Supplemental vitamin D enhanced calcium absorption very little among women with mild vitamin D insufficiency.

In a recent randomized trial, 163 postmenopausal women with mild vitamin D insufficiency (mean 25[OH]D level, 16 ng/mL) received doses of vitamin D3 ranging from 400 IU to 4800 IU daily. Doses 800 IU daily were sufficient to boost levels above 20 ng/mL in nearly all women who received these doses (JW Gen Med Apr 26 2012). Because a goal of vitamin D supplementation is to ensure adequate intestinal absorption of calcium, these researchers now present additional findings on the relation between vitamin D dosing and calcium absorption. Participants ingested a standard dose of radioactive calcium, and serum radiocalcium was measured 2 hours later.

At baseline, a mean 54% of ingested calcium was absorbed. After 1 year of vitamin D supplementation, the percent absorption rose by only about 3% on average, with trivial differences among the seven vitamin D dosages (range, 400–4800 IU daily). Moreover, among patients whose 25(OH)D levels exceeded 60 ng/mL after supplementation, calcium absorption was only 6% higher than in patients whose 25(OH)D levels reached only 20 ng/mL (58% vs. 52%).

CITATION(S):

Gallagher JC et al. The effect of vitamin D on calcium absorption in older women. J Clin Endocrinol Metab 2012 Oct; 97:3550.