Salt: What Is It Good For?

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Other than saturated fat, I can’t think of a nutrient that’s been so universally maligned and demonized as salt. All the experts hate it and recommend that we get as little of it as possible. They even all seem to have their own little anti-salt slogans. The American Diabetes Association recommends between 2300 and 1500 mg of sodium per day (“Be Sodium Savvy“). The American Heart Association wants you eating less than 1500 mg per day (“Shaking the Salt Habit“) and claims that 97% of young people already eat way too much salt. The other ADA – the American Dietetic Association – also recommends between 2300 and 1500 mg, but their slogan is far inferior (“Slice Your Sodium Intake“). It’s quite the pile-on, isn’t it?

Why does salt strike mortal terror into the hearts of so many?

Back in the 1980s, a massive global study of salt intake and blood pressure called INTERSALT was undertaken. Overall, it showed a modest association between the two, but some groups, particularly the undeveloped, non-industrial peoples who had very little access to salt (and other trappings of industrialization), had blood pressure that was generally extremely low. Foremost among these groups were the Yanomami of the Amazon rainforest. The Yanomami have very low sodium excretion, which indicates very low sodium intake, and very low blood pressure. Even the elderly Yanomami enjoyed low blood pressure. This was convincing. I mean, it sounds convincing, right? Low salt intake, low lifelong incidence of hypertension – how much more cut and dry can you get? This low salt/low blood pressure connection seemed to also apply to other groups who happened to be living more traditional ways of life.

Except that there’s another non-industrialized group (and you only need one) whose slightly different results kinda muck up the Yanomami argument: the Kuna of Panama.

Among the Kuna, a tribe native to Panama, both salt intake and blood pressure were also historically low well into old age. To study whether the two variables were linked, researchers examined a group of “acculturated” Kuna with ample access to salt and an otherwise strict adherence to their traditional way of life. Little changed but the salt intake, in other words. But, despite consuming an average of 2.6 daily teaspoons of salt (and sometimes up to 6 teaspoons), the Kuna did not have hypertension, not even in old age. There was no change between the hypertensive statuses of 20 year old Kuna and 60 year old Kuna.

All in all, drastic reduction of sodium can reduce blood pressure by a few points. The evidence is pretty consistent on that. But the example of the Kuna shows that there’s way more to blood pressure than how much salt you eat, like how much potassium you eat.

Consider two recent Cochrane meta-analyses. The first, on sodium restriction and blood pressure, found that for people with hypertension the mean effect of sodium restriction was -5.39 mm Hg for systolic blood pressure and -2.82 mm Hg for diastolic blood pressure. In normotensive people, the figures were -2.42 mm Hg and -1.00 mm Hg, respectively. Decent reductions, I suppose, but what aboutpotassium and blood pressure?

The upper intake of potassium was associated with over a 7-point drop in systolic blood pressure and a 2-point drop in diastolic blood pressure, but only in people with hypertension (the people who actually should lower blood pressure). Unfortunately, the official recommendations for sodium and potassium intake cannot be met simultaneously. Yep – the experts want you to eat in a way that is literally impossible to accomplish. Inspires confidence, doesn’t it?

Let’s forget about blood pressure for a second, because there’s also way more to health than the meager drops in blood pressure afforded by sodium restriction. Recent evidence suggests that for many people, all out salt reduction has an overall negative impact on several other aspects of health:

In 2011, one study showed that seven days on a low salt diet increased insulin resistance in healthy men and women when compared to a higher-salt diet.

Another study showed that while reducing salt moderately improved the blood pressure of hypertensive patients by a mere 4.18 and 1.98 points for systolic and diastolic, respectively (but not of people with normal blood pressure), it also had negative effects on multiple other health markers, including increased triglycerides and LDL and elevated stresshormones.

Another 2011 study found that eating a low salt diet (under 3 grams of sodium per day, or just over a teaspoon of salt) and a high salt diet (from 6-7 grams of sodium per day, or well over two teaspoons of salt) both increased the risk of stroke and heart attack, while eating between four and six grams of sodium, or about two teaspoons of salt, each day was associated with the lowest risk of cardiovascular incidents.

A recent study found that salt intake followed a J-curve, with low and high intakes increasing arterial plaque formation and a medium intake decreasing it.

Sodium depletion due to “low-sodium nutrition” has been shown to trigger overtraining-like symptoms, including hypertension and sleeping disorders.

The greatest health marker of all – being alive – also has an interesting association with salt intake. It seems that, time and time again, folks with a “medium” salt intake live longer than people who eat too little salt or too much salt. That amounts to roughly 4000 mg of sodium, or close to two teaspoons of regular salt.

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