Taking vitamins to prevent health problems and disease may not be helpful in the long-run, according to a couple of studies this week — and in some cases it may even harm you.

Research questioning the effectiveness of vitamin supplements has surged in recent years. But what's the deal with vitamin supplements? Why are they under scrutiny, and when can they be good for you?

One recent study found that older men taking the recommended daily dose of vitamin E had an increased risk of having prostate cancer. Roughly 35,000 healthy men partook in the experiment, which required taking selenium, vitamin E, both or a placebo for 7 years. Out of every 1,000 participants, 76 men from the vitamin E group developed prostate cancer, compared to 65 taking a placebo. This 17 percent increased risk wasn't due to chance, scientists say, and may point to vitamin E supplements.

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Vitamin E in foods is thought to minimize cell damage that might turn into cancer. Medical recommendations usually center around one form of the vitamin, alpha-tocopherol, which can be absorbed from foods such as nuts, seeds and some vegetables. Research has shown that the lab-made version of the nutrient boasts only half of effectiveness of its naturally-occurring form in foods.

Other controlled trials have shown the pill form of the vitamin fails to measure up in preventing diseases and might contribute to death if taken at high doses.

Since the risk of developing prostate cancer also increases with age, men might want to reconsider taking vitamin E supplements or bring up their concerns to their doctors, researchers said in a press release for the government-funded study.

Another analysis looked at vitamin and multivitamin use in older women. The team discovered a relationship between taking certain supplements with an increased chance of death. Using data from the Iowa Women's Health Study, researchers looked at the health of more than 38,000 women, most around 60 years old, on three occasions in the 80s, 90s and after 2000.

Women who took multivitamins, vitamin B6, folic acid, iron, magnesium, zinc or copper had a slightly higher risk of dying than those not taking the vitamins. It's suggested that taking these vitamins may have toxic effects over time, especially if the women taking them don't have deficiencies.

Vitamins are a hot commodity, as U.S. adults pay more than $20 billion for multivitamins each year, according to one USA Today article.

But pinning the outcomes on vitamins alone would be difficult for both studies, and researchers think other studies are needed to find out more.

Should you take vitamins, even a multivitamin?

Opinions are mixed, but evidence shows a lack of long-term benefits.

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People with well-tracked vitamin deficiencies should listen to their doctors about taking supplements and finding ways to ingest more of the vitamin naturally. The idea isn't to give up micronutrient vitamins if you have a demonstrated need for them; it's to think twice about using them in lieu or in addition to nutritious foods. For some people, especially pregnant women, certain vitamins such as folic acid are still recommended.

"There really is not any compelling evidence that taking these dietary supplements above and beyond a normal dietary intake is helpful in any way, and this is evidence that it could be harmful," one researcher involved in the prostate cancer study told The New York Times. Another MyHealthNewsDaily article covering the women's multivitamin study sided against "the more, the better" type of reasoning with supplements.

A USA Today interview with two vitamin experts suggests that few studies show a relationship between vitamin use and increased risk of death, but many fail to show positive long-term pay-offs for supplements.

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