Strong evidence of sexual dimorphic effect of adiposity excess on insulin sensitivity.

AIMS: Our aims were to investigate in several large samples, with a wide range of adiposity, whether: (1) the effect of BMI on insulin sensitivity is different between sexes; (2) also waist circumference plays a sex-specific role on insulin sensitivity; and (3) serum adiponectin and resistin are mediators of such sex-dimorphic effect.

METHODS: Samples used were: Gargano study 1 (GS1), GS2 and Catania study (CS) comprising 3274 individuals. Adiponectin and resistin were measured by ELISA. Associations between variables were tested by linear models.

RESULTS: In all samples, relationship between BMI and HOMAIR was steeper in males than in females (BMI-by-sex interaction p = 0.04-0.0007). No interaction was observed on serum adiponectin and resistin (p = 0.40-059), which are therefore unlikely to mediate the sex-dimorphic effect of BMI on insulin resistance. Relationship between waist circumference and HOMAIR was similar between sexes in GS1 and GS2 but not in CS (waist-by-sex interaction p = 0.01), comprising much heavier individuals. This suggests that a sex-dimorphic effect of abdominal adiposity on insulin resistance is observable only in the context of high BMI.

CONCLUSIONS: Our findings represent a proof of concept that BMI and insulin sensitivity are associated in a sex-specific manner. This may explain why females are protected from diabetes and cardiovascular disease, compared to males of similar BMI.