Conference Coverage

Mega vitamin D harms bone in women, not men, without osteoporosis


“More is not necessarily better” when it comes to vitamin D supplements for women with adequate serum levels, new research suggests.

In a study of healthy 55- to 70-year-old women who took very-high-dose vitamin D supplements – either 4,000 IU/day or the previously identified “upper safe limit” of 10,000 IU/day – for 3 years had a significantly greater loss of total bone mineral density (BMD) at the radius and tibia than did women who took 400 IU/day. However, this effect was not seen in men. And the higher-dose vitamin D supplements did not improve bone strength in men or women.

But this was an exploratory post hoc analysis, and these were healthy community-dwelling adults with sufficient serum vitamin D levels (and no osteoporosis) at study entry, stressed lead researcher Lauren A. Burt, PhD, from the University of Calgary, in Alberta, Canada.

Dr. Burt presented these findings Sept. 11 at the virtual American Society of Bone and Mineral Research (ASBMR) 2020 annual meeting, and the study was also recently published online in the Journal of Bone and Mineral Research.

The results suggest that, “if you have normal bone density and adequate levels of vitamin D, there is no bone benefit in taking doses of vitamin D above the standard recommendations designed to prevent vitamin D deficiency, and doses at or above 4,000 IU/day might even be detrimental to bone, especially in females,” Dr. Burt said in an interview.

“These results are clinically relevant,” Dr. Burt and her coauthors wrote, “as vitamin D supplementation is widely administered to postmenopausal females for osteoporosis prevention.”

“Our findings do not support a benefit of high-dose vitamin D supplementation for bone health and raise the possibility of harm for females.”

Invited to comment, Meryl S. LeBoff, MD, of Harvard Medical School, Boston, said in an interview that this finding “warrants further research” because it is “important” to discover sex differences in bone responses to vitamin D.

“This doesn’t apply to osteoporosis”

Dr. LeBoff was lead author of a subanalysis of the Vitamin D and Omega-3 Trial (VITAL).

As she reported at last year’s ASBMR meeting, that analysis showed that, in healthy adults who did not have vitamin D insufficiency, taking vitamin D3 supplements for 2 years did not improve BMD, compared with placebo (recently published), nor was this linked with fewer fractures.

Dr. LeBoff pointed out that the current study investigated “very high doses of vitamin D” – at least double the 2,000 IU/day doses examined in VITAL.

Also, the serum vitamin D levels in this study were “above what we considered the upper normal limit for our assay in our hospital,” she noted, and there was no placebo control.

“We did not see any adverse effects of 2,000 IU/day vitamin D,” Dr. LeBoff stressed.

“At the same time, we didn’t see any significant benefits in terms of bone density because they already had achieved a normal level of vitamin D sufficient for bone.”

But “this doesn’t apply to patients with vitamin D deficiency, patients with osteoporosis, or low bone mass, in which case we would recommend vitamin D.”

Some patients take more vitamin D than they need because they think more is better, said LeBoff, but this study suggests “more is not necessarily better.”

“There’s been a concern for several years that too much vitamin D may be associated with increased fractures,” she emphasized.


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