SERUM LEVELS OF VITAMIN-D METABOLITES AND THE SUBSEQUENT RISK OF COLON AND RECTAL-CANCER IN FINNISH MEN

Experimental and human epidemiologic data suggest a protective role fo r vitamin D in large bowel cancer. To investigate this association, we conducted a nested case-control study within a Finnish clinical trial cohort. Cases (n = 146) were participants diagnosed with primary aden ocarcinoma of the large bowel. Controls were matched (2:1) to cases on age, date of baseline blood draw, and study clinic. Prediagnostic ser um levels of the vitamin D metabolites, 25-hydroxyvitamin D (25-OH D), and 1,25-dihydroxyvitamin D (1,25-DIOH D) were used as primary exposu re measures. The baseline geometric-mean serum level of 25-OH D was 11 .6 percent lower in cases than in controls (12.2 cf 13.8 ug/l, P = 0.0 1) while serum levels of 1,25-DIOH D did not differ by case-control st atus. No association was seen between serum levels of 1,25-DIOH D and large bowel cancer risk. However, the estimated relative risk (RR) of large bowel cancer decreased with increasing level of serum 25-OH D an d the association was more pronounced for rectal cancer (55 cases; RR by quartile = 1.00, 0.93, 0.77, 0.37; trend P = 0.06). Neither exclusi on of early cases nor multivariate adjustment for potential confounder s materially altered these estimates. There was no evidence of effect modification by level of 1,25-dihydroxyvitamin D or with other known r isk-factors for large bowel cancer.