High levels of Vitamin B12 may be too much of a good thing.
Vitamin B12 is an essential nutrient, important in nerve and blood cell health, and most people obtain enough of it in food. Those with B12 deficiency, or an inability to absorb it, can use supplements.
But a study in JAMA Network Open suggests that very high blood levels of vitamin B12 may be life-threatening.
Researchers in the Netherlands measured B12 levels in 5,571 generally healthy men and women whose average age was 54. None were taking supplements. They followed them for an average of eight years.
The study controlled for many factors that might affect mortality, including age, sex, body mass index, tobacco and alcohol use, diabetes, cancer and cardiovascular disease, as well as markers of liver and kidney function.
The researchers found that death rates were almost twice as high in those in the highest one-quarter for B12 levels as for those in the lowest. The reasons are unclear.
“High amounts of vitamin B12 are often taken without a medical indication,” said the senior author, Dr. Stephan J.L. Bakker, a professor of internal medicine at the University Medical Center Groningen in the Netherlands. Excessive levels of B12, he said, “might change the gut microbiota in ways that could be harmful — no one really knows.”
Still, Dr. Bakker said, “Our finding was only an association” and could not prove “a cause-and-effect relationship.”