Findings from a randomized clinical trial, published in the Journal of the American Geriatrics Society, demonstrated that a high dose of vitamin D3 may help prevent acute respiratory infections (ARIs) in older adults. The study included 107 long-term care residents, aged 60 and older, who were divided into a high-dose and standard-dose group. The high-dose group was given a monthly supplement of 100,000 IU of vitamin D3. Participants in the standard-dose group were given either a monthly supplement of 12,000 IU of vitamin D3 or a placebo with no vitamin D3 (depending on how much vitamin D they were already receiving as part of their usual care). After participants had been given vitamin D3 or a placebo for 12 months, researchers discovered that:
There were fewer ARIs—nearly 40% less—in the high-dose group compared with the standard-dose group. Average blood levels of 25-hydroxyvitamin D (a type of vitamin D used to measure vitamin D in the body) were 32 ng/ml in the high-dose group and 25.1 ng/ml in the standard-dose group. This indicates that the monthly high-dose vitamin D3 supplement led to increased blood levels of vitamin D.
There was one negative finding: the high-dose group experienced more than double the number of falls. However, there were no significant differences between the groups in the incidence of kidney stones, hypercalcemia (excessive blood levels of calcium), or fractures.
The results are promising and point to a convenient, relatively affordable supplement that could reduce ARIs in older adults, who, because of their age, may be more prone to them. However, more research is needed to understand the relationship between high doses of vitamin D3 and an increased risk of falling. There have been numerous other studies on vitamin D and falls. Most of them have shown a reduction in falls, but the ones that gave periodic high doses, such as those in the present study, often found an increase in falls. A reasonable explanation is that giving a very high dose at one time causes transient vitamin D toxicity, which leads to impaired balanced and decreased muscle strength. In one study, the excess in falls was clustered in the first three months after the study participants received their annual, very high dose. So, one might argue that daily dosing of a moderate amount of vitamin D is preferable to intermittent dosing with a very large amount.
Source: Journal of the American Geriatrics Society