In a dramatic scientific turnaround, researchers have found that far from helping to prevent cancer, high-dose supplementation with B vitamins actually increases the risk of lung cancer in men.
The study from the Ohio State University Comprehensive Cancer Center in Colombus, Ohio, looked at data from the Vitamins and Lifestyle (VITAL) cohort in the United States, a large population grouping specifically designed to study the long-term effect of dietary supplements on cancer risks.
Researchers evaluated results on 77,118 patients between the ages of 50 and 76, all recruited from Washington State, who reported on their B-vitamin intake (in both multivitamin and individual B-vitamin forms) over the previous ten years. Of that cohort, 808 patients had developed primary invasive lung cancers, numbers which were then correlated with B6 and B12 vitamin usage and dosage.
The results, which were arrived at after adjusting for cofactors such as personal smoking history, age, race, education, body size, alcohol consumption and personal history of cancer or lung disease, showed no association between lung cancer risk and B vitamin intake of any strength in women, but for men the findings showed a 30 to 40 per cent increase in lung cancer.
In fact, use of vitamin B6 or B12 in high doses, usually achieved through individual B-vitamin supplements, for an extended period turned out to be associated with almost double the risk of lung cancer for men and three to four times greater for male smokers.
“When the 10-year average supplement dose was evaluated, there was an almost two-fold increase in lung cancer risk among men in the highest categories of vitamin B6 (more than 20 mg per day) and B12 usage (more than 55 mcg per day) compared with nonusers,” say the study’s authors. “For vitamin B6 and B12, the risk was even higher among men who were smoking at baseline.”
Previous studies have traced links between other vitamins such as vitamin E, beta-carotene and folic acid and increased cancer risk.
As to why the extra B vitamins would increase the risk for men and not women, the authors suggest that men and women are known to have different susceptibility to tobacco-induced lung cancer and that the B vitamin supplementation may serve to increase cell growth and promote cancer cell proliferation in men. As well, previous studies have shown that excess supplementation of B vitamins is linked to changes in DNA expression of some genes linked to cancer growth.
The findings suggest that high-dose B6 and B12 supplements should not be taken for lung cancer prevention, say the study’s authors, and that most people should be getting enough of both vitamins from daily intakes of healthy foods.
Another study last year by researchers at the University of Alberta in Edmonton found that, contrary to recent assumptions about the benefits of vitamin D in warding off disease, researchers found no strong evidence to support the claim that supplementing with vitamin D will reduce the risk of cancer, respiratory infections or rheumatoid arthritis.
The new study is published in the Journal of Clinical Oncology.