TUESDAY September 11, 2007 (Foodconsumer.org) -- A new study estimates that 50 percent of colon and breast cancer cases can be avoided if people take high doses of vitamin D supplements.

Previous studies based largely on the cancer rates at different latitudes of the globe suggest that deficiency in vitamin D may increase cancer risk.

People who are exposed more often to sunshine are less likely to develop cancers such as breast, colon and ovarian cancers, studies show. Sunshine triggers the skin to synthesize vitamin D in the human body.

Lab studies also show that vitamin D helps prevent cancer from growing and spreading.   Even some trials suggest that taking high vitamin D supplements reduced cancer risk.

This current study, led by researchers at the University of California, analyzes data on average blood levels of vitamin D in the winter and rates of breast and colon cancers in 15 countries.

The cancer rates drop as the vitamin D level in the blood increases, according to the study published in the journal Nutrition Reviews.

The researchers found 22 nanograms of serum vitamin D per milliliter (ng/mL) was the minimal level to provide a protective effect against colon cancer while the level of vitamin D at 32 ng/mL was the lowest that is effective in preventing breast cancer.

Unfortunately, according to the researchers, the late-winter time vitamin D level among Americans is 15 to 18 ng/mL, which is not enough to provide any protective effect against cancer.

The researchers suggest based on their calculations 60,000 cases of colon cancer and 85,000 cases of breast cancer, almost 50 percent of each cancer, could be prevented each year if Americans by all means maintain their serum vitamin D level at least 55 ng/mL.

This level of vitamin D may not be acquired from exposure to sunshine alone for most people.   To increase the vitamin D level, one may take supplements such as oily fish oil and vitamin D pills.

Lead study author Dr. Cedric F. Garland, a cancer prevention specialist at the University of California San Diego, was cited by Reuters as saying that exposure of 40 percent of the skin to sunshine for a few minutes in the midday sun will result in enough vitamin D for protection against cancer.  

Specially, for fair-skinned people, three minutes may be enough and for those with darker skin, it may take 15 minutes.  In Southern California where sunshine is abundant, people may not need to take extra vitamin D to boost their levels of the vitamin in their bodies.

But those who are not often exposed to sunshine may take 2000 IU of vitamin D supplements a day to have a protective effect although the current recommended daily allowance is 200 IU for adults.   Early studies indicate it is safe to consume up to 10,000 IU a day.