Comment

Case control and cohort studies consistently suggest that high intakes of vegetables are associated with a decreased risk of colorectal cancer1 but the specific nutrients involved have not been identified. Interest in the possible aetiological importance of folate has been stimulated by observations suggesting that hypomethylation of DNA is an early step in colorectal carcinogenesis and by evidence of a positive association with alcohol, which has an adverse effect on folate metabolism.2

Giovannucci and colleagues3 provide evidence of an inverse association between folate intake and colon cancer. Compared with women whose intake was ⩽200 μg/day, the relative risk of colon cancer associated with an intake of 201–300 μg/day was 0.9, with an intake of 301–400 μg/day it was 0.8, and with an intake >400 μg/day it was 0.7 (p for trend=0.01). There was no evidence of confounding. Among women with the highest category of intake, 86.3% used multivitamin supplements. The other three categories reflect primarily dietary sources. The inverse relationship with folate persisted when adjustment was made for other nutrients present in multivitamin …