Humans, like many other animals, crave the taste of salt. Animals frequent salt licks, humans have traded salt for equal weights of gold, and the word “salary” comes from the Roman soldier’s allowance for purchasing salt. Salt appears in our language in idioms like “worth its salt” and “salt of the earth.” Shakespeare’s play King Lear is a variant of a folktale where a daughter tells her father she loves him as much as meat loves salt. In a murder mystery I read years ago, a character listed the four food groups as sweet, salty, sticky, and chocolate.
It’s no fair: everything that tastes good turns out to be bad for us. We love the taste of salt, but dietary guidelines tell us we should all limit our sodium intake to less than 2.3 grams (2300 mg) a day to avoid high blood pressure and death from cardiovascular disease. And those who are fifty-one, African American, or who have high blood pressure, chronic kidney disease or diabetes should limit their intake even further, to 1500 mg a day or less.
(Note: the salt molecule consists of an atom of sodium and an atom of chloride; 40% of the weight is sodium, so 1500 mg of sodium equals 3750 mg of salt, roughly ¾ of a teaspoon. Over 75% of our salt is already in the food, not added from the salt shaker.)
In 2010, the American Heart Association lowered its recommendations to 1500 mg a day for everyone. We thought that was good advice, but new evidence has muddied the waters.
In the latest issue of The New England Journal of Medicine, three new studies about the role of salt in cardiovascular disease were published. Instead of providing clear answers, they raise more questions. In a cute NEJM QuickTake cartoon video they summarize the findings of the studies. If you’d rather spend three minutes watching cartoons than reading my explanation, feel free.
Salt and health: the background
High blood pressure is a known risk factor for heart attacks and strokes. Numerous studies have shown a correlation between salt intake and blood pressure, but the correlation between salt intake and cardiovascular outcomes like stroke and death has not been so clearly established. The large INTERSALT study found a modest association between higher levels of sodium intake and higher blood pressure. Some systematic reviews of the literature have confirmed that association, others have not. A 2013 review in the British Medical Journal found that lower sodium intake was correlated not only with a lower risk of hypertension but also with a lower risk of stroke and fatal coronary heart disease. Prospective cohort studies have shown inconsistent associations between sodium intake and cardiac risk.
Larger studies were needed to settle the issue.
First study: Association of Urinary Sodium and Potassium Excretion with Blood Pressure, by Mente et al.
Subjects: 102,216 adults from 18 countries. Method: single fasting urine levels of sodium and potassium were used to estimate 24-hour excretion, providing an indirect estimate of dietary intake. Findings: the association of sodium with BP was greatest in hypertensives, the elderly, and those who had the highest intakes of salt. It was greatest in those ingesting over 6 grams of sodium a day, modest in those ingesting 3-5 grams, and not significant in those ingesting less than 3 grams a day. They found an inverse relationship for potassium: higher levels of potassium were associated with lower blood pressures.
Second study: Urinary Sodium and Potassium Excretion, Mortality, and Cardiovascular Events, by O-Donnell et al.
Subjects: 101,945 adults from 17 countries. Method: as in the first study, single fasting urine tests were used to estimate 24-hour urinary sodium and potassium excretion; those estimates were compared to a composite outcome of death and major cardiovascular events. Findings: mean sodium excretion was 4.93 g. Compared to a reference range of 4.00-5.99 g a day, the odds ratio for death and cardiovascular events was 1.15 for high sodium excretion (over 7 g a day) but was even greater at 1.27 for a low sodium excretion (below 3 g). Higher potassium excretion was associated with decreased risk.
Third study: Global Sodium Consumption and Death from Cardiovascular Causes, by Mozaffarian et al.
The authors reviewed 205 studies on sodium consumption from 66 countries. Estimated mean global consumption was 3.95 grams a day, with regional means varying from 2.18 to 5.51. Daily sodium intake >6 grams a day was associated with increased risk of mortality and cardiovascular events. Surprisingly, so was intake of <3 grams. The lowest risk was in the 3-6 gram range. They used a computer model to estimate that 1.65 million deaths a year could be attributed to a sodium intake of greater than 2 grams a day. That’s about 10% of all cardiovascular deaths. The rate ranged from 4 deaths per million adults per year in Kenya to 1,967 per million in Georgia.
