Vitamin D is not actually a vitamin, but a steroid hormone. The traditional role for vitamin D was seens as regulating calcium homeostasis, whereby increased circulating levels of the vitamin D metabolite 25-hydroxyvitamin D increased the intestinal absorption of calcium. Vitamin D therefore plays an important role in bone health. However, as a steroid hormone that can interact directly with genetic material through activation of the vitamin D receptor in the nucleus of cells, vitamin D has a number of role that revolve around cell regulation. In particular vitamin D is thought to be involved in the proliferation, differentiation and apoptosis of cells. Epidemiological evidence suggests that higher intakes of vitamin D and higher plasma levels of 25-hydroxyvitamin D are associated with a lower risk of cancer. Therefore the known cell regulatory effects of vitamin D may explain the epidemiological evidence that shows a protective effect against the development of cancer in humans.
The anti-cancer effects of vitamin D have been suggested to be beneficial in the survival rates from those with pre-existing cases of cancer, and a number of studies have shown that higher plasma levels of 25-hydroxyvitamin D are associated with improved cancer survival. For example in one study, women diagnosed with ovarian cancer had their 25-hydroxyvitamin D levels measured. Researchers then investigated the survival of the women from their medical records at a subsequent date. In the follow up analysis it was found that 59 % of the women had died from ovarian cancer. However, higher 25-hydroxyvitamin D levels in the plasma of the women was significantly associated with longer survival times. This suggests that 25-hydroxyvitamin D may be a useful prognostic indicator of survival from ovarian cancer. Further, it supports the contention that 25-hydroxyvitamin D levels may be protective of cancer development or mortality from cancer.
Dr Robert Barrington’s Nutritional Comments: It is becoming increasingly evidenced that vitamin D nutrition is highly important to health. Vitamin D has a much wider role in human health that its traditional role in bone health and calcium homeostasis. In this study the researchers showed that the vitamin D status of the women was significantly associated with the season that the measurement was taken, with concentrations being significantly higher during summer and autumn compared to winter. In addition, the study was performed in Australia, and those subjects living closer to the equator (Queensland) had significantly higher concentrations of 25-hydroxyvitamin D compared to those living further south (Tasmania). This supports the evidence that sun exposure is the primary determinant of vitamin D status, and that regular sun exposure may actually be protective of cancer. Dietary sources of vitamin D are limited and so sun exposure and supplements remains the best way to maintain adequate vitamin D.
RdB
