Salt, Science, and Health: FAQ
Competitive Enterprise Institute consumer policy analyst Michelle Minton answers 8 questions on what recent medical research tells us about the effects of salt on human health. Minton is the author of the recent CEI study Shaking up the Conventional Wisdom on Salt: What Science Really Says about Sodium and Hypertension.
Why does CEI care about sodium policy and how does it relate to CEI’s mission?
CEI’s mission is to help people live freer, more economically secure lives by lifting government barriers to opportunity and success. Government policies that impact people’s lives should be based on sound scientific research and analysis. Too often, however, science itself gets politicized, as with government-issued dietary restrictions and recommendations.
As CEI’s consumer policy expert, I have a passion for protecting consumers from heavy-handed government regulations that do more harm than good. I became especially interested in the politics of sodium after the publication of a 2013 Institute of Medicine report assessing the evidence supporting current government recommendations on dietary sodium. Though IOM’s conclusion was that population efforts to reduce sodium intake to 2,300 mg per days were supported by the evidence, it became disturbingly clear that there is little evidence to support the notion that this sort of extreme sodium reduction is beneficial or easily achievable for the majority of people.
In fact, the assessment also included discussion of a number of well-conducted population surveys hinting at a possible association between low sodium intake and poor health outcomes. This raises multiple questions. Where did the original 2,300 mg upper limit come from? What research was it based on? Does more recent research support sodium restriction for most people?
What is the FDA doing on sodium and why?
Cajoled by public health advocates, the Food and Drug Administration has proposed “voluntary” sodium reduction goals for a broad range of prepared, ready-to-eat foods sold in grocery stores nationwide.
When finalized, the FDA’s new sodium limits would be phased-in in two stages:
- Food manufacturers are expected to institute the initial short-term reductions in the first two years.
- Within ten years, manufacturers would be expected to reach even lower sodium targets in their products. The goal of reducing sodium in the food supply is to lower the amount of sodium in the average American’s diet from the current 3,400 mg/day to the government-recommended upper limit of 2,300 mg/day. The hope is that doing so will lower the prevalence of high blood pressure and, ultimately, result in fewer premature deaths.
The government’s plan is modeled on strategies tested in other nations and based on research showing some success with gradual, “stepwise” sodium reduction for individual foods – cases where consumers adapt to a lower salt taste in single food items, such as bread, soup, and dairy products.
Notably, while the UK and Finland have apparently had some success in reducing population sodium intake after instituting similar plans, these countries started with higher average intakes than the U.S. So the sodium reduction achieved in the UK and Finland merely brought intake down to current U.S. levels—and within the observed average range of most of the world’s populations. In short, we can’t assume that the UK/Finland approach will have the same impact here in the U.S. More troubling, there is little data to show that sodium reduction will result in actual health gains in the population; but there is evidence indicating it could worsen health in some. And isn’t this why we are supposedly trying to reduce sodium in the first place, for health gains?
If the FDA’s guidelines for sodium are voluntary, can food makers simply choose not to adopt them?
Though described as voluntary, due to the nature of the regulator-regulated relationship between industry and the FDA, suggestions made by government regulators can’t be blithely defied or ignored. Food makers will feel pressure to comply and fear of retaliation and will likely comply instead of risking the ire of regulators.
What’s the difference between eating 3,400 milligrams of sodium, like people do now, versus cutting back to 2,300 milligrams, like the FDA recommends?
Currently, the average American consumes about 3,400 milligrams of sodium, which is roughly equivalent to one and a half teaspoons of table salt (sodium chloride). Meeting the government’s current recommended limit on dietary salt would require the average American to cut about 1,100 milligrams of sodium—or a half teaspoon—from their daily diet.
But people don’t really consume salt in teaspoons—it’s dispersed throughout the food we eat. And not just in processed snacks foods like potato chips, pretzels, and fast food. Most foods contain some salt, making it more difficult than you might think to cut sodium without simultaneously reducing the intake of other vital nutrients.
Take, for example, some common foods and their average levels of sodium:
- A cup of low-fat cottage cheese contains about 850 mg
- A glass of milk has just over 100 mg of sodium
- Two tablespoons of hummus contain about 120 mg of sodium
- Two large stalks of celery contain about 100 mg of sodium
- A medium pickle has nearly 800 mg of sodium
- 1/2 a cup of salsa has about 800 mg of sodium
- Two ounces of cheese (e.g. brie or cheddar) contains about 350 mg of sodium
- Two ounces of goat cheese (e.g. feta) contains 650 mg of sodium
- Two slices of white bread contain about 300 mg of sodium
- A tablespoon of hot sauce has almost 400 mg of sodium
- And adding a “pinch” of salt to any meal adds about 200 mg of sodium.
Do we know what sort of people should cut back on salt, compared to what sort people should eat the same or more, based on scientific research?
