There's an NPR radio program called "Wait, wait.... don't tell me!" that has relevance to science these days, as is easy to see. We see frequent reports of how to live if we want to stay healthy, such as to keep an eye on our cholesterol if we want to avoid heart disease.....
But wait, should we obsess about our cholesterol numbers or shouldn't we? And, if we obsess too much, will the stress cause the very heart disease we're trying to prevent? A short piece in Sunday's New York Times refers to new analysis of an old study of Australian men, and effects of various dietary components on blood lipid levels and risk of death. The new analysis was published in the British Medical Journal last month, with an accompanying commentary by Philip Calder.
We've known for decades, in large part due to the never ending Framingham Heart Study, which began in 1948 and is now looking at third generation subjects from Framingham, Massachusetts, that saturated fats raise the risk of heart disease because they raise cholesterol levels. And, we've known that polyunsaturated fatty acids (PUFA's) -- safflower, sunflower, corn and soybean oils -- reduce cholesterol, and thus lower heart disease risk. Framingham may have led the way, but many other studies confirmed these findings, and eating more PUFA's and less animal fat has been the basis of heart friendly dietary advice for decades.
But wait! Now researchers have reanalyzed the Australian data, which originally took place between 1966-1973. In this study, one group of men with heart disease ate more omega-6-rich polyunsaturated fat, linoleic acid, and the control group, also with heart disease, ate as usual. According to the NYT:
The men were followed for an average of 39 months, and those on the polyunsaturated-rich diet lowered their cholesterol levels by an average of 13 percent. But they also were more likely to die, and in particular to die of a heart attack, than those who stuck with their usual diet, which consisted of about 15 percent saturated fat.What does this mean? Yes, polyunsaturated fats do seem to lower cholesterol, but they also raise risk of death from heart disease. Does this mean we need to question the link between cholesterol levels and heart disease? Or, maybe there's another pathway -- polyunsaturated oils may decrease cholesterol but at the same time increase inflammation, which has been shown subsequent to these and early Framingham results, to be involved in heart disease, though it's not clear how. And this may override the supposed positive effects of lowered cholesterol.
Indeed, according to the editorial in the BMJ, proper studies of the effect of replacing saturated fat with PUFA's without other dietary changes have rarely been done, so that it has been impossible to evaluate the effect of linoleic acid alone on cardiovascular disease risk. Until now, with the re-evaluation of the Australian data.
The original analysis showed an increased risk of all cause mortality in the study group, the men who increased their intake of linoleic acid, but the new analysis shows that death from cardiovascular disease also increased.
These findings argue against the “saturated fat bad, omega 6 PUFA good” dogma and suggest that the American Heart Association advisory that includes the statement “higher [than 10% of energy] intakes [of omega-6 PUFAs] appear to be safe and may be even more beneficial” may be misguided. The more cautious UK dietary recommendations on fat and fatty acids, which include the statement, “There is reason to be cautious about high intakes of omega 6 PUFAs,” seem fully justified in the light of the current study’s findings.Calder suggests, and rightly, that "subtle, and in some cases unsubtle aspects of study design" have effects on results that are too often not considered when results are interpreted, and dietary advice made public. This of course always pertains, not just in the case of diet and heart disease risk factors.
So, advice is often given on shaky evidence. A piece in Nature on 26 February -- "Cholesterol limits lose their lustre" -- is another example. People all over the world are on statins for life to lower their cholesterol to prescribed targets, making pharmaceutical companies very rich, but how valid are those targets?
Most people who have heart attacks, it turns out, don't have high LDL's ('bad' cholesterol). A cardiologist at the University of Minnesota Medical School in Minneapolis is quoted in the piece saying, "If your arteries and heart are healthy, I don't care what your LDL or blood pressure is."
So, cholesterol guidelines established by the US National Heart, Lung and Blood Institute may soon be changed, and LDL targets abolished.
Expected to be released later this year, the fourth set of guidelines, called ATP IV, has been drawn up by an expert panel of 15 cardiologists appointed by the institute. The guidelines will set the tone for clinical practice in the United States and beyond, and will profoundly influence pharmaceutical markets. They will also reflect the growing debate over cholesterol targets, which have never been directly tested in clinical trials.And, a report last week suggests that processed meats like bacon and sausage are lethal. But, wait, not if you're Italian and eat a lot of Parma ham! Does that mean that the Chianti and Valpolicella of the Mediterranean diet compensate? All of this gives 'bringing home the bacon' a suddenly negative connotation!
|From "Processed meat 'early death' link," BBC|
But wait, if the new report that post-traumatic stress disorder raises the risk of heart disease is true, mediated by increased insulin resistance, then perhaps attention will be taken off cholesterol and diet entirely, and turned to reducing stress!
How to recognize dangerous warnings and avoid risks....
It isn't just your health that's at risk with all of these confusing never-ending contradictory reports. Whenever you hear (as you almost always do!) an investigator say "studies show that" or "we need further research," grab hold of your wallet and run for cover! Because you're about to be pick-pocketed, and that, unlike the epidemiological studies, is something you can rely on!
There are many reasons for resisting the understandable desire of epidemiologists and geneticists to seize on these uncertainties as a rationale for more funding to study the same problems essentially with the same methods but on a bigger, longer scale. We'll go over them in a forthcoming post.