2.1. Study population

This study was based on the linkage of several Swedish population‐based registers linked by unique personal numbers: The Swedish Military Service Conscription Register (MSCR), the Multi‐Generation Register, Longitudinal Integration Database for Health Insurance and Labor Market Studies (LISA), Prescribed Drug Register (PDR), and National Patient Register (NPR). The MSCR includes extensive medical and psychological assessments for all men at 18 years of age. Military service was obligatory by law to all Swedish men until year 2010 unless individuals were in prison, presented with severe chronic medical or mental conditions or handicaps documented by a medical certificate (approximately 2%–3% annually). All individuals born between 1973 and 1991 who enlisted for military service after 1991 with information on SBP, DBP, RHR, BMI, and physical fitness were identified (N = 395,978). Further, using the Multi‐generation Register, we linked these individuals with their biological parents, which allowed us to identify full‐sibling relationships within the same birth cohort (N = 208,060) in which the individual and their full sibling shared both of their biological parents. We carried out additional analysis in a unmedicated cohort (before ADHD medication was introduced in Sweden) restricted to military conscription between 1978 and 1991 (N = 269,503).