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Last Updated: Jun 30, 2008 - 11:14:37 AM |
Intake of enough vitamin D may drastically lower the risk of developing certain cancers, suggests a study in the Feb. 2006 issue of The American Journal of Public Health.
The study, led by Dr. Cedric Garland of the University of California – San Diego (UCSD) found daily intake of 1,000 international units (IU) or 25 micrograms(μg) of vitamin D3 may lower the risk of developing colon, breast, prostate and ovarian cancers by up to 50 percent.
1,000 IU of vitamin D per day is 50 percent the safe upper intake established by the National Academy of Sciences, according to the authors who recommend use of vitamin D-rich diets and vitamin D supplements, which costs about 5 cents a day, for protective effects.
The findings resulted from a systematic review of more than 60 scientific papers on the association between vitamin D and cancer published between 1966 and 2004, including 30 investigations into colon cancer, 13 of breast cancer, 26 of prostate cancer and seven of ovarian cancer.
The study found that residents of the northeastern US, who are exposed to less sunshine, and African-Americans with dark skin pigments, which prevent sunshine-induced biosynthesis of vitamin D, were at an increased risk of vitamin D deficiency, which is linked to higher risk of cancer.
"African-American women who develop breast cancer are more likely to die from the disease than White women of the same age," said Garlan, professor with UCSD's Moores Cancer Center and the Department of Family and Preventive Medicine at the UCSD School of Medicine.
"Survival rates are worse among African-Americans for colon, prostate and ovarian cancers as well."
Even after adjustments that removed the effect of socioeconomic status and access to healthcare, blacks had substantially poorer survival rates, a difference that the authors link with the decreased ability of blacks to make Vitamin D.
In a study of patients in Norway who were diagnosed with cancer between 1964 and 2000, Professor Johan Moan, of the Institute for Cancer Research in Oslo, found the risk of dying within three years was 50 percent lower for those diagnosed during summer and autumn, when blood levels of vitamin D are highest, than in winter. This indicates that higher exposure to sunshine, leading to increased levels of serum vitamin D, is inversely linked with a lower risk of cancer death.
"The high prevalence of vitamin D deficiency, combined with the discovery of increased risks of certain types of cancer in those who are deficient, suggest that vitamin D deficiency may account for several thousand premature deaths from colon, breast, ovarian and other cancers annually," the authors conclude in their article.
Authors of the study call for prompt public health action to increase intake of vitamin D3 as an inexpensive tool for prevention of diseases that claim millions of lives every year.
"For instance, breast cancer will strike one in eight American women in their lifetime. Early detection using mammography reduces mortality rates by approximately 20 percent. But use of vitamin D might prevent this cancer in the first place," said Dr. Garland.
"A preponderance of evidence, from the best observational studies the medical world has to offer, gathered over 25 years, has led to the conclusion that public health action is needed," Garland said.
"Primary prevention of these cancers has largely been neglected, but we now have proof that the incidence of colon, breast, and ovarian cancer can be reduced dramatically by increasing the public's intake of vitamin D."
Vitamin D is well known for its role in calcium absorption, prevention of rickets in children, or osteoporosis in the elderly. Unaware by the public is that the vitamin also plays an important role in protecting against a range of other diseases including: heart disease, lung disease, cancer, diabetes, high blood pressure, schizophrenia and multiple sclerosis.
The role of vitamin D in cancer prevention has not been widely understood or accepted. However, evidence has showed biologically active forms of vitamin D induces cell differentiation and/or inhibit proliferation of a number of cancerous and noncancerous types of cultured cells, S. E. Blutt and N. L.Weigel reported in 1999 in "Proceedings Of The Society For Experimental Biology And Medicine."
When it comes to colon cancer prevention, prospective studies are less likely to associate vitamin D intake with significant reductions in colorectal cancer when other risk factors are considered. However, a five-year study of more than 120,000 subjects found that men with the highest vitamin D intakes were 29 percent less likely to have colorectal cancer compared to men with the lowest vitamin D intakes. "Calcium, Vitamin D, Dairy Products, and Risk of Colorectal Cancer in the Cancer Prevention Study II Nutrition Cohort" was conducted by McCullough M.L. and colleagues and published in 2003 in Cancer Causes Control.
As for the association of vitamin D with breast cancer, one study of women who participated in the first National Health and Nutrition Examination Survey (NHANES I) found that sunlight exposure and dietary vitamin D intake were associated with reduced risk of breast cancer 20 years later, according to John E.M. and colleagues in a 1999 issue of Cancer Epidemiol Biomarkers Prev.
Another 16-year study of more than 88,000 women, conducted by Shin MH and colleagues, found that higher intakes of vitamin D were linked with significantly lower breast cancer risk in pre-menopausal women but not postmenopausal women. "Intake of dairy products, calcium, and vitamin D and risk of breast cancer" was published in a 2002 issue of the Journal of National Cancer Institute.
Although the role of vitamin D in cancer prevention is not largely understood, it is known that vitamin D deficiency can lead to health problems. Certain groups of people are at a higher risk of vitamin D deficiency. The risk factors include exclusively breastfeeding, dark skin, aging, sunscreen overuse, fat malabsorption syndromes, inflammatory bowel disease and obesity.
Foods rich in vitamin D include cod liver oil, eggs, milk and vitamin D supplemented processed foods. Vitamin D supplements may be needed to supplement dietary sources of vitamin D, which are likely not enough to provide 1,000 IU daily recommended by the researchers of the current study. One glass of milk may offer only 100 IU of vitamin D. Sunshine is a good source for vitamin D, but it has its own limitation and concerns.
Caution needs to be exercised. Too much vitamin D can be toxic. More than 2,000 IU per day may lead to the body absorbing too much calcium, and possible damage to the liver and kidneys.
Correction: We have corrected an error in the article. "25 milligrams (mg) of vitamin D" should be "25 micrograms (μg) of vitamin D."
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