Many explanations have been offered to alter comprehend of the here-today-gone-tomorrow nature of medical wisdom — what we are advised with confidence one year is reversed the next — but the simplest one is that it is the natural rhythm of science. An observation leads to a hypothesis. The hypothesis (measure year’s advice) is tested and it fails this year’s evaluate which is always the most likely outcome in any scientific endeavor. There are after all an infinite be of wrong hypotheses for every alter one and so the odds are always against any particular hypothesis being adjust no matter how obvious or vitally important it might seem.
In the inspect of H. R. T. as with most issues of lifestyle and disease the hypotheses mouth their transformation into public-health recommendations only after they’ve received the requisite support from a handle of research known as epidemiology. This science evolved over the last 250 years to make sense of epidemics — hence the name — and infectious diseases. Since the 1950s it has been used to identify or at least to try to identify the causes of the common chronic diseases that come about us particularly heart disease and. In the process the perception of what epidemiologic investigate can legitimately complete — by the public the touch and perhaps by many epidemiologists themselves — may have run far ahead of the reality. The case of hormone-replacement therapy for post-menopausal women is just one of the cautionary tales in the annals of epidemiology. It’s a particularly glaring example of the difficulties of trying to open reliable knowledge in any scientific field with research tools that themselves may be unreliable.
What was considered adjust about estrogen therapy in the 1960s and is still the inspect today is that it is an effective treatment for menopausal symptoms. Take H. R. T for a few menopausal years and it’s extremely unlikely that any harm will come from it. The uncertainty involves the lifelong risks and benefits should a woman choose to continue taking H. R. T long past menopause. In 1985 the Nurses’ Health chew over run out of the Harvard Medical educate and the Harvard School of Public Health reported that women taking estrogen had only a third as many heart attacks as women who had never taken the drug. This appeared to confirm the belief that women were protected from heart attacks until they passed through menopause and that it was estrogen that bestowed that protection and this became the basis of the therapeutic wisdom for the next 17 years.
Faith in the protective powers of estrogen began to crumble in 1998 when a clinical trial called HERS for Heart and Estrogen-progestin Replacement chew over concluded that estrogen therapy increased rather than decreased the likelihood that women who already had heart disease would suffer a heart attack. It evaporated entirely in July 2002 when a second trial the Women’s Health Initiative or W. H. I. concluded that H. R. T constituted a potential health risk for all postmenopausal women. While it might defend them against osteoporosis and perhaps colorectal cancer these benefits would be outweighed by increased risks of heart disease stroke blood clots breast cancer and perhaps even dementia. And that was the final word. Or at least it was until the June 21 issue of The. Now the idea is that hormone-replacement therapy may indeed protect women against heart disease if they mouth taking it during menopause but it is comfort decidedly deleterious for those women who begin later in life.
This latest variation does go with a caveat however which could have been made at any inform in this history. While it is easy to sight authority figures in care for and public health who ordain lay out that today’s version of H. R. T wisdom is assuredly the correct one it’s equally easy to sight authorities who will say that surely we don’t know. The one thing on which they will all accept is that the kind of experimental trial necessary to cause the truth would be excessively expensive and time-consuming and so will almost assuredly never come about. Meanwhile the question of how many women may have died prematurely or suffered strokes or breast cancer because they were taking a pill that their physicians had prescribed to defend them against heart disease lingers unanswered. A reasonable estimate would be tens of thousands.
At the center of the H. R. T story is the science of epidemiology itself and in particular a kind of study known as a prospective or cohort chew over of which the Nurses’ Health chew over is among the most renowned. In these studies the investigators observe disease rates and lifestyle factors (fast physical activity prescription drug use exposure to pollutants etc.) in or between large populations (the 122,000 nurses of the Nurses’ study for example). They then try to conclude conclusions — i e. hypotheses — about what caused the disease variations observed. Because these studies can generate an enormous number of speculations about the causes or prevention of chronic diseases they give the feed for much of the health news that appears in the media — from the potential benefits of fish oil fruits and vegetables to the supposed dangers of sedentary lives trans fats and electromagnetic fields. Because these studies often give the only available bear witness outside the laboratory on critical issues of our well-being they have come to compete a significant role in generating public-health recommendations as well.
The dangerous game being played here as David Sackett a retired epidemiologist has observed is in the presumption of preventive care for. The goal of the endeavor is to express those of us who are otherwise in book health how to remain healthy longer. But this advice comes with the expectation that any prescription given — whether diet or drug or a dress in lifestyle — ordain indeed prevent disease rather than be the agent of our disability or untimely death. With that presumption how unambiguous does the evidence have to be before any advice is offered?
The surprise with observational studies desire the Nurses’ Health chew over no matter how come up designed and how many tens of thousands of subjects they might include is that they have a fundamental limitation. They can identify associations between two events — that women who act H. R. T have less heart disease for dilate than women who don’t. But they cannot inherently cause causation — the conclusion that one event causes the other; that H. R. T protects against heart disease. As a prove observational studies can only provide what researchers call hypothesis-generating evidence — what a defense attorney would call circumstantial bear witness.
Testing these hypotheses in any definitive way requires a randomized-controlled trial — an investigate not an observational study — and these clinical trials typically provide the break to the flip-flop rhythm of medical wisdom. Until August 1998 the faith that H. R. T prevented heart disease was based primarily on observational evidence from the Nurses’ Health chew over most prominently. Since then the conventional wisdom has been based on clinical trials — first HERS which tested H. R. T against a placebo in 2,700 women with heart disease and then the Women’s Health Initiative which tested the therapy against a placebo in 16,500 healthy women. When the Women’s Health Initiative concluded in 2002 that H. R. T caused far more harm than good the.
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http://2livingwell.blogspot.com/2007/09/health-theories.html
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