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An estimated 40 percent
of Americans don’t get enough vitamin D, a nutrient linked to bone and muscle health. That includes a large number of seniors, and some past studies suggest that vitamin D supplementation could help prevent falls in nursing home residents.

Yet high monthly doses of the sunshine vitamin actually increased falls in people over age 70, according to a randomized clinical trial published last week in the journal JAMA Internal Medicine.

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“For a long time, we thought ‘the higher the better,’ ” says study author Heike Bischoff-Ferrari, chair of the Department of Geriatrics and Aging Research at the University Hospital in Zurich. “Now we know vitamin D has a therapeutic range, and a high monthly dose for seniors is not advantageous.”

Vitamin D is often touted as a supplement that everyone should take. Yet over the past several years, studies have shown that the vitamin appears to have a Goldilocks zone: too little or too much may be detrimental. Vitamin D deficiency causes muscle weakness and poor bone health, for example, while too much vitamin D appears to increase the risk of upper respiratory infections and even of death.

In a yearlong study, Bischoff-Ferrari and colleagues divided 200 men and women age 70 or older, all of whom had had at least one fall the previous year, into three groups. A third of the participants received a low monthly dose of vitamin D, equivalent to the recommended 800 IU per day, while the two other groups received a high monthly dose of vitamin D, administered in different formulations. Fifty-eight percent of all participants were vitamin D-deficient at the beginning of the study.

Three years earlier, Bischoff-Ferrari’s team had found that high doses of vitamin D did improve leg mobility among a small group of young postmenopausal women. “With that finding, our assumption was that giving more would give us an improvement in falls and a greater benefit on muscle health,” says Bischoff-Ferrari.

But among the seniors in the trial, those who received a high dose of vitamin D each month experienced significantly more falls than the ones who received a low dose: 66 percent compared to 48 percent, respectively. And while the low-dose group improved their mobility and leg strength, the high-dose group showed no such improvement.

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The results suggest there is an optimal, or “just right,” blood level of vitamin D with respect to fall prevention, says Bischoff-Ferrari — somewhere between 21 and 30 nanograms per milliliter (ng/mL). A little higher is OK too, she notes, but above 45 ng/mL is too high and associated with increased risk of falling. The researchers aren’t yet sure why that is. One possibility is that high blood levels of vitamin D increase physical activity in seniors, thereby providing the opportunity to fall more often, yet an analysis of the physical activity of the trial participants did not support that hypothesis.

In an accompanying editorial to the article, three researchers, including Douglas Kiel of Harvard Medical School, argue that vitamin D supplementation should only be recommended to seniors living at institutions who are vitamin D-deficient. Others should obtain vitamin D from natural sources.

Bischoff-Ferrari disagrees, noting that it is “virtually impossible” to get the recommended level of 800 IU per day from food sources. One would have to consume two portions of fatty fish or a dozen eggs per day to achieve those levels, she says.

Instead, she continues to encourage standard low-dose vitamin D supplementation of 800 IU daily or 24,000 IU monthly. Her team is now conducting a larger clinical trial of more than 2,000 seniors in Switzerland to investigate the roles of daily vitamin D, omega-3 fatty acids, and home exercise in healthy aging.