Insufficient vitamin D supply as a possible co-factor in colorectal carcinogenesis.

Vitamin D, the "sunshine vitamin", may play a role in the development of colorectal cancer. In a prospective open study, the plasma levels of 25-hydroxyvitamin D [25(OH)D], the marker for sufficient or insufficient vitamin D supply, were determined in three groups of patients whose diagnoses were confirmed by colonoscopy: healthy individuals (n = 239), patients with colorectal adenoma (n = 203) and with carcinoma (n = 98). In order to assess other factors such as nutrition, sunlight exposure and physical activity as co-variates for the risk of colorectal cancer, the individuals completed a questionnaire. Patients with colorectal cancer (CRC) had significantly decreased plasma 25(OH)D levels (p < 0.001) compared to the controls in contrast to patients with adenomas, who had lower levels exclusively in the winter (p = 0.01). When analyzed by the Kruskal-Wallis test, the groups of patients with adenomas (p = 0.03) and colorectal carcinomas (p < 0.0001) had significantly different mean plasma values compared to the controls. The plasma 25(OH)D levels showed an inverse correlation to the UICC stages of CRC; however, the differences were not significant. Patients with CRC were significantly older than the controls, but regression analysis showed no significant correlation between the plasma 25(OH)D levels and age, and the influence of age on the plasma levels of 25(OH)D was minimized in a group of individuals over 65 years of age, in which the patients with CRC had significantly decreased plasma levels of 25(OH)D in the winter. About one-half of the individuals with normal colonic mucosa had plasma 25(OH)D levels below 25 microg/l (the normal range) and one-third even had plasma levels below 20 microg/l. Regression analysis showed a significant influence of age on plasma 25(OH)D levels in healthy individuals, of physical activity in patients with adenomas and of season in patients with CRC. Other covariates, such as nutrition or sunlight exposure, had no significant influence on plasma 25(OH)D. In conclusion, an insufficient vitamin D supply might act as a co-factor in colorectal carcinogenesis.