High doses of vitamin D can reduce the risk of developing some common cancers by as much as 50%, US scientists claim. This benefit of vitamin D is seen more in women.
Most Americans and others are not taking enough vitamin D, a fact that may put them at significant risk for developing cancer, according to a landmark study conducted by Creighton University School of Medicine.
The four-year, randomized study followed 1,179 healthy, postmenopausal women from rural eastern Nebraska.* Participants taking calcium, as well as a quantity of vitamin D3 nearly three times the U.S. government?s Recommended Daily Amount (RDA) for middle-age adults, showed a dramatic 60 percent or greater reduction in cancer risk than women who did not get the vitamin.
The results of the study, conducted between 2000 and 2005, were reported in the June 8 online edition of the American Journal of Clinical Nutrition.
The vitamin D hormone, calcitriol, has been found to induce death of cancer cells in vitro and in vivo. Although the anti-cancer activity of vitamin D is not fully understood, it is thought that these effects are mediated through vitamin D receptors expressed in cancer cells, and may be related it its immunomodulatory abilities. The anti-cancer activity of vitamin D observed in the laboratory has prompted some to propose that vitamin D supplementation might be beneficial in the treatment or prevention of some types of cancer.
Very few foods are naturally rich in vitamin D, and most vitamin D intake is in the form of fortified products including milk, soy milk and cereal grains.
A blood calcidiol (25-hydroxy-vitamin D) level is the accepted way to determine vitamin D nutritional status. The optimal level of serum 25-hydroxyvitamin D remains a point for debate among medical scientists. One recent consensus concluded that for optimal prevention of osteoporotic fracture the blood calcidiol concentration should be higher than 30 ng/mL (US units), which is equal to 75 nmol/L (System International units).
The U.S. Dietary Reference Intake for Adequate Intake (AI) of vitamin D for infants, children and men and women aged 19?50 is 5 micrograms/day (200 units/day). Adequate intake increases to 10 micrograms/day (400 units/day) for men and women aged 51?70 and to 15 micrograms/day (600 units/day) past the age of 70.
Exposure to sunlight is the primary method of obtaining vitamin D. In clear summer weather, approximately ten minutes per day in the sun will produce adequate amounts, even when only the face is exposed. In the winter, it may require as much as two hours.
Vitamin D is naturally found in fish liver oils, butter, eggs, and fortified milk and cereals in the form of vitamin D2. Milk products are the main dietary source for most people.