In the meantime, the evidence is so compelling that some experts already recommend at least 800 to 1,000 IU of vitamin D per day for adults. women and men has been proposed by Harvard researchers and will be considered for funding by the National Institutes of Health. In fact, a large-scale randomized trial that would include 20,000 U.S. More trials are needed to elucidate vitamin D's benefits and risks at different doses and in different populations. Critics say that the dose, 400 IU per day, was too small to make a difference. In the only other randomized trial of vitamin D and cancer - part of the Women's Health Initiative - researchers found no effect on colorectal cancer. The 1,100 IU dose - nearly three times the 400 IU per day recommended in federal and other expert guidelines - was correlated with a 35% higher blood level of vitamin D, on average. However, in one of the few randomized trials testing the effect of vitamin D supplements on cancer outcomes, postmenopausal women who took 1,100 international units (IU) of vitamin D plus 1,400 to 1,500 milligrams of calcium per day reduced their risk of developing non-skin cancers by 77% after four years, compared with a placebo and the same dose of calcium. Promising findings from observational studies don't always pan out when put to the test in clinical trials. The findings of such studies can suggest correlations between disease risk and certain factors - sun exposure or blood levels of vitamin D, for example - but they don't prove cause and effect. The picture of vitamin D's health benefits beyond bones has been drawn mainly from epidemiologic and observational investigations. And a large study of aging in the Netherlands published in the May 2008 issue of Archives of General Psychiatry found a relationship between vitamin D deficiency and depression in women and men ages 65 to 95. At a scientific meeting in May 2008, Canadian researchers reported that vitamin D deficiency was linked to poorer outcomes in women with breast cancer. In June 2008, a study published in the Archives of Internal Medicine found that low blood levels of vitamin D were associated with a doubled risk of death overall and from cardiovascular causes in women and men (average age 62) referred to a cardiac center for coronary angiography. Hardly a month goes by without news about the risks of vitamin D deficiency or about a potential role for the vitamin in warding off diseases, including breast cancer, multiple sclerosis, and even schizophrenia. But researchers have discovered that it's active in many tissues and cells besides bone and controls an enormous number of genes, including some associated with cancers, autoimmune disease, and infection. Vitamin D would be essential if it did nothing else. Vitamin D also helps maintain normal blood levels of phosphorus, another bone-building mineral. Without this "sunshine vitamin," the body can't absorb the calcium it ingests, so it steals calcium from bones, increasing the risk of osteoporosis and fractures. (The skin actually produces a precursor that is converted into the active form of the vitamin by the liver and kidneys.) Vitamin D is best known for its vital role in bone health. The sun's rays provide ultraviolet B (UVB) energy, and the skin uses it to start making vitamin D. September brings the end of summer in the northern hemisphere and, for many of us, that means less time in the sun. Missing out on the "sunshine vitamin" has consequences for more than just bone health. No content on this site, regardless of date, should ever be used as a substitute for direct medical advice from your doctor or other qualified clinician. Please note the date each article was posted or last reviewed. ARCHIVED CONTENT: As a service to our readers, Harvard Health Publishing provides access to our library of archived content.
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