It seems likely that dietary folate produces different results, as least based on this study of the link between folic acid vs. natural sources of folate on risk of prostrate cancer:
Among the 643 men who were randomly assigned to placebo or supplementation with folic acid, the estimated probability of being diagnosed with prostate cancer over a 10-year period was 9.7% (95% confidence interval [CI] = 6.5% to 14.5%) in the folic acid group and 3.3% (95% CI = 1.7% to 6.4%) in the placebo group (age-adjusted hazard ratio = 2.63, 95% CI = 1.23 to 5.65, Wald test P = .01). contrast, baseline dietary folate intake and plasma folate in nonmultivitamin users were inversely associated with risk of prostate cancer, although these associations did not attain statistical significance in adjusted analyses. These findings highlight the potential complex role of folate in prostate cancer and the possibly different effects of folic acid–containing supplements vs natural sources of folate.
As the Editors noted:
Folic Acid and Risk of Prostate Cancer: Results From a Randomized Clinical Trial
Folate metabolism may have a complex role in prostate cancer; the effects of folic acid–containing supplements on the risk of prostate cancer may be different those of natural dietary sources...
Given the small number of prostate cancers in this study, the estimates of prostate cancer risk in the placebo and folic acid groups should be interpreted with caution.
An article published in 2007 article came to a similar conclusion about the risks of folic acid as the recent study. This is from a 3-year follow-up in a
Folic acid for the prevention of colorectal adenomas: a randomized clinical trial.
double-blind, placebo-controlled, 2-factor, phase 3, randomized clinical trial conducted at 9 clinical centers between July 6, 1994, and October 1, 2004. Participants included 1021 men and women with a recent history of colorectal adenomas and no previous invasive large intestine carcinoma....incidence of at least 1 advanced lesion was 11.6% for folic acid (n = 35) and 6.9% for placebo (n = 21) (unadjusted RR, 1.67; 95% CI, 1.00-2.80; P = .05). Folic acid was associated with higher risks of having 3 or more adenomas and of noncolorectal cancers. There was no significant effect modification by sex, age, smoking, alcohol use, body mass index, baseline plasma folate, or aspirin allocation...CONCLUSIONS:
Folic acid at 1 mg/d does not reduce colorectal adenoma risk. Further research is needed to investigate the possibility that folic acid supplementation might increase the risk of colorectal neoplasia.
None of these studies addressed ApoE 4 as a variable. So my personal, non-randomized take-away: people with a history of familial colorectal cancer and/or previous polyps (hand raised twice) probably should keep having those colonoscopies as recommended--and maybe focus on natural folate sources.