Vitamin D Research: Beyond Building Bones Muscle strength Several promising areas of vitamin D research look far beyond vitamin D’s role in building bones. And, as you might expect, the news media release a flurry of reports every time another study links vitamin D to some new ailment. These reports can be confusing, however, because some studies are stronger than others, and any report needs to be interpreted in the light of all other evidence. More answers may come from randomized trials, such as the Vitamin D and OmegA-3 TriaL (VITAL), which will enroll 20,000 healthy men and women to see if taking 2,000 IU of vitamin D or 1,000 mg of fish oil daily lowers the risk of cancer, heart disease, and stroke.
Here, we provide an overview of some of the more promising areas of vitamin D research, highlighting the complex role of vitamin D in disease prevention—and the many unanswered questions that remain.
Vitamin D and Bone and Muscle Strength
Several studies link low vitamin D levels with an increased risk of fractures in older adults, and they suggest that vitamin D supplementation may prevent such muscle strength long as it is taken in a high enough dose.
A summary of the evidence comes from a combined analysis of 12 fracture prevention trials that included more than 40,000 elderly people, most of them women. Researchers found that high intakes of vitamin D supplements—of about 800 IU per day—reduced hip and non-spine fractures by 20 percent, while lower intakes (400 IU or less) failed to offer any fracture prevention benefit.
Vitamin D may also help increase muscle strength, which in turn helps to prevent falls, a common problem that leads to substantial disability and death in older people. Once again, vitamin D dose matters: A combined analysis of multiple studies found that taking 700 to 1,000 IU of vitamin D per day lowered the risk of falls by 19 percent, but taking 200 to 600 IU per day did not offer any such protection.
A recent vitamin D trial drew headlines for its unexpected finding that a very high dose of vitamin D increased fracture and fall risk in older women. The trial’s vitamin D dose—500,000 IU taken in a once-a-year pill—was much higher than previously tested in an annual regimen. After up to 5 years of treatment, women in the vitamin D group had a 15 percent higher fall risk and a 26 percent higher fracture risk than women who received the placebo.
It’s possible that giving the vitamin D in one large dose, rather than in several doses spread throughout the year, led to the increased risk. The study authors note that only one other study—also a high-dose, once-a-year regimen—found vitamin D to increase fracture risk; no other studies have found vitamin D to increase the risk of falls. Furthermore, there’s strong evidence that more moderate doses of vitamin D taken daily or weekly protect against fractures and falls—and are safe.
So what is the significance of this study for people who want to take vitamin D supplements? A reasonable conclusion would be to continue taking moderate doses of vitamin D regularly, since these have a strong safety record, but to avoid extremely high single doses. This recent finding does present a challenge to scientists who will work to understand why the extreme single dose appears to have adverse effects.
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