OBJECTIVE: The association between attention-deficit/hyperactivity disorder (ADHD) and shorter height is unclear. This study examined the risk of shorter height in individuals with ADHD, and the influence of prenatal factors, ADHD medication, psychiatric comorbidity, socioeconomic factors and familial liability.

METHOD: We draw on Swedish National Registers for two different study designs. First, height data for 14,268 individuals with ADHD and 71,339 controls were stratified into two groups: 1: Before and 2: After stimulant treatment were introduced in Sweden. Second, we used a family-based design including 833,172 relatives without ADHD with different levels of relatedness to the individuals with ADHD and matched controls.

RESULTS: ADHD was associated with shorter height both before (below average height: OR=1.31, 95 % CI=1.22-1.41) and after (below average height: OR=1.21, 95 % CI=1.13-1.31) stimulants for ADHD were introduced in Sweden and was of similar magnitude in both cohorts. The association between ADHD and shorter height attenuated after adjustment for prenatal factors, psychiatric disorders and SES. Relatives of individuals with ADHD had an increased risk of shorter height (below average height in full siblings: OR=1.14, 95 % CI=1.09-1.19; maternal half siblings: OR=1.10, 95 % CI=1.01-1.20; paternal half siblings: OR=1.15, 95 % CI=1.07-1.24, first full cousins: OR=1.10, 95 % CI=1.08-1.12).

CONCLUSION: Our findings suggest that ADHD is associated with shorter height. On a population level, this association was present both before and after ADHD-medications were available in Sweden. The association between ADHD and height was partly explained by prenatal factors, psychiatric comorbidity, low SES and a shared familial liability for ADHD.