One of the most popular supplements on the market is fish oil. Celebrities and wellness gurus alike take it to make their hair thicker, their skin more supple, and their nails stronger. Doctors recommend it for its anti-inflammatory benefits: It can actually help reduce the risk of heart disease, cancer, dementia, symptoms of rheumatoid arthritis, and age-related macular degeneration, among other diseases, says Sydney Axelrod, a dietitian at the Mount Sinai Health System. "For people who are at high risk of developing cardiovascular disease, taking fish oil supplements for at least six months has been shown to reduce risk of heart-related events, such as a heart attacks, and even death," she says.

Omega-3 fatty acids are the star nutrients in fish oil that give them these healthful, anti-inflammatory benefits. In a nutshell, omega-3s are a group of polyunsaturated fats that the body doesn't make on its own, so it's essential to get them from food. There are three well-known types of omega-3s: alpha-linolenic acid (ALA), eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA). ALA can be found in nuts and plants, but EPA and DHA can only be sourced from fish. All three, however, are needed for healthy mental and physical functionand fish oil supplements can help increase DHA and EPA levels. However, these supplementsas with everythingare neither a magic pill nor a quick fix. Here, everything you need to know about fish oil supplements.

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"As with many supplements, there is a difference between getting the nutrient from its source and getting it extracted into a supplement," says Dr. Richard Firshein, founder of the Firshein Center for Integrative Medicine. "My advice is always to get nutrients from foods first. With fish, twice per week would be ideal. Salmon and sardines are the best source of omega-3s, without the risk of excessive mercury exposure," he says.

Choose your supplement wisely, since fish oils can be contaminated with mercury or heavy metals. An easy way to protect yourself? Use one that's pharmaceutical grade. Look for a "third-party tested" stamp on them, too (a popular third-party tester is GOED, the Global Organization for EPA and DHA Omega-3); it's essentially a stamp of approval for purity. "It shows the supplements are probably safe and actually contain what they say they do," Alexrod says. Ensure that your supplement contains about 1,000 milligrams of fish oil, with 180 milligrams of EPA and 120 milligrams of DHA, she explains, adding that Nutrigold Triple Strength Fish Oil Omega-3 Gold ($22.38, nutrigold.com)covers all of those bases.

Finally, Axelrod says to consider fish oil that is certified by the Marine Stewardship Council, the Environmental Defense Fund, or a similar organization, as "small fish with short lifespans tend to be more sustainable," she says. And don't forget to check the expiration date. "Omega-3s are prone to going rancid," she says. "Once they go bad, they will have a foul smell, and become less potent or even harmful." Make sure the supplement contains an antioxidant, like vitamin E, which will keep it fresh and help prevent oxidation, she adds.

"Omega-3s are essential nutrients for both mom and baby," says Perri Halperin, clinical nutrition coordinator at Mount Sinai. "Research has shown that including EPA and DHA in the diet during pregnancy has a positive effect on the cognitive development of the baby and reduces the risk of pre-term labor."

The anti-inflammatory properties in fish oil can protect hair follicles and reduce dryness and irritation, Dr. Firshein says. "Some studies have shown a positive relationship between omega-3 fatty acids containing supplements and hair health," Halperin adds. "However, these studies are limited and more research is needed to examine the effect of fish oil on hair growth."

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While Axelrod says the anti-inflammatory factor in fish oil may reduce acne in some people, in others, they may actually cause blemishes, Dr. Firshein warns. "Fish oils may interact with hormones, and this may create an imbalance that promotes acne in people who are predisposed," he says. "Other less understood factors may include reactions to bacteria in the gut, and excess oil or sebum production, which stimulate bacterial growth on the skin."

"Taking too much fish oil can lead to vitamin toxicities and an overdose of omega-3 fatty acids," Halperin says. "The FDA recommends no more than three grams per day of EPA and DHA combined, including up to two grams per day from dietary supplements." Side effects from over-supplementation can include bleeding problems, compromised immune function, nausea, vomiting, and diarrhea. (Plus, fish oils may thin blood, Dr. Firshein says, so if you have a history of bleeding disorders or stroke, be sure to discuss taking supplements with your doctor; take the same approach if you have a diagnosed fish allergy.)

"This is a relatively new concern as we continue to pollute the earth with plastics and marine life consumes them," Dr. Firshein says. "At this point, I wouldn't recommend people just taking a fish oil pill without understanding why they are taking them. But with current purification processes, we can be relatively assured there is a low risk of plastic exposure. We currently lack tests to determine the smallest molecules, however fish liver would most likely be contaminated the most."

As for mercury? Halperin says that one independent study regarding fish oil supplements found that all of the products tested contained only very low levels of mercury, ranging from one six parts per billion per serving, which is well below 100 parts per billion, the upper safety limit set by the Global Organization for EPA and DHA Omega-3s. Even if fish oil supplements don't do everything doctors hoped, "they're still an important supplement to consider for anyone concerned about their health," Dr. Firshein says.

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Here's Everything You Need to Know About Fish Oil Supplements - Yahoo Lifestyle