Millions of Americans spend billions of dollars on vitamin combinations, presumably to boost their health and fill gaps in their diets. But while people who don't eat enough of certain nutrients may be urged to get them in pill form, the government doesn't recommend routine vitamin supplementation as a way to prevent chronic diseases.
The studies released Monday are the latest to test if multivitamins might go that extra step and concluded they don't.
"Evidence is sufficient to advise against routine supplementation," said a sharply worded editorial that accompanied Monday's findings in the journal Annals of Internal Medicine.
After all, most people who buy multivitamins and other supplements are generally healthy, said journal deputy editor Dr. Cynthia Mulrow. Even junk foods often are fortified with vitamins, while the main nutrition problem in the U.S. is too much fat and calories, she added.
But other researchers say the jury's still out, especially for the country's most commonly used dietary supplement - multivitamins that are taken by about a third of U.S. adults, and even more by people over the age of 50.
Indeed, the U.S. Preventive Services Task Force is deliberating whether vitamin supplements make any difference in the average person's risk of heart disease or cancer. In a draft proposal last month, the government advisory group said for standard multivitamins and certain other nutrients, there's not enough evidence to tell. (It did caution that two single supplements, beta-carotene and vitamin E, didn't work). A final decision is expected next year.
"For better or for worse, supplementation's not going to go away," said Dr. Howard Sesso of Brigham and Women's Hospital in Boston. He helps leads a large multivitamin study that has had mixed results - suggesting small benefits for some health conditions but not others - and says more research is needed, especially among the less healthy.
Still, "there's no substitute for preaching a healthy diet and good behaviors" such as exercise, Sesso cautioned.
As scientists debate, here are some questions and answers to consider in the vitamin aisle:
Q: Why the new focus on multivitamins?
A: Multivitamins have grown more popular in recent years as research showed that taking high doses of single supplements could be risky, such as beta-carotene.
Multivitamins typically contain no more than 100 percent of the daily recommended amount of various nutrients. They're marketed as sort of a safety net for nutrition gaps; the industry's Council for Responsible Nutrition says they're taken largely for general wellness.
Q: What are the latest findings?
A: With Alzheimer's on the rise as the population ages, Harvard researchers wondered if long-term multivitamin use might help keep older brains agile. They examined a subset of nearly 6,000 male doctors, age 65 or older, who were part of a larger study. The men were given either multivitamins or dummy pills, without knowing which they were taking.
After a decade of pill use, the vitamin-takers fared no better on memory or other cognitive tests, Sesso's team reported Monday in the journal Annals of Internal Medicine.
Q: Did that Harvard study find any other benefit from multivitamins?
A: The results of the Physicians Health Study II have been mixed. Overall it enrolled about 15,000 health male doctors age 50 and older, and the vitamin-takers had a slightly lower risk of cancer - 8 percent. Diet and exercise are more protective. They also had a similarly lower risk of developing cataracts, common to aging eyes. But the vitamins had no effect the risk for heart disease or another eye condition, Sesso said.
Q: Might vitamins have a different effect on people who already have heart disease?
A: As part of a broader treatment study, a separate research team asked that question. They examined 1,700 heart attack survivors, mostly men, who were given either a special multivitamin containing higher-than-usual doses of 28 ingredients or dummy pills. But the vitamins didn't reduce the chances of another heart attack, other cardiovascular problems, or death.
Q: What about women?
A: Research involving postmenopausal women a few years ago also concluded multivitamins didn't prevent cancer or heart disease. But it wasn't nearly as rigorous a study as Monday's research, relying on women to recall what vitamins they used.
Q: What's the safety advice for multivitamin users?
A: The preventive services task force cited no safety issues with standard multivitamins. But specialists say to always tell your doctor what over-the-counter supplements you use. Some vitamins interact with some medications, and Sesso said anyone worried about nutrition should be discussing their diet with their doctor anyway.