Vitamin D Supplementation: How Much Is Too Much?

Supplementation with vitamin D does not improve bone health in otherwise healthy adults, according to the results of a recent study.

Although many US adults report vitamin D intake of at least 4000 IU per day, there is a lack of data on the long-term effects of supplementation at high doses.

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In order to examine the effects of supplementation on bone mineral density (BMD) and strength in healthy adults, the researchers conducted a 3-year, double-blind, randomized clinical trial involving 311 community-dwelling adults aged 55 to 70 years without osteoporosis. All participants had baseline levels of 25-hydroxyvitamin D (25[OH]D) of 30 to 125 nmol/L.

The participants were randomly assigned to receive daily doses of vitamin D3 for 3 years at dosages of 400 IU (n = 109), 4000 IU (n = 100), or 10 000 IU (n = 102). Of the 311 participants, 287 completed the study.

Baseline, 3-month, and 3-year 25(OH)D levels were 76.3, 76.7, and 77.4 nmol/L for the 400-IU group; 81.3, 115.3, and 132.2 for the 4000-IU group; and 78.4, 188.0, and 144.4 for the 10 000-IU group.

Overall, radial and volumetric BMD was lower in the 4000 IU group and 10,000 IU group compared with the 400 IU group, with mean percent change in volumetric BMD of −2.4%, −3.5%, and −1.2%, respectively. Tibial volumetric BMD was also lower in the 4000 IU and 10,000 IU group than in the 400 IU group, with mean percent change of −1.0%,−1.7% and −0.4%, respectively.

No significant differences for changes in failure loads were observed.

“Among healthy adults, treatment with vitamin D for 3 years at a dose of 4000 IU per day or 10 000 IU per day, compared with 400 IU per day, resulted in statistically significant lower radial BMD; tibial BMD was significantly lower only with the 10 000 IU per day dose.”

“These findings do not support a benefit of high-dose vitamin D supplementation for bone health; further research would be needed to determine whether it is harmful,” the researchers concluded.

—Michael Potts


Burt LA, Billington EO, Rose MS, et al. Effect of high-dose vitamin d supplementation on volumetric bone density and bone strength. JAMA. 2019;322(8):736-745.