What you’ve heard about salt and hypertension may not be right.
Hypertension, or chronically elevated blood pressure, effects about 70 million Americans. The condition is associated with a significantly increased risk for several deadly diseases and conditions including heart attack and stroke. Finding and promoting solutions that reduce the prevalence of hypertension could save and improve many lives and reduce healthcare costs.
Government agencies and public health organizations have targeted sodium as both the cause of and solution to the problem. Although there is much evidence indicating a link between blood pressure and salt for some people, salt reduction is neither helpful, nor always appropriate, for all people. And the myopic focus on salt has obscured a robust and growing body of research indicating that other approaches might be as—if not more—effective than sodium reduction for reducing hypertension. That’s the finding of my new CEI study, Shaking up the Conventional Wisdom on Salt: What Science Really Says about Sodium and Hypertension.
Four decades of concerted effort to lower American’s sodium intake has failed. Hypertension has increased over the last 20 years while Americans’ intake of salt has remained largely unchanged since the 1950s. If we truly hope to conquer this disease, we must pay attention to all of the science on salt, giving consumers and doctors the information and tools they need to create personalized treatment plans. Whether sodium reduction is or isn’t part of the plan should be a decision left to patients and their doctors.
How did salt become the standard?
The world of scientific research on salt and health is the geekiest gangland war of all time. Or, as science journalist Gary Taubes described it in his award-winning 1998 article, “one of the longest-running, most vitriolic, and surreal disputes in all of medicine.” It began in the early 20th century and continues today with seemingly contradictory news headlines like “Too Much Sodium Is a Global Killer” and “A Low-Salt Diet May Be Bad for the Heart.” Despite more than a century of scientific research, we seem no closer to definitive answers. Even as the U.S. Food and Drug administration last summer unveiled plans to lower sodium levels in the food supply, hoping that would finally counteract America’s salt-tooth, some in the research community questioned the value of sodium restriction for everyone and noted that it might even be harmful for some.
So, who’s right? To find out, I walked willingly—maybe naïvely—into this storied scientific history. What I discovered were mean streets with opposing “gangs” of researchers, some funded by industry and some by government, but all guarding their turf and mostly shouting past one another. Stuck in the middle of this noise are consumers, trying to figure out the healthiest diet to follow.
Official recommended limits on sodium came about only in the late 1970s, stemming from U.S. Senate hearings and a subsequent report based on preliminary and often questionable science. Politics and pet-theories drove much of the conversation and recommendations. Since then, subsequent research has made it clear that there isn’t a single “perfect” method for everyone to reduce blood pressure and hypertension risk.
In the real world, science is slow. Teams of researchers battle over hypotheses in the pages of academic journals until one proves to be the more accurate representation of phenomena. Back when Sen. George McGovern (D-SD) convened his Select Committee on Nutrition to come up with recommendations for the nation, the science was even less clear. But our elected leaders insisted on coming up with answers anyway, even over the protestations of experts who pleaded with the committee to wait for more research before developing recommendations for the entire population. “Senators don’t have the luxury that the research scientist does of waiting until every last shred of evidence is in,” McGovern quipped.
Thus, based mainly on imperfect data, staffers for the Select Committee issued their report—a balancing act between personal agendas and industry demands. The U.S. Department of Agriculture subsequently translated this report into the first Dietary Recommendations for Americans in 1980. Many aspects of the recommendations were controversial, with Philip Handler—President of the National Academy of Sciences—calling the low-fat and low-cholesterol recommendations “utter and complete nonsense.” Also controversial were the recommendations to limit salt to about 8 grams (about 3100 mg of sodium). While the Committee’s cholesterol and fat recommendations have since been challenged and largely debunked, the salt recommendations remain firmly part of nutritional dogma.
The most influential researcher on the development of the sodium guidelines was, arguable, Lewis K. Dahl. His work on blood pressure in observational studies of various human populations and in rats demonstrated that a high level of sodium intake is related to blood pressure and possibly health outcomes. Since Dahl’s work in the 1960s, a steady stream of high-quality evidence has shown that dietary sodium can indeed influence blood pressure. But most showed a surprising, but statistically insignificant inverse correlation between salt and blood pressure, as well. That means some people with higher dietary sodium also had lower blood pressure.
More recent work has demonstrated that, even though groups of people averaged together may show a uniform trend in the association between sodium and blood pressure, there are wildly different blood pressure responses to dietary sodium within populations. For example, research indicates that about 25 percent of the population is “salt sensitive,” meaning their blood pressure rises as dietary sodium is increased. However, most—perhaps upwards of 75 percent—are insensitive to moderate increases and decreases in dietary salt. A small percentage, an estimated 11 to 16 percent, however, are “inverse-salt-sensitive,” and will experience higher blood pressure as dietary sodium is decreased. The cause of this heterogeneity in response to dietary sodium is not yet known but may be related to the other components of a person’s diet, their genetic background, and other lifestyle factors.
Furthermore, an increasing body of research has shown that decreasing salt consumption—even if it does lower blood pressure—may not be associated with better health. Blood pressure is, of course, merely a marker of health not an outcome; people don’t die as a result of high blood pressure, but rather from the conditions closely associated with blood pressure like heart attack and stroke.
What does all this mean? Frankly, it means the research is inconclusive for population-wide sodium recommendations. For certain individuals, like those who are salt-sensitive and consuming higher than average sodium intakes, sodium restriction may make sense. On the other hand, for certain groups, such as those who are inverse salt-sensitive, or those who are diabetic (for whom studies have found lower salt increases mortality risk) it might not be the best approach. Put more simply: the research doesn’t support sodium restriction in the general population consuming average sodium levels as a means to reduce blood pressure.
Perhaps the most interesting finding, however, is that the literature has been quietly affirming the effectiveness of other—possibly more appropriate—ways to lower blood pressure. At the top of the list is dietary potassium, which researchers had identified as lowering blood pressure at nearly the same time they began studying the effects of sodium on blood pressure. Consistently, almost without fail and on both sides of the sodium debate, studies have shown that doubling dietary potassium is as effective as halving dietary sodium. More importantly, the effect has been observed in almost every population in which it has been studied, regardless of race, sex, age, location, and other genetic and lifestyle factors.
In addition to potassium, other factors have shown promise in lowering blood pressure and hypertension risk, including losing weight (generally measured by body mass index) and increasing hydration levels. Most studies show that the effects are synergistic, meaning that combining these approaches is more effective than any one on its own. The difference, perhaps, is in the likelihood of adhering to any one or any combination of these therapies. Sodium reduction, as experimental scientists have observed, is frustratingly difficult. Subjects seem to unconsciously alter their diet in order to obtain the level of sodium their bodies crave. Even those actively trying to lower sodium—told by their doctors that their lives may depend on restricting the mineral—struggle to stay within the government’s recommended limits. Anecdotally, this failure to maintain a low salt diet may result in people simply giving up; throwing up their hands and declaring that they’d rather eat well for a few years than suffer and live to be 100.