Most people remember cod liver oil as nasty, fishy-tasting stuff, high in vitamins A and D, that was given to kids to prevent rickets until convenient artificial vitamins were invented in the 1950s. Cod liver oil usage, so it seemed, had waned.
In recent years, though, there has been a renewed--and, many experts say, potentially dangerous--popularity of the oil due to a number of medical studies showing that fish oils may reduce cardiovascular disease.
In fact, the largest producer of cod liver oil in the world, the Marflet Refining Co. in England, reported a shortage of 600,000 tons of oil last April because of the increased demand, according to self-taught nutritionist-author Dale Alexander.
Known in the health food industry as "The Codfather," Alexander has heralded cod liver oil during the last 30 years for "bringing elasticity to the arteries." Alexander has written five books proclaiming the wondrous effect of cod liver oil on common colds, dry skin, healthy hair, arthritis and general health. When cod liver oil usage decreased in the 1950s, Alexander staged a campaign to renew its popularity by encouraging people to mix the oil with milk or orange juice to disguise the bad taste. He said his perseverance has paid off, because heart disease researchers seem to be confirming his fervent belief in the oil.
Though such studies have been completed, researchers tend to discourage people from taking daily fish oil supplements, according to Dr. Basil Rifkind, chief of a section of the federal government's National Heart, Lung and Blood Institute that specializes in diseases of the coronary arteries.
"No doubt fish oils do have an effect on quite a few body functions," Rifkind said. "But we're only beginning to get a picture of this fairly complex series of effects on the body."
Bonnie Weiner, chief of atherosclerosis research in the division of cardiology at the University of Massachusetts Medical School in Worcester, recently published the results of one of her studies on heart disease in swine in the New England Journal of Medicine. The results indicated that in pigs, cod liver oils clearly retard development of atherosclerosis, a disease involving the build-up of fatty deposits in the arteries that can lead to heart failure or heart attacks.
Weiner said she used pigs because they are excellent models of human beings in heart disease research. In fact pig and human circulatory systems are so similar that pig heart valves are commonly used to replace defective human valves. All 18 pigs in the eight-month experiment were fed a diet extremely high in fat, and seven of the animals were given cod liver oil supplements. Weiner found that without actually lowering those seven pigs' cholesterol levels, cod liver oil prevented clogging of the arteries despite the oil's own high cholesterol content.
The high percentage of eicosapentaeonic acid (EPA), a fatty compound specifically contained in cold water ocean fish, seemed to counteract the effects of the cholesterol, according to Weiner. "The fish oil protected the arteries even without lowering cholesterol levels," she said.
The pigs used in the study had not developed atherosclerosis and therefore could be compared with children before their arteries had started to block. "What we don't know is whether these fish oils can be important after you've already developed the problem. People want to be told that (fish oils) are the magic remedy, but they may not be," Weiner said.
Weiner's research is the most recent in a series of studies that have consistently determined fish oils may help prevent heart disease.
A research group in Denmark conducted the first such major project in the 1970s, showing that Greenland Eskimos, who eat a diet high in the fatty acids found in fish, had a lower incidence of heart disease than those Eskimos living in Denmark with a diet high in butter fats. But in a subsequent comparison of Eskimos living in Denmark with Danes, researchers found a lower incidence of heart disease among the Eskimos.
Another research group in Japan discovered lower incidences of heart conditions in people living in a fishing village on the coast than in an inland population.
In the third major epidemiological study, published in the New England Journal of Medicine in 1985, nutritionists interviewed a group of Dutch men about their diet in the prior sixth months, concentrating on fish intake. The study concluded that consumption of as little as one to two fish meals a week is beneficial in preventing heart disease.
As a practical interpretation of the Dutch study, Ruth Johnson, a USC nutritionist and heart disease researcher, said she would advise people to consume six ounces of lean meat, fish or poultry a day and at least 12 ounces of fish weekly.