Data collected over the course of about nine years from over 525,000 people following the introduction of folic acid fortification in the US revealed that people with the highest folate levels were 30% less likely to develop colorectal cancer.
Findings published in the American Journal of Clinical Nutrition go some way to confirming the additional health benefits of folic acid fortification, introduced in the US in 1998.
However, researchers from the US National Institutes of Health (NIH) note that colorectal cancer has a long latency period of between 10 and 20 years, and that additional follow-up time is required before firm conclusions can be drawn. The latency period is the time between the first exposure to a cancer-causing agent and the clinical recognition of the disease.
Benefits for babies
An overwhelming body of evidence links has linked folate deficiency in early pregnancy to increased risk of neural tube defects (NTD) - most commonly spina bifida and anencephaly - in infants.
The first country to fortify flour on a national scale with folic acid – the synthetic, bioavailable form of folate – was Oman, which introduced this in 1996. The US and Canada followed in 1998. Preliminary evidence indicates that the measure is having an effect with a reported 15 to 50 per cent reduction in NTD incidence.
A total of 51 countries now have some degree of mandatory fortification of flour with folic acid.
The US Centers for Disease Control and Prevention (CDC) recently listed the prevention of neural tube defects through flour fortification amongst its list of 10 great health achievements in the US for the last decade.
Study details
The NIH scientists analysed data from 525,488 individuals aged between 50 and 71 participating in the NIH-AARP Diet and Health Study.
Results showed that over a period of about nine years, 7,212 people developed colorectal cancer, 6,484 of which occurred after the introduction of fortification. For people with the highest average intakes of folate/folic acid (at least 900 micrograms per day) the risk of colorectal cancer was 30 % lower than in people with the lowest average intakes (less than 200 micrograms per day).
In addition, the highest intakes specifically from supplements or the diet were associated with 18% and 19% reductions, respectively.
Contradictory results
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 tumour.
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).
Source: American Journal of Clinical Nutrition
Published online ahead of print, doi: 10.3945/ajcn.110.002659
“Pre- and postfortification intake of folate and risk of colorectal cancer in a large prospective cohort study in the United States”
Authors: T.M. Gibson, S.J. Weinstein, R.M. Pfeiffer, A.R. Hollenbeck, A.F. Subar, A. Schatzkin, S.T. Mayne, R. Stolzenberg-Solomon