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||Last Updated: Dec 4th, 2006 - 12:49:01
Exposure to lots of sunshine or sufficient intake of dietary vitamin D may reduce the incidence and mortality of various cancers, according to a Harvard study published in the December issue of the journal Cancer Epidemiology Biomarkers & Prevention.
The study by Edward Giovannucci from Harvard School of Public Health and colleagues meant to confirm early findings that low vitamin D in blacks is associated with their high risk of suffering and dying from cancers.
The link between vitamin V intake and cancer incidence can be traced back to the 1940s when studies found cancer deaths are associated with latitude, which affects the exposure of residents to sunshine. Sufficient exposure to sunshine is the common way to get enough vitamin D.
Researchers said higher incidence and mortality of cancer found in black people may be due to the fact that the black people absorb less sunshine because of their dark skin, leading to a low level of vitamin D.
In the Health Professionals Follow-up Study, Giovannucci and his team examined the associations between the vitamin D status and the total cancer incidence, digestive system cancers (oral, stomach, colorectum) and their mortality rates between African American and Caucasian participants.
They surveyed dietary intakes of about 130 food and beverages in both black and white participants every four years for 16 years. During the follow-up, a form of cancer was developed in 99 out of 481 African-American participants (21 percent) and 7,019 out of 43,468 white participants (16 per cent).
After considering all other possible risk factors, they found that cancer incidence among the black participants was 30 percent higher, total cancer mortality 89 percent higher, and death from digestive system cancers 124 percent higher, compared to their white counterparts.
When vitamin D status was considered, the total cancer incidence among African Americans with a poor vitamin D status was 57 percent higher, and total cancer mortality 127 percent higher.
The study results do not mean that increasing the vitamin D level in the body can definitely reduce the incidence and mortality of various cancers as the study revealed merely an association between vitamin D status and cancer risk.
Still, researchers believed that vitamin D may reduce the formation of blood vessels in cancer cells and enhance intercellular communication, leading to a possible stopping of proliferation of cancer cells.
Sunshine (UVB radiation at 290 to 320 nm) is the major source of vitamin D for humans, which triggers formation of an inactive form of vitamin D known as cholecalciferol (D3). Another form of inactive vitamin D is known as ergocalciferol or D2, which can be obtained through some foods. Both D2 and D3 need to be hydroxylated in the liver and kidneys to become an active form of vitamin D, 25-hydroxyvitamin D or 25(OH) D.
The current recommended daily allowance (RDA) for vitamin D is 200 IU (5 mcg) for those aged 0 to 50, 400 IU (10 mcg) for those aged 51 to 70, and 600 IU (15 mcg) for those aged 71 or older. Many researchers believe that the RDA is too low. The tolerable upper intake level (UL) for vitamin D is 1000 IU for infants (0-12 months), 2000 IU for children (1-18 years) and adults.
Vitamin D has been associated with a low risk of colorectal cancer, breast cancer and prostate cancer, three major cancers in the US. Those who are not often exposed to sunshine may consider increasing their intake of vitamin D by using vitamin D supplements or oily fish such salmon and sardines. Cod liver oil is another excellent source of vitamin D.
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