Vitamin D's Effect on Calcium Absorption

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 supplementatio…