Is Salt Bad For You?
Could a pillar of medicine be wrong?
For the last 50 years, we’ve been told to lower our salt intake. You doctor was taught in medical school that too much salt will raise your blood pressure. The paradigm of “higher salt equals higher blood pressure equals more heart attacks” is a pillar of medicine – a sacred cow, so widely believed that it has become heresy to question. But, questioning is exactly what science is supposed to do.
Consider that the human body is salty. Taste your blood or lick your sweat and it’s kind of obvious - those white sweat stains on caps and shirts after intense exercise are salt. And indeed, the average person loses 1.15g of sodium per litre of sweat, which takes about an hour of hard exercise.
When a person is clinically dehydrated, hospitals give a saline drip. Saline solution is 0.9% sodium chloride, which works out to 9 grams of salt per litre! That’s salt water directly into your veins. In other words, sodium belongs in our bodies.
And yet, in 2023, the World Health Organization (WHO) renewed the attack on salt, issuing sweeping guidelines recommending that people consume less than 2g of sodium per day. Let’s explore the salt guidelines in a bit more detail and unpack some of the history, science and evidence that supports a low salt intake… or doesn’t.
Measuring sodium and salt correctly
One fundamental point to note at the outset: sodium is not salt. Sodium is one component of salt. The other is chloride. The chemical name for salt is sodium chloride (NaCl). But the two molecules aren’t equal in weight. Sodium is approximately 38% the weight of salt with chloride making up the remainder. Salt also contains moisture which is the reason some salts have more sodium than others – it’s the water content that creates the difference. Using 40% is a good enough guide when approximating how much sodium is present in salt. So, if you take the weight of salt, say 10g, and multiply by 40%, you’ll get sodium of 4g. Going the other way, from sodium to salt, you can multiply by 2.5. Therefore, if the guideline says 2.3g of sodium per day, it translates to 5.75g of salt (2.3 x 2.5 = 5.75).
This can be confusing because sodium and salt are often used interchangeably, and the guidelines refer to sodium, not salt. Why? Because sodium doesn't come only from salt; it comes from sodium bicarbonate (baking soda), sodium citrate and other substances as well. Having said that, most sodium does come from salt. When working out your own consumption, be careful. Pay attention to whether you’re measuring sodium or salt.
What are the sodium guidelines and where do they come from?
Various medical associations and public health authorities issue guidelines on how much of a nutrient we should be getting. These guidelines, often referred to as RDAs (recommended daily allowances), are quite contentious in terms of the science behind them. A critical question is whether they should apply to all people equally or whether adjustments should be made for weight, gender, health status, genetics and other factors. Does one size really fit billions of people?
The most common RDA for sodium is a maximum of 2.3g per day for healthy adults, and 1.5g per day for people with hypertension. Some countries refer to slightly different amounts, but 2.3g is the most frequently used. Going back to the salt conversion factor, 2.3g of sodium equates to 5.75g of salt, and 1.5g of sodium is 3.75g of salt.
Dahl and the rats
Fears over salt have a long history. They surfaced as early as 1904, but it wasn’t until 1980, when the first dietary guidelines were published in America, that lowering salt become official government health policy.
The most influential sodium scientist in the 20th century was an American physician by the name of Lewis Dahl. Dahl compared hypertension across various populations and found that it was more common in societies with higher average salt consumption. These kinds of population-based studies, called epidemiological studies, are useful for generating hypotheses that require further study. But they should never be used to draw firm conclusions. For one thing, it’s impossible to isolate, or control, one variable in a population where everyone eats differently. There are hundreds of variables at play in someone’s diet, never mind the diet of an entire country.
Population studies also don’t have control groups. Measurement is a further problem. Subjects are typically measured once, and then it’s assumed that nothing changes, sometimes over decades. We aren’t sure about you, but we don't eat the same thing on two consecutive days, let alone a decade. Some types of population-based studies use self-reported questionnaires. These rely on memory and guesswork, not measurement.
Nonetheless, Lewis Dahl claimed that he had "unequivocal" evidence that salt causes hypertension. To be fair, not all the data came from epidemiology. Dahl also experimented with rats and he managed to induce high blood pressure in rats after feeding them gigantic quantities of sodium – the equivalent of giving a human 200 times the recommended daily amount. Yet, in 1977, the U.S. Senate’s Select Committee on Nutrition and Human Needs released a report recommending that Americans cut their salt intake by 50 to 85 percent, based largely on Dahl's work. Shortly thereafter, in 1980, the first official guidelines were born.
