Taking vitamins seems like the easiest healthy choice you can make. But, recent research suggests that we don't know as much about them as we think: In a review study published in 2012 and discussed at a forum this week at the Annual Meeting of the American Association for Cancer Research, scientists revealed just how murky vitamin research can be. For instance, the pooled knowledge on antioxidants is contradictory. As explained in this review from way back in 1989, lower levels of carotenoids (essential precursors of vitamin A) are linked to an increased risk for cancer. However, other research shows that supplementing them in healthy people may not do much: A 2008 Cochrane review found that neither beta-carotene nor vitamins A, C, or E significantly prevented gastrointestinal cancer. Instead, taking antioxidant supplements was actually correlated with higher mortality risk overall. Another Cochrane review from 2012 found similar results. Of course, many of these studies are not necessarily correlational, so it's unclear whether the vitamins are truly to blame or if there's something else going on. For example, people who take more vitamins may already be dealing with less optimal health, which could make them more susceptible to other illnesses. And, the idea definitely sounds counterintuitive, especially because we know the value of eating our vitamin-packed fruits and veggies. But, it's an idea that's come up again and again. As we learned when we talked to Catherine Price, PhD, author of Vitamania, the truth is we're still learning a lot about isolated vitamins and nutrition in general. It's clear that supplements can be extremely helpful — nearly miraculous — when it comes to curing deficiencies. But, there's less evidence for what a little (or a lot of) extra vitamin D will do for someone who's already at a healthy level. This continuing line of research suggests that if you're not deficient, at best, you'll end up with expensive, neon pee. But, at worst, excess vitamins may actually do some harm. So, now might be the time to rethink (with a healthcare professional's advice, of course) those daily supplements.