Dose Response to Vitamin D Supplementation in Postmenopausal Women

Annals of Internal Medicine, 03/27/2012

A vitamin D3 dosage of 800 IU/d increased serum 25–(OH)D levels to greater than 50 nmol/L in 97.5% of women; however, a model predicted the same response with a vitamin D3 dosage of 600 IU/d. These results can be used as a guide for the RDA of vitamin D3, but prospective trials are needed to confirm the clinical significance of these results.

Methods

  • Creighton University Medical Center, Omaha, Nebraska.
  • 163 healthy postmenopausal white women with vitamin D insufficiency enrolled in the winter or spring of 2007 to 2008 and followed for 1 year.
  • Participants were randomly assigned to receive placebo or vitamin D3, 400, 800, 1600, 2400, 3200, 4000, or 4800 IU once daily.
  • Daily calcium supplements were provided to increase the total daily calcium intake to 1200 to 1400 mg.
  • The primary outcomes were 25–(OH)D and PTH levels at 6 and 12 months.

Results

  • The mean baseline 25–(OH)D level was 39 nmol/L.
  • The dose response was curvilinear and tended to plateau at approximately 112 nmol/L in patients receiving more than 3200 IU/d of vitamin D3.
  • The RDA of vitamin D3 to achieve a 25–(OH)D level greater than 50 nmol/L was 800 IU/d.
  • A mixed–effects model predicted that 600 IU of vitamin D3 daily could also meet this goal.
  • Compared with participants with a normal body mass index (<25 kg/m2), obese women (≥30 kg/m2) had a 25–(OH)D level that was 17.8 nmol/L lower.
  • 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% and hypercalciuria in 12.0% to 33.0% of participants; events were unrelated to dose.

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