Taking supplements does not have the same effect of reducing the risk of stroke as eating fish high in omega-3s, a study shows.
Questioning the Superpowers of Omega-3 in Diets
Name the affliction—heart disease, Alzheimer's, arthritis, depression, asthma—and omega-3 fatty acids can help prevent it.
Or not.
Taking omega-3 fatty acids doesn't reduce
deaths from heart attacks, strokes or other cardiovascular events, a new
study states. But there's much more to be said about omega-3's, as Dr.
Drew Ramsey and WSJ's Melinda Beck explain on Lunch Break. Photo: Getty
Images.
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.
Illustrations by Tim Foley
Illustrations by Tim Foley
"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."
Write to Melinda Beck at
HealthJournal@wsj.com
