Women taking multivitamins don't live longer than those who get their nutrients from food alone, according to a US study that found they in fact appear to have slightly higher death rates.
About half of adult US residents take dietary supplements, and the industry now boasts of annual sales as high as $20bn (¤14.6bn). Yet research suggests that some of the largely unregulated substances, such as vitamins A and E, could be harmful in high doses, according to an editorial published with the study in the Archives of Internal Medicine.
"There is very little evidence showing that common dietary supplements would be beneficial in prevention of major chronic diseases," said Jaakko Mursu of the University of Minnesota in Minneapolis.
"Unless you are deficient, there is hardly any reason to take them," he said.
Mursu and his colleagues used data from nearly 39,000 older women who participated in the Iowa Women's Health Study and filled out questionnaires starting in 1986.
The survey asked about use of multivitamins, vitamins A, C, D and E as well as beta-carotene, B vitamins and minerals such as calcium, copper, magnesium, selenium and zinc.
Only calcium supplements were linked to a lower risk of death over 19 years of follow-up, with 37pc of users dying compared with 43pc of non-users.
By contrast, women taking other supplements did not live longer.
Mursu also cautioned that his study doesn't prove supplements cause harm.
"I would rather conclude that there is no evidence for benefits," he said.