Welcome to Dear Julia, a column where readers submit everyday health questions. Which over-the-counter painkillers work best? Will intermittent fasting help you lose weight? Julia Belluz sifts through the research and consults experts in the field to figure out how science can help us live happier and healthier lives.
Dear Julia: How much do I need to worry about salt in my diet?
Along with sugar, salt has become a major dietary villain of late. Health officials in at least one city (New York) are trying to put sodium warning labels on menus to inform citizens about high levels in food. (The measure was passed in December but has yet to be implemented.) Meanwhile, the US Department of Agriculture has told schools with national school lunch and school breakfast programs that they have to cut back on the salt in the meals they prepare for kids.
There's good reason for these efforts. The average American consumes 3,400 milligrams of sodium (one and half teaspoons) each day, well above the recommended 2,300 mg for most people. And a diet that's high in sodium is associated with all kinds of health issues, like heart attacks and strokes. If you've ever been diagnosed with high blood pressure, your doctor has surely warned you off this essential seasoning.
But figuring out how much salt might be too much for any individual is no straightforward matter. Many people aren't even aware of where the most problematic salt is hiding in their diet. (Hint: It's not the saltshaker.) And too little salt can be harmful for some.
Here's what we know about how that can impact your health, and how to cut back.
Why too much salt matters for health
Blood pressure is the force your heart uses to pump blood through your circulatory system. When you have high blood pressure (also known as hypertension), the blood is pumping too hard, sometimes through arteries that are too narrow, which stresses your heart and causes it to work harder than it should.
How does this relate to salt? Blood is basically made up of platelets, and red and white blood cells, suspended in a saltwater solution.
When you eat a lot of salt, it’s absorbed into the body, but your body retains water along with it so that the ratio of sodium to water holds stable. (That's why you crave water when you eat very salty foods.) Because your body is retaining water along with the salt, your cells — including blood cells — expand. The volume of your blood, therefore, swells, boosting the pressure on your arteries.
Some people’s bodies do a good job of filtering excess sodium, while others’ don’t. "Salt sensitivity" increases as we get older and our arteries harden. It's also more common among African Americans, obese people, and those who have diabetes and chronic kidney disease. (These are all "high risk" groups for hypertension.)
The reason this matters for health is simple: High blood pressure is associated with heart attacks and heart failure, which are among the leading causes of death in America. The thinking is that if we cut back on salt, we’d reduce the risk of high blood pressure — and all the health problems that come with it.
But the question of how much impact reducing one's salt intake can have on tangible health outcomes like death and cardiovascular disease has been the subject of fervent debate among researchers for two reasons.
There are a number of factors that can affect blood pressure: genetics, exercise, bodyweight, alcohol consumption, stress, age, overall diet. So salt isn't the only factor in the risk equation.
Second: Many of the studies linking salt consumption to endpoints like disease and death have only tracked changes in blood pressure over a short period of time. But blood pressure is just an indicator, or "surrogate endpoint," in health research. It’s not a real health outcome, like heart attacks or death.
Doing an experiment