Young men's fitness levels predict whether they'll have children later
Swedish researchers tracking 70+ years of data found that men's physical strength and cardiovascular health in their late teens strongly predict later fertility—with the least fit men 10-20% more likely to remain childless. The discovery matters for workforce planning, social policy, and understanding how health disparities compound across generations.
Originaltitel: The Multidimensional Influence of Health on Fertility Outcomes for Men: Evidence From Swedish Military Conscription Data
We examine how health in early adulthood predicts men’s later-life fertility using Swedish population registers linked to military conscription examinations. We study men born 1951–1979, observed for fertility through 2024, and exploit objective health measured at ages 18–20 across twelve indicators: muscular strength (handgrip, arm, leg, combined), cardiovascular health (resting heart rate, blood pressure, ECG pathology, maximal working capacity on cycle ergometer), and blood/urine biomarkers (hematocrit, erythrocyte sedimentation rate, U-glucose, U-albumin). Outcomes are completed parity, childlessness, ever-marrying, and childlessness among the ever-married. We estimate linear models for all men and sibling fixed-effects models that compare full brothers. Men in the lowest strength and fitness deciles have 0.25–0.45 fewer children and a 10–20 percentage-point higher probability of childlessness than those in the highest deciles. High resting heart rate shows similar but slightly smaller gradients. Blood pressure categories and ECG abnormalities exhibit modest associations. Biomarkers indicative of metabolic and renal stress also have modest associations with fertility. Findings are consistent with multiple potential explanatory mechanisms and indicate that early-adult health is an important explanation for which men have children. We find particularly low fertility among those with the worst health, and that a substantial share of the association is driven by childlessness.