A study with 458 Japanese men and women found that the risk of developing a benign colorectal tumor (adenoma) was decreased when blood level of the B vitamin were above 8.0 nanograms per milliliter.
“We thus offer the first evidence-based recommendation of a minimum essential serum folate concentration level of at least 8.0 ng/ml for effective reduction of the risk of colorectal adenoma,” wrote the researchers from Nippon Medical School in Tokyo in Clinical Nutrition.
“Regrettably, the concentration of serum folate that increases the risk of colorectal cancer is still unknown.
“Therefore, further studies are required to determine the appropriate serum folate concentration level for reduced risk of colorectal adenoma and colorectal cancer,” they added.
The results have implications for other populations, suggested the researchers, since folate levels were higher for the participants of this study that for participants in the US NHANES III survey, where white men had a mean folate level of 5.8 ng/ml and white women had a level of 7.2 ng/ml.
Concerns that folic acid – the synthetic form of folate – may increase the risk of colorectal cancer have surfaced over recent years, with some experts noting that folic acid, and not folate, may promote the formation of cancers under select circumstances where a person may already have a pre-cancerous or cancerous tumor.
This has led to some finger pointing at the synthetic form of the vitamin. On passage through the intestinal wall, folic acid is converted to 5-methyltetrahydrofolate, the naturally circulating form of folate. However, some studies have suggested that oral intake of folic acid in high doses may overwhelm this conversion pathway, leading to measurable levels of folic acid in the blood (Nutrition Reviews, 2009, Vol 67, pp. 206-212).
However, a recent analysis of data from almost 100,000 men and women from the American Cancer Society indicated that increased intakes of folic acid from fortified foods and dietary supplements are not linked to an increased risk of colorectal cancer (Gastroenterology, doi:10.1053/j.gastro.2011.04.004).
The new study focused on colorectal adenoma and not colorectal cancer. Blood samples from 258 men and 200 women were obtained and the folate levels compared between people with and without adenoma.
Results showed that there were no differences in the incidence of adenoma when blood levels exceeded 8.0 ng/ml, said the researchers.
Men with blood levels below this figure were 50 percent more likely to develop a colorectal adenoma while women were 23 percent more likely.
“The salient characteristic of our study was that the ratio of the frequency of colorectal adenoma was compared to the serum folate concentration for each individual patient,” explained the researchers.
Source: Clinical Nutrition
Published online ahead of print, doi:10.1016/j.clnu.2011.04.007
“Determination of the minimal essential serum folate concentration for reduced risk of colorectal adenoma”
Authors: S. Fujimori, K. Gudis, Y. Takahashi, M. Kotoyori, et al.