Simultaneous supplementation of the two B-vitamins increased the response to low-dose folate in the double-blind randomized placebo-controlled intervention study (the FAB2 Study) involving 98 healthy people and 106 patients with colorectal polyps.
The study, published in the journal Cancer Epidemiology, Biomarkers & Prevention , reports however that the combined supplements did not produce folate increases in the healthy people, suggesting benefits are limited to people with colorectal polyps.
Colorectal polyps are small, generally benign growths that occur in about 30 per cent of middle-aged and older Americans.
While most polyps do not become cancerous, they do raise the risk of cancer.
The subject of folate and colorectal cancer is controversial, however, with some studies reporting that the B-vitamin may in fact increase the risk of the disease.
On the other hand, other studies have reported protective benefits from folate for colorectal cancer.
The new study did not look at risk levels, but focussed on measuring increases in certain markers as a result of different supplementation regimes.
Researchers from the University of Sheffield, Newcastle University, North Tyneside General Hospital, and University College, Dublin randomised the subjects to receive daily supplements of folic acid alone (400 or 1,200 micrograms), folic acid (400 micrograms) plus riboflavin (5 milligrams), or placebo for six to eight weeks.
The researchers collected blood samples and colon biopsy samples in order to measure biomarkers of folate and riboflavin status.
Lead author Hilary Powers reports that supplementation with folic acid alone produced significant, dose-dependent increases in 5-methyltetrahydrofolate (MTHF), the reduced form of folate, in the mucosal layer of the colon.
MTHF levels also increased in red blood cells and plasma, she said.
Simultaneous supplementation with riboflavin enhanced the response to low-dose folate in people with polyps, but not the healthy controls.
No differences between the healthy and polyp subjects were observed in relation to the mucosal MTHF concentrations, they added.
In the mucosal layer, the magnitude of the response in mucosal folate was positively related to the increase in plasma 5-methyl tetrahydrofolate but was not different between the healthy group and polyp patients.
"Colorectal mucosal folate concentration responds to folic acid supplementation to an extent comparable to that seen in plasma, but with a suggestion of an upper limit," wrote Powers.
The data adds to an ever-growing body of science linking B-vitamin intake to reduced risk of certain cancers, including vitamin B6 and colorectal cancer ( J. Nutr. , Vol. 137, pp. 1808-1814), folate and breast cancer ( Am.
J. Clin.
Nutr ., Vol. 86, pp.
434-443), and folate, B6 and B12 and pancreatic cancer ( Cancer Research , Vol. 67, Issue 11).
Folate is found in foods such as green leafy vegetables, chick peas and lentils, and 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.
Source: Cancer Epidemiology, Biomarkers & Prevention Volume 16, Number 10, Pages 2128-2135 "Responses of Biomarkers of Folate and Riboflavin Status to Folate and Riboflavin Supplementation in Healthy and Colorectal Polyp Patients (The FAB2 Study)"
Authors: H.J. Powers, M.H. Hill, M. Welfare, A. Spiers, W. Bal, J. Russell, Y. Duckworth, E. Gibney, E.A. Williams and J.C. Mathers