Thousands of scientific studies have investigated the actions of omega-3 fatty acids on the body and mind, with an emphasis on the heart, brain, lungs, joints, and immune system. The omega-3s decrease inflammation, the source of many chronic diseases. They thin the blood, helping prevent the blood clots that can cause heart attack and stroke. They slow down heart rate, reducing lifetime stress on the heart. And they make the membranes of brain cells more flexible, aiding cognition.

The overall conclusion these studies have generated is definitive: An optimal intake of omega-3s throughout life can help reduce your risk for many diseases.

But if you listen to the news, you may come away with a very different impression: that increasing your intake of omega-3s through diet or supplementation will have little or no effect on your health. So let’s first look at why there is conflicting information.

Evolving research

In the 1970s, researchers found that Greenland Eskimos with a high intake of omega-3s were uniquely protected against heart disease—even though their diet was very high in fat. In subsequent decades, many clinical trials showed that increasing the daily intake of omega-3s through diet or supplementation reduced the risk for heart disease. But in the 2000s, a few clinical trials showed that omega-3 supplementation didn’t have much effect.

There are many possible reasons why these studies didn’t show a benefit. The participants took very low doses of omega-3. The studies were too short. The people in the studies often already had heart disease and were taking medications that significantly reduced risk—so adding omega-3s to the equation didn’t make that much difference. Bottom line: While some studies have shown that omega-3s have no effect, researchers who look carefully at the preponderance of evidence on omega-3s have come to a different conclusion.

Good for your heart

FORCE stands for Fatty Acids and Outcomes Research Consortium, a collaborative group of more than 50 scientists from Tufts University, Harvard Medical School, UCLA, and other leading institutions. Each member of the group has been involved in analyzing health data from one or more cohorts—large groups of people who have been studied for 10, 20, or more years. In these observational studies using FORCE data, people with the highest blood levels of omega-3s have a lower risk of:

  • heart disease and stroke (6 percent and 22 percent)
  • type 2 diabetes (19 percent)
  • chronic kidney disease (13 percent)
  • dying from any cause (15 percent)

In a recent clinical study, published in the New England Journal of Medicine, people who took four grams a day of eicosapentaenoic acid (EPA) had a 25 percent reduced risk of cardiovascular events (unstable angina, coronary angioplasty, coronary bypass surgery, heart attack, stroke, and death from heart attack or stroke).

A study in the Proceedings of the Nutrition Society summed up the evidence on omega-3s and cardiovascular disease: “Taken together, the evidence is strong for a cardioprotective effect of EPA and DHA [docosahexaenoic acid], especially when consumed in sufficient amounts to raise blood levels into healthy ranges.”

More benefits

Additional research shows many other ways omega-3s may help prevent and reverse health problems.

Alzheimer’s disease (AD). In a seven-year study of nearly 1,500 people ages 65 and older, those with the highest blood level of DHA had a 49 percent lower risk of developing AD, compared with those with the lowest level. And those with the highest level of omega-3s had an onset of AD that was nearly 5 years later than those with the lowest. Increasing one’s dietary intake of DHA is a potential strategy “to prevent or delay AD,” the researchers concluded in the June 9, 2022, issue of Nutrients.

Osteoarthritis. In a six-month study published in the American Journal of Clinical Nutrition, people with mild to moderate knee arthritis who took an omega-3 supplement (krill oil) had a greater improvement in knee pain, knee stiffness and everyday physical function compared with people taking a placebo.

Lung disease. In a study in the American Journal of Epidemiology, people with chronic lung disease who had the highest levels of DHA were 31 percent less likely to be hospitalized for the disease, and 32 percent less likely to die of the disease. Additionally, CT scans showed they had 35 percent fewer lung abnormalities.

Depression. A study in Frontiers of Psychiatry, published on July 28, 2023, analyzed 36 other studies on depression and levels of omega-3, and found that low levels were a risk factor for major depression, postpartum depression, and bipolar disorder.

COVID-19. Using data from the UK Biobank, a very large observational study in the UK, researchers found that people who had the highest blood levels of omega-3 were 21 percent less likely to test positive and 26 percent less likely to be hospitalized with COVID-19. There was also a trend for lower risk of death from COVID.

