A new study testing B vitamins and omega-3 fatty acids for cancer prevention has found no beneficial effect and — at least for women — some possibility of harm.

In this placebo-controlled five-year study, published Monday in The Archives of Internal Medicine, French researchers divided 2,501 survivors of cardiovascular illness ages 45 to 80 into four groups. The first took daily supplements of vitamin B9, vitamin B6 and vitamin B12; the second took two kinds of omega-3 fatty acids; the third took vitamin B6, vitamin B12 and omega-3; and the last took a placebo.

There were 174 cases of primary cancers among the participants, all confirmed by pathology. After controlling for dozens of other factors, the researchers found that neither the B vitamins nor the omega-3 fatty acids had any effect among the men. But there was an increased rate of cancer incidence and mortality among women who took the omega-3 supplements.

Valentina A. Andreeva, a postdoctoral researcher in epidemiology at the University of Paris who led the study, said that only 29 cancers were found in women, not a large enough number to draw broad conclusions. Still, she said, “we’re dealing with active substances that may not have beneficial effects and may have adverse effects, especially over the long term.”

By Nicholas Bakalar

The New York Times