Taking vitamin D and calcium supplements that provide no more than the usual recommended daily allowance does not help prevent bone fractures in older women and may actually cause harm, according to the U.S. Preventive Services Task Force.
In a draft recommendation issued Tuesday, the USPSTF said there is no value for postmenopausal women in supplements up to 400 IU of vitamin D and 1,000 mg of calcium.
However, the group took no position on higher doses of these nutrients for fracture prevention, saying "the current evidence is insufficient to assess the balance of the benefits and harms."
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The USPSTF also found the evidence too scant to draw conclusions about vitamin D supplements, at any dose and with or without calcium, for cancer prevention in adults.
Other purported benefits of vitamin D, such as preventing autoimmune disorders, were not addressed in the document. However, in a final recommendation issued last month based on studies showing a reduced risk of falls, the USPSTF recommended vitamin D supplementation at 600 to 800 IU/day, depending on age, for older community-dwelling adults.
The new draft recommendation on low-dose supplements for fracture and cancer prevention is open for public comment until July 10.
It was based on an evidence review finding that "in postmenopausal women, there is adequate evidence that daily supplementation with 400 IU of vitamin D3 combined with 1,000 mg of calcium carbonate has no effect on the incidence of osteoporotic fractures. However, there is inadequate evidence regarding the effect of higher doses of combined vitamin D and calcium supplementation on fracture incidence in postmenopausal women."
At the same time, the USPSTF found, doses at or below 400 IU of vitamin D and 1,000 mg of calcium increase the risk of kidney stones, albeit to a small degree.
But with no benefit from the supplements, even the small risk of harm is enough to tip the balance against them at these low doses, the group indicated.
Much of the evidence for the recommendation came from a Women's Health Initiative study of more than 36,000 postmenopausal women.
It randomized participants to oral supplements of 400 IU of vitamin D and 1,000 mg of calcium, with no significant reduction in rates of hip fracture or total fracture compared with placebo.
Other, smaller trials have also failed to show a significant fracture-prevention benefit for low-dose supplements.
The USPSTF also noted that a 2011 Institute of Medicine report indicated that daily intake of 600 IU for vitamin D and 1,200 mg of calcium for women ages 51 to 70 had a clearer net benefit in fracture prevention.
Last month, the USPSTF finding that vitamin D supplements reduce the risk of falls in community-dwelling older people who may be prone to falling.