It's useful to note that the guideline to reduce saturated fat was also reached in a similar way, based mainly on population studies done in the 1950s - 1970s. Only recently, in 2020, did a group of leading nutrition scientists release a consensus statement saying that current scientific evidence “fails to support” the limit on saturated fat. It was a quiet announcement. The vast majority people - including doctors - are unaware of this development. How is this possible? For half a century, we've been wary of saturated fat. Now, all of a sudden, there's no evidence for a limit. Was it all wrong? Such is the power of the guidelines. They are so entrenched that even when the science changes, it's as if nothing happened.
What does more recent evidence say about salt?
In 1988, the Intersalt study was published. This large study, covering 32 countries, compared salt intake with blood pressure. Although it was found that people in countries with higher salt consumption had higher blood pressure, on average, the differences were small, and it was also found that individual responses to salt varied a lot. Within a single country, the correlations did not hold up, suggesting that some people are more sensitive to salt than others. This mirrored Dahl’s rat studies. In his experiments, genetic differences in rats meant that some were salt sensitive and some were salt resistant. The latter did not experience increased blood pressure, no matter how much salt was given to them. We’ll come back to salt sensitivity.
Fast forward to 2011. A meta-analysis of seven studies covering 6,250 people subjects in the influential American Journal of Hypertension found no clear evidence that cutting salt intake reduces blood pressure or the risk of cardiovascular events.
The study suggested that the relationship between salt intake and health outcomes might be more complex than previously thought, and that low salt intake could potentially lead to adverse health effects in certain populations. This conclusion challenges (to put it mildly) the long-standing public health recommendations that call for universal salt reduction. At worst, the guidelines may be harmful to people.
Earlier that same year, European researchers publishing in the respected Journal of the American Medical Association (JAMA) reported that the less urinary sodium people excreted—a proxy of prior sodium consumption—the greater their risk was of dying from heart disease. That’s an inconvenient finding. Less sodium, more cardiovascular deaths. It might be more appropriate to say “WTF?”.
Take a look at the graphs below. People were split into thirds by their assumed sodium consumption – high, medium and low. Look carefully at the key. The small dashed line represents the lowest sodium but has the HIGHEST number of cardiovascular deaths. And the solid line, representing the highest sodium, has the LOWEST death rate. This study was done on healthy subjects.
In another 2011 study, published in JAMA, this time analysing people who were not so healthy, a similar pattern emerges. People who limited sodium to 3g per day or less had more heart attacks and strokes than those consuming 4-6 grams per day. See the graph below.
In fact, the Goldilocks zone is 4-6 grams of sodium per day – double the guideline recommendation - with 5g being about the optimum point.
Remember to multiply these numbers by 2.5 to get salt. So, 5g of sodium equals 12.5g of salt, or about 2 ½ heaped teaspoons. Consuming less than 1g of sodium (2.5g of salt) per day looks positively disastrous, as does consuming more than 10g of sodium (25g of salt) per day.
The 3 different lines in the above graph refer to 3 different classifications of cardiovascular events, but all 3 have the same basic pattern of poor outcomes at low levels of sodium consumption and very high levels, with the best outcomes occurring at 4-6 grams of sodium per day.
In 2004, the reputable Cochrane Collaboration, an international, independent, non-profit research organization, funded by the US Government, published a review of 11 salt reduction trials. Over the long term, the review found that seriously reducing salt intake led only to a modest reduction of 2 mmHg in systolic blood pressure and 0.6 mmHg in diastolic blood pressure. (These were people who did not have hypertension). That’s like going from 120/80 to 118/79.
In people with hypertension, the reduction was equally undramatic, though a little better. The conclusion was that “intensive interventions provide only minimal reductions” in blood pressure. The evidence for improved cardiovascular outcomes was even less convincing, resulting in the conclusion that “direct evidence for a reduction in cardiovascular events is limited.” We love how understated these phrases are! The conclusions should be screamed from the rooftops, but perhaps someone forgot to pay the headline writers.
It seems that for every study showing benefit from salt reduction, there's another showing no benefit. And, where benefits are shown, they are small. Then, there’s the nagging concern that too little salt is harmful, something shown in enough studies to be concerning. You’d expect a guideline as important as sodium to have compelling evidence. After all, lower salt is not just universal medical advice – it has pervaded popular culture. But there you have it.
Why does it take so long for new science to emerge?
