The accepted wisdom is that high levels of folate protect against the disease, and there are currently moves in Europe to fortify foodstuffs with folate, primarily to prevent birth defects, but also to boost the health of populations.
The research team base their findings on more than 660 people who were part of the Northern Sweden Health and Disease Cohort, which included 85,000 people at the time of the study.
Participation in the study involved completing questionnaires on lifestyle and diet and the donation of blood samples at regular intervals. After 17 years of monitoring, 226 people had been diagnosed with bowel cancer.
People with the highest blood levels of folate were just as likely to develop bowel cancer as those with the lowest blood levels, whereas people in between were almost twice as likely to develop the disease.
A reduced risk for bowel cancer was also found in those people with a common mutation in the MTHFR gene. This is known to lower a person's circulating folate levels.
No link was found between circulating homocysteine and the risk of bowel cancer. Homocysteine is an amino acid implicated in the thickening and hardening of arteries, levels of which are kept in check by B vitamins, including folate.
The authors conclude that while high levels of folate may indeed protect against the development of bowel cancer, so too may low levels, suggesting something of a bell shaped curve in risk levels.
Journal
Gut