It's been a tough week for vitamins. Researchers published back-to-back studies this week suggesting that daily diet supplements have few benefits and could even be harmful.
The findings leave many people wondering if taking a daily diet supplement is a good idea.
One study found that older women who take daily diet supplements of iron, copper, magnesium and other vitamins faced a slightly higher risk of death than women who did not. Researchers at the National Cancer Institute (NCI) published another study linking daily intake of vitamin E to a 17 percent greater risk of prostate cancer.
So should people really be taking vitamins?
Experts say some people should. Pregnant women or people with specific vitamin deficiencies can benefit from adding vitamins to their diets.
But other healthy people take vitamins believing that they can help prevent disease or simply maintain health.
In the past few decades, scientists have conducted multiple studies investigating how supplemental vitamins affect a person's risk of heart disease, cancer, dementia and other chronic conditions.
Dr. Steve Nissen, chairman of cardiology at the Cleveland Clinic, said the evidence showing that supplements actually help with those conditions has been scarce.
"The concept of multi-vitamins was sold to Americans by an eager nutraceutical industry to generate profits. There was never any scientific data supporting their usage," he said.
Dr. Lee Green, a family physician at the University of Michigan, said it's a misconception that supplemental vitamins can lead to better health and help prevent disease.
"You should stop trying to look for health in a pill," Green said. "Health is not found in pills. It's found in good food and regular exercise. Why didn't vitamins deliver on the promise of better health? Because it was a false promise."
Duffy MacKay is the vice president for scientific and regulatory affairs for the Council for Responsible Nutrition (CRN), an industry group representing supplement manufacturers. He said scientists usually aren't willing to give vitamins a chance.
"Basically these researchers would rather wait till we all get scurvy before acknowledging any need for supplemental nutrients," MacKay said, in a CRN statement.
He added that most consumers shouldn't and don't view vitamins as a magical cure for all their ills.
"Dietary supplements are commonly taken to help prevent chronic disease," MacKay said. "In other words, dietary supplements should not be expected, in and of themselves, and without the synergy of other healthy habits, to prevent chronic disease."
Dr. David Katz, director of the Yale University Prevention Research Center, said the main problems with taking diet supplements are uncertainties and misunderstandings about the proper dose and combination of these vitamins. People often take large doses of vitamins, believing that if the small amounts of nutrients in foods are good, than a lot of them must be better.
"We know that nutrients are beneficial in foods, but divorced of that context, and packaged somewhat 'arbitrarily' by us, the effects may be very different," Katz said. "Imagine if you had all the right materials to build a house but in all the wrong proportions, and then tried to put together a well-built house."