To investigate, researchers studied more than 6,000 elderly women for 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, including muscle weakness, exhaustion and slow walking speed.
However, when the researchers looked at the women's risk of becoming frail over time, only low vitamin D levels were linked to increased risk.
Researchers found no additional benefit of having vitamin D levels at or above 30 ng/mL, a level that some researchers have advocated for optimal health.
Researcher say that despite what many people think, more isn't always better when it comes to vitamin D and bone health. More studies are needed to determine the optimal level of vitamin D for bone health.
The findings come less than two weeks after a long-awaited report on vitamin D from the Institute of Medicine (IOM), which suggested the recommended intake of vitamin D be increased for Canadians.
The findings were reported in the Journal of Clinical Endocrinology & Metabolism.
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