Name the affliction—heart disease, Alzheimer’s, arthritis, depression, asthma—and omega-3 fatty acids can help prevent it.
That is the confusion being stirred up by new research on omega-3s, fats found in cold-water fish and plant oils that have intrigued nutrition scientists ever since the 1970s discovery that Greenland Eskimos rarely die from heart disease, despite a diet of fatty fish.
Some 21% of U.S. adults report using omega-3 fish-oil supplements, according to the Council for Responsible Nutrition, an industry trade group, making it the most popular supplement after multivitamins and vitamin D.
But last month, the Journal of the American Medical Association published a meta-analysis of 20 clinical trials involving nearly 70,000 people that found that omega-3 fatty acids didn’t prevent heart attacks, strokes or deaths from heart disease. Other recent studies in the New England Journal of Medicine and the Archives of Internal Medicine found that omega-3 supplements didn’t prevent heart problems in people with Type 2 diabetes or a history of heart disease.
Experts say such studies should be viewed with caution—just like studies with positive findings.
Critics noted that the JAMA study combined clinical trials that used different doses and sources of omega-3s. Many of the subjects were also on heart medication, which may have blunted the impact. Plus, diet studies are also notoriously imprecise. “It’s impossible for five researchers to control the diet of almost 70,000 patients over several years,” says Duffy MacKay, the CRN’s vice president for scientific and regulatory affairs.
What’s more, the JAMA authors imposed an unusually strict standard for statistical significance. Using the typical standard, the analysis would have concluded that omega-3 supplements are associated with a 9% reduction in cardiac deaths.
“My colleagues are writing letters to the editor about this,” said University of Pennsylvania nutritionist Penny Kris-Etherton, a spokeswoman for the American Heart Association. She says, for now, the association will continue recommending that everyone eat omega-3 rich fish at least twice a week; people with heart disease or high triglycerides could also consider taking fish-oil supplements under a doctor’s care. The American Psychiatric Association and the World Health Organization have similar advice.
Omega-3 fatty acids are essential for building cell membranes and maintaining the connections between brain cells. They also may reduce inflammation,increasingly recognized as a cause of chronic diseases.
Humans can’t produce omega-3 fatty acids, so we must get them from outside sources. The two most important kinds—EPA and DHA—are primarily found in fish such as salmon, sardines, tuna and herring; a third kind, ALA, is found in walnuts, flaxseed, soybean oil and some green vegetables, including Brussels sprouts, spinach and kale.
The typical American diet is far higher in omega-6 fatty acids, which come from corn and safflower oil and are plentiful in processed foods and cornfed beef and poultry. Some experts believe that reducing the ratio of omega 6s to 3s is even more important than increasing omega-3s, but the evidence is mixed.
Blood tests (typically $100 to $200) can measure the amount of omega-3s in red blood cells or plasma and a growing number of doctors are ordering them. No official deficiency standard has been set, but according to one lab, OmegaQuant Analytics, having 4% or less omega-3s out of total fatty acids is “undesirable” and indicates an elevated heart risk; 8% or more is “desirable.” Most Americans score between 3% and 5% omega-3s, says William Harris, a veteran heart researcher who founded OmegaQuant. “In Japan, it’s about 10%, and they have much less cardiovascular disease and live, on average, four years longer than we do,” he says.
Thousands of studies since the 1970s have shown that people with high levels of omega-3s have lower triglycerides, lower blood pressure, lower LDL cholesterol, less inflammation and a lower risk of heart disease. Those with low levels of omega-3s are more likely to be depressed, to commit suicide and have memory loss and brain shrinkage as they age.
Many of those are observational studies that can’t prove cause-and-effect; it may be that people who eat more fish have more healthy behaviors in general. The evidence from randomized-controlled trials is more mixed—but experts say that’s not surprising in dietary studies, where researchers often have to rely on patients to accurately report what they ate over long periods.
Recent research offers a tantalizing mix of healing possibilities:
Alzheimer’s disease and dementia: Several studies show that older people who eat plenty of fish have lower levels of beta-amyloid protein, associated with Alzheimer’s, than those who eat less. But giving elderly people omega-3 fish-oil supplements didn’t help ward off cognitive decline, according to a meta-analysis published in June. (The authors conceded that the trials may not have been long enough to show much effect.) Giving omega-3s to people with Alzheimer’s did not slow the disease’s progression.
Macular degeneration: A 2011 Harvard study found that women who ate fish at least once a week were 38% less likely to develop age-related macular degeneration than women who ate it less than once a month.
Attention-Deficit Hyperactivity Disorder: Children with ADHD tend to have lower omega-3 levels than their peers, and a study in the journal PLOS One last month found that DHA can improve reading and behavior in underperforming children. Still, there is no evidence to date that omega 3s are as effective as medication.
Depression: Rates of depression, bipolar disorder and postpartum depression are all lower in fish-eating populations, writes psychiatrist Drew Ramsey in his 2011 book, “The Happiness Diet.” He also lists wild salmon and shrimp as the top foods for good mood, and encourages his patients to increase their fish intake. Supplements with a high ratio of EPA to DHA appear to be most effective.
Cancer: Animal studies suggest that omega-3s may suppress the growth of some cancers. But a 2006 review of 40 years of research concluded that omega-3 supplements are unlikely to prevent cancer in humans.
Rheumatoid arthritis: Fish oil doesn’t appear to slow the progression of rheumatoid arthritis, but small studies show that it helps reduce symptoms like joint pain and morning stiffness, and may allow people to lower their dose of anti-inflammatory drugs.
Fetal development: Omega-3s are needed for brain and vision development in unborn babies, but concerns about mercury levels have scared some pregnant women away from eating fish. Health authorities say that many good omega-3 sources, including shrimp, salmon and tuna, are relatively low in mercury. Nursing women and young children should avoid shark, swordfish and tilefish.
Many physicians are more comfortable urging patients to eat more fish than take fish-oil supplements, since fish also contain protein, vitamin B-12, zinc and iodine.
Side effects from fish-oil supplements are minor—mostly gastrointestinal upset and burping with a fishy aftertaste. (Freezing the capsules or taking them with food may help.) In doses of 3 grams and above, EPA and DHA can increase the risk of bleeding, so people on blood thinners should consult their physician before taking them. Some hospitals advise patients to discontinue taking omega-3s before surgery.
What’s the bottom line? Does it make sense to consume more omega-3s? “There is no single answer here,” says Paul Coates, director of the Office of Dietary Supplements, part of the National Institutes of Health. “Given that there is a potential for benefit, and the harm has not yet been fully explored, at reasonable levels of intake, it’s not a bad idea.”
Melinda Beck at HealthJournal@wsj.com