Fighting the last war
Today’s Wall Street Journal reports a recent study on “The Preventable Causes of Death in the United States: Comparative Risk Assessment of Dietary, Lifestyle, and Metabolic Risk Factors ” published online by the Public Library of Medicine. With scientists from major institutions and high powered statistical techniques, the study addresses the public health burden of a dozen “modifiable dietary, lifestyle, and metabolic risk factors” including dietary salt. Putting aside evidence that salt intake may not be “modifiable,” the authors tip off readers as soon as Table 1, footnote h that they’ve failed to take advantage of their opportunity to address this important question of mortality related to salt intake.
The footnote reads:
The effect of reduction in salt intake on SBP and the effect of subsequent decline in SBP on the relevant disease outcomes, were estimated at the individual level to account for possible correlation between salt intake and SBP.
Actually, there’s no need to read any further. The authors confine their concern for dietary sodium to extrapolated “benefits” based solely on blood pressure, totally ignoring both the two published studies of a randomized trial of the health outcomes of reducing dietary sodium and the entire literature of observational health outcomes studies which does not support the conclusion that SBP is the only relevant variable in determining disease outcomes. The authors term blood pressure a “disease outcome,” further weakening their credibility as examiners of mortality.
Even employing a fundamentally and fatally flawed methodology, they employ high powered statistics to examine the same question addressed earlier in the week by the Center for Science in the Public Interest which claimed salt caused 150,000 American deaths each year. This study puts the figure about 35,000 – wrong, but underscoring how fast and loose CSPI and NHLBI have been in playing with these projections.
Unfortunately, as has become the pattern, journalists pick up the news release and run with the story line. For example, Daniel Akst in the WSJ story reports:
Too many of us appear to be bent on slow-motion suicide. Consider smoking; if we could get every American to stop, we'd save 467,000 lives annually. Solving high blood pressure (much of it arising from unhealthy lifestyles) would save 395,000. And if we could get everyone to slim down to an appropriate body weight, we'd save 216,000 lives.
Great headlines. Lousy science.
Generals are often accused of preparing to fight the last war, not recognizing that events have moved on. The grand strategy of reducing the global burden of chronic diseases should remain our mission, to be sure, but we need to understand whether we’re using the right weapons in our battlefield tactics. The “last war” mentality is represented in the simplistic, one-size-fits-all campaign against blood pressure. Now we know there are many ways to reduce blood pressure. Some improve health; others, don’t. We used to bleed patients to improve their health. That certainly reduced their blood pressure. And many died. We used to urge pregnant women to reduce salt intakes; today that would be medical malpractice. Some interventions work to advance our mission of improving human health, other well-intended tactics have proved counterproductive, creating “unintended consequences,” like the 37% greater cardiovascular mortality among Americans consuming (recommended) low-salt diets. Think of salt reduction as waterboarding. Extreme, for sure. Some would argue unethical. But, bottom line, ineffective and possibly counterproductive.
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