Serum phosphate is related to adiposity in healthy adults.

BACKGROUND: Inorganic phosphate is a crucial component of cellular energy metabolism. We have identified an inverse relationship between serum phosphate concentration and fat mass in a cohort of healthy men. This study reports those data and determines whether this association is present in two female populations.

METHODS: Cross-sectional data from three independent cohorts, consisting of healthy adult males (Male Cohort, n = 323) and healthy postmenopausal women (Female Cohort 1, n = 185; and Female Cohort 2, n = 1471), are reported. Associations between serum phosphate and weight, body mass index (BMI), fat mass and bone mineral density (BMD) were assessed. In a fourth cohort of postmenopausal women (FGF23 Cohort, n = 20), associations between fibroblast growth factor 23 (FGF23), weight and BMI were assessed.

RESULTS: Serum phosphate correlated inversely with weight, BMI and fat mass across all three cohorts (r = -0·13 to -0·31, P < 0·0001-0·02). Associations were diminished after adjustment for PTH, but remained significant. In the FGF23 Cohort, FGF23 was positively correlated with weight (r = 0·60, P = 0·007) and BMI (r = 0·49, P = 0·03). Phosphate was inversely associated with BMD in Female Cohorts 1 and 2 (r = -0·08 to -0·29, P < 0·0001-0·02). This relationship was attenuated, but remained significant at most sites, following adjustment for age, fat mass, renal function and 25-hydroxyvitamin D.

CONCLUSIONS: Serum phosphate is inversely associated with measures of adiposity in both women and men, largely independently of PTH. FGF23 might mediate these associations. This relationship may be an unrecognized confounder in some of the correlates of serum phosphate already described.