New Discoveries on the Role of Vitamin D in Cancer Prevention

1.0 INTRODUCTION

The therapeutic properties of the sun can never be overemphasizes, when exposed to sunlight, bare skin produce Vitamin D (Schwartz and Hanchette (1) which is an important Vitamin needed for body general well being. However low level of Vitamin D increases risk of diseases and abnormalities such like Rickets, Osteomalacia, Osteoporosis, Diabetes mellitus, hypertension, heart diseases, myopathy, multiple Sclerosis, Schizophrenia, Hyperparathyroidism (2 – 7) among others. Further more Colon, Breast Ovarian, Prostrate and Gastrointestinal Cancer could also be developed by hypovitaminosis D (Schwartz et al. (8, 9) and Garland et al. (10)

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, agiogenesic and metastatic potential [2]. 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

1.1 VITAMIN D SYNTHESIS AND CLASSIFICATION

The principal circulating metabolite 25(OH)D₃ is produced by exposure to UV radiation on the skin and cholecalciferol oxidation at the liver which is transform into active hormones (1,25(OH₂)D₃ by kidney (3,11). This metabolites and Vitamin D are transported in the circulation by a binding protein which act as hormones and promote the absorption of calcium and phosphorus and their deposition in the bones and teeth

There are 3 systems that regulate the vitamin activities within tissue: VDR and 2 other major Vitamin D metabolizing enzymes which contribute significantly to determination of serum level with aging (3, 4)

1.2 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.

1.2.1 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( 12, 13) other new factors to determine breast cancer risk and also double as preventive therapy include lifestyle, sun exposure [Moan et al 14], 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.

A review by Garland et al. (15) showed 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. [Berube et al 16]

1.2.2 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 (Mohr et al 17). High intake of Vitamin D can however lower risk significantly of endometrial cancer (Salazar-Martinez et al [18]

1.2.3 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 (Evan et al 19). However Vitamin D deficiency can trigger ovarian cancer while high intake of total dairy food can lower the risk (20) and Garland et al (21). Also VDR has ability in suppressing tumor due to increase in apoptotic rate and a reduction in cell proliferation. Although this field required more research. [22]

1.2.4 Cervic and Vulva Cancer

This unlike the other cancer affect women in developing countries cervical cancer is commonly found world wide, 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 system’s 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 (23). VDR immunore-activity [24] is a new area that can be explored for prevention or therapy for cancer of the cervix

1.2.5 Gastro intestinal cancer

This is affected by, skin pigmentation, adiposity, geographic residence, leisure time and physical activities. Giovannucci et al [25] reported that Vitamin D status was significantly protective with greatest for digestive system

1.3 Conclusion:Vitamin D and Cancer Prevention

It has been established by Moan et al. (26) that 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.

Several researches has been carried out on Vitamin D supplement, although is well established that doses of 900IU or greater arte required to prevent Osteoporosis (27). The US institute of medicine recommends different Vitamin D for various age groups among which are 200IU for children, 400IU for up to age 50 and 600 IU for those above 71 years of age. Although this prescription has been challenged as grossly inadequate (28) however, 1000IU daily during fall and winter has been recommended by Canadian Cancer society (29) while adult at risk of having lower Vitamin D level as a result of lifestyle and color of skin should not go above 2000IU

Conclusion

Although studies have shown that Vitamin D may be beneficial for cancer prevention however further studies is needed to explore precise way in which Vitamin D and its related Compound could be harnessed in both prevention and treatment of cancer