The role of insulin-like growth factor I in age-related changes in calciumhomeostasis in men

The aim of this study was to evaluate hormonal influences on age-related ch anges in calcium homeostasis in men. We recruited 178 healthy men, ages 20-79 (about 30 per decade). We measured serum calcium, phosphate, urinary calcium, and creatinine clearance. Dieta ry calcium intake and use of fish oils were determined by questionnaire. Fr actional calcium absorption was estimated using the stable strontium techni que in a subgroup of 60 men. PTH, 1,25-dihydroxyvitamin D [1,25(OH)(2)D], 2 5-hydroxyvitamin D (25OHD), serum insulin-like growth factor I (IGF-I), and testosterone were measured in all men. There was no change in serum calcium with age. There were decreases in seru m phosphate, urinary calcium, and creatinine clearance with age (P < 0.02). Dietary calcium was unchanged. Strontium absorption decreased (P < 0.01), and PTH increased (P < 0.001) with age. The data for 1,25OH(2)D were biphas ic, reaching a peak at age 55 yr (P = 0.003). There was a linear increase i n 25OHD with age (P = 0.009) that persisted after correcting for seasonal v ariation and was positively associated with fish oil use, therefore, the ag e-related changes in 25OHD were masked by self medication. There were logli near decreases in IGF-I and testosterone with age (P < 0.0001). Strontium absorption was not related to 25OHD or 1,25(OH)(2)D, but was posi tively correlated with IGF-I. 1,25(OH)(2)D correlated negatively with serum phosphate and calcium, but not PTH or creatinine clearance. IGF-I was posi tively associated with creatinine clearance, serum calcium, and phosphate a nd negatively associated with PTH (P < 0.001). In this cross-sectional study of otherwise healthy, normally aging men, age -related decreases in IGF-I seem to have a greater impact on mineral absorp tion than does vitamin D status.