NMA: Nonprescription Medicines Academy

Study of Dose Response to Vitamin D Supplementation Supports Recommended Dietary Allowances

May 1st, 2012

In a randomized, placebo-controlled trial that included 163 healthy postmenopausal white women with vitamin D insufficiency, a vitamin D3 dosage of 800 IU/day increased serum 25-hydroxyvitamin D (25-[OH]D) levels to >50 nmol/L in 97.5% of participants.

In a randomized, placebo-controlled trial that included 163 healthy postmenopausal white women with vitamin D insufficiency, a vitamin D3 dosage of 800 IU/day increased serum 25-hydroxyvitamin D (25-[OH]D) levels to >50 nmol/L in 97.5% of participants.

The women—all 57 to 90 years of age, with a mean baseline serum 25-(OH)D level of 39 nmol/L—enrolled in the study at Creighton University Medical Center in Omaha, Nebraska, during winter 2007 or spring 2008. Participants were randomly assigned to receive placebo or vitamin D3 once daily for 1 year; the doses of vitamin D3 ranged from 400 IU to 4,800 IU. Participants also received calcium supplements to increase their total daily calcium intake to 1,200–1,400 mg. The primary outcomes were serum 25-(OH)D and parathyroid levels at 6 and 12 months.

The vitamin D dose response was curvilinear and suggestive of a rate-limiting mechanism for serum 25-(OH)D. The curve started to plateau at approximately 112 nmol/L in participants receiving more than 3,200 IU/day of vitamin D3. A vitamin D3 dosage of 800 IU/day increased serum 25-(OH)D levels to >50 nmol/L in 97.5% of participants. A mixed-effects model predicted the same response with a vitamin D3 dosage of 600 IU/day (a dosage that was not tested in this study). Parathyroid hormone levels at 12 months decreased with an increasing dose of vitamin D3 (P = 0.012). Depending on the criteria used, hypercalcemia occurred in 2.8% to 9.0% of participants, and hypercalciuria occurred in 12.0% to 33.0% of participants; events were unrelated to dose.

Ann Intern Med. 2012;156:425-37.