Older men and women who took vitamin B, omega-3 fatty acids, or a combination of both supplements for approximately 5 years were no less likely to develop cancer than those who took placebo, according to a randomized clinical trial reported in the April 9 issue of Archives of Internal Medicine.
"This study does not support dietary use of B vitamins or omega-3 fatty acids for cancer prevention," said Valentina A. Andreeva, Ph.D., of the nutritional epidemiology research unit, University of Paris, and her associates.
The B vitamins have been proposed as potential cancer prevention therapy because deficiency of these nutrients is thought to affect DNA methylation, which in turn modulates cell differentiation and chromosomal stability. Similarly, omega-3 fatty acids have been suggested as chemoprevention because they may restrict tumor cell proliferation, and they modulate inflammation and immunity.
However, research regarding both nutrients has yielded inconclusive results. Dr. Andreeva and her colleagues studied the issue using data from a randomized clinical trial of cardiovascular disease. In that trial, 2,501 patients aged 45-80 years who had had an acute myocardial infarction, unstable angina, or ischemic stroke during the preceding year were randomly assigned to one of four supplementation groups and followed for a mean of 5 years for recurrent cardiovascular disease–related events.
The vitamin B and fatty acid supplements were not found to affect cardiovascular disease recurrence in that trial.
In their secondary analysis of the data, Dr. Andreeva and her associates instead assessed the development of incident cancer in these study subjects. The 1,987 men and 514 women had a mean age of 61 years at baseline. They were assigned to take 2 oral capsules each day.
The first group took B vitamins 5-methyltetrahydrofolate (0.56 mg), pyridoxine HCl (vitman B6, 3 mg), and cyanocobalamin (vitamin B12, 0.02 mg); the second group took eicosapentaenoic and docosahexaenoic acids (600 mg); the third group took both types of supplement; and the fourth group took oral placebos.
Treatment adherence was judged to be high, based on subjects’ self-report and on their increased blood levels of both nutrients.
During follow-up, 174 subjects (7%) developed an incident primary cancer. A total of 145 men developed prostate (50 cases), lung (22 cases), bladder (16 cases), colorectal (13 cases), or other (44 cases) malignancies. Twenty-nine women developed breast (9 cases), lung (4 cases), colorectal (3 cases), or other (13) malignancies.
Neither B vitamins nor omega-3 fatty acids affected the incidence of cancer, the investigators said (Arch. Intern. Med. 2012;172:540-7). Among men, 74 who took B vitamins developed cancer, compared with 71 in the comparison groups, a nonsignificant difference. Similarly, 72 men who took fatty-acid supplements developed cancer, compared with 73 in the comparison groups, also a nonsignificant difference.
Among women, 20 who took B vitamins and 9 in the comparison groups developed cancer, a difference of borderline significance. And 21 who took fatty acid supplements developed cancer, compared with 8 in the comparison groups. This difference was significant, but the low number of cancer cases in women "resulted in unstable and equivocal risk estimates," the researchers said.
This study was supported by Candia, Danone, Merck Eprova AG, Pierre Fabre Laboratories, Roche Laboratories, Sodexo, Unilever, the French National Research Agency, and the French Ministry of Health. The investigators reported no relevant financial disclosures.