Vitamin D
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The epidermal strata of the skin. Production is greatest in the stratum basale (colored red in the illustration) and stratum spinosum (colored light brown).
influenza infection during winter; however, see flu season for the factors apart from vitamin D that are also hypothesized to influence rates of infection during winter. The molecular basis for thinking vitamin D has the potential to prevent cancer lies in its role in a wide range of cellular mechanisms central to the development of cancer. These effects may be mediated through vitamin D receptors expressed in cancer cells. Polymorphisms of the vitamin D receptor (VDR) gene have been associated with an increased risk of breast cancer. Women with mutations in the VDR gene had an increased risk of breast cancer. A 2006 study using data on over 4 million cancer patients from 13 different countries showed a marked increase in some
Cancer
cancer risks in countries with less sun and another metastudy found correlations between vitamin D levels and cancer. The authors suggested that intake of an additional 1,000 international units (IU) (or 25 micrograms) of vitamin D daily reduced an individual's colon cancer risk by 50%, and breast and ovarian cancer risks by 30%. Low levels of vitamin D in serum have been correlated with breast cancer disease progression and bone metastases. However, the vitamin D levels of a population do not depend on the solar irradiance to which they are exposed. Moreover, there are genetic factors involved with cancer incidence and mortality which are more common in northern latitudes. A 2006 study found that taking the U.S. RDA of vitamin D (400 IU per day) cut the risk of pancreatic cancer by 43% in a sample of more than 120,000 people from two long-term health surveys. However, in male smokers a 3-fold increased risk for pancreatic cancer in the highest compared to lowest quintile of serum 25-hydroxyvitamin D concentration has been found. A randomized intervention study involving 1,200 women, published in June 2007, reports that vitamin D supplementation (1,100 international units (IU)/day) resulted in a 60% reduction in cancer incidence, during a four-year clinical trial, rising to a 77% reduction for cancers diagnosed after the first year (and therefore excluding those cancers more likely to have originated prior to the vitamin D intervention). Although the study was criticized on several grounds including failing to take into account a long term overall increase in cancer