Salt has been demonized by nutritionists for decades. But we need it, and the risks from typical consumption levels appear overstated. 05/17/2021
In mainstream media articles on nutrition, common ingredients are often portrayed as simply good or bad. Vitamins are good; fat is bad. Fiber is good; sugar and salt are bad. But for years, the best research has shown that the complex science of food metabolism resists these simplistic classifications.
Many fats, such as omega-3 fatty acids, actually play vital roles within our bodies. And while vitamins certainly are good for us, there’s a lot of complexity surrounding how much we need of each, what’s the best form, and how to best combine them.
But perhaps no dietary staple is more confusing — and hotly debated — than salt. Conventional wisdom holds that we should limit our salt intake as much as possible to avoid high blood pressure and other ills, but the scientific evidence is far more complex.
Most recently, studies have critiqued the popular assumption that salt at levels previously labeled excessive is always bad, or otherwise failed to find strong links between “high” salt intake and poorer health. The latest study to look at the connection examines salt consumption and health in more than 150 countries. The study failed to find a link between higher salt consumption and increased mortality. In fact, the researchers found exactly the opposite: Higher salt intake was associated with less mortality around the world.
While the research has a few necessary caveats, it's a potentially provocative finding that’s adding to a body of research hinting that our relationship with salt is far more complex than we may think.
What Does Salt Do to Our Bodies?
There’s an important distinction to be made between salt and sodium. Sodium is a part of salt, and it’s an element that our bodies rely on. We get sodium from salt, which is a compound consisting of a sodium atom and a chlorine atom, commonly written using the chemical notation NaCl. So, recommended intake levels of salt, which contains both sodium and chlorine, are higher than recommended levels of pure sodium.
The World Health Organization recommends that people consume no more than two grams, or around a teaspoon, of sodium per day. But a number of studies contests that number, arguing that sodium is bad for our health only in much higher amounts.
The subject is likely more complex than we might think. Processed foods, which are known to be bad for us, are often high in salt. But that doesn’t mean the high salt content is necessarily what makes them so unhealthy. And other nutrients, potassium in particular, could play an important role in regulating our blood pressure as well.
The debate over salt largely boils down to a single letter: U. That’s the rough shape of the relationship between salt and health on a graph (Graudal et al., 2014). It means, at its most basic level, that both too much and too little salt is bad for us. In the middle there’s a sweet spot for salt where we’re consuming enough for our bodies to function, but not so much that it becomes bad for us. Much of the debate in recent years has centered on where exactly that salty sweet spot is.
Very low levels of salt intake (the left side of the U on the graph) are clearly bad for us. That’s because our bodies need sodium to function at their most basic levels. Sodium is a key player in our nervous system, and our bodies use it to help balance fluid levels, among other things. If sodium levels in our bodies fall dangerously low we can die, a condition known as hyponatremia. It happens only very rarely, though, such as when athletes drink far more water than they need (Hew-Butler et al., 2017).
How Much Salt is Bad?
There’s also evidence that very high levels of sodium, typically more than five grams per day, can be bad for us. Sodium contributes to high blood pressure, especially when consumed in excess, and chronically high sodium levels could also lead to kidney disease. In line with this mechanism, large-scale studies of salt and health have pointed to a potential benefit from lowering salt consumption in people with high blood pressure. (Read more: Americans are Getting Worse at Controlling Their Blood Pressure.)
For example, a review study from 2018 confirmed a link between higher salt intake and mortality (Malta et al., 2018). What’s been harder to prove, however, is whether it’s actually the salt itself that’s ultimately leading to worse health outcomes.
Going beyond correlations like these to find causation can be difficult. We might find a correlation between playing beach volleyball and getting eaten by a shark, for example, but that doesn’t mean volleyball actually leads to shark attacks. Instead, people who play volleyball at the beach might be more likely to go swimming in shark-infested waters afterwards.
Another long-term study, published in 2016, compared two groups of people: One lowered their salt intake for up to three years, while the other kept their dietary habits the same (Cook et al., 2016). Following up over the course of two decades, the researchers found lower mortality in the salt-restricted group died. They attribute this in part to better cardiovascular health due to a diet lower in salt.
But in a corresponding editorial, another group of researchers contested those findings. They pointed out that the number of participants, around 3,000 in all, was too low for this kind of study, and that there are a number of potentially confounding variables involved (Mente et al., 2016). The study didn’t account for other dietary factors that could have influenced mortality, for example. The editorial authors also note that the relationship between salt intake and health that the study found was not statistically significant, meaning it wasn’t big enough to point to a clear relationship. The editorial authors concluded that the study is “not robust evidence” of the effect of salt intake on health.
