ROLE OF VITAMIN D IN PREVENTION OF CANCERPRESENTED BY:MR. ASHWIN THOMAS, MSNHIND COLLEGE OF NURSING,LUCKNOW, U.P.
INTRODUCTION: Among the diseases of modern times, the term cancer has encircled the health sectors nowadays. Because of the limited treatment modalities available in medicine today, the emphasis is shifting on finding a way or ways to prevent cancers. In that relation, recent research results and studies are pointing towards vitamin D as the possible aid in preventing malignancy.
OVERVIEW OF VITAMIN 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). The term vitamin D also refers to metabolites and other analogues of these substances. Vitamin D3 is produced in skin exposed to sunlight, specifically ultraviolet B radiation.
FUNCTIONS OF VITAMIN D: Maintenance of organ systems. Vitamin D regulates the calcium and phosphorus levels in the blood by promoting their absorption from food in the intestines, and by promoting re- absorption of calcium in the kidneys. It is also needed for bone growth and bone remodeling by osteoblasts and osteoclasts. In the absence of vitamin K Vitamin D can promote soft tissue calcification. It inhibits parathyroid hormone secretion from the parathyroid gland. Vitamin D affects the immune system by promoting phagocytosis, and immunomodulatory functions.
VITAMIN D IN CANCER PREVENTION AND RECOVERY: The vitamin D hormone, calcitriol, has been found to induce death of cancer cells. Although the anti-cancer activity of vitamin D is not fully understood, it is thought that these effects are mediated through vitamin D receptors expressed in cancer cells, and may be related to its immunomodulatory abilities. The anti-cancer activity of vitamin D observed in the laboratory has prompted some to propose that vitamin D supplementation might be beneficial in the treatment or prevention of some types of cancer.
Vitamin D regulates the expression of genesassociated with cancers and autoimmunedisease by controlling the activation of thevitamin D receptor (VDR), a type 1 nuclearreceptor and DNA transcription factor. Researchhas indicated that vitamin D deficiency is linkedto colon cancer and more recently, to breastcancer.The Canadian Cancer Society recommends thatadults should consider supplementing with 1,000IU of vitamin D per day during the fall and winter.They base this recommendation on the growingevidence for a link between vitamin D and areduced risk for colorectal, breast and prostatecancers.
Cancer prevention specialists haveconcluded that taking 1,000 internationalunits (IU) of vitamin D3 per day may loweran individual’s risk of developing certaincancers, including breast, colon, prostate,and ovarian, by up to 50 percent.
In 2007, scientists released a study whichdemonstrated a beneficial correlationbetween vitamin D intake and prevention ofcancer. Drawing from a meta analysis of 63published reports, the authors showed thatintake of an additional 1,000 internationalunits (IU) (or 25 micrograms) of vitamin Ddaily reduced an individuals colon cancerrisk by 50%, and breast and ovarian cancerrisks by 30%. Research has also showna beneficial effect of high levels of calcitriolon patients with advanced prostate cancer.
A randomized intervention study involving 1,200women, published in June 2007, reports thatvitamin D supplementation (1,100 internationalunits (IU)/day) resulted in a 60% reduction incancer incidence, during a four-year clinical trial,rising to a 77% reduction for cancers diagnosedafter the first year (and therefore excluding thosecancers more likely to have originated prior tothe vitamin D intervention).In 2006, a study at Northwest University foundthat taking the U.S. RDA of vitamin D (400 IUper day) cut the risk of pancreatic cancer by43% in a sample of more than 120,000 peoplefrom two long-term health surveys.
A 2008 study using data on over 4 millioncancer patients from 13 different countriesshowed a marked difference in cancer riskbetween countries classified as sunny andcountries classified as less–sunny for anumber of different cancers. Research hasalso suggested that cancer patients whohave surgery or treatment in the summertherefore make more endogenous vitamin Dand have a better chance of surviving theircancer than those who undergo treatment inthe winter when they are exposed to lesssunlight.
The breast cancer study, published online in thecurrent issue of the Journal of SteroidBiochemistry and Molecular Biology, pooleddose-response data and found that individualswith the highest blood levels of 25-hydroxyvitamin D, or 25(OH)D, had the lowestrisk of breast cancer.New research published this month shows thatvitamin D supplementation produces anastonishing 77 percent reduction in all cancersin women, making it the single most effectivemedicine for preventing cancer that has everbeen discovered by modern medical science.
Recently, research led by Kimmie Ng,M.D., M.P.H., of the Dana-Farber CancerInstitute has revealed that vitamin D canimprove the survival rates of people withcolorectal cancer. The findings of this studyare very significant because, in a way, theybreak new ground. While previous researchhad largely centered on how vitamin D levelsreduce colorectal cancer incidence, thisstudy has established a connection betweenvitamin D levels and the survival chances ofpeople who have already gotten the disease.
FUTURE DIMENSIONS OF DISCOVERY: Although the cohort findings are likely to increase enthusiasm for the cancer prevention potential of vitamin D, inherent limitations of observational epidemiologic studies combined with a history of prior disappointments with other potential chemo preventive agents suggest caution in their interpretation.
Two decades ago there was intense interestand hope that supplementation with beta-carotene might reduce the risk of severalcancers. Epidemiologic studies haveconsistently reported that men and women withthe highest dietary intakes of beta-carotene aswell as with elevated blood levels experiencedlower risks of respiratory, gastrointestinal, andother cancers. The zeal was crushed, however,when randomized trials in the United States andFinland showed increased rather thandecreased risks of lung cancer among adultsreceiving beta-carotene supplements.
Vitamin E was similarly touted as aninhibitor of cancer, as well as ofcardiovascular disease, but again the "goldstandard" of randomized trials failed toconfirm the preventive correlations noted incohort and case–control studies.
In each of these examples, the agentsmay have demonstrated benefit withmodification of the dose, formulation, ortiming of the intervention or with longerfollow-up, but the sobering lesson is thattrends observed in non experimentalsettings, including cohort studies, are notalways confirmed experimentally whentested in randomized clinical trials.
Science, after all, is a continual process ofhypothesis formulation, testing, andrefinement. Ecologic (e.g., geographic correlations)and analytic (e.g., cohort and case–control)studies provide the evidence-based clues tocancer etiology, but randomized trials aregenerally needed to confirm these leads anddevelop effective disease preventionstrategies.
CONCLUSIONS: The role of vitamin D in cancer prevention is strongly suggested by epidemiologic observations and potential mechanisms have been identified by experimental studies. The promising results from both observational and laboratory studies should usher in a new era of intervention studies of vitamin D and cancer risk. Because many public health scientists are already clamoring for higher levels of vitamin D supplementation for bone and other health, randomized trials of vitamin D and cancer risk should be undertaken speedily.
If the promise of vitamin D holds, a brief walk in the sun may turn out to be a step toward cancer prevention.
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