Association Between Handedness and Type 2 Diabetes: The E3N Study.

Some studies reported decreased longevity in left-handed individuals as compared with right-handed individuals without a clear underlying explanation. We examined the unexplored relationship between handedness and type 2 diabetes (T2D) among 65,732 women from the prospective Etude Epidémiologique auprès de Femmes de la Mutuelle Générale de l’Education Nationale (E3N) cohort study (1) between 1990 and 2008. As comparedwith right-handedwomen, there was an increased risk of T2D in lefthanded women (hazard ratio 1.21 [95% CI 0.96–1.53]) and a significantly increased risk in mixed-handed women (1.36 [1.17–1.57]) (Table 1). When both leftandmixed-handed womenwere grouped, the increased risk of T2D persisted (1.31 [1.16–1.49]). Adjusting for T2D risk factors had little impact on the estimations (model M1). Associations were decreased but remained significant when adjusting for BMI, suggesting alternative mechanisms (model M2). We have also shown that nonright-handedness was predictive of a higher incidence of obesity (1.19 [1.05–1.34], data not shown). Some hypotheses could explain our results. Hand preference is influenced by cortex hemisphere dominance (2), which therefore could be involved in the development of T2D. Handedness formation is also related to prenatal testosterone exposure (3), which is predictive of T2Ddevelopment inwomen (4). Even though we considered self-reported handedness, this is the first study to highlight a relationship between hand preference and T2D risk. These findings deserve further explorations.