Discussion of the results
We knew too much sodium was risky, but these studies raise concerns that too little sodium might be even worse. As the accompanying editorial points out,
They call into question the feasibility and usefulness of reducing dietary sodium as a population-based strategy for reducing blood pressure…the alternative approach of recommending high-quality diets rich in potassium might achieve greater health benefits, including blood-pressure reduction, than aggressive sodium reduction.
It may not be the potassium itself; diets rich in potassium are also rich in a lot of other healthy nutrients from fruits and vegetables.
These studies were large and well designed. They gathered an immense amount of data, looked at a variety of associations, and did their best to rule out possible confounding factors. But epidemiologic studies like these are imperfect by nature. The authors themselves pointed out several limitations of their studies, including the indirect way they measured sodium and potassium excretion.
So what did we learn?
None of this really sheds any light on what we should do as individuals. Should we continue asking “pass the salt?” Should we abstain from adding salt at the table? Should we read labels and monitor the total amount of salt in our diet? Should we aim for 3–5 g a day?
These studies found associations, but they couldn’t determine causes, and they did not even attempt to measure what would happen if people changed the amount of sodium and potassium in their diets. If anything, they suggest that existing guidelines for salt restriction for the general population may be too extreme.
They also suggest that “moderation in all things” and “eat your vegetables” are still good advice.
Bonus question: What kind of salt should we use?
A related question is whether some kinds of salt are healthier than others. Sea salt, table salt, kosher salt, flavored salt, fleur de sel, Hiwa Kai, Black Hawaiian Sea Salt, Kala Namak, “organic salt,” and Pink Himalayan Sea Salt are all basically the same chemical, sodium chloride. Only the trace amounts of other substances vary. Table salt is fortified with iodine and is a highly effective way to prevent iodine deficiency and goiter. Gourmet cooks swear by the taste differences of different salt varieties.
(Don’t eat Epsom salt. You’d regret it: it’s has a significant laxative effect when taken internally.)
Pink Himalayan sea salt was introduced to me by an e-mail correspondent who questioned the claim that it contained “84 trace minerals that promote health and well being.” I questioned it too, so I did a little research.
Mike Adams, the infamous Health Ranger, explains that Himalayan Pink Crystal Salt contains the full complement of minerals and trace elements “just like Mother Earth intended.” It is an unrefined, unprocessed raw salt mined by hand from salt caves that formed 250 million years ago as ocean salt settled into geologic pockets. It is stone-ground, which apparently doesn’t count as “processing.” Table salt is bad stuff, you see, since it was processed to remove all the good stuff and then they had to replace the iodine because people who ate it started to get goiters. Oh, and incidentally he sells the good stuff on his website and even offers a discount.
I found a website that reports the results of a spectral analysis of Himalayan salt. I think this is where the claim comes from. Even if this analysis is accurate, it is meaningless for health and if anything is worrisome. The amount of minerals in it is too minuscule to make any difference, and we already get plenty of the same trace minerals from other foods. They claim that two double-blind studies were done, but no such studies are listed in PubMed. There is no evidence published in peer-reviewed journals that replacing white salt with pink salt makes a shred of difference or leads to any improvement in health.
If you read down the list of minerals, you will notice that it includes a number of radioactive substances like radium, uranium, and polonium. It also includes substances that act as poisons, like thallium. I wouldn’t be worried, since the amounts are so small; but if anyone believes the trace amounts of “good” minerals in Himalayan sea salt are good for you, why not believe the trace amounts of poisons and radioactive elements are bad for you?
The claim that pink Himalayan salt contains 84 trace minerals may be true, but the claim that it “promotes health and wellness” is false until proven otherwise by legitimate clinical studies. While waiting for evidence, I’d just as soon my salt didn’t contain uranium.
This article was originally published in the Science-Based Medicine Blog.