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Having high levels of vitamin D is of no use in conferring cancer protection except in colon cancer, a large study by researchers from the U.S. National Cancer Institute has found. The results are a direct contradiction to earlier studies which suggested high serum levels of the fat soluble vitamin D could prevent breast cancer and colon cancer.
Earlier studies had suggested vitamin D could avert the risk of cancer by maintaining healthy cells and preventing over-production of cells, which is one of the main events to trigger cancer development. One study by researchers at the University of California at San Diego suggested vitamin D could lower the risk of cancer by preventing formation of new blood vessels for tumors.
However all these observations appear to be limited to colon cancer only. In the present study, the NCI team examined data on 16,818 individuals in the third Health and Nutrition Examination Survey. All participants were 17 or older and were followed for six to twelve years.
During the follow-up some 536 people died of cancer. There was no relationship between cancer mortality and blood levels of vitamin D in these individuals, the researchers noted.
But people having high blood levels of vitamin D had a 72 percent lower risk of colon cancer, they reported in the October 30 issue of the Journal of the National Cancer Institute.
The deaths in the study had occurred from blood cancer or leukemia, lung cancer, breast cancer, prostate cancer, other digestive cancers and non-Hodgkin's lymphoma. There was no link whatsoever between cancer mortality and circulating vitamin D levels.
"We were uncertain what association we would find, partly because there were no previous studies that had looked at overall cancer mortality after vitamin D blood measurements," said lead author Dr. D. Michal Freedman, from the National Cancer Institute.
In an accompanying editorial, Dr. Cindy D. Davis, from the NCI, and Dr. Johanna T. Dwyer, from Tufts University in Boston warned that while vitamin D was beneficial in many ways, consumers must not assume it is a magic bullet against cancer.
The study authors also admitted limitations saying vitamin D level was measured only once in the study and that it is unclear if the level fell or rose in subsequent years. Nevertheless there seems to be no substantiation on claims of cancer preventing effects attributed to vitamin D.
According to the National Institutes of Health's Office of Dietary Supplements, adults should get 400 IU (International Units) of vitamin D each day. Those over 70 years old need 600 IU daily, but no one should consume more than 2,000 IU a day.
Vitamin D is present in many foods including salmon, mackerel, cod liver oil, tuna, margarine and vitamin D fortified milk. Sun exposure is also one of the important ways to increase blood levels of vitamin D.
Vitamin D is an important element, but claims that it prevents cancer need to be cautiously treated if the above study is to be believed.
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