There is one kind of polyunsaturated oil that may be especially protective against heart attacks—yet, you’d never want to sprinkle it over your beautiful fresh spinach salad. Fish oil.
The first clues that there might be something “fishy” about fish oil turned up some years ago, when scientists studying the health of different world populations noticed an especially low incidence of coronary heart disease among Eskimos of Greenland and Japanese people living in fishing villages on the sea. Though widely separated geographically, these two populations had at least one thing in common: Both groups consumed tremendous amounts of fatty fish, fish oil, whale blubber and other marine life that fed on fish. At first, their healthy hearts seemed incongruous, since very high levels of fat in the diet—regardless of the source of that fat—are considered a risk factor in heart disease. Further studies revealed that both the maritime Japanese and Eskimos had low levels of triglycerides (a kind of blood fat), high levels of HDL (high-density lipoprotein) cholesterol—the good kind of cholesterol—and a reduced tendency for their blood to clot. All those things are classic signs suggesting a sound, healthy cardiovascular system. W hat was going on?
Digging deeper, researchers found that these fish-loving people also had high levels of a class of fatty acids called omega-3 in their blood. Specifically, the omega-3 fatty acids they found are known to scientists as eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA).Where do EPA and DHA come from? From fish, fish oil and the fat of marine animals like seals and whales that live on fish. Could these substances be the key to the healthy hearts of the Eskimos and the Japanese?
At least two studies suggest that may well be the case. Over a period of a year, researchers at Northern General Hospital in Sheffield, England, measured the effect of fish oil taken in capsule form on 76 subjects. Some took enough to give a daily intake of 1.8 grams (a tiny fraction of an ounce) of EPA, while others took twice that amount, for 3.6 grams a day. Meanwhile, cholesterol levels, triglycerides and bleeding times were monitored
Elevated cholesterol and triglycerides may be warning signs of coronary trouble. Bleeding time is also an important measurement, because the tiny blood cells called platelets, crucial to the clotting process, may also aggregate, or clump, along blood vessel walls, forming a clot, or thrombus, that could cause a heart attack or stroke. “The narrowing of blood vessels through atherosclerosis is a very dangerous situation,” William E. M. Linds, Ph.D., head of the department of biological chemistry at the University of Illinois, explains. “But what really causes a coronary event is the clot; platelet aggregation plays an important role in this formation.” Apparently because their platelets are less “sticky,” and so don’t clump up as easily, Eskimos have long bleeding times.
Although the British volunteers receiving 1.8 grams of EPA didn’t show any change in bleeding time, those getting twice that amount “showed a highly significant increase in bleeding time,” the researchers noted. Serum triglycerides also dropped “markedly” in all subjects within a month after they began taking the oil, and after a year the change was still apparent.
“These changes,” the scientists observed, “are consistent with the reduction in the incidence of thrombosis [pathological clotting] and a slowing down of the atherosclerotic process. An increased dietary intake of marine oils, particularly those rich in EPA, may reduce the risk of coronary artery disease in patients on a mixed diet” (Lancet, July 31, 1982).
Further research by other British scientists suggests yet another way that EPA can help the circulatory system. Anything that cuts down on the interaction between blood vessel walls and platelets, they explain, probably lessens your chances of developing an atheroma, or abnormal fatty mass that clings to a vessel wall and blocks blood flow. That’s because this encounter between platelets and blood vessel walls triggers the secretion of thromboxane, a substance that causes platelets to clump and also causes the vessels to constrict—a bad combination. But five weeks of fish oil supplements given to heart patients produced changes that, in effect, cut down on this dangerous interaction—for example, by reducing the total number of platelets in their blood by 15 percent. “These findings suggest that a diet rich in omega-3 polyunsaturated fatty acids, such as eicosapentaenoic acid (EPA), will reduce platelet/ vessel-wall interaction and may reduce the risk of ischemic [constricted blood flow] heart disease,” they observed (Lancet, June 5, 1982).
Taking the cue from their English counterparts, American researchers have also been exploring the potential of fish oils. One group, at the Oregon Health Sciences University in Portland, designed a study using both fish oil and salmon meat (rich in both EPA and DHA). After 28 days on the salmon diet, the researchers found that plasma cholesterol levels in apparently healthy volunteers dropped 17 percent, while triglycerides plunged by as much as 40 percent. Among subjects whose blood fats were already elevated, the change was even more dramatic: Cholesterol levels dropped 20 percent or more, and triglycerides went down by as much as 67 percent (Journal of the American Medical Association, February 12, 1982).
“Subjects with elevated cholesterol and triglycerides seemed to show the most marked response to the fish oil,” says William S. Harris, Ph.D., one of the Oregon researchers. “As a rule, the higher these levels at the outset, the further they dropped when the fish oil program was started.”
Is there any danger that EPA might thin the blood to the point where excessive bleeding becomes a problem? “We’ve never had anybody with a clinical bleeding problem, even at 70 to 100 grams [of fish oil] a day,” Dr. Harris told us
How much would a person need to take to possibly enjoy the benefits of EPA? “That’s the question,” Dr. Harris laughs. “We simply don’t know yet.” In his study at the University of Oregon, volunteers consumed a half pound to a pound of salmon daily, plus two or three ounces of fish oil, depending on their body size. That, he admits, is more than even most dedicated fish lovers would care to eat—if they could afford it in the first place. Yet other studies have shown beneficial effects from much smaller amounts.
One British doctor, writing in the British medical journal Lancet, suggests that “A realistic way of improving the EPA level of the diet is the regular consumption of an EPA-rich oil from fish, such as cod-liver oil. Two teaspoons daily (10 grams) would contribute 1 gram of EPA to the diet, about ten times the present level of intake.” Fortunately, there are now fish-oil capsules on the market. One that I checked contained a total of 300 milligrams of EPA and DHA. To reach the 1-gram level, you would have to take three or four a day.
Another way to take advantage of this exciting research is simply to increase your consumption of fish. “It certainly wouldn’t hurt, and some people may even be glad to know they don’t have to avoid fatty fish,” says Dr. Harris. “Eating more fish would also tend to replace red meat in the diet, which many of us eat too much of anyway.” Which fish are richest in EPA and DHA? Almost all fish contain some EPA, Dr. Harris says, but among the richest are salmon, tuna, trout, mackerel and sardines. The oil content is highest when the fish are fresh. Canned fish are rich in EPA only when packed in their own oil.