Dietary supplements may seem like a smart way to optimize our health, yet too many of us are taking a haphazard approach to pills and powders that may not help and can potentially even hurt, experts say.

Dietary supplements are a $37 billion-a-year business in the U.S., according to the National Institutes of Health. Some of this consumption is medically necessary, even lifesaving. And yet, for every person who takes a supplement that’s medically warranted, experts say more of us are taking something because our neighbor or colleague swears by it.

For those looking to science for guidance, it can be confusing when a new study comes out and a nutrient that was seen as beneficial one day is questioned the next. “Medicine is an art as well as a science, and through the years we’ve made a lot of mistakes,” said Dr. Roxanne B. Sukol, medical director, Wellness Enterprise at the Cleveland Clinic.

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Sukol says that she doesn’t let a single scientific study sway her practice. Instead, she looks for themes and corroboration from additional studies in reputable publications such as JAMA and the New England Journal of Medicine.

Sukol and other doctors say that while the supplement literature continues to evolve, a nutritious diet will never go out of style. “There’s no question that diet is very important,” said Dr. Emily Chew, deputy director of the division of epidemiology and clinical applications at the National Eye Institute of the National Institutes of Health. “We are what we eat.”

The food we eat affects our bodies differently than supplements for a number of reasons. For starters, a nourishing diet is made up of many different nutrients that interact with one other in beneficial ways, whereas a supplement is often one element in isolation.

What’s more, supplements are usually made up of a vitamin, mineral or other nutrient in a higher dose than we would get from food. “Too much of just about any nutrient is a problem,” said Dr. Tod Cooperman, president of ConsumerLab.com, a White Plains, N.Y.-based independent firm that tests supplement quality and tracks research on nutritional products. Those who do take supplements shouldn’t exceed the dose recommended on the bottle, Cooperman said.

Federal oversight of supplements is less stringent than it is for prescription drugs. Supplement manufacturers generally do not have to prove the safety and effectiveness of their product before it is sold to the public. Consumers should also keep in mind that most supplement formulas on the market have not been clinically tested as packaged by the manufacturer, Cooperman said.

The benefits of a healthy diet, on the other hand, are indisputable. But that doesn’t mean that we have to come home from a long day’s work and cook a three-course dinner. Slow cookers make meals easy and economical. Put one onion, one can of whole tomatoes and a cup of white beans into a crockpot with water, and “eight hours later, you have something delicious to eat,” Sukol said.

Below are some considerations to weigh with popular supplements. Some of these might interact with prescription drugs in negative ways — or they might be harmful on their own given your particular circumstances —so it’s important to tell your doctor what supplements you’re taking. “As a general recommendation, if you take a pill every day for any reason, it’s a good idea to talk to a doctor about it,” said Dr. Martin Dalin, cancer researcher at Memorial Sloan Kettering Cancer Center in New York City.

Omega- 3

Omega 3 is an essential fatty acid that we need to consume because our bodies don’t make it, Sukol said. This fat is an integral part of cell membranes, yet its role in preventing and slowing the progression of diseases remains under debate.

While some studies have found that omega-3 fats have helped lower blood pressure and maintain a regular heart rhythm, a review of randomized clinical trails published in JAMA in 2012 found that omega-3 supplementation was not associated with a lower risk of death from heart attack, stroke and other cardiovascular events.

Separately, in results published last year in JAMA, a large, long-running trial found that omega-3 supplements didn’t slow cognitive decline or slow the progression of macular degeneration, a major cause of vision loss among older Americans.

That randomized clinical trial followed more than 3,000 participants over five years. Randomized trials are generally considered the most rigorous; to isolate the effect of whatever is being studied, subjects are randomly assigned to one group or another. What’s more, for the duration of the study neither the participants nor the researchers knew who was taking omega-3s and who was taking a placebo, another sign of rigorous methodology.

The findings questioned the use of omega-3 supplements to improve cognitive function and slow the progression of eye disease, said Chew, who led research on that study. That doesn’t mean that people should eschew eating fish, a dietary source of omega-3s and a low-fat, high-quality protein packed with vitamins and minerals. “What in fish is so important?” Chew said. “Maybe we haven’t captured it yet — maybe it’s not the omega-3.”

Probiotics

Probiotics are a type of so-called “good bacteria” that live in our intestines. Probiotic supplements — as well as the probiotics found in some yogurts and other foods — have been found in some studies to alleviate the symptoms of inflammatory diseases such as rheumatoid arthritis and irritable bowel syndrome.

Probiotics are also thought to help restore friendly bacteria to people whose intestinal stores have been depleted through antibiotic use. Yet a large-scale study published in the Lancet in 2013 found that giving probiotics to adults 65 and older on antibiotics didn’t lower the risk of diarrhea compared to subjects who took a placebo.

Food sources of probiotics include some yogurts and also fermented foods such as sauerkraut and kimchi. (Much of American yogurt is packed with enough sugar to offset the benefits of the probiotic, so gravitate toward less-sweetened varieties for the maximum benefit, Sukol said.)

Those considering a probiotic supplement should ask their doctors which of the bewildering array of strains might be most beneficial to them. While probiotic use is generally not associated with serious side effects, some patients, including those with compromised immune systems, may be advised to proceed with caution.

Anti-oxidants

Anti-oxidants have been thought to help prevent cancer by saving normal cells from DNA damage, but recent research has challenged the benefits of anti-oxidant supplements. One study, published last fall in Science Translational Medicine, found anti-oxidant supplements caused cancer to spread in mice with malignant melanoma, a dangerous skin cancer.

A separate study last year out of the Children’s Research Institute at UT Southwestern in Dallas, Texas had similar findings.

More research is needed to fully interpret the studies’ results, said Dalin of Memorial Sloan Kettering Cancer Center, who worked on the research published in Science Translational Medicine while at the University of Gothenburg, Sweden. His working theory is that, if anti-oxidants save normal cells from DNA damage, they are also saving the cancer cells, causing them to spread. “On a personal level, I would tell cancer patients to be very careful about taking anti-oxidants,” Dalin said.

Even those who think they are cancer-free should approach anti-oxidant supplements with caution, Dalin said. An undetected cancer could potentially become more aggressive with supplement use. And if there isn’t definitive research that anti-oxidants supplements cause cancer to spread, there also isn’t definitive research that they help prevent the disease, Dalin said.

Glucosamine and chondroitin

Glucosamine and chondroitin are components of healthy cartilage, and supplements containing both are popular among those with osteoarthritis. Even so, there isn’t robust research supporting their effectiveness. A long-term study published in 2010 found that those who took glucosamine and chondroitin supplements to treat knee pain from osteoarthritis experienced results similar to those who took a placebo.

Those experiencing joint pain should try movement before supplements, Sukol said. Exercise can help lubricate the joints. “If you don’t use it, you lose it,” Sukol said. Those still experiencing pain after exercising as their doctor recommends could try glucosamine and chondroitin pills for a month and see if they provide any relief, Sukol said.