Researchers wanted to see which group developed less osteoporosis, but they were startled to discover that after only one year, the women taking vitamin D had only 25% of the risk of developing cancer, compared with the other group. In another large study, women taking 1,000 IU of vitamin D every day decreased their risk of breast cancer by 50%.
No one is sure how much vitamin D is needed in supplements or fortified foods. Many scientists advocate getting vitamin D the natural way—through sunshine. Some even argue that the use of sunscreen is increasing the risk of cancer in the United States population. Writing in Nutrition in the Prevention and Treatment of Disease, nutrition professor Susan J. Whiting and her colleagues conclude, “Although sun exposure increases the risk of developing skin cancer, it has the potential to reduce the risk of developing more severe forms of cancer.”
Other scientists, however, argue for increased food fortification and use of vitamin D3 supplements by almost everyone. Dr. Cedric Garland is one of the scientists of D Action and the lead investigator of a new five-year study to determine cancer rates in people with adequate vitamin D in their blood. He believes that vitamin D protects against cancer by damaging the ability of cancer cells to stick together and communicate with one another. This probably happens because vitamin D influences gene expression.
In a study published in 2009 in the journal Annals of Epidemiology, Garland and his scientific team argue that everyone should take 2,000 IU of vitamin D3 year round. He explains that if everyone in the United States and Canada had adequate blood levels of vitamin D and calcium, 58,000 cases of breast cancer and 49,000 cases of colon cancer would be prevented every year. Also, he says, fatalities in people who are already diagnosed with cancer would be cut in half.
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