Omega-3 fatty acid heart benefits still unproven after decades of research
Despite numerous studies over decades, dietary benefits of omega-3 fatty acids remain unproven
In the 1970s, a pair of Danish researchers ventured north of the Arctic Circle and into medical lore. Studying a scattered Inuit population, they concluded that eating plenty of fish and other marine animals protected this group from heart disease.
The researchers would eventually suggest that everyone else's hearts and arteries might also benefit from the "Eskimo diet", promoting a health food trend that continues to this day.
The only trouble is, Hans Olaf Bang and Jorn Dyerberg never proved the Inuit had low rates of heart disease. They never tested it at all. But today the market for fish oil pills is booming, even as scientists conduct trial after trial to hunt for a link to heart health that has never quite solidified.
Bang and Dyerberg were clinical chemists at Aalborg in Denmark. Curious about the nutrition of the Inuit, they "undertook an expedition" to the northwest coast of Greenland, which they described in a 1971 Lancet paper.
They stopped at a town called Uummannaq. Counting the surrounding settlements, the population totalled 1,350 people, living off what they could hunt and fish from the unforgiving land.
The researchers drew blood from 130 natives. Compared to Danes, the Inuit had lower levels of lipids such as cholesterol and triglycerides. Yet they had a higher proportion of the molecules known as omega-3 fatty acids, which are common in oily, cold-water fish.
Chemical analysis of food samples showed that, compared to Danes, the Inuit ate more protein, more cholesterol and a higher proportion of omega-3 fatty acids. As the researchers described it, the Inuit diet was "mostly of meat of whales, seals, sea birds, and fish", with the main bread product being "some sort of ship biscuit".
You might expect such a carnivorous diet to be a recipe for heart disease. But plentiful omega-3 fatty acids seemed to be protecting the Inuit. By 1980 the researchers were suggesting that following a similar diet might prevent heart disease.
How did they know the Inuit weren't prone to heart disease? Bang and Dyerberg were nutritionists, not cardiologists, and they relied on numbers provided by Greenland's chief medical officer for parts of the 1960s and 1970s. These reports, based on death certificates and hospital admissions, included only a handful of confirmed heart disease cases from Uummannaq.
But there's a problem with relying on official medical records in a part of the world so remote that 30 per cent of people lived in settlements with no medical officer at all. This meant many death certificates were filled out by whoever was nearby, without a doctor ever seeing the body.
So how could official records be expected to catch every heart attack that happens in an icy outpost far from any doctor? "It's highly unlikely," says George Fodor, a veteran cardiologist at the University of Ottawa Heart Institute. What matters most to a disease researcher, Fodor says, is overall mortality, "the number of corpses you count".
A study found that from the late 1960s to early 1980s, Inuit died from all causes at twice the rate of Danes - hardly a lifestyle to aspire to.
Today, the American Heart Association says that people with coronary artery disease should take daily fish oil supplements. Nutritional guidelines in the US, Canada, and Europe call for fish twice a week. Yet the performance of these fatty acids in clinical trials has been mixed.
One of those clinical trials is being run now by Brigham and Women's Hospital, an affiliate of Harvard Medical School. The Vitamin D and Omega-3 Trial, VITAL for short, is looking at the effect of both omega-3s and vitamin D in healthy adults.
To truly learn whether omega-3s guard heart health or not, we need research that goes a step further: large-scale, randomised trials. A couple of early omega-3 trials got positive results, but they lacked a placebo control group. That is, there were no subjects swallowing sham pills instead of the real thing.
More recently, randomised and placebo-controlled studies didn't find any benefit from fish oil. But these studies looked at patients who already had heart disease; they didn't ask whether omega-3s help healthy people.
And medications such as statins or aspirin could have masked any positive effects of fish oil in these trials, said JoAnn Manson, principal investigator of VITAL and a professor at Harvard.
VITAL will follow more than 25,000 healthy people taking real or placebo pills over five years. By 2018, there will be an answer.