The relationship between handedness and risk of multiple sclerosis

Background Left-handedness has been studied as a marker for in-utero exposure to sex steroid hormones, and an increased risk of autoimmune and immune disorders among left-handed individuals has been suggested. Objective This study examines the relationship between hand preference and risk of multiple sclerosis, a presumed autoimmune disorder of unknown etiology. Methods The study population comprised participants in the Nurses' Health Study, an ongoing prospective cohort study of 121,701 female nurses in the United States with followup from 1976 to 2002. The nurses were asked to report their natural hand preference (right, left, ambidextrous, forced to change). Results During followup 210 incident cases with multiple sclerosis were confirmed. A 62% increased risk of multiple sclerosis was observed among women who were naturally left handed as compared to those who were naturally right handed (95% CI: 1.04-2.53). Conclusions This study suggests a modest increase in risk of multiple sclerosis among left-handed women. Further investigation of this relationship is suggested in other populations including both males and females. While the current results suggest that prenatal exposure to sex hormones may play a role in multiple sclerosis risk, direct examination of the relationship between in-utero hormone exposure and hand preference is necessary before any conclusions can be drawn. Multiple Sclerosis 2009; 15: 587-592. http://msj.sagepub.com