Guidelines are remarkably resistant to change. Why is this? Well, that's a long and complicated story. Vested interests, commercial distortions, money, politics and egos get in the way. People joke that science advances one death at a time. What they mean is that you have wait for a prominent scientist to die before a different view can emerge. For a lesson on the subject, read Nina Teicholz's wonderfully researched The Big Fat Surprise, named one of the best books of 2014 by The Economist and The Wall Street Journal. It reads more like a mafia story than a scientific history. Don't expect guideline authorities to say, "oh sorry, we got it wrong," anytime soon.
Unfortunately, new science often takes a very long time to be adopted, especially when it threatens entrenched interests. Bad science takes an equally long time to disappear. It took decades for doctors to accept that they should wash their hands before delivering babies, after Ignaz Semmelweis showed, convincingly, in the mid-1800s, that the simple practice of hand hygiene saved lives. Many mothers died of puerperal fever in the time it took for good science to take hold. With current nutrition guidelines, that’s time people don’t have.
New York’s assault on salt
In 2010, New York undertook an anti-salt campaign, aiming to reduce the salt content of restaurant and packaged food by 25% over 5 years. An article in the publication “reason” called the assault on salt "astonishingly presumptuous", affecting the diet of the entire country and saying that the policy could cause more harm than good. The criticism was rooted in the acknowledgment that “only 10% of the population may benefit.”
Michael Alderman, former editor of the American Journal of Hypertension said at the time, “They want to do an experiment on a whole population without a good control. That’s not science.” Alderman warned that the benefits may not outweigh the hazards.
"The human kidney is made, by design, to vary the accretion of salt based on the amount you take in," explained Alderman. Rather than create drastic salt policies based on conflicting data, Alderman and his colleague proposed that the government sponsor a large, controlled clinical trial to see what happens to people who follow low-salt diets over time. “Such a trial will not be done, in part because it would be so expensive. But unless we have clear data, evangelical anti-salt campaigns are not just based on shaky science; they are ultimately unfair."
The importance of salt sensitivity
Time and time again, it has been shown that people respond differently to changes in salt consumption. Just like the rats in Dahl’s experiments, some people are sensitive to salt, meaning their blood pressure rises in response to more salt and drops in response to less, and some are resistant, meaning their blood pressure doesn’t change in response to salt. You’d expect the majority of people to be sensitive, given our low salt guidelines, but the opposite is true. Best estimates are that only 25% of people are sensitive to salt.
In 2013, researchers at the University of Virginia (UVA) developed a test than could identify the 25% of people who are salt sensitive. They demonstrated that each person has a “personal salt index.” Unfortunately, the test involved isolating kidney cells from urine and seeing how they metabolize sodium. It isn’t exactly a home kit. Senior author on a paper on the topic, Robin Felder, echoed the “25% are sensitive to salt” estimate. To confuse things further, he also said that about 15% of the population exhibit an increase in blood pressure in response to a low salt diet, the opposite of what’s supposed to happen.
Salt sensitivity may be more concentrated in African American populations, in older people and in people with existing hypertension, but, overall, the majority are not salt sensitive. Given that low salt intake may be harmful, it makes no sense to have a universal recommendation that suits only a minority and may harm many others.
Understanding our powerful survival switch
One of the world’s leading experts on blood pressure, kidney function and metabolic disease is Dr Richard Johnson, author of “Nature Wants Us To Be Fat.” In his fascinating book, he explores various mechanisms leading to weight gain and metabolic disease, including the role of salt.
One of the key takeaways from Dr Johnson's work is the identification of the mechanism by which salt can cause higher blood pressure. But, it is not the salt itself that causes the problem. It is dehydration. The implication of this is profoundly important. When salt is taken together with water, the negative effects do not occur.
Rick explains that our bodies have a survival mechanism designed to protect us during times of water shortage or food scarcity. This mechanism, or "switch", as he calls it, raises blood pressure and causes us to store more fat. By activating the hormone vasopressin, which inhibits urine, our bodies are able to increase blood pressure by retaining water. Higher blood pressure protects us because blood flow ensures the delivery of oxygen and nutrients to cells. Fat storage increases energy reserves in preparation of future shortages, and also helps us retain water. This is a wonderful system for survival, but if it is chronically elevated, we will eventually run into health problems.
We become dehydrated when we lose too much water. The sodium concentration in our blood rises, picked up by sensors in our brain which make us thirsty. When water doesn't arrive, our body takes action by triggering the survival switch to hold onto the water we have, raising blood pressure. But here's the thing - when we take in too much salt without enough water, the same rise in sodium concentration occurs, and our brain perceives dehydration. When sodium concentration is raised constantly, our blood pressure becomes raised, especially if we are salt sensitive.
