Generally, the public accepts that science advances using a time-honored discipline that subjects our current understanding of the world around us to rigorous testing which refines that understanding and generates new hypotheses to be tested. If scientists are successful, our understanding will always be evolving as we discard unsupported theories. So it is with medical science. Or should be.
The progress of clinical investigation would be sterile, however, if it were not translated into advancing the medical treatment of people who are or who may become ill or improving public health recommendations applicable broadly to the general population. Yet these recommendations to doctors treating their patients or public health authorities charged with safeguarding the population contain an inherent tension between the educational axiom that the teaching message be repeated in order to be absorbed and the inevitability that scientific advance requires that the teaching message be modified and refined. Couple that truism with the fact that some medical science is strictly-disciplined and objective while the credibility of other studies is clouded by concerns about the bias of the investigators, and it is small wonder that the public pronounces itself confused at the welter of conflicting recommendations. So it is with dietary recommendations.
Seeking resolution of this conundrum, or at least guidelines for doctors and the public to determine how much confidence to place in a particular recommendation, an international consortium based at Oxford University in the UK, led by British epidemiologist Dr. Archie Cochrane was founded in 1993. It is now worldwide and maintains the Cochrane Database of Systematic Reviews published quarterly as part of The Cochrane Library. It coined the term “evidence-based medicine and health care,” defined as the careful discipline it advocates. While all doctors and committees counseling health improvements unanimously claim to be producing “evidence-based” recommendations, adherence to the strict standards of the Cochrane Collaboration distinguish those which should be valued as truly “evidence-based.” To assess the quality of data, “evidence-based” healthcare insists on using a hierarchy of evidence, referred to as the evidence pyramid, to assign different levels of value to various sources of data based pri­marily on research design. [insert pyramid from Spring 2006 S&H)
The public can be harmed following advice based on poor evidence or poor interpretation of good evidence. A generation ago, acting on the logical and plausible – though clinically unconfirmed – theory that post-menopausal women would benefit from hormone supplements, many women undertook Hormone Replacement Therapy until careful investigation proved HRT was killing many. Examples abound. Physicians no longer do blood-letting, another widely-known lesson from medical history.
Understanding the discipline of “evidence-based” recommendations offers indispensable insight into understanding the current controversy among medical researchers on the potential for health benefit of reducing dietary sodium which is advocated by many expert committees but which the Cochrane Collaboration finds unsupported by the scientific evidence. Using the Cochrane Collaboration techniques, The U.S. Preventive Services Task Force Recommendations for a healthy diet, chapter 56 on "Counseling to Promote a Healthy Diet," at pages 625, 629 and 634 states:
“There is insufficient evidence that, for the general population, reducing dietary sodium intake or increasing dietary intake of iron, beta-carotene, or other antioxidants results in improved health outcomes ("C" recommendation); recommendations to reduce sodium intake may be made on other grounds, including potential beneficial effects on blood pressure in salt sensitive persons.
“[C]ontrolled prospective studies will ultimately be necessary to provide definitive evidence that normotensive persons who practice dietary sodium restriction are at lower risk of developing hypertension over time than are those with more typical sodium consumption.”
Only one country has claimed successful salt reduction, Finland, and public health statistics show that reducing salt may have retarded Finn’s health improvements compared to neighboring countries.