The association between leisure time physical activity in adolescence and poor mental health in early adulthood: a prospective cohort study

BACKGROUND The incidence of poor mental health (MH) is increasing in Denmark and worldwide, especially among 16-24 year olds. Low physical activity (PA) during adolescence seems to be a risk factor for poor MH in early adulthood. Among adults, it appears that a high level of PA may be protective against poor MH. We aimed to examine whether high levels of leisure time physical activity (LTPA) during adolescence reduced the risk of poor MH at age 20/21. METHODS Prospective cohort study with data collected during 2004-2010 in the western part of Denmark. The study population was 3031 young people (age 14/15 in 2004). LTPA was the exposure variable and originates from questionnaires in 2004/2007. MH was the outcome variable and was measured at age 20/21 in 2010. MH was evaluated using a short version of the CES-DC. Logistic regression was used to analyse the associations between levels of LTPA and MH. All analyses were stratified by gender. RESULTS 1,589 adolescents were included in the final analyses. Girls at 14/15 years of age with a low level of LTPA had an Adjusted Odds Ratio(AOR) of 1.63 (95% CI = 1.23-2.17) for poor MH as 20/21 year olds, compared to girls with a high level of LTPA. Among boys, the corresponding AOR = 1.19 (95% CI = 0.85-1.66). We found an exposure-response relationship between levels of LTPA and MH among girls, but not among boys. Girls with a reduction/persistent low level of LTPA between the ages of 15-18 had an increased risk for poor MH at age 20/21 compared to the reference group. CONCLUSIONS Among girls, we found an association between a low level of LTPA among 14/15 year olds as well as a reduction/persistent low level of LTPA over time with poor MH at 20/21 years. We found no association between low levels of LTPA and poor MH among 14/15 year olds boys however it appears that a reduction/persistent low level of LTPA over time may have some influence on the risk of poor MH at 20/21 years. It is important to address the change in habits of LTPA during adolescence to prevent poor MH.