Secondary hyperparathyroidism in elderly people: combined effect of renal insufficiency and vitamin D deficiency.

The relative effects of renal insufficiency and vitamin D deficiency on parathyroid gland function were assessed in 29 free-living elderly subjects by using a sensitive assay for intact parathyroid hormone (PTH). Serum calcium, phosphate, alkaline phosphatase, creatinine, 25-hydroxyvitamin D [25(OH)D], and PTH were measured after an overnight fast during wintertime, after oral vitamin D therapy (20 micrograms cholecalciferol/d for 4 wk), and at the end of the subsequent summer. Hypovitaminosis D [serum 25(OH)D < 25 nmol/L] was evident in 86% of the subjects during wintertime and 52% had elevated PTH concentrations. Multiple-regression analysis identified serum creatinine as the strongest predictor variable for serum PTH (multiple r = 0.73, P < 0.001). Mean (+/- SD) serum PTH declined from 6.3 +/- 2.8 to 5.0 +/- 2.0 pmol/L (P < 0.001) by the end of the summer season, coincident with an increase in serum 25(OH)D). Secondary hyperparathyroidism is common in elderly people, and in Ireland is the result of both renal insufficiency and hypovitaminosis D.