There’s still a lot we don’t know about salt. But research continues, most recently with a paper in the European Heart Journal looking at the relationship between health and salt consumption around the world (MEsserli et al., 2020). The paper takes a broad look at trends of salt intake and mortality in 181 countries, with the goal of seeing whether any meaningful trends emerge.
Surprisingly, the authors say they did find a meaningful relationship between the two — but not in the direction you might expect. Countries in which people consumed more salt actually saw less mortality, and greater lifespans, than countries where people consumed less salt. The results seem to contradict decades of popular advice on salt intake. But recent evidence suggests the authors’ conclusions might actually make sense.
We should note that there several factors that could distort the data in this latest study. Large-scale studies like this cannot account for all of the factors that could influence the data, so their results must be viewed in light of those potential shortcomings.
The authors call out a number of potential confounding factors that their study doesn’t account for, like the quality of healthcare in a country. This would produce a statistical trend toward both higher salt consumption and better health, but it wouldn’t necessarily mean more salt causes better health.
“Countries in which people consumed more salt actually saw less mortality, and greater lifespans, than countries where people consumed less salt.”
They also state that their data are observational (observational studies in nutrition can be unreliable, as people often track their consumption inaccurately). The scientists don’t want their findings to be seen as nutritional recommendations. But their work is relevant nonetheless. Because they failed to find a relationship between higher salt intake and mortality, the authors add credence to a growing number of studies indicating that, for most people, our salt consumption may not be something to worry about.
This takes us back to that U. Very high levels of sodium, somewhere north of five grams a day, seem to be clearly bad for us. However, most people around the world eat significantly less than that. One study puts the global average at around 3.95 grams of sodium per person per day (Powles et al., 2010). Americans are slightly under that, at an average of 3.4 grams daily.
And a 2020 paper suggests there’s just not enough evidence to say that eating anything under five grams of sodium a day is bad for people (O’Donnell et al., 2020). The same study also notes that achieving sodium levels below two grams per day is relatively difficult for most people.
What does all this mean? Americans have been berated by nutrition writers for decades about their awful dietary habits, and much of that is justified – but it appears that most of us are actually doing just fine when it comes to salt intake — we’re in the bottom part of the U, getting just enough salt.
On the other hand, because ambiguity clings to the issue, if your physician strongly recommends a low-salt diet, they are not necessarily wrong, and you may wish to stick with no-salt products, for example. Some people prefer them in any case.
If there’s one takeaway, it’s that our understanding of salt is still evolving. A consistent theme of most papers looking at the relationship between salt and health is “more research is needed.” All that can be stated clearly is that salt consumption levels once regarded as excessive may not be. We will keep you posted as the research comes in!
- Cook NR, Appel LJ, Whelton PK. Sodium Intake and All-Cause Mortality Over 20 Years in the Trials of Hypertension Prevention. Journal of the American College of Cardiology. 2016;68(15):1609-1617. doi:10.1016/j.jacc.2016.07.745
- Hew-Butler T, Loi V, Pani A, Rosner MH. Exercise-Associated Hyponatremia: 2017 Update. Frontiers in Medicine. 2017;4. doi:10.3389/fmed.2017.00021
- Graudal N, Jürgens G, Baslund B, Alderman MH. Compared With Usual Sodium Intake, Low- and Excessive-Sodium Diets Are Associated With Increased Mortality: A Meta-Analysis. American Journal of Hypertension. 2014;27(9):1129-1137. doi:10.1093/ajh/hpu028
- Malta D, Petersen KS, Johnson C, et al. High sodium intake increases blood pressure and risk of kidney disease. From the Science of Salt: A regularly updated systematic review of salt and health outcomes (August 2016 to March 2017). The Journal of Clinical Hypertension. 2018;20(12):1654-1665. doi:10.1111/jch.13408
- Mente A, O’Donnell MJ, Yusuf S. How Robust Is the Evidence for Recommending Very Low Salt Intake in Entire Populations? Journal of the American College of Cardiology. 2016;68(15):1618-1621. doi:10.1016/j.jacc.2016.08.008
- Messerli FH, Hofstetter L, Syrogiannouli L, et al. Sodium intake, life expectancy, and all-cause mortality. European Heart Journal. Published online December 22, 2020. doi:10.1093/eurheartj/ehaa947
- O’Donnell M, Mente A, Alderman MH, et al. Salt and cardiovascular disease: insufficient evidence to recommend low sodium intake. European Heart Journal. 2020;41(35):3363-3373. doi:10.1093/eurheartj/ehaa586
- Powles J, Fahimi S, Micha R, et al. Global, regional and national sodium intakes in 1990 and 2010: a systematic analysis of 24 h urinary sodium excretion and dietary surveys worldwide. BMJ Open. 2013;3(12):e003733. doi:10.1136/bmjopen-2013-003733