If you had to guess the most-used natural product in the country, you might say melatonin, or maybe probiotics. It turns out, though, the answer is fish oil: According to the National Center for Complementary and Integrative Health, nearly 8% of adults take it. Whether you're among them, or you're thinking about buying a supplement, you may be curious about the exact benefits of fish oil—and whether there any downsides to popping a pill. So we put together this primer on what you should know, starting with its impressive range of possible health perks.

Fish oil may fight chronic inflammation

Oils extracted from fatty fish like sardines, anchovies, and mackerel provide two types of omega-3 fatty acids—eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA)—that are known to help lower inflammation, and generally improve inflammatory conditions in the body. Because chronic, low-grade inflammation is associated with premature aging and a number of diseases, fish-derived omega-3s may offer a broad spectrum of health protection.

It's thought to be heart protective

Fish oil might help boost bone density

In the typical American diet, it's common to consume far more omega-6 fatty acids—which are found in plant oils, like corn and sunflower oils—than omega-3 fatty acids, particularly DHA and EPA. That imbalance has been implicated as a culprit of low bone density in both men and women. But the good news is that older adults with higher omega-3 intakes have been shown to maintain greater bone density, making fish oil a potential mediator of age-related bone loss.

And support eye health

While study results are mixed, some research shows that fish oil may help lower the risk of age-related macular degeneration. This condition, which becomes more prevalent with age, results in the loss or distortion of the central field of vision.

Fish oil could lower child asthma risk

Research suggests that consuming fish oil during pregnancy may help reduce the risk of asthma in children. And one small study found that consuming fish oil during pregnancy reduced infant allergies. It’s important to note, however, that if you’re expecting, you shouldn't take fish oil on your own. Be sure to talk to your doctor about if it’s appropriate, and if so, the proper dosage and form.

It may even keep your brain sharp

In one study, fish oil improved cognitive performance in healthy adults between the ages of 51 and 72 in just five weeks, compared with the effects of a placebo. Research has also connected higher blood levels of omega-3s with a lower risk of depression and anxiety. What's more, when used as an adjunct to standard antidepressant therapies, fish oil supplementation is beneficial in the treatment of depression compared to a placebo.

And help you stay physically fit

Some research has linked omega-3s to fat loss. And supplemental fish oil has also been shown to slow the normal decline in muscle mass and function in men and women between 60 and 85. The good fats if fish oil also help to stimulate muscle protein growth, and improve muscle mass, even in sedentary older adults, and bolster resistance training-induced increases in muscle strength. Other research has demonstrated that fish oil may also have an indirect effect on weight management, by stimulating areas in the brain that control food intake.

But don't go overboard on fish oil

Given this long list of potential fish oil benefits, you may be ready to start gulping the stuff. But you can get too much of a good thing.

Fish oil has a blood thinning effect, so too much can increase bleeding risk, especially if it's combined with other blood thinners, like aspirin, or supplemental vitamin E, garlic, ginger, ginseng, ginkgo, and turmeric. Fish oil can also interact with some prescription medications, so be sure to discuss it with your doctor before you start taking a pill.

You may not even need a supplement if you eat fatty fish (like salmon, mackerel, or sardines) a few times a week. Ask your doctor or a registered dietitian if taking fish oil is appropriate for you.

Seek pro advice when choosing a product

Some experts recommend choosing a supplement that provides 1,000 mg of DHA and EPA combined daily. (If you're vegan or allergic to fish, there are plant-based options made from algal oil, the marine algae fish eat to produce DHA and EPA.) But I recommend working with your doctor or a registered dietitian to determine the right product, and ideal dose for your body’s needs. The only way to benefit from a supplement of any kind is to use it properly, and with the guidance of a knowledgeable health professional.

Cynthia Sass, MPH, RD, is Health's contributing nutrition editor, a New York Times best-selling author, and a nutrition consultant for the New York Yankees.