Effects of Serum Levels of Vitamin A and Its Precursors on Colorectal Cancer Mortality: An 18-Year Follow-Up Study of a National Cohort

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Vitamin A is essential for normal cell functioning. It is involved in cell growth, differentiation, and arrest, and eventually apoptosis which can inhibit tumor cell growth. A-carotenoids, precursors of vitamin A, are also important to maintain optimum physiological levels of this antioxidant. Colorectal cancer is the abnormal growth of cells in the colon or rectum. Of the cancers affecting both men and women, colorectal cancer is the second leading cancer killer in the US. One of the major risk factors for colorectal cancer is diet. Several studies have examined the association between vitamin A and various types of cancer. However, the relationship between serum vitamin A levels (and its precursors) and risk of colorectal cancer death is unclear. Thus, the goal of this study was to examine the relationship between serum levels of vitamin A (and A-carotenoid) and colorectal cancer mortality. A retrospective cohort study was conducted with 14,358 adults who participated in phase II of the National Health and Nutrition Examination Survey III (1991–1994)(NHANES III). This served as baseline and was correlated with the National Death Index database for a 15-yr (1991-2006) follow-up study. Hazard ratios (HRs) for all-cause and cancer-related deaths for individuals with high, medium, and low serum vitamin A and A-carotenoid levels were calculated using Cox Proportional Hazards Regression Model. Unadjusted HR of deaths associated with low serum levels of vitamin A were 1.84 (95%CI=1.02-3.30) and 1.00 (reference). After adjustment for multiple colorectal cancer risk factors including age and sex, the HR for colorectal cancer fatalities were 1.00 (reference) and 1.85 (95%CI=1.02-3.37). Adjusted HR for colorectal cancer death for A-carotenoid serum levels, using 3-level categorization and adjusted for fruits and vegetables were 2.92 (95%CI=1.49-5.71) and 1.89 (95%CI=1.03-3.45) for low and medium compared to high, respectively. Results indicate that there is a significant association between serum levels of vitamin A (and A-carotenoids) and colorectal cancer mortality. Further studies are warranted to determine the mechanism(s) of this phenomenon.


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