When it comes to vitamins, it appears you could have too much of a good thing, say researchers.

研究人员称，就维生素而言，服用太多也不是好事。

Experts have suspected for some time that supplements may only be beneficial if a person is deficient¹ in a nutrient².

And excess may even harm, as the study in Archives of Internal Medicine finds.

All of the women, in their 50s and 60s, were generally well nourished yet many had decided³ to take supplements.

Multivitamins, folic acid（叶酸） , vitamin B6, magnesium⁴（镁） , zinc⁵, copper⁶ and iron in particular appeared to increase mortality risk.

The researchers believe consumers are buying supplements with no evidence that they will provide any benefit.

Harms vs gains

They are quick to stress that their study relied on the 38,000 US women who took part in it recalling what vitamins and minerals they had taken over the previous two decades.

And it is difficult to control for all other factors, like general physical health, that might have influenced the findings.

But they say their findings suggest that supplements should only be used if there is a strong medically based cause for doing so because of the potential to cause harm.

"Based on existing evidence, we see little justification⁷ for the general and widespread use of dietary supplements," Dr Jaakko Mursu of the University of Eastern Finland and his research colleagues said.