Endocrine Abstracts

Calcium and Vitamin D deficiency is a common cause of falls and fracture and supplementation with 1 g of calcium and 800 IU of vitamin D is commonly recommended.

However, the serum level of 25 OHD that defines deficiency is controversial, and the 25 OHD level required to normalise serum parathyroid hormone (PTH)-in the presence of normal calcium- is often used. In this study we set out to explore how effective is 1 g of calcium and 800 IU of vitamin D in suppressing PTH in an unselected population of postmenopausal women with low bone density and normal serum calcium.

From the osteoporosis clinic computerised database 947 women had recorded values of serum PTH and 25 OHD as well as a biochemical profile including renal function and serum calcium levels. We excluded women with high serum calcium (>2.6 mmol/l) or severe renal impairment (glomerular filtration rate <60 ml/min/1.73 m²). A total of 723 women, all white Caucasian females were entered in the analysis.

Receiver Operating Characteristic (ROC) plotting showed that the lowest threshold value for plasma 25 OH vitamin D that prevents elevated PTH levels was 27.7 nmol/l (Sensitivity 90% Specificity 30%). Two-hundred-eleven women has normal serum calcium and raised PTH levels (29%). A total of 298 women were supplemented with 1000 mg of calcium and 800 IU of ergocalciferol, in spite of this 113 (53%) women still had unsuppressed PTH.

Serum Vitamin D levels are not very reliable in identifying patients who are vitamin D deficient. Furthermore over 53% of patients in spite of recommended doses of Calcium and Vitamin D supplementation are still Vitamin D deficient. This may compromise skeletal health and explain some recent negative findings on the fracture preventing effect of calcium and vitamin D supplementation.