You may have seen a concerning headline recently about dietary supplements. Research presented at the American Association for Cancer Research Annual Meeting suggested that taking supplements doesn’t curb cancer, and taking more than needed may actually drive up cancer risk. Specifically, researchers concluded that “taking more than the recommended daily allowance of folic acid, Vitamin E and beta-carotene were all shown to increase cancer risk.

The interest in research on supplements and cancer began 20 years ago, when scientists observed that people who ate more fruits and vegetables tended to have less cancer. Researchers wanted to find out if taking supplemental doses of vitamins and minerals would further reduce the chances of developing various forms of this disease.

They found that in some human studies, cancer risk actually increased while taking supplements. For example, beta-carotene supplements tended to up the risk of both heart disease and cancer in people who smoke or drink heavily; and folic acid–which was thought to help reduce the number of polyps in a colon–increased the number in one trial.

Scrutiny has also been directed at supplements recently for findings about products being mislabeled or even tainted. So what does all of this mean? Should you chuck your supplements? I don’t think so–at least not across the board–but there are common misconceptions that may translate into incurring more risks than benefits.

Here are three biggies I see, and my advice about how to be sure the supplements you take are right for you.

Supplements aren’t a fix for a bad diet

Optimal nutrition is multifaceted. It involves getting the right balance and amounts of protein, good fats, healthy carbs, fiber, fluid, vitamins, minerals, and antioxidants, and timing is also key. Simply popping a multivitamin or other supplements can’t possibly make up for an inconsistent diet or unhealthy habits, like regularly skipping meals or overeating. To really protect your health, it’s all about the big picture. Here’s an analogy I sometimes use with clients: if your car’s engine is overheating and the transmission is shot, pumping in premium gas won’t make it run smoothly.

More isn’t always better

If vitamin C helps support immunity, it may seem like megadoses would offer even more protection. But the truth is overdoing it on nearly any nutrient can lead to health risks. Large supplemental doses of vitamin C can cause cramps and diarrhoea and under certain conditions, this antioxidant may act as a pro-oxidant and thus trigger DNA damage. Nearly anything you consume in an amount that far surpasses your body’s needs may create risk. While it’s rare, this is true even for water (it’s called water intoxication). Balance–no shortfall and no surplus–is always optimal.

Natural can be harmful

One myth I hear often is that natural substances can’t possibly be harmful. Clearly excess can be dangerous, but natural substances can also carry risks even in moderate doses. For example, kava, often used as a sleep aid or to reduce anxiety, has been linked to liver toxicity; St. John’s wort, used for depression, interacts with several medications including birth control pills, and can decrease their effectiveness; and yohimbe, touted as an aphrodisiac, has been tied to high blood pressure, anxiety, dizziness, nervousness, and sleeplessness.

The bottom line

I don’t believe that all supplements are a waste of money. But I do believe that they should be used, as their name indicates, as supplements to an overall healthy diet, or when it would difficult to obtain the amount you need from food alone, which is often the case for vitamin D, probiotics, or omega-3 fatty acids. I also believe that a supplement regime should be highly personalized. There should be clear benefits without unnecessary risks, which means careful consideration to how much and how often they’re consumed, as well as any potential interactions with existing health conditions, personal and family medical history, over-the-counter and prescription meds, and other supplements. How do you figure all of this out? Talk to your doctor, or consult with a registered dietitian nutritionist. For supplementation, one size definitely does not fit all.