Handedness and mortality: A follow-up study of Danish twins born between 1900 and 1910

The declining prevalence of left-handed individuals with increasing age has led to two main avenues of hypotheses; the association is due either (1) t o a birth cohort effect and/or an age effect caused by a switch to right-ha ndedness with advancing age or (2) to mortality selection that reduces surv ival in left-handed individuals, or both. It is uncertain whether a cohort or age effect can explain the decline in age-related prevalence, and confli cting evidence exists in favor of the mortality hypothesis. We compared mor tality in a subgroup of 118 opposite handed twin pairs by counting in how m any instances the right-handed twin died first. There was no evidence of di fferential survival between right-handed and non-right handed individuals i n the entire 1900-1910 cohort. With respect to the number of right-handed t wins who died first, there was no material disadvantage among those who wer e not right-handed. In 60% (95% confidence interval = 49.0-71.5%) of dizygo tic pairs, the right-handed twins died first. In 50% of monozygotic pairs, right-handed twins died first. The prevalence of not being right handed was higher among males (9.2%) than females (6.5%); there was a similar frequen cy of non right-handedness in monozygotic (8.0%) and dizygotic (7.8%) twins . We did not find evidence of excess mortality among non-right-handed adult twins in this follow up study.