Aging. A 2021 study in the American Journal of Clinical Nutrition showed that people with the highest blood levels of omega-3s live an average of 4.7 years longer than people with the lowest levels—the same amount of “extra” years you get from being a nonsmoker.

Optimizing intake

The simplest and most accurate way to tell if your intake of omega-3s is optimal is with the “Omega 3 Index”—a test that measures the percentage of omega-3s in the membranes of red blood cells. A level of 8 percent to 12 percent is optimal. A level below 4 percent puts you at high risk for many diseases, including cardiovascular disease (heart disease and stroke). A level between 4 and 8 percent puts you at medium risk.

Fortunately, it’s easy to increase omega-3 blood levels with two simple strategies.

Eat more fatty fish. Eat two or more servings of fatty fish per week. To remember which fish to eat, use the acronym SMASH: sardines, mackerel, anchovies, salmon, and herring. And don’t forget about albacore tuna, which is twice as high in omega-3 as chunk light tuna. Many fish (and other types of seafood) have virtually no omega-3, like catfish, cod, tilapia, shrimp, and lobster. Most Americans get about 150 milligrams (mg) a day of omega-3s, but this can be boosted to 500 to 1,000 mg daily by eating more SMASH fish.

Take an omega-3 supplement. In a 2021 study in Nutrition Research, the only people consuming two or more servings of fatty fish a week who had an Omega 3 Index above 8 percent were also taking an omega-3 supplement delivering a daily average of 1,100 mg of EPA and DHA. For people who don’t eat fish, a supplement delivering an average of 1,300 mg was sufficient to boost levels to 8 percent.

But double check the details on the label. Many supplements show they deliver 1,000 or so milligrams of fish oil—but far less EPA and DHA. Make sure you’re getting at least 1,000 mg daily of combined EPA and DHA. Aim for a 50-50 ratio of EPA to DHA, or 60 to 40, or 40 to 60.

There are various forms of fish oil—triglyceride-based oil, ethyl esters, re-­esterified triglycerides, and others—with various degrees of concentration. (For example, triglyceride-based oil has 30 percent EPA/DHA and 70 percent other fatty acids).

There’s a lot of hype about which forms are best. But, again, when it comes to a fish oil supplement, the basics are what really matters: Make sure you’re getting around 1,000 mg of EPA/DHA daily.

Fish oil is not the only choice. Krill are marine crustaceans, and krill oil is rich in omega-3s. Microalgae can make EPA and DHA from sunlight, carbon monoxide, and water, and algae-based omega-3 supplements are available.

Don’t rely on plant sources of omega-3s. Alpha-linoleic acid is a plant-based form of omega-3 that turns into EPA and DHA in the body. But the conversion level is very low. To boost omega-3s effectively, you must consume EPA and DHA directly.

Measure your omegas

Eating fatty fish regularly and taking an omega-3 supplement daily is the best way to boost levels into the optimal range. But for maximum certainty, get an omega-3 blood test, ideally one that measures EPA+DHA in the red blood cells like the Omega-3 Index.

Omega-3 and Bleeding Risk

Because omega-3s thin the blood, and because there was anecdotal evidence that Eskimos had a propensity for excessive bleeding, doctors began to warn surgical patients not to take the supplement before surgery, and also told patients on blood thinners that the supplement was contraindicated. These precautions are unwarranted. According to the FDA, an intake of omega-3s as high as 4 grams daily does not increase the risk for clinically significant bleeding. Adding omega-3 supplements to blood-thinning medications does not increase the risk of bleeding. People with higher omega-3 blood levels bleed less during surgery. Bottom line: More current research debunks the idea that omega-3s increase bleeding.

What About the Mercury in Fish?

You may have read that the amount of mercury in fish makes it inadvisable to eat fish regularly. Only four types of fish contain significant amounts of mercury, and they’re rarely eaten: shark, swordfish, king mackerel, and tilefish. And even if there are small amounts of mercury in fish, the benefits of consuming omega-3s far outweigh any possible negative effect from mercury.

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