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Harvard Heart Letter | July 2008
Fish and fish oil: Good for most folks, but not all
Whether you benefit from taking fish oil depends on the state of your heart.
Back in 2002, the American Heart Association recommended that people
with coronary artery disease take fish oil. Its reasoning was sound. At
the time, solid research showed that eating fish or, for some people,
taking fish oil, helped protect against dying of heart disease.
Since
then, research has generally supported the benefits of eating more fish
or taking fish oil. At the same time, studies have raised a red flag
about whether people with severe angina, seriously compromised heart
function, or potentially lethal rhythms in the heart’s lower chambers
should eat a lot of fish or take fish oil.
What’s so
special about fish or the oil extracted from it? In addition to being
an excellent source of protein, fish tends to be rich in omega-3 fats.
Our bodies need these healthful fats, but can’t make them. The two
omega-3s we get from seafood are eicosapentaenoic acid (EPA) and
docosahexaenoic acid (DHA). A third type, alpha-linolenic acid (ALA),
is found in many plants.
Omega-3 fats help the heart’s
ventricles maintain a steady beat and guard against potentially deadly
erratic rhythms. They ease inflammation and help prevent the formation
of dangerous clots in the bloodstream. Omega-3 fats also lower levels
of triglycerides, the most common type of fat-carrying particle in the
bloodstream.
Refining the prescription
A
European trial tested the impact of eating oily fish at least twice a
week or taking fish oil among men with easily provoked severe angina.
Surprisingly, those who got more omega-3s were more likely to have died of heart disease during the several-year study.
Another
note of caution came from trials of fish oil for folks prone to
potentially deadly disturbed rhythms in the ventricles, notably
ventricular tachycardia and ventricular fibrillation. Most people who
experience one of these and live to tell about it get an implanted
cardioverter-defibrillator (ICD) to detect and halt these arrhythmias.
In one trial, people with an ICD who took high-dose fish oil had more episodes of ventricular tachycardia or fibrillation than those taking a
placebo. In two similar trials, fish oil prevented ventricular
arrhythmias in one and had no harm or benefit in another.
Experiments
by Dr. Alexander Leaf and his colleagues show that omega-3 fats prevent
potentially fatal rhythms by suppressing the function of hyperexcitable
cells that live in scar tissue or in heart muscle that doesn’t get
enough oxygen. That’s great when there’s plenty of healthy heart
tissue. But what about when these hyperexcitable cells are responsible
for the lion’s share of cardiac function, such as in people with severe
angina or other conditions in which the heart is chronically deprived
of oxygen? Stifling them with fish oil could conceivably snuff out the
heartbeat, explains Dr. Leaf, emeritus professor of clinical medicine
at Harvard Medical School.
Fish oil capsule
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Recasting recommendations
As is the case for most cardiac interventions, a single recommendation on fish and fish oil can’t cover all the bases.
Yellow light.
Go easy on fish and avoid fish oil if you have hard-to-control angina,
severe heart failure, or an ICD. Ongoing research could modify that
advice, but for now it’s a prudent approach, says Dr. Leaf.
Go fish.
Everyone else could benefit from eating fish, preferably fatty fish
like salmon, sardines, mackerel, and trout, twice a week. It can help
keep a seemingly healthy heart in good shape, and protect one that may
be in trouble. Baked or broiled fish is best; deep-fried, fast-food
fish doesn’t count. On non-fish days, have a handful of walnuts or
ground flaxseeds, use flaxseed or canola oil, or try some tofu, all
good sources of alpha-linolenic acid.
Try oil. If you have one or more narrowed coronary arteries, have had bypass surgery or angioplasty, or had a heart attack, and
your heart function is good, try to get 1 gram of DHA plus EPA daily.
In Europe, doctors routinely prescribe fish oil for heart attack
survivors. American doctors are more reluctant to follow the American
Heart Association’s recommendation.
High triglycerides. Taking 2 to 4 grams of EPA plus DHA a day can help control high triglycerides.
Practical matters
Even though you can buy fish oil without a prescription, talk with your doctor first before taking it.
Taking
fish oil may be cheaper than eating fish, but it isn’t nearly as
pleasant. Gulping down the large capsules can be difficult, and some
people don’t like the fishy aftertaste or belches. Freezing the
capsules can help with those.
Fish oil is free of mercury
and other contaminants found in some fish. A prescription version,
Lovaza, delivers nearly 1 gram of DHA plus EPA per capsule.
Over-the-counter kinds may be cheaper, but many contain less DHA and
EPA, so you need to take more capsules. Over-the-counter supplements
aren’t closely regulated by the FDA, so you don’t always know what you
are getting. For vegetarians, V-Pure capsules contain EPA and DHA
extracted from algae, which is where fish get them.
The
best way to get omega-3 fats, though, is to eat oily fish. It’s better
for you than red meat, and is far tastier than a capsule.
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