Name the ailments – heart disease, Alzheimer’s, arthritis, depression, asthma – and omega-3s can help prevent it.
This is the confusion caused by new research on omega-3 fatty acids, fats in cold-water fish, and vegetable oils that has fascinated nutritionists since the 1970s when they discovered that Greenland Eskimos rarely die of heart disease, despite a diet of fatty fish .
According to the Council for Responsible Nutrition, an industry group, 21% of adults in the United States report using omega-3 fish oil supplements. This makes it the most popular preparation after multivitamins and vitamin D.
Last month, the Journal of the American Medical Association published a meta-analysis of 20 clinical studies involving nearly 70,000 people that found that omega-3s did not prevent heart attacks, strokes, or deaths from heart disease. Other recent studies in the New England Journal of Medicine and the Internal Medicine Archives found that omega-3 supplements did not 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 results.
Critics noted that the JAMA study combined clinical trials that used different doses and sources of omega-3 fatty acids. Many of the subjects were also given heart medication, which may have softened the impact. In addition, diet studies are notoriously inaccurate. “It is impossible for five researchers to monitor the diets of nearly 70,000 patients for several years,” said Duffy MacKay, CRN vice president for scientific and regulatory affairs.
In addition, the JAMA authors have set an unusually strict standard for statistical significance. Using the typical standard, the analysis would have shown that omega-3 supplements are linked to a 9% reduction in cardiac death.
Illustrations by Tim Foley
Illustrations by Tim Foley
“My colleagues are writing letters to the editor about it,” said University of Pennsylvania nutritionist Penny Kris-Etherton, a spokeswoman for the American Heart Association. She says the association will continue to recommend everyone eat omega-3-rich fish at least twice a week for the time being. People with heart disease or high triglycerides might also consider taking fish oil supplements under medical supervision. The American Psychiatric Association and the World Health Organization have similar advice.
Omega-3 fatty acids are important for building cell membranes and maintaining connections between brain cells. They can also reduce inflammation, which is increasingly recognized as a cause of chronic illness.
Humans cannot produce omega-3 fatty acids, so we have to get them from outside sources. The two main species – EPA and DHA – are mainly found in fish such as salmon, sardines, tuna, and herring. A third type, ALA, is found in walnuts, flax seeds, soybean oil, and some green vegetables, including Brussels sprouts, spinach, and kale.
The typical American diet contains far more omega-6 fatty acids, which come from corn and safflower oil and are found in abundance in processed foods, as well as beef and poultry. Some experts believe that reducing the ratio of omega-6 fatty acids to 3 fatty acids is even more important than increasing omega-3 fatty acids, but the evidence is mixed.
Blood tests (usually $ 100 to $ 200) can measure the amount of omega-3 fatty acids in red blood cells or plasma, and a growing number of doctors are ordering them. No official standard of deficiency has been set, but according to a laboratory, OmegaQuant Analytics, having 4% or less omega-3s of total fatty acids is “undesirable” and indicates an increased cardiac risk. 8% or more is “desirable”. Most Americans get between 3% and 5% omega-3 fatty acids, says William Harris, a veteran heart researcher who founded OmegaQuant. “In Japan, it’s about 10% and they have far fewer cardiovascular disease and live an average of four years longer than we do,” he says.
Thousands of studies since the 1970s have shown that people high in omega-3s have lower triglycerides, lower blood pressure, lower LDL cholesterol, less inflammation, and a lower risk of heart disease. People with low omega-3 levels are more likely to be depressed, commit suicide, and experience memory loss and brain shrinkage as they age.
Many of these are observational studies that cannot prove cause and effect. People who eat more fish may be healthier in general. The evidence from randomized controlled trials is more inconsistent – but experts say this is not surprising in nutrition studies, where researchers often rely on patients to report exactly what they have eaten over long periods of time.
Recent research offers a tempting mix of healing options:
Alzheimer’s disease and dementia: Several studies show that older people who eat a lot of fish have less beta-amyloid protein, which is associated with Alzheimer’s, than those who eat less. However, according to a meta-analysis published in June, giving omega-3 fish oil supplements to the elderly did not help stave off the cognitive decline. (The authors acknowledged that the studies may not have been long enough to show much effect.) Giving omega-3s to people with Alzheimer’s did not slow the progression of the disease.
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 fish less than once a month.
Attention Deficit Hyperactivity Disorder: Children with ADHD tend to have lower omega-3 levels than their peers. A study in the journal PLOS One last month found that DHA can improve reading and behavior in underperforming children. So far, however, there is no evidence that omega-3 fatty acids are as effective as drugs.
depression: The rates of depression, bipolar disorder and postpartum depression are lower in fish-eating populations, writes psychiatrist Drew Ramsey in his 2011 book “The Happiness Diet”. He also lists wild salmon and shrimp as staple foods for good mood and encourages his patients to increase their fish intake. Supplements with a high EPA to DHA ratio seem to be the most effective.
cancer: Animal studies suggest that omega-3 fatty acids can suppress the growth of some cancers. However, a 2006 review of 40 years of research found that omega-3 supplements are unlikely to prevent cancer in humans.
Rheumatoid arthritis: Fish oil doesn’t seem to slow the progression of rheumatoid arthritis, but small studies show that it relieves symptoms such as joint pain and morning stiffness, and it may allow people to lower their dose of anti-inflammatory drugs.
Development of the fetus: Omega-3s are needed for brain development and eyesight in unborn babies, but concerns about mercury levels have deterred some pregnant women from eating fish. Health officials say many good sources of omega-3s, including shrimp, salmon, and tuna, are relatively low in mercury. Breastfeeding women and young children should avoid sharks, swordfish, and tilefish.
Many doctors are more comfortable asking patients to eat more fish than they take in fish oil supplements, because fish also contain protein, vitamin B-12, zinc, and iodine.
The side effects of fish oil supplements are minor – mostly gastrointestinal upset and belching with a fishy aftertaste. (Freezing the capsules or taking them with food can help.) In doses of 3 grams and more, EPA and DHA can increase the risk of bleeding. Therefore, people with blood thinners should consult their doctor before taking them. Some hospitals advise patients to stop taking omega-3s before surgery.
What’s the bottom line? Does it make sense to consume more omega-3 fatty acids? “There’s no single answer here,” says Paul Coates, director of the Office of Dietary Supplements, which is part of the National Institutes of Health. “Given that there is potential for benefits and the harm, with appropriate intake, has not yet been fully explored, this is not a bad idea.”
Write to Melinda Beck at HealthJournal@wsj.com
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