Article's URL: http://www.health.harvard.edu/article.cfm?id=74,
---------------------------

Angling for a Healthier Heart
By: Harvard Heart Letter (Monday, 01-07-2002)


A few years ago, the emerging connection between fish and heart disease sounded like a real fish story, full of flip-flops and exaggerated claims. Things have settled down since then, with a more consistent stream of evidence now favoring fish (see Harvard Heart Letter, November 2001).

In the space of just two weeks this spring, reports from three large studies showed that eating fish could help your heart and may even save your life. The diversity of these studies helps solidify the role of fish as a heart-healthy food. They involved women and men, initially healthy people and those with cardiovascular disease. Two were observational studies that track many individuals' habits and health, while the other was a clinical trial in which volunteers were assigned to one treatment or another.

Arctic Beginnings
The idea that eating fish might be good for the heart emerged from British physiologist Hugh Sinclair's visits to the Inuit (Eskimos), beginning in 1944. In spite of a generally high-fat diet, they had remarkably low rates of heart disease. Sinclair chalked this up to the fish they ate, especially those rich in omega-3 fatty acids. Omega-3s are known as essential fatty acids because the body can't make them from scratch, but must get them from food. The main ones in fish are eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA).

Some — but not all — subsequent studies have demonstrated a connection between eating fish and lower rates of heart disease. Here are the latest results:

Nurses' Health Study: Among almost 85,000 women initially free of heart disease followed for 16 years, those who reported that they ate fish at least once a week were 30% less likely to have had a heart attack or have died of heart disease compared to those who ate fish less than once a month. (Journal of the American Medical Association, April 10, 2002, pp. 1815–21.)

Physicians' Health Study: Among more than 22,000 initially healthy men followed for 17 years, the chance of dying suddenly was 80% lower among men with the highest blood levels of omega-3 fatty acids compared to those with the lowest levels. (New England Journal of Medicine, April 11, 2002, pp. 1113–18.)

GISSI Prevenzione: In this Italian trial, more than 11,000 heart attack survivors were assigned to take capsules containing fish oil or a placebo every day for 3.5 years. Those taking fish oil were 50% less likely to have died suddenly. (Circulation, April 23, 2002, pp. 1897–1903.)

What's So Special About Fish?
Researchers haven't exactly answered this question yet. There are several leading possibilities.

Eating fish instead of red meat reduces the amount of saturated fat in the diet. Less saturated fat could translate into a lower risk for heart disease.

People who eat fish tend to eat more omega-3 fatty acids. These compounds appear to prevent erratic heart rhythms, a common cause of sudden cardiac death. The effect is almost immediate, preventing sudden death within months, not years.

Fish oils also keep blood clots from forming by making platelets less sticky and less likely to clump, just like aspirin does. They may also improve blood vessel function and ease system-wide inflammation. (What they apparently don't do all by themselves is slow the artery-clogging process known as atherosclerosis. In a report from a German trial that also appeared this spring, taking omega-3 fatty acid supplements for two years didn't slow or stop the narrowing of coronary arteries among 171 men and women with cholesterol-narrowed arteries.)

Finally, people who eat fish regularly may also tend to do other healthy things, such as exercise, not smoke, or eat more fruits and vegetables. It could be these things, not fish itself, that protect the heart, although most researchers use statistical methods to account for factors like these.

How Much Fish Is Enough?
If you enjoy seafood, eating it every day is perfectly fine. If you aren't that fond of it, once a week is a good start. (The American Heart Association recommends twice a week.)

As an alternative, eating walnuts, soybeans, or flaxseeds, or using oils made from them, gives you the omega-3 fatty acids that could be the "active ingredient" in fish that protects the heart. You have to make sure, though, that you store these away from heat and air, and that the oils aren't highly processed. Omega-3 fatty acids are fairly fragile; air, heat, and processing can destroy them.

Adding good fats without eliminating bad ones can make you gain weight, and this could cancel out any possible benefits from omega-3 fatty acids. You should also try to trim saturated and trans fats from your diet.

Why not skip the fish or seeds and take concentrated fish-oil supplements instead? Although they seemed to work in the GISSI-Prevenzione study, other studies (such as the German trial described earlier) showed little effect on the heart. Until there's more and better evidence, the American Heart Association and others don't recommend using fish oil supplements. If you want to try a supplement, pick one containing about 1 gram (1,000 mg) total of EPA and DHA. To be on the safe side, tell your doctor you are doing this, especially if you are taking blood-thinning medications such as Coumadin (warfarin). The combined effects of Coumadin and concentrated omega-3 fatty acids can lead to bleeding problems.

Omega-3 Fatty Acids in Fish and Oils

Fish
Grams of omega-3 fatty acids
per 100 grams of fish

Albacore tuna (fresh)
4.2

Tuna (canned)
0–0.5

Mackerel
2.6

Atlantic herring
1.7

Chinook salmon
1.5

Anchovy
1.4

Coho salmon
1.0

Greenland halibut
0.9

Rainbow trout
0.6

Atlantic cod
0.5

Atlantic white shrimp
0.4

Catfish
0.3

Northern lobster
0.2

Flounder
0.2

Seeds and Oils
Grams of omega-3 fatty acids

Flaxseed oil (1 tbl)
7

Flaxseed, ground (1 oz)
2

Walnut oil (1 tbl)
1.2

Walnuts, chopped (1 oz)
0.7

Canola oil (1 tbl)
1.5

Soybean oil (1 tbl)
0.9

Soybeans (1/2 cup)
0.5