Hardly a month goes by without a study suggesting that the omega-3 fatty acids in fish oil can fend off disease - including heart attack, stroke, Alzheimer's disease, depression, rheumatoid arthritis, asthma, psoriasis and even attention-deficit hyperactivity disorder.
The problem is, to get the health benefits seen in clinical trials, you probably need to take fistfuls of the capsules.
"The kind of benefits seen in most of the clinical trials with omega-3 generally have involved much higher doses than you see recommended on supplement labels," says Charles Serhan, a Harvard Medical School expert on omega-3's activity.
"But although a large number of studies have used 'industrial-level' doses," he adds, "we don't have rigorous scientific evidence about what the doses should be."
Regardless of the recommended dose, hundreds of foods are being fortified with omega-3. And research is showing ways of enhancing the omega-3 benefits with other therapies.
The National Institutes of Health concluded after a massive review three years ago that consuming omega-3 fatty acids cuts the risk of death from heart attacks and other cardiovascular causes, can reduce the joint pain of rheumatoid arthritis and "appears" important for proper brain development and function.
Because of news like that, the market for fish-oil supplements is booming.
U.S. omega-3 supplement sales reached an estimated $600-million last year, up 20 percent from a year earlier, says the trade group Global Organization for EPA and DHA Omega-3s. (The two key omega-3 fatty acids are called EPA and DHA.)
Omega-3 fatty acids rank as the fifth-bestselling dietary supplement, behind multivitamins, calcium and vitamins C and E.
In trials aimed at lowering high blood levels of triglycerides, a contributor to heart disease, patients took four particularly potent capsules that contained a total of more than 3 grams of EPA and DHA a day.
You would have to pop a dozen of the typical omega-3 capsules on the market to get that much - four to six times the suggested daily dose usually specified on their labels.
That many capsules could cost you more than $2 a day, and it is a lot more than you are likely to get from consuming fish: You would need more than six servings a day of tuna, or about three of salmon, to get that much EPA and DHA.
The omega-3 doses used in the studies have varied widely.
- Heart disease: 1 gram or more.
- Rheumatoid arthritis: 2 grams or more.
- Brain health: 1/2 gram or more.
Fish is good for you, but you also can get risky doses of mercury and other toxins by consuming lots of fish.
The suggested capsule dose is 2 to 4 grams of EPA and DHA a day, which supplements can provide toxin-free.
For healthy adults seeking merely to cut cardiac risks, the heart association says eating fatty fish, such as salmon, at least twice a week is probably enough.
But how much omega-3 should you take if you are trying to ease the joint inflammation of rheumatoid arthritis? Or ward off Alzheimer's disease?
There aren't enough clinical data to give firm answers. But the omega-3 literature affords hints:
Results in various rheumatoid arthritis trials indicate that you need to take more than 2 grams - perhaps 10 typical capsules - of omega-3 fatty acids a day to significantly curtail joint inflammation and pain.
For maintaining brain health, overall data on omega-3's potential are inconclusive, according to the NIH. But a recent Dutch study showed that about 400 milligrams of EPA and DHA a day - which you can get from two typical omega-3 capsules - helped elderly men maintain mental acuity.
All this suggests that you may have to take at least six pills a day to get the benefits observed in clinical trials with fish oil.