J. Christopher Gallagher, Vinod Yalamanchili and Lynette M. Smith
Bone Metabolism Unit (J.C.G., V.Y.), Creighton University Medical Center, Omaha, Nebraska 68131; and Department of Public Health (L.M.S.), University of Nebraska Medical Center, Omaha, Nebraska 68198
Address all correspondence and requests for reprints to: Dr. Christopher J. Gallagher, M.D., Creighton University Medical Center, 601 North 30th Street, Suite 6718, Omaha, Nebraska 68131. E-mail: jcg at creighton.edu.
Context: Vitamin D is often recommended for use with calcium supplements to increase absorption.
There are no systematic studies of vitamin D on calcium absorption that indicate what dose should be recommended.
Objective: Our objective was to study the effect of increasing doses of vitamin D3 on calcium absorption.
Design and Setting: We conducted a randomized double-blind placebo-controlled trial at Creighton University Medical Center, Omaha, NE.
Participants: Participants included 163 postmenopausal Caucasian women with vitamin D insufficiency, defined as a serum 25-hydroxyvitamin D (25OHD) below 20 ng/ml (50 nmol/liter).
Intervention: Participants were randomized to receive one of the vitamin D3 doses, 400, 800, 1600, 2400, 3200, 4000, or 4800 IU/d, or placebo for 1 yr.
Calcium intake was increased to 1200–1400 mg daily by giving daily calcium citrate.
Main Outcome: We evaluated the change in calcium absorption on vitamin D.
Results: Mean serum 25OHD increased from baseline 15.6 ng/ml (39 nmol/liter) to 46.5 ng/ml (112 nmol/liter) in subjects randomized to the highest dose of vitamin D (4800 IU). Calcium absorption was more significantly related to serum 25OHD (R2 = 0.50; P = 0.001) than dose (R2 = 0.47; P = 0.033). Calcium absorption of a 100-mg dose increased from 52–58% (6 mg) over a serum 25OHD range of 20–66 ng/ml (50–165 nmol/liter).
Conclusions: There was no evidence of a threshold for reduced calcium absorption in the serum 25OHD range of 10–66 ng/ml (25–165 nmol/liter).
The increase in absorbed calcium of 6% on high doses of vitamin D is so small that the same amount could be obtained from half a glass of milk (100 ml) or 100 mg elemental calcium.
The results challenge assumptions about the value of adding vitamin D to increase calcium absorption except when serum 25OHD is very low that is less than 10 ng/ml (25 nmol/liter).
Received April 20, 2012, Accepted July 5, 2012, Copyright © 2012 by The Endocrine Society
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