SALT MAY no longer be a villain. Arguments for the dangers of too-low salt intake are “gaining ground,” according to the BBC, “casting doubt on decades of research and shedding light on the questions that still remain unanswered about our favorite seasoning.”
High salt consumption will remain a problem for people with hypertension or high sensitivity to salt, which can depend on age as well as ethnicity, body mass index and family history—although some now argue that a “low-salt diet is just as much of a risk factor for developing high blood pressure as high salt consumption.”
But in studies on healthy individuals, low-salt diets have been linked to insulin resistance—which causes high blood sugar levels and can lead to Type 2 diabetes, heart disease and other metabolic complications—as well as increased risk of death from heart disease and stroke.
The American Heart Association recommends an upper limit of 2,300 mg of sodium/day, equal to about 1 teaspoon of salt, but some researchers now suggest a daily intake between 3,000 and 5,000 mg of sodium—closer to what Americans consume each day. (Sodium makes up 40% of salt, and the remaining 60% is chloride.)
The body relies on sodium to help transport oxygen and nutrients, to provide the electricity to conduct nerve impulses, to contract and relax muscles, and to maintain the right balance of water and minerals. Healthy kidneys maintain a stable amount of stored sodium, retaining sodium when levels are low and excreting more when they are high. Decreasing effectiveness of kidneys, which can happen with age, allows sodium to accumulate in the blood, causing excess water retention that in turn increases pressure on the arterial walls.
“Randomised trials showing salt’s effect on the body are almost impossible to carry out,” according to cardiologist and epidemiologist Francesco Cappucio at the University of Warwick, whose eight-year literature review found positive effects of lowering salt intake by 1,400 mg/day: a 42% decline in fatal strokes and 40% drop in heart disease-related deaths.
Most agree that it’s difficult to separate the effects of lowering salt from other diet and lifestyle behaviors, because people more conscious of salt intake are more likely to have healthier diets overall—if only by reducing processed foods, including canned and frozen food, packaged food, meat, bread, breakfast cereals and some dairy products like cheese.
For most people, about one-quarter of their daily sodium intake comes from the salt shaker. The rest is mostly from processed foods, such as 1,000 mg in a cup of spaghetti sauce and more in some canned soups; and condiments, such as soy sauce, with 1,000 mg/tablespoon.
Many less-processed products also contain sodium: milk—about 100 mg. in one cup of lowfat; and the saltier cheeses—about 1,000 mg in 30 grams of Roquefort, compared to 500 mg for cheddar and 300 for mozzarella. And one survey found great differences among products within each variety: for gorgonzola, one option was six times saltier than the least salty.
Questions about limiting dietary salt began with the ongoing National Health and Nutrition Examination Survey studies involving thousands of people and producing intermittent sets of results: in one set, those eating the least salt died at a rate 18% higher than those eating the most salt; and in another, the low-salt group had a 15.4% higher risk of death.
Additional observational studies have found daily sodium intake below 3,000 mg increased the risk of dying from heart disease and stroke. For people with heart failure (when the heart is unable to pump sufficient blood for the body’s oxygen needs), those who restricted sodium intake had a 160% higher risk of death—although results from other studies disagree.
In an early-2000s review by the Institute of Medicine, the committee found that for heart failure, there was “sufficient evidence to suggest a negative effect of low sodium intakes.”
What may be more important than the quantity of sodium consumed is its ratio to that of potassium, which relaxes blood vessels—decreasing blood pressure—and helps the body excrete sodium. In the ratio of the two, potassium should be higher, but most Americans eat about 3,300 mg of sodium/day compared with about 2,900 mg of potassium.
Every Tuesday, well-being editor Mary Carpenter delivers health news you can use.