Associations of mortality with own height using son's height as an instrumental variable

Abstract

Height is associated with mortality from many diseases, but it remains unclear whether the association is causal or due to confounding by social factors, genetic pleiotropy,(1) or existing ill-health. The authors investigated whether the association of height with mortality is causal by using a son's height as an instrumental variable (IV) for parents' height among the parents of a cohort of 1,036,963 Swedish men born between 1951 and 1980 who had their height measured at military conscription, aged around 18, between 1969 and 2001. In a two-sample IV analysis adjusting for son's age at examination and secular trends in height, as well as parental age, and socioeconomic position, the hazard ratio (HR) for all-cause paternal mortality per standard deviation (SD, 6.49cm) of height was 0.96 (95% confidence interval (CI): 0.95, 0.96). The results of IV analyses of mortality from all causes, cardiovascular disease (CVD), respiratory disease, cancer, external causes and suicide were comparable to those obtained using son's height as a simple proxy for own height and to conventional analyses of own height in the present data and elsewhere, suggesting that such conventional analyses are not substantially confounded by existing ill-health.

Fig. 1

Flow of participants through the study; parents of Swedish men born between 1951 and 1980 and subjected to conscription examination.

Fig. 2

Hazard ratios (with 95% confidence intervals) for mortality from (a and b) any cause, (c and d) cardiovascular disease and (e and f) external causes, adjusted for age and socio-economic position, among the parents of Swedish men born between 1951 and 1980 and subjected to conscription examination. The hazard ratio for each tenth of son's height (adjusted for secular trends and age at examination) is plotted at its median value, with the first tenth as the reference group. Plots for all mortality causes, and by father's own height, are available in Fig. A2 of Appendix.