Sex Hormones and Serum Phosphorus in Older Men: The Osteoporotic Fractures in Men (MrOs) Study

Older women have higher phosphorus levels than men. Estradiol causes phosphaturia in rodents. Whether sex hormones associate with phosphorus levels in humans is unknown. In 1,346 community-living older men, we evaluate the cross-sectional association of sex hormones with serum phosphorus, using linear regression with serum phosphorus levels as the dependent variable. Mean age was 76 years, phosphorus was 3.2±0.4mg/dl, and 18% had moderate kidney disease. Each 10pg/ml higher total estradiol associated with 0.05mg/dL lower serum phosphorus levels (95 % CI −0.09 to −0.02; P < 0.01) in a model adjusted for age, race, testosterone, sex hormone binding globulin, calcium, eGFR, intact PTH, 25(OH) vitamin D, body mineral density, and alkaline phosphatase. Results were similar in individuals with or without CKD. Serum testosterone levels were also associated with lower serum phosphorus levels (β per 200ng/dL greater total testosterone = −0.08; 95% CI −0.13 to −0.04; P < 0.001). Results were confirmed in an independent sample of 2,555 older men, and associations were not attenuated when adjusted for fibroblast growth factor-23 levels. Estradiol may induce phosphaturia in humans. Future studies are required to elucidate potential effects of testosterone on phosphorus homeostasis.