So what do you think?
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This is also called bias of compliance. People who follow their doctors recommendations for one thing will often follow it for everything. While those who do not follow it for one thing will likely not follow it for most suggestions (i.e.: not exercise, smoke, drink, etc.). Hence one of the major issues with observational epidemiology.Conflicting results are quite common in nutrition. I think the key here is that JAMA believes fatty fish benefits the cardiovascular system but fish oil supplements do not. If I had to theorize, I'd chalk it up to association (people who eat fatty fish often eat pretty wholesome diets), absorption of the fats (vs supplements which must be taken with a high fat meal to be absorbed), and lower EPA/DHA content found in many fish oils.
The Bias of Compliance
A still more subtle component of healthy-user bias has to be confronted. This is the compliance or adherer effect. Quite simply, people who comply with their doctors’ orders when given a prescription are different and healthier than people who don’t. This difference may be ultimately unquantifiable. The compliance effect is another plausible explanation for many of the beneficial associations that epidemiologists commonly report, which means this alone is a reason to wonder if much of what we hear about what constitutes a healthful diet and lifestyle is misconceived.
The lesson comes from an ambitious clinical trial called the Coronary Drug Project that set out in the 1970s to test whether any of five different drugs might prevent heart attacks. The subjects were some 8,500 middle-aged men with established heart problems. Two-thirds of them were randomly assigned to take one of the five drugs and the other third a placebo. Because one of the drugs, clofibrate, lowered cholesterol levels, the researchers had high hopes that it would ward off heart disease. But when the results were tabulated after five years, clofibrate showed no beneficial effect. The researchers then considered the possibility that clofibrate appeared to fail only because the subjects failed to faithfully take their prescriptions.
As it turned out, those men who said they took more than 80 percent of the pills prescribed fared substantially better than those who didn’t. Only 15 percent of these faithful “adherers” died, compared with almost 25 percent of what the project researchers called “poor adherers.” This might have been taken as reason to believe that clofibrate actually did cut heart-disease deaths almost by half, but then the researchers looked at those men who faithfully took their placebos. And those men, too, seemed to benefit from adhering closely to their prescription: only 15 percent of them died compared with 28 percent who were less conscientious. “So faithfully taking the placebo cuts the death rate by a factor of two,” says David Freedman, a professor of statistics at the University of California, Berkeley [who passed away, regrettably, in 2008]. “How can this be? Well, people who take their placebo regularly are just different than the others. The rest is a little speculative. Maybe they take better care of themselves in general. But this compliance effect is quite a big effect.”
The moral of the story, says Freedman, is that whenever epidemiologists compare people who faithfully engage in some activity with those who don’t—whether taking prescription pills or vitamins or exercising regularly or eating what they consider a healthful diet—the researchers need to account for this compliance effect or they will most likely infer the wrong answer. They’ll conclude that this behavior, whatever it is, prevents disease and saves lives, when all they’re really doing is comparing two different types of people who are, in effect, incomparable.
This phenomenon is a particularly compelling explanation for why the Nurses’ Health Study and other cohort studies saw a benefit of H.R.T. [hormone replacement therapy, one subject of the article] in current users of the drugs, but not necessarily in past users. By distinguishing among women who never used H.R.T., those who used it but then stopped and current users (who were the only ones for which a consistent benefit appeared), these observational studies may have inadvertently focused their attention specifically on, as Jerry Avorn says, the “Girl Scouts in the group, the compliant ongoing users, who are probably doing a lot of other preventive things as well.”
It may change the general public outlook on fish oil because they are too lazy to read the actual study and just believe everything that the television tells them.I ask that and would follow up with - if someone has read it - why do I not think it changes a thing?
D_
I guess you were reading my mind... although I thought the average was 1.5 grams (still not appropriate for most).Study was based on just 1 gram of fish oil and low epa/dha. So it's actually worthless information to me because I don't waste my time with low EPA/DHA and take way more than just 1 gram a day.