MS Speaks

SUMMARY AND COMMENT | GENERAL MEDICINE
Vitamin D Supplementation: Is More Better?

Thomas L. Schwenk, MD reviewing Burt LA et al. JAMA 2019 Aug 27

In a randomized trial, higher doses unexpectedly were associated with greater declines in bone-mineral density.

The “if some is good, more is better” approach to supplementation has led to as many as 3% of U.S. adults taking high-dose vitamin D supplements (≥4000 IU daily). To address uncertainty about incremental benefit of vitamin D doses higher than 400 to 1000 IU daily, Canadian investigators randomized 311 adults (mean age, 62); without osteoporosis and with normal hydroxyvitamin D (25[OH]D) and serum calcium levels to one of three levels of supplementation (400 IU, 4000 IU or 10,000 IU) daily. At baseline, mean serum 25(OH)D was 32 ng/mL (79 nmol/L). Patients with prior high-dose vitamin D use, disorders of vitamin D metabolism, or high 10-year risk for osteoporotic fractures were excluded. Dietary calcium intake was supplemented to recommended levels.

Participants were assessed serially through 36 months. Bone-mineral density (BMD) and bone strength were assessed at the distal radius and tibia by high-resolution computed tomography (a method used in clinical research).

Serum 25(OH)D levels increased significantly for participants who received 4000 IU or 10,000 IU daily but not for participants who received 400 IU daily. At 3 years, declines in BMD at the radius were significantly steeper in the 4000 IU and 10,000 IU groups (−2.4% and −3.5%, respectively) than in the 400 IU group (−1.2%). A similar pattern was noted in the tibia. Bone-strength estimates declined in all three groups, with nonsignificant trends toward lower strength in the high-dose vitamin D groups than in the 400 IU group.
COMMENT

The authors speculate that this somewhat unexpected finding might be due to increased bone resorption secondary to parathyroid hormone suppression. In any case, the findings point to no benefit for bone integrity — and even potential harm — with high-dose vitamin D supplementation in patients whose vitamin D levels are adequate.

Burt LA et al. Effect of high-dose vitamin D supplementation on volumetric bone density and bone strength: A randomized clinical trial. JAMA 2019 Aug 27; 322:736.