Influence of Cardiovascular Fitness and Muscle Strength in Early Adulthood on Long-Term Risk of Stroke in Swedish Men

Abstract

Background and Purpose— Low cardiovascular fitness (fitness) in mid- and late life is a risk factor for stroke. However, the respective effects on long-term stroke risk of fitness and muscle strength in early adulthood are unknown. Therefore, we analyzed these in a large cohort of young men. Method— We performed a population-based longitudinal cohort study of Swedish male conscripts registered in 1968 to 2005. Data on fitness (by the cycle ergometric test; n=1 166 035) and muscle strength (n=1 563 750) were trichotomized (low, medium, and high). During a 42-year follow-up, risk of stroke (subarachnoidal hemorrhage, intracerebral hemorrhage, and ischemic stroke) and fatality were calculated with Cox proportional hazards models. To identify cases, we used the International Classification of Diseases - Eighth to Tenth Revision in the Hospital Discharge Register and the Cause of Death Register. Results— First-time stroke events were identified (subarachnoidal hemorrhage, n=895; intracerebral hemorrhage, n=2904; ischemic stroke, n=7767). For all stroke and fatality analysis any type of first-time stroke was recorded (n=10 917). There were inverse relationships in a dose–response fashion between fitness and muscle strength with any stroke (adjusted hazard ratios for the lowest, compared with the highest, tertile of each 1.70 [1.50–1.93] and 1.39 [1.27–1.53], respectively). There were stronger associations for fatal stroke. All 3 stroke types displayed similar associations. Associations between fitness and stroke remained when adjusted for muscle strength, whereas associations between muscle strength and stroke weakened/disappeared when adjusted for fitness. Conclusions— At the age of 18 years, low fitness and to a lesser degree low muscle strength were independently associated with an increased future stroke risk.