Increased exposure to sunlight or increased intake of vitamin D leads to higher circulating concentrations (> 80 nmol/L) of 25(OH)D. 25(OH)D acts as a substrate for the 25-hydroxyvitamin D-1-hydroxylase in various tissues, including colon, breast, and lung. These tissues can produce 1,25(OH)2D, which acts in an autocrine fashion to regulate cell growth and decrease proliferative activity . It can also induce apoptosis when called on. Thus, 1,25(OH)2D3 can effectively manipulate cell growth and maintain it in a normal proliferative state under most circumstances. Once it accomplishes this, it induces the 25-hydroxyvitamin D-24-hydroyxlase, which hydroxylates the 1,25(OH)2D in the side chain on carbons 23 and 24, and this results in cleavage between carbons 23 and 24 that forms the water-soluble, biologically inert calcitroic acid . This is the likely explanation for why patients with renal failure develop a 1,25(OH)2D deficiency that results in secondary hyperparathyroidism and renal osteodystroph.
The therapeutic properties of the sun can never be overemphasizes, when exposed to sunlight, bare skin produce Vitamin D which is an important Vitamin needed for body general well being. However low level of Vitamin D increases risk of Colon, Breast Ovarian, Prostrate and Gastrointestinal Cancer.
The VDR (Vitamin D Receptor) is a protein located in the cell nucleus, sensible to 1,25(OH)2D3 stimulation by altering transcription rate of target genes. The presence and activation of VDR (by Vitamin D hormones) induces differentiation and apoptosis, inhibit proliferation, invasiveness, angiogenesis and metastatic potential . However, inadequate exposure or low Vitamin D places people with darker skin, older people who have low sunlight exposure and wear clothing covering most of the skin, people leaving with fewer hours of sunlight, pregnant women and new born baby are always at risk.
TYPE OF CANCER AND INFLUENCE OF VITAMIN D
Below are different types of cancers with various factors affecting them and the role of Vitamin D in their prevention and treatments.
1. Breast Cancer
This is one of the most dreaded malignancies in women in western world, it is a multifactorial disease and changes in cellular biology are fueled by genetic predisposition, breast density, hormonal effect and age. Although Age has been most significant risk factor which incidence double about every 10years until menopause rate of increase diminish other new factors to determine breast cancer risk and also double as preventive therapy include lifestyle, sun exposure tanning habits, foods and micro nutrients. Studies also confirmed that 1, 25(OH)2D3 can inhibit cell proliferation, promote cell differentiation in breast tumor tissue, thus have ability to protect against breast cancer.
Although young women have low risk of cancer but often aggressive however maintaining a continuous high level of 1, 25(OH)2D3 level may be protective measure against breast cancer. There are medications to reduce risk in post menopausal women against breast cancer unlike pre-menopausal women. However calcium, vitamin D and mammographic breast density could give protective effect.
2. Endometric Cancer
It is the most common type of gynecologic cancer in western world. Country, age overweigh, skin pigmentation, cigarette consumption, health expenditure and low level of UVB increases the incidence rate of this cancer . High intake of Vitamin D can however lower risk significantly of endometrial cancer.
3. Ovarian cancer
This is the most deadly among gynecologic malignancies. This occur as a result of hypercalcemia associated to high rate of 1, 25(OH)2D3 blood level. It primary target include middle and upper class women in industrialized nation. Among factors that increase risk are gene, diet, hormones, lifestyle habits, reproductive choices, overweight and obesity. However Vitamin D deficiency can trigger ovarian cancer while high intake of total dairy food can lower the risk. Also VDR has ability in suppressing tumor due to increase in apoptotic rate and a reduction in cell proliferation.
4. Cervic and Vulva Cancer
This unlike the other cancer affect women in developing countries cervical cancer is commonly found worldwide, attacking middle to older women of lower socio economic status. Its development is related with high risk Human Papillonna Virus (HPV) which reduces the immune systems ability to fight infections therefore allow precancerous cells to develop. However Vitamin D acquired primarily through exposure to sun seems to inhibit tumor development and growth at vulva. VDR immunore-activity is a new area that can be explored for prevention or therapy for cancer of the cervix.
5. Gastro intestinal cancer
This is affected by, skin pigmentation, adiposity, geographic residence, leisure time and physical activities. Vitamin D status was significantly protective with greatest for digestive system.
6. Pancreatic cancer
The good news on vitamin D continued recently in a study from Northwestern University in Chicago. Researchers reported in the journal Cancer Epidemiology Biomarkers & Prevention that vitamin D...exhibit(s) potent antitumor effects in many tissues, including the pancreas. Higher intakes of vitamin D were associated with lower risks for pancreatic cancer, prompting researchers to suggest that vitamin D may have a role in the future prevention of this specific form of cancer.
Conclusion: Vitamin D and Cancer Prevention
Vitamin D status may influence cancer survival due to its role in inhibiting proliferation of cancer development, sun exposure is natural way to obtain a dose of vitamin D needed to maintain endocrine, paracrine, and autocine equilibrium. But also sun exposure is greatly risky for skin aging, cancer and melanoma, even atmospheric pollutions and ozone condition call for caution. Then the question is how we combine the sunlight benefit from mild exposure to prevent tumor development and the alarming data about cumulative risk of UV radiation.