As simple as it seems, we can avoid triggering this mechanism by drinking enough water. This keeps sodium concentration levels in our blood normal. The humble act of hydration (water + salt) makes all the difference.
Low sodium presents another problem. If we don't get enough sodium, a system called RAAS (renin-angiotensin-aldosterone system) responds. The hormone aldosterone tells our kidneys to retain sodium, and angiotensin constricts blood vessels to maintain blood pressure in a low sodium environment. Think of squeezing a hosepipe to increase water pressure. These stressors are also not good for us if they are constantly activated. One can see that both high and low sodium concentrations can be problematic.
The simple antidote for all this is enough sodium along with water, allowing our bodies to regulate properly. If we are healthy, our kidneys and hormones know what to do.
Health-conscious people and exercisers need more salt
It is well documented that people who ditch processed food and follow a healthy, whole-foods diet, especially one that is lower in refined carbohydrates and sugar, exhibit a noticeable loss of more fluid and sodium, often leading to feeling lethargic, and "headachy", and being prone to muscle cramps, even though their health markers improve. The antidote is simple - higher sodium. Prominent doctors and researchers on the subject, like Drs Finney and Volek recommend 5g of sodium per day and enough water, along with additional potassium and magnesium. This advice applies to low carb, keto, paleo, carnivore and low sugar, whole-food diets, but it doesn’t need a label. If you’re eating healthy, you need more salt.
The same is true of intermittent fasting. Sufficient sodium, potassium, magnesium and water is needed. Taken in a clean format, in other words without sugar or additives, this doesn’t break a fast and will make you feel a lot better. Dr Jason Fung, a Canadian nephrologist and expert in this area, has written two great books, The Obesity Code and The Complete Guide To Fasting that are worth reading.
Higher sodium has become pretty standard advice among doctors who practice lifestyle medicine. It is echoed by experts, nutritionists and researchers like Dr James Dinicolantonio, author of The Salt Fix. Healthy people feel a lot better when they up their salt.
Perhaps that's why hydration and electrolytes have become such a thing. Popular podcasters such as Tim Ferris, Dr Andrew Huberman, Dr Peter Attia, Chris Williamson and Steven Bartlett (Diary of a CEO) mention hydration regularly.
For those who exercise, it’s worth remembering that the guidelines and recommendations do not take into account sweating, so add extra sodium to replace what you lose, especially when engaging in activities like hot yoga. The same goes for sauna.
Where does that leave us?
Aside from being disappointed with the guidelines and disillusioned with public health authorities, it leaves us with quite a clear message on what to do. Very high, or very low, sodium is not a good idea. Both the evidence, and the mechanisms for how (and why) we regulate sodium point in the same direction – 5g per day (12.5g of salt) is a good place to be. It’s a lot more than the guidelines suggest, but you’ll feel better, and the outcomes from many peer reviewed studies and published reviews are good. Just make sure you measure correctly.
Also, remember to replace additional sodium when you exercise or sweat. And drink enough water. It’s not just a “nice to have”. Your body needs water for many reasons, but, crucially, it makes the salt benign, even in those with sensitivity.
If you’re eating a healthy diet or fasting, add another gram or two of salt to your diet. Use muscle cramps, your exercise performance and general fatigue as your guide for when you aren’t getting enough.
Lastly, and importantly, buy a home blood pressure machine and learn how to use it. Dr Peter Attia has an entire podcast on measuring blood pressure. It’s not as simple as you think, but once you know how, it’s quick and easy. You won’t have to guess if you’re running into trouble with hypertension.
If your blood pressure does get to an unhealthy range, try lowering carbohydrates or fasting. Use exercise, breathing techniques and sauna to manage stress. You’ll be surprised at how often these lifestyle changes can get your blood pressure into range. Medication should be the last resort, not the first. Don't tell the pharma companies.
It's high time we ditched our fear of sodium. We aren't in the 1980s. There's good science out there, if we look properly. We can't wait for the gatekeepers to wake up. Stay hydrated, stay healthy, and let’s be salty.
DISCLAIMER: This article should not be taken as medical or dietary advice. Make sure to check with your healthcare practitioner before any making changes to your diet, medication or supplementation.
For a critique on the 2023 WHO guideline for sodium, check out Robb Wolf's excellent blog post.
