Early-Life Cardiorespiratory Fitness and Long-term Risk of Prostate Cancer

Background: Adolescence is a period of rapid prostatic growth, yet is understudied for susceptibility for future risk of prostate cancer. We examined cardiorespiratory fitness (CRF) in late adolescence in relation to long-term prostate cancer risk. Methods: A population-based cohort study was conducted of all 699,125 Swedish military conscripts during 1972–1985 (97%–98% of 18-year-old men) in relation to risk of prostate cancer overall, aggressive prostate cancer, and prostate cancer mortality during 1998–2017 (ages 50–65 years). CRF was measured by maximal aerobic workload, and prostate cancer was ascertained using the National Prostate Cancer Register. Muscle strength was examined as a secondary predictor. Results: In 38.8 million person-years of follow-up, 10,782 (1.5%) men were diagnosed with prostate cancer. Adjusting for sociodemographic factors, height, weight, and family history of prostate cancer, high CRF was associated with a slightly increased risk of any prostate cancer [highest vs. lowest quintile: incidence rate ratio (IRR), 1.10; 95% CI, 1.03–1.19; P = 0.008], but was neither significantly associated with aggressive prostate cancer (1.01; 0.85–1.21; P = 0.90) nor prostate cancer mortality (1.24; 0.73–2.13; P = 0.42). High muscle strength also was associated with a modestly increased risk of any prostate cancer (highest vs. lowest quintile: IRR, 1.14; 95% CI, 1.07–1.23; P < 0.001), but neither with aggressive prostate cancer (0.88; 0.74–1.04; P = 0.14) nor prostate cancer mortality (0.81; 0.48–1.37; P = 0.43). Conclusions: High CRF or muscle strength in late adolescence was associated with slightly increased future risk of prostate cancer, possibly related to increased screening, but neither with risk of aggressive prostate cancer nor prostate cancer mortality. Impact: These findings illustrate the importance of distinguishing aggressive from indolent prostate cancer and assessing for potential detection bias.