Fish oil Buying Guide

Getting started

People are snapping up more fish-oil supplements than ever. They're taking them to treat a long list of ailments: menstrual cramps, heart disease, asthma, bipolar disorder, high blood pressure, depression, psoriasis, attention deficit hyperactivity disorder (ADHD), and pregnancy complications. But the supplements--made from mackerel, herring, and other fish rich in omega-3 fatty acids, especially EPA and DHA--aren't a cure-all. And based on our new tests, some of them aren't as pure as you might expect.

Who should take fish oil?

It could help people who have high levels of triglycerides, an artery-clogging fat that increases the risk of heart attack and stroke. Fish oil may reduce those levels by 20 to 50 percent. People who have coronary heart disease should also consider taking it. Fish oil may lower their risk of a second heart attack, possibly because it slows or slightly reverses hardening of the coronary arteries.

How much?

Those with high triglycerides may need as much as 4 grams of combined EPA and DHA from capsules a day, used under a doctor's care. People with heart disease should consume 1 gram of those two fatty acids a day, either from eating 3.5 ounces of fatty fish, such as salmon, lake trout, or sardines, or from capsules after consultation with a physician. Healthy people should protect against heart disease by eating fatty fish at least twice a week. But women who are or may become pregnant and nursing mothers should avoid eating fish that is high in mercury, such as shark, swordfish, and tuna, and should eat only up to 12 ounces of fatty fish a week.

Who else might benefit?

Although the evidence isn't overwhelming, the supplements may modestly lower high blood pressure, ease menstrual and rheumatoid arthritis pain, and improve the symptoms of ADHD and asthma in children. They might also help with osteoporosis, kidney disease, bipolar disorder, and Raynaud's syndrome, a disorder that affects the arteries to the fingers and toes.

Who shouldn't bother?

Fish oil is unlikely to lower blood sugar in people with type 2 diabetes or help gum infection, liver disease, migraines, allergic skin rashes, and stomach ulcers. There isn't enough evidence to say whether it protects against Alzheimer's disease, heart arrhythmia, depression, dry eyes, inflammatory bowel disease, chronic fatigue syndrome, pregnancy complications, or cancer.

Is fish oil fattening?

A capsule containing 500 milligrams of omega-3 fatty acids in 1 gram of oil has about 13 calories.

Who should never take it?

Fish oil is probably safe for most people in doses of 3 grams or less per day. Higher amounts might increase the risk of bleeding, increase LDL (bad) cholesterol, and impair immune function. And talk to your doctor before taking it if you have liver disease, bipolar disorder, depression, or diabetes, or if you take a blood pressure-lowering drug or a blood-thinning drug such as aspirin, or if you're getting chemotherapy treatments for cancer. (It's always a good idea to tell your doctor about all the supplements you take, whether you have one of those ailments or not.) Skip fish-oil supplements if you're allergic to fish or seafood, or if you have an implanted defibrillator to prevent irregular heartbeat.

Bottom line

Most people can get enough omega-3s by eating fatty fish--such as salmon and sardines, which are also low in mercury--at least twice a week. But people who have coronary heart disease require about a gram a day of those fatty acids, an amount that often requires taking a supplement. Check with a doctor before taking omega-3 pills because they can interact with some medications. Choose one listed under "met quality standards." Those cost anywhere from 17 to 64 cents a day for 1 gram of EPA and DHA combined, the amount the American Heart Association recommends for people with coronary heart disease.