Multivitamins, folate, and colon cancer

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Abstract
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 supplements. Analysis of duration of use of multivitamins containing folic acid showed that the inverse relationship was apparent only after at least five years of use and the most marked effect was after at least 15 years of use.