficulties over the past 6 months on a scale from 0 (never) to 4 (every day). Subgroup analyses, particularly according to sex and level of education, factors already known to be capable of influencing this relationship, were also carried out to better understand the dose-response relationship between BMI standardized according to age and gender and mental health.
The association between BMI and psychosomatic disorders follows a U-shaped curve
All the data from the subjects included in HBSC were analyzed (mean age 13.5 years, 50.9% girls) and measured an average psychosomatic difficulty score of 8.5 (standard deviation of 6.15, on a scale of increasing difficulty ranging from 0 to 32). They reveal the existence of a U-shaped curve linking BMI (standardized for age and sex, BMI z score defined by the WHO) and mental health. Thus, after adjustment for the various confounding factors, adolescents who had a low BMI, that is to say a BMI z score ≤ −2, had more psychosomatic symptoms than those who had a normal weight (BMI z score including between −0.99 and 0.99). This was also the case for those who were overweight (BMI z score between 1 and 1.99) and those who were obese (BMI z score ≥ 2).
This association following a U-shaped curve could be observed over the different years analyzed and regardless of gender and level of education. It lessened over time. However, compared to the year 2002, for the same BMI, psychosomatic difficulties increased significantly until 2018, the greatest difficulties being recorded among adolescents who attended University. At the same BMI and at different times, girls reported greater difficulties than boys, and the U-shaped curve was less pronounced in them than in boys.
