Physical Fitness Among Swedish Military Conscripts and Long-Term Risk for Type 2 Diabetes Mellitus: A Cohort Study.

Background: Early-life physical fitness has rarely been examined in relation to type 2 diabetes mellitus (DM) in adulthood because of the lengthy follow-up required. Elucidation of modifiable risk factors at young ages may help facilitate earlier and more effective interventions.

Objective: To examine aerobic capacity and muscle strength at age 18 years in relation to risk for type 2 DM in adulthood.

Design: National cohort study.

Setting: Sweden.

Participants: 1 534 425 military conscripts from 1969 to 1997 (97% to 98% of all men aged 18 years nationwide) without prior type 2 DM.

Measurements: Aerobic capacity and muscle strength (measured in watts and newtons per kilogram of body weight, respectively) were examined in relation to type 2 DM identified from outpatient and inpatient diagnoses from 1987 to 2012 (maximum age, 62 years).

Results: 34 008 men were diagnosed with type 2 DM in 39.4 million person-years of follow-up. Low aerobic capacity and muscle strength were independently associated with increased risk for type 2 DM. The absolute difference in cumulative incidence of type 2 DM between the lowest and highest tertiles of both aerobic capacity and strength was 0.22% at 20 years of follow-up (95% CI, 0.20% to 0.25%), 0.76% at 30 years (CI, 0.71% to 0.81%), and 3.97% at 40 years (CI, 3.87% to 4.06%). Overall, the combination of low aerobic capacity and muscle strength was associated with a 3-fold risk for type 2 DM (adjusted hazard ratio, 3.07 [CI, 2.88 to 3.27]; P < 0.001), with a positive additive interaction (P < 0.001). These associations were seen even among men with normal body mass index.

Limitation: This cohort did not include women and did not measure physical fitness at older ages.

Conclusion: In this large cohort of Swedish male military conscripts, low aerobic capacity and muscle strength at age 18 years were associated with increased long-term risk for type 2 DM, even among those with normal body mass index.

Primary Funding Source: National Institutes of Health.