There are currently no studies establishing the lowest level of salt a healthy adult should consume, but the National Academy of Medicine, a professional association, noted in a 2013 report that a diet with at least 1,500 mg per day is typically enough to ensure that one is consuming an adequate intake of other nutrients.
Standard dietary advice is that older and/or African-American patients pay special attention to their sodium intake, because they are at a greater risk for developing hypertension. This is particularly true if they consume more than the upper end of the average range (greater than 5,000 mg of sodium a day).
However, even for these groups, research indicates that increasing potassium—particularly via increasing intake of fruits and vegetables—is also beneficial in reducing hypertension risk and may confer other benefits. Though such decisions should be made with the consultation of a medical professional, research indicates that combining weight loss (if overweight) and increased vegetable and fruit consumption (with or without sodium restriction) would likely be the most beneficial approach for people at risk of developing hypertension.
A few conditions might prompt a doctor to recommend increasing a person’s sodium intake. For example, if a patient has low blood pressure, is inverse salt sensitive, or consumes an extremely low level of sodium. However, the vast majority of Americans—if they consume a sufficient number of calories—likely consume an adequate amount of sodium.
If people can’t count on the FDA for good advice on nutrition, like how much sodium they should consume, where should people go instead?
The scientific process is not a sport where teams play until a referee decides on a winner and then everyone goes home. Rather, it’s an ongoing process. We gain greater understanding over time, as researchers propose, test, and retest hypotheses and confirm, refute, or refine what we know. Sometimes, this understanding can reach a level where we can say it is likely that a certain course of action will result in benefits or harms for large swaths of the population, but it is almost never the case that a single, one-size-fits-all recommendation is helpful or without risk for everyone.
Individuals should do their own research, consult with their medical advisers, and monitor how any lifestyle modifications affect their personal health.
Do researchers themselves ever have a bias that people should know about?
Human beings all have biases, and researchers are no exception. However, good researchers—including all those mentioned in CEI’s study—make an effort to acknowledge and control for as many biases as they can. Despite that, there is still bias in what researchers choose to study and often how they design their investigations. Funding is one big motivator. For example, if research grants are only available to study the effect of sodium on hypertension, researchers might be less inclined to focus on other aspects of the disease. By looking for a connection or lack of connection between sodium and blood pressure, it’s possible they may not see or ignore the impact of other factors.
Another form of bias that we are all susceptible to is confirmation bias. We pay more attention to and tend to emphasize evidence that seems to confirm what we hoped or expected to see. Again, most well-designed studies will attempt, in some way, to establish a protocol and methods that limit this sort of bias. For example, in a study attempting to combine the results of many studies, researchers will search all relevant databases and include all studies that meet pre-determined, objective standards. However, even in applying “objective standards,” researchers may unintentionally exclude or include studies in a way that skew the results.
Lastly, many researchers are guilty of drawing conclusions that just aren’t fully established by the data. For example, when comparing sodium intake in populations to their mortality risk, even if an association is found (e.g. high or low sodium populations have higher rates of mortality), it is usually inappropriate to assume one factor is caused by the other. (Correlation is not causation!) It may be that the same factors leading to a greater risk of death also push populations toward high or lower sodium diets. For example, people who are ill tend to consume less food and thus less sodium, so they may already be more likely to die regardless of their sodium intake. But it’s not true that low sodium caused those deaths. Correlation is valuable, but drawing definitive conclusions from such observations is usually inappropriate.
As noted, few—if any—of the studies discussed in CEI’s report, Shaking up the Science on Salt, are egregiously guilty of failing to control for biases. Furthermore, none appears to be guilty of intentional bias—that is, altering data or methods in order to obtain certain results. However, many are “biased” in what it is they choose to investigate. The focus on sodium, for example, seems to have obscured the significant impact of dietary potassium on blood pressure.
What should Congress or the president do to change FDA policy?
The FDA was created with the purpose of improving the safety of our food, drug, and cosmetic products. That is, to prevent acute harms caused by faulty products or erroneous claims. But there has been what’s called “mission creep.” In recent decades, the agency has turned from focusing on these acute harms to trying to mitigate chronic disease—that is, conditions caused by an individual’s lifestyle and dietary choices.
Due to the nature of the scientific process, it is almost never appropriate for government to promote population-wide dietary recommendations. Meddling in personal choices in this way may not only fail to improve population health but could influence what questions researchers choose to ask. While it might be beneficial for government agencies to offer an overview of the current state of research on various dietary issues, such statements should encourage consumers to get informed and work with their physicians before modifying their diet.
Congress and the president should direct government health agencies to refocus their efforts on the missions for which Congress established them. In the case of the FDA, that means putting more energy into investigating food and cosmetic safety and approving new drugs and devices.