And don’t get me started on metabolism. If you want to “supercharge your metabolism and energy levels,” Amazon can deliver you a tall bottle of B12 supplements by the end of the day. Your metabolic processes will be the envy of the neighborhood. (“Is Janice … on something?” “Yes—B12!”)
These are the sort of vague marketing claims that have propelled the cobalt-based compounds sold as B12 into American hearts and minds and blood in ever-growing quantities. They are extrapolations from the fact that B12 deficiency causes anemia, and correcting that deficiency will alleviate symptoms of fatigue and weakness. But as the National Institutes of Health notes, “Vitamin B12 supplementation appears to have no beneficial effect on performance in the absence of a nutritional deficit.”
This is a heavy claim about a very common substance, so it’s worth spending a minute on the methodology. Concerns about B-vitamin supplements and cancer have been percolating for years. They came up quietly in a large trial in Norway that concluded ten years ago. Starting in 1998, researchers assigned 6,837 people with heart disease to take either B vitamins or a placebo.
The researchers then watched as people died and contracted diseases in ensuing years—and the vitamin group raised concerns. In 2009, the researchers reported in the Journal of the American Medical Association that taking high doses of vitamin B12 along with folic acid (technically vitamin B9) was associated with greater risk of cancer and all-cause mortality.
Using more than 55 micrograms daily appeared to quadruple cancer risk.
The largest increase in cancer risk was in the lung. Still, the number of cases of lung cancer among these 6,837 Norwegians was relatively small—so the actual risk was difficult to quantify. But it was big enough to catch the attention of Theodore Brasky and Emily White, two researchers at the Fred Hutchinson Cancer Research Center in Seattle. White had been overseeing a cohort study that involved more than ten times as many people as the Norwegian trial, some 77,000 people across the state of Washington. The cohort is tracking their supplement intake as we speak, and it is also being followed for cancers by the National Cancer Registry.
Lung-cancer risk among men who took 20 milligrams of B6 daily for years was twice that of men who didn’t. Among people who smoke, the effect appeared to be synergistic, with B6 usage increasing risk threefold. The risk was even worse among smokers taking B12. Using more than 55 micrograms daily appeared to almost quadruple lung-cancer risk.
There was no apparent risk among women—which is not to say it doesn’t exist, only that it wasn’t apparent.
Why or how would B vitamins increase a person’s risk of cancer?