A PROSPECTIVE COHORT STUDY OF INTAKE OF CALCIUM, VITAMIN-D, AND OTHERMICRONUTRIENTS IN RELATION TO INCIDENCE OF RECTAL-CANCER AMONG POSTMENOPAUSAL WOMEN

To investigate whether high intakes of calcium and other micronutrient s (carotene, retinol, and vitamins C, D, and E) are related to reduced risks of rectal cancer, we analyzed data from a large cohort study of postmenopausal Iowa women who responded to a mailed survey in 1986. A fter 9 years of follow-up, 144 incident rectal cancer cases were ascer tained among the 34,702 women at risk. Intake levels of micronutrients at baseline were derived from self-reported data on vitamin supplemen ts and dietary intake of 127 foods included in a semiquantitative food frequency questionnaire. After adjustment for total energy intake and other potential confounding factors, a dose-response inverse associat ion was observed between total calcium intake and the risk of rectal c ancer: adjusted relative risks (RRs) were 1.00, 0.90, and 0.59 (trend test, P = 0.02) from the lowest to the highest calcium intake tertiles . High intakes of dietary and supplement calcium were both related to a slightly reduced risk of rectal cancer, but neither of the trend tes ts,vas statistically significant. Reduced risks of rectal cancer were also observed for high intake of carotene and vitamins A, C, and D, al though none of the associations were statistically significant. For vi tamin D, the adjusted RRs mere 1.00, 0.71, and 0.76 (trend test, P = 0 .20) for increasing intake tertiles. Compared with women who consumed low levels of both total calcium and vitamin D, those in the highest i ntake group of both nutrients were at a 45% reduced risk of rectal can cer (RR, 0.55; 95% confidence interval, 0.32-0.93). This study support s the hypothesis that high intake of calcium and possibly other micron utrients may be beneficial in the prevention of rectal cancer.