High vitamin D may not protect against frailty

Older women with low blood levels of vitamin D may have an increased risk of frailty - but the high vitamin D levels that some experts recommend may offer no special protection, a new study suggests.

Researchers found that among 6,300 elderly women followed for 4.5 years, those with relatively low blood levels of vitamin D at the outset - below 20 nanograms per milliliter (ng/mL) - were somewhat more likely to become frail than those with higher circulating levels of the vitamin.

However, there was no evidence of any extra benefit from having vitamin D levels at or above 30 ng/mL - a level that some researchers have advocated for optimal health.

"People tend to assume that more is better," said lead researcher Dr. Kristine E. Ensrud, of the University of Minnesota and VA Medical Center in Minneapolis.

But as far as frailty risk, she told Reuters Health, "We found no evidence that this 'magic level' of vitamin D was protective."

The findings come on the heels of a long-awaited report on vitamin D from the Institute of Medicine (IOM), an independent scientific body that advises the federal government.

Released in November, the IOM report raised the recommended intake of vitamin D for children and adults, but also stressed that the average American or Canadian already has vitamin D blood levels at or above 20 ng/mL (equivalent to 50 nanomoles per liter, the more common measure used in Canada).

And that level, the IOM said, is all that is needed for good bone health. Vitamin D has long been known to help the body use calcium to build bone. The report found insufficient evidence that vitamin D, of any level, has health benefits beyond building and maintaining strong bones.

Ensrud said her group's current findings, reported in the Journal of Clinical Endocrinology & Metabolism, fit in with the IOM conclusions.

"Society has sort of gotten ahead of the evidence," Ensrud said, referring to a craze for vitamin D in recent years, spurred by studies linking the vitamin to everything from immune system function, to depression and heart disease.

But whether vitamin D deficiency produces excess risks in such diverse aspects of health - and whether taking supplements can curb those risks - has yet to be shown.

When it comes to frailty, Ensrud explained, some studies have also linked lower levels of the vitamin to muscle weakness and slowed movement, but evidence was sparse and conflicting.

To test whether low vitamin D levels increased women's risk of becoming frail, Ensrud and her colleagues followed 6,307 U.S. women age 69 and older for an average of 4.5 years.

They found that, at the outset, women with either relatively low vitamin D levels (below 20 ng/mL) or high levels (above 30 ng/mL) were somewhat more likely than women with moderate levels (20 - 29.9 ng/ml) to be frail - meaning they had limitations like muscle weakness, exhaustion and slow walking speed.