updated 12/8/2010 2:49:05 PM ET 2010-12-08T19:49:05

Taking large doses of vitamin D supplements may not reduce women's risk of frailty later in life, according to a new study.

  1. Don't miss these Health stories
    1. Splash News
      More women opting for preventive mastectomy - but should they be?

      Rates of women who are opting for preventive mastectomies, such as Angeline Jolie, have increased by an estimated 50 percent in recent years, experts say. But many doctors are puzzled because the operation doesn't carry a 100 percent guarantee, it's major surgery -- and women have other options, from a once-a-day pill to careful monitoring.

    2. Larry Page's damaged vocal cords: Treatment comes with trade-offs
    3. Report questioning salt guidelines riles heart experts
    4. CDC: 2012 was deadliest year for West Nile in US
    5. What stresses moms most? Themselves, survey says

In fact, the study found that both low and high levels of vitamin D in the blood were associated with an increased likelihood of frailty among older women. The researchers considered women to be frail if they had symptoms such as a slow walking speed, weak hand grip or exhaustion.

While the link between high levels of vitamin D and frailty was not consistent over time, there was no evidence that higher levels were protective, the researchers say.

The results come on the heels of a report released last week by the Institute of Medicine issuing new guidelines for daily vitamin D intake. Older adults need about 800 international units (IU) a day — an amount achievable without taking supplements — and most Americans and Canadians get enough, the report said.

  1. MyHealthNewsDaily
    1. Workers Want Employers to Help Them Stay Healthy
    2. Girls Struggle More When Friends Let Them Down
    3. Psychotherapy May Help Teens with Fibromyalgia
    4. Collective Brands Recalls KEDS Girls' Shoes

The new findings underscore the need for more well-designed clinical trials in order to evaluate the health effects of vitamin D supplements, the researchers said.

Although vitamin D deficiency has been linked with adverse health effects, that doesn't mean that more vitamin D is beneficial, said study researcher Dr. Kristine Ensrud, a professor of medicine and epidemiology at the University of Minnesota.

"Sometimes people get so convinced that something's good for you," Ensrud said. "In a way, vitamin D supplementation sort of got put in the 'water supply' when the evidence wasn’t really wasn't behind that."

Story: How much vitamin D is enough? Report sets new levels

Vitamin D deficiency can lead to weakness and slowness, both components of frailty. Some experts have recommended vitamin D supplements for older adults whose blood levels of vitamin D are below 30 nanograms per milliliter (ng/ml), the researchers said. This would likely require taking supplements of 1000 to 2000 IU of vitamin D per day.

Ensrud and her colleagues measured the vitamin D blood levels of 6,307 women 69 years and older, and also determined how frail the women were.

Women with vitamin D levels less than 20 ng/ml and greater than 30 ng/ml had higher odds of being frail than women whose vitamin D levels fell in between those marks. This association held even when the researchers included only the vitamin D in the blood produced by the body in response to sunlight. They performed this analysis to rule out the possibility that frail women might be prescribed vitamin D supplements.

The researchers also looked at the impact of vitamin D levels over time among 4,551 women who were not frail at the beginning of the study. They examined the frailty status of these women 4 1/2 years later. In this case, only vitamin D levels lower than 20 ng/ml were associated with increased risk of frailty or death later in life.

The researchers said that the fact that they didn't find a link between high vitamin D levels and frailty after the 4.5-year study period may mean the association between these two factors found in the earlier part of the study was not a true link. However, it might also be that there were too few women in the follow-up study to observe a link later on, Ensrud said.

Nonetheless, even over time, having high levels of vitamin D at the study's start didn't lessen a woman's chances of later developing frailty, Ensrud said.

The study will be published in an upcoming issue of the Journal of Clinical Endocrinology & Metabolism.

Follow MyHealthNewsDaily staff writer Rachael Rettner on Twitter @Rachael_MHND.


Discussion comments