Not all vitamins are good for you...

Bad news for the vitamin industry.

A study published in Archives of Internal Medicine examining the use of vitamin and mineral supplements among 38,772 postmenopausal women over a 19 year period found that copper supplements and high-dose iron supplements actually caused a statistically significant increase in mortality. Daily multi-vitamins, vitamin B6, folic acid, magnesium, and zinc were also found to cause a slight increase in the mortality rate.

Use of a daily calcium supplement, on the other hand, was associated with a lower risk of death.

Absolute increases in risk were low, and ranged from 2.4% with multivitamins to 18% with copper. Use of calcium supplementation was associated with a 3.8% lower risk of death.

The mortality risk associated with iron supplementation increased in a dose-dependent manner, rising with doses more than 200 mg/day, and highest for doses more than 400 mg/day.

"Based on existing evidence, we see little justification for the general and widespread use of dietary supplements," the authors wrote. "We recommend that they be used with strong medically based cause, such as symptomatic nutrient deficiency disease."

Taking dietary supplements to hopefully improve health and prevent diseases is widespread in the U.S., with about half of American adults using supplements, according to the study authors. Annual sales of supplements exceed $20 billion.

Editor's note: Eat a healthy diet. Save your money. Older women should take calcium.