The main dietary source for vitamin D is from the diet. However, body can synthesis it through use of ultra-violet rays from the sun. One of the main functions of vitamin D in the body is to help calcium absorption and bone integrity. In addition to these functions it has been found that vitamin D may have an important role in prevention of cancer as it is found to check the uncontrollable growth of body cells. As such, vitamin D has protective effect against cancer especially on colorectum and neoplastic cells from a hormone produced by circulating 25-hydroxly-vitamin D (Jenab et al, 2010).
It has been speculated that this may have direct responsibility in modulating growth of normal and neoplastic colonic cells. But such evidence is not really substantiated and there lacks supporting pre-diagnostic data particularly from European populations to verify this. This was what made the authors to undertake an investigation on correlation between pre-diagnostic of circulating 25- (OH) D concentration in the body and dietary intakes of vitamin D and calcium with colon and rectum cancer risk among European populations. Therefore, the purpose of this paper is to give statistical summary and results of this study (Jenab et al, 2010).
The type of study design used was nested case control design. Study site was in ten European countries namely Denmark, Germany, France, Italy, Greece, the Netherlands, Spain, Sweden and United Kingdom. About 520,000 subjects from ten western European countries were enrolled in the study. Statistical analysis indicated that the mean age of participants in the study both colon group and rectum group were similar. For colon case had 59.6 with standard deviation (SD) of 7.2 and controls had 58.0 with SD of 7.2 while rectum cases had 58.0 with SD of 6.8 and controls had 58.0 with SD of 6.9.
It was considered that level greater or equal to 50nmol/l to <70nmol/l of circulating 25-(OH) D was associated with reduced risk of cancer while circulating levels than these were linked with increased risk of cancer. Higher circulating 25-(OH) D concentration were found to be associated with lower colorectal risk in a dose-response trend. Incidence rate ratio for lowest to highest quintile was 0.60(95% CL 0.46 to 0.80) with stronger association in colon as compared to that of rectum (Jenab et al, 2010).
There was colorectal cancer risk for a 10% increment in 25-(OH)D for specific incidence rate ratios at 95% confidence levels in Denmark, France, Germany, Greece, Italy, the Netherlands, Spain, Sweden and United Kingdom. Nevertheless, dietary intake of vitamin D did not indicate any correlation with colorectal cancer risk. Higher consumption of dietary calcium revealed some association with reduced cancer risk for rectum. There was inverse association (p=0.154) between colorectal cancer risk and circulating 25-(OH) D concentration and its interaction with dietary calcium. In terms of heterogeneity, cancer risk did not neither differ by sex (25-(OH) D=0.782, vitamin D=0.600 nor by dietary calcium=0.500. However, there was variation between colon and rectal anatomical sub sites (Jenab et al, 2010).
Therefore, study results indicate that pre-diagnostic concentrations of circulating 25-(OH) D below 50nmol/l have association with an increased risk of colon cancer. On the other hand, circulating 25-(OH) D above 70nmol/l does not have significant reduction of colon cancer risk. Participants in highest quintiles of 25(OH) D were found to have 40% lower colorectal cancer risk. But there is need to carry out new randomized trials to confirm these results before making recommendations for vitamin D supplementation.
Reference
Jenab, M., Bueno-de-Mesquita, H. B., Ferrari, P., Franzel, J. B., Duijnhoven, V., Norat, T., Pischon, T.… Eugene, H. J., (2010). Association between pre-diagnostic circulating vitamin D concentration and risk of colorectal cancer in European populations: a nested case-control study. BM Journal, vol. 340 p 1-10.