Association between serum vitamin D levels and colonic carcinomatous polyps.

BACKGROUND: Vitamin D has been postulated to play a role in colonic carcinogenesis by modulation of apoptosis and inhibition of angiogenesis. However, data supporting this theory are conflicting, and most studies include only Asians and Caucasians. This retrospective study aims to determine whether there is a correlation between an increased total vitamin D level and a lower incidence of carcinomatous polyps in a multi-race but predominantly Hispanic population in East Harlem, New York City.
METHODS: A case-control study was conducted involving all patients who underwent colonoscopy at Metropolitan Hospital Center in 2011 and who also had serum total vitamin D levels taken within 1 month before or after the date of colonoscopy. Total vitamin D levels and the presence of carcinomatous polyps were the main variables studied. Colonic polyp-positive (CP+) samples were designated as the case group, while colonic polyp-negative (CP-) samples were assigned to the control group. Logistic regression analysis was used to estimate odds ratio at a 95% confidence interval. Adjusted variables were chosen a priori and included age, sex, race, smoking and alcohol history, body mass index, and folate and aspirin use.
RESULTS: We identified 1,640 patients who underwent colonoscopy from January 1 to December 31, 2011. Of these, 136 also had a vitamin D serum level drawn within 1 month before or after the colonoscopy. Forty-three were CP+ and assigned to the cases group, and 93 were CP- and assigned to the control group. Thirty-five percent of the sample had total serum vitamin D levels of <20 ng/ml, and 65% had total serum vitamin D levels 20-29 ng/ml. Using <20 ng/ml as a cutoff point, the association of vitamin D with CP+ was statistically nonsignificant. In a multivariate model using vitamin D levels of <20 and <30, the association with CP+ appeared stronger, though, here too, the associations were not statistically not significant. A post hoc analysis was done excluding vitamin D levels of 20-29. In this analysis, the association between vitamin D levels and colonic polyps grew stronger with increased cutoff levels with vitamin D level of <20, suggesting a threshold effect.
CONCLUSION: Vitamin D levels, using two established cutoffs, are not significantly associated with increased odds of membership in the CP+ group. However, our data suggest a possible threshold effect of vitamin D at <30 ng/ml associated with increasing odds of being CP+.