What's the sweet spot for sodium intake?

M3 Global Newsdesk Aug 15, 2019

The idea that lowering your sodium intake can improve both your blood pressure and cardiovascular health has been well-documented. But recently, more and more studies are beginning to demonstrate that too little sodium may also be bad.

Let’s take a look at what this lowly mineral—an electrolyte like calcium, magnesium, phosphate, and potassium—does for your body.

Sodium helps your nerves fire to regulate autonomic functions including heart rate, digestion, respiration, brain activity, and blood pressure. It also helps maintain both intercellular and intracellular fluid balances.

Too much sodium (> 145 mEq/L) can adversely affect these fluid balances and thus contribute to high blood pressure. But, too little sodium (< 135 mEq/L) can have detrimental effects as well.

For optimal function, the body needs < 500 mg/d of sodium—less than a quarter of a teaspoon. The American Heart Association recommends a sodium intake of ≤ 2,300 mg/d (about 1 teaspoon), with 1,500 mg/d being ideal for adults. Yet, on average, Americans consume about 3,400 mg/d.


Albeit rare, the problem of getting too little sodium can have wide reaching effects on the body.

In the Prospective Urban & Rural Epidemiological (PURE) study—the largest international study to date on sodium and potassium intake and their effects on blood pressure, death, heart disease, and stroke— researchers found that consuming too little sodium is associated with some health risks.

“In the PURE study, we found the lowest risk of death and cardiovascular events in those who consumed moderate amounts of sodium intake (3 to 6 g per day), with an increased risk above and below that range. While this finding has been reported in previous smaller studies, PURE is the largest international study to study sodium intake and health outcomes and adds considerable strength to the contention that moderate sodium intake is optimal,” said lead author Martin O’Donnell, MB, MRCPI, PhD, associate clinical professor, Divisions of General Internal Medicine and Hematology and Thromboembolism, Department of Medicine, McMaster University, Hamilton, Ontario, Canada.

“Low sodium intake does reduce blood pressure modestly, compared to moderate (or average) intake, but low sodium intake also has other effects, including adverse elevations of certain hormones that are associated with an increase in risk of death and cardiovascular diseases. The key question is whether these competing physiologic effects result in net clinical benefit or not,” he added.


With these results in mind, here are some of the possible negative side effects of getting too little sodium in your diet:

  1. Increased risk of hyponatremia. Hyponatremia has many causes and, in severe cases, can result in coma or death. Too little salt and the associated risk for hyponatremia are particularly concerning in the elderly and athletes. The elderly are particularly at risk because of chronic illnesses or medications they take that can reduce sodium levels. Conditions such as chronic kidney disease, cirrhosis, congestive heart failure, and hypothyroidism increase the risk of hyponatremia. Medications that also up this risk include diuretics, mirtazapine, carbamazepine, and tricyclic antidepressants. Athletes are also at risk due to several factors, including overexertion, losing large amounts of sodium via sweating, drinking too much water, and not replacing the sodium lost in sweating.
  2. Increased LDL cholesterol and triglyceride levels. In a Cochrane review, researchers found that low-sodium diets caused a 4.6% increase in LDL cholesterol levels, a 5.4% increase in total cholesterol, and a 5.9% increase in triglyceride levels compared with high-sodium diets. In a more recent Cochrane review, sodium reductions brought about a 1% decrease in blood pressure levels in normotensive adults and a 3.5% decrease in hypertensive adults, but a 2.5% increase in cholesterol levels, as well as a 7% increase in triglyceride levels.
  3. Increased insulin resistance. Results from clinical trials are conflicting—some investigators have found no effect of a low-sodium diet on insulin resistance while others have found a decrease in insulin resistance. But, researchers of one study, done in 152 healthy participants, noted an increase in insulin resistance after only 7 days on a low-sodium diet.
  4. Increased risk of death in patients with diabetes. In two observational studies, researchers demonstrated a link between low sodium intake and an increased risk of mortality in patients with both type 1 and type 2 diabetes. In the first study in patients with type 1 diabetes, researchers found an increased risk of all-cause mortality in patients with the highest daily urinary sodium excretion as well as in those with the lowest sodium excretion. In addition, those with the lowest sodium excretion also had the highest incidence of end-stage renal disease. In the second study, patients with type 2 diabetes demonstrated significant associations between lower 24-hour urinary sodium excretion and increased risks of all-cause and cardiovascular mortality.
  5. No benefits for heart disease. Besides the effects of low-sodium diets on cardiovascular risk factors, researchers of several observational studies have also looked at the incidence of myocardial infarctions or death. In one study, consuming less than 3,000 mg/d of sodium was linked to an increased risk of cardiovascular mortality. In yet another study, researchers found a higher risk of cardiovascular mortality when the low sodium levels recommended by many guidelines were followed.
  6. Increased risk of heart failure mortality. In a Cochrane review of reduced dietary salt for the prevention of cardiovascular disease, researchers concluded that low-sodium diets did not reduce the risk of cardiovascular or stroke mortality, and actually increased the risk of death from heart failure. The risk of death was 160% higher in participants who restricted their sodium intake. Low-sodium diets, therefore, are not recommended in patients with congestive heart failure.

Although these studies are far from definitive—indeed, many of them conflict with other studies—they are grounds for considering the possible drawbacks of a diet that includes too little salt. As with everything, moderation is key. Too much or too little salt can both have serious consequences on the body.

 

This story is contributed by Liz Meszaros and is a part of our Global Content Initiative, where we feature selected stories from our Global network which we believe would be most useful and informative to our doctor members.

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