First some facts about Vit. D

Vitamin D is a group of fat-soluble prohormones, the two major forms of which are vitamin D2 (or ergocalciferol) and vitamin D3 (or cholecalciferol). Vitamin D obtained from sun exposure, food, and supplements, is biologically inert and must undergo two hydroxylation reactions to be activated in the body. Calcitriol (1,25-Dihydroxycholecalciferol) is the active form of vitamin D found in the body. The term vitamin D also refers to these metabolites and other analogues of these substances.

Video to Vitamin D topic

Calcitriol plays an important role in the maintenance of several organ systems. However, its major role is to increase the flow of calcium into the bloodstream, by promoting absorption of calcium and phosphorus from food in the intestines, and re absorption of calcium in the kidneys; enabling normal mineralization of bone and preventing hypocalcemic tetany. It is also necessary for bone growth and bone remodeling by osteoblasts and osteoclasts.

Now to the interesting Part of the information about this interesting, but over looked Vitamin D :

The anti-cancer activity of vit. D is thought to result from its role as a nuclear transcription factor that regulates cell growth, differentiation, apoptosis and 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.

Increasing body of research supporting the hypothesis that the active form of vitamin D has significant, protective effects against the development of cancer. Studies show an inverse association between sun exposure, serum levels of 25(OH)D, and intakes of vitamin D and risk of developing and/or surviving cancer. 2005, scientists released a metastudy which demonstrated a beneficial correlation between vitamin D intake and prevention of cancer. Drawing from a meta-analysis of 63 published reports, the authors showed 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%. A scientific review undertaken by the National Cancer Institute found that vitamin D was beneficial in preventing colorectal cancer, which showed an inverse relationship with blood levels of 80 nmol/L or higher associated with a 72% risk reduction. However, the same study found no link between baseline vitamin D status and overall cancer mortality.

Video from University of California Vitamin D and Cancer

Low levels of vitamin D in serum have also been correlated with breast cancer disease progression and bone metastases, and studies suggest that increased intake of vitamin D reduces the risk of breast cancer in premenopausal women.

The Canadian Cancer Society was the first to recommend, in 2007, that all of its adult citizens begin taking 1,000(IU) per day of vitamin D. The country’s northern latitude was a factor in the decision, as was the growing body of evidence showing the vitamin’s effectiveness in lowering instances of cancer.

Recently, Cannell and colleagues have suggested that vitamin D deficiency is a major risk factor for influenza and that vitamin D may be effective in reducing influenza incidence and severity.

In both publications, the authors concluded that physiological doses of vitamin D (5,000 IU/day for adults and 1,000 IU/day for every 25 pounds of body weight in children) might reduce the incidence of influenza, and proposed that pharmacological doses (2,000 IU/kg/day for 3–4 days) may have a treatment effect in influenza. The authors present epidemiological evidence suggesting that the seasonality of vitamin D deficiency may explain the seasonality of influenza epidemics and that the epidemiology of vitamin D deficiency may help explain the confusing epidemiology of influenza. However, the seasonality of influenza may also be explicable by other factors. For example, it has been shown that low absolute humidity favours the survival of the influenza virus. We recommend for adults about 5-10.000 iu per day to have Protective responce.

Vitamin D can potentially play a significant role in prevention of influenza, given a well demonstrated link between vitamin D deficiency and the incidence of respiratory infections. The diagnosis and treatment of vitamin D deficiency is straight-forward, cheap and without substantial risk. Thus, physicians should make an effort to diagnose and adequately treat vitamin D deficiency to prevent influenza recurrence. Given what is known about vitamin D and influenza, many contend that vitamin D should be considered an important public health issue.

Now if this is not some interesting reading, I dont know what is, if you are interested in Health.