Muscular strength in male adolescents and premature death: cohort study of one million participants

Objectives To explore the extent to which muscular strength in adolescence is associated with all cause and cause specific premature mortality (<55 years). Design Prospective cohort study. Setting Sweden. Participants 1 142 599 Swedish male adolescents aged 16-19 years were followed over a period of 24 years. Main outcome measures Baseline examinations included knee extension, handgrip, and elbow flexion strength tests, as well as measures of diastolic and systolic blood pressure and body mass index. Cox regression was used to estimate hazard ratios for mortality according to muscular strength categories (tenths). Results During a median follow-up period of 24 years, 26 145 participants died. Suicide was a more frequent cause of death in young adulthood (22.3%) than was cardiovascular diseases (7.8%) or cancer (14.9%). High muscular strength in adolescence, as assessed by knee extension and handgrip tests, was associated with a 20-35% lower risk of premature mortality due to any cause or cardiovascular disease, independently of body mass index or blood pressure; no association was observed with mortality due to cancer. Stronger adolescents had a 20-30% lower risk of death from suicide and were 15-65% less likely to have any psychiatric diagnosis (such as schizophrenia and mood disorders). Adolescents in the lowest tenth of muscular strength showed by far the highest risk of mortality for different causes. All cause mortality rates (per 100 000 person years) ranged between 122.3 and 86.9 for the weakest and strongest adolescents; corresponding figures were 9.5 and 5.6 for mortality due to cardiovascular diseases and 24.6 and 16.9 for mortality due to suicide. Conclusions Low muscular strength in adolescents is an emerging risk factor for major causes of death in young adulthood, such as suicide and cardiovascular diseases. The effect size observed for all cause mortality was equivalent to that for well established risk factors such as elevated body mass index or blood pressure.