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.