"Everyone" knows that blood pressure (BP) is an important risk factor for heart attacks and strokes. There's solid evidence. And "everyone" knows that interventions to lower BP will improve these health outcomes. Or will they?

A new Cochrane Review concludes: "Aiming for blood pressure targets lower than 140/90 mmHg is not beneficial ." In their study, published July 8, Drs. J.A. Arguedas, M.I. Perez and J.M. Wright conclude:

High blood pressure (BP) is linked to an increased risk of heart attack and stroke. High BP has been defined as any number larger than 140 to 160 /90 to 100 mmHg and as a result this range of BPs has become the standard blood pressure target for physicians and patients. Over the last five years a trend toward lower targets has been recommended by hypertension experts who set treatment guidelines. This trend is based on the assumption that the use of drugs to bring the BP lower than140/90 mmHg will reduce heart attack and stroke similar to that seen in some population studies. However, this approach is not proven.

This review was performed to find and assess all trials designed to answer whether lower blood pressure targets are better than standard blood pressure targets. Data from 7 trials in over 22,000 people were analysed. Using more drugs in the lower target groups did achieve modestly lower blood pressures. However, this strategy did not prolong survival or reduce stroke, heart attack, heart failure or kidney failure. More trials are needed, but at present there is no evidence to support aiming for a blood pressure target lower than 140/90 mmHg in any hypertensive patient.

The Cochrane Collaboration invented the discipline of substituting "evidence-based" decisions for the opinions of doctors . We have recommendations on all sides of various medical issues and these Cochrane Reviews try to separate the sheep from the goats, identifying recommendations based on expert opinion as opposed to those based on scientific data.

I was reminded of an extended conversation I had more than 20 years ago with two of the world's foremost advocates of universal sodium reduction, the husband and wife team of Jerry and Rose Stamler. I asked the Stamlers whether the BP target for intervention was the "normal" 120/80. Jerry responded, no it should be lower. I pressed: 110/70? Jerry: lower. 100/60? Jerry: lower. 90/50? Lower. I tried the query from the other direction, noting that a corpse had 0/0 BP but was hardly "healthy." Jerry's final response was that any intervention that could lower BP was healthier and that practical limits on the amount that people could lower would represent both the minimum achievable BP and the healthiest BP.

The data in this study demolish that expert opinion.

For years "everyone" has known that having the entire population reduce its intake of dietary salt would reduce the rates of heart attacks and strokes. An earlier Cochrane Review of "Advice to reduce dietary salt for prevention of cardiovascular disease ," however, found no evidence supporting this platitude, though the fable continues to enjoy popularity among some experts despite the absence of confirming data.

Award-winning investigative journalist Gary Taubes described the situation in his "The (Political) Science of Salt " where he pointed out that while the data for universal salt reduction were eroding confidence in the theory, advocates of the intervention were becoming more strident and vocal. Said Taubes:

The dispute over salt, however, is an idiosyncratic one, remarkable in several fundamental aspects. Foremost, many who advocate salt reduction insist publicly that the controversy is a) either nonexistent, or b) due solely to the influence of the salt lobby and its paid consultant-scientists. Jeremiah Stamler, for instance, a cardiologist at Northwestern University Medical School in Chicago who has led the charge against salt for 2 decades, insists that the controversy has "no genuine scientific basis in reproducible fact." He attributes the appearance of controversy to the orchestrated resistance of the food processing industry, which he likens to the tobacco industry in the fight over cigarettes, always eager to obfuscate the facts. "My considerable experience indicates that there is no scientific interest on the part of any of these people to tell the truth," he says.

While Stamler's position may seem extreme, it is shared by administrators at the NHBPEP and the NHLBI, which funds all relevant research in this country. Jeff Cutler, director of the division of clinical applications and interventions at NIH and an advocate of salt restriction for over a decade, told Science that even to publish an article such as this one acknowledging the existence of the controversy is to play into the hands of the salt lobby. "As long as there are things in the media that say the salt controversy continues," Cutler says, "they win." Roccella concurs: To publicize the controversy, he told Science, serves only to undermine the public health of the nation.

After interviews with some 80 researchers, clinicians, and administrators throughout the world, however, it is safe to say that if ever there were a controversy over the interpretation of scientific data, this is it. In fact, the salt controversy may be what Sanford Miller calls the "number one perfect example of why science is a destabilizing force in public policy." Now a dean at the University of Texas Health Sciences Center, Miller helped shape salt policy 20 years ago as director of the Center for Food Safety and Applied Nutrition at the Food and Drug Administration. Then, he says, the data were bad, but they arguably supported the benefits of salt reduction. Now, both the data and the science are much improved, but they no longer provide forceful support for the recommendations.

This was written a decade ago. We've learned a lot since then. We have the Cochrane Review finding inadequate science to support general salt reduction. And now we have a new Cochrane Review that the approach of experts to treat lower and lower BP levels can be classified as expert opinion, not scientific fact.

What we need is more reliance on scientific data and less on the opinion of scientific experts. We need more confidence in the scientific method and more humility by many who profess to embrace its results. In the area of salt and health, including blood pressure, the role of overall dietary quality, the role of hormones, insulin resistance, etc.

In 2007, the poet Ted Sheridan wrote "The More We Learn, the Less We Know For Sure ." In our present circumstance, these humbling observations strike home. But they're hardly new. In the last century, Albert Schweitzer observed: "As we acquire more knowledge, things do not become more comprehensible, but more mysterious." And far earlier, Lao Tsu rendered this enduring reminder: "To know that you do not know is the best."

It all leads back to the core principle: primum non nocere, "first, do no harm ." Confining our interventions to those with solid evidence avoids unintended consequences. Pride is one of the Seven Deadly Sins.