This information could factor into the debates now taking place in Europe regarding mandatory folate fortification of foods.
Most studies that have described an anticancer effect of folate have focused on dietary intake, not on circulating levels, lead researcher Dr. B. Van Guelpen, from Umea University in Sweden, and colleagues note. By contrast, the three prospective studies that have looked at circulating folate levels have yielded conflicting results.
In the present study, reported in the journal Gut, the researchers assessed the effect of prediagnostic blood levels of folate on the risk of colorectal cancer. A total of 226 colorectal cancer patients and 437 matched controls were drawn from the population-based Northern Sweden Health and Disease Cohort.
In the overall analysis, researchers noticed a bell-shaped curve between folate levels and colorectal cancer risk. Subjects in the middle quintile for folate levels were twice as likely to develop colorectal cancer as those in the lowest quintile.
By contrast, when the analysis was confined to subjects who were followed longer than a median of 4.2 years, a direct relationship between folate levels and cancer risk was seen.
In this analysis, subjects in the highest folate quintile were nearly four times more likely to develop colorectal cancer than those in the lowest quintile.
As to why the current findings seem to contradict previous research, the authors suggest that it may relate to the inadequate folate status of the population being studied. The present cohort may represent the ''lower end of the biological folate spectrum,'' they add.
The authors conclude that the present findings do not necessarily negate a beneficial effect for high folate levels, but do indicate such an effect for low levels.
''Mandatory folic acid fortification is probably the most important...intervention in nutrition and public health in decades,'' Dr. Y-I Kim, from the University of Toronto, comments in a related editorial. ''Some proponents of mandatory folic acid fortification have labeled the delay in...fortification in European countries as public health malpractice.'' However, findings such as those from the present study give pause to the drive for folate fortification, Kim notes. ''Long term follow-up studies are urgently warranted to determine the effect of folic acid fortification and supplementation on the incidence of cancer and other potential adverse effects.'' Reuters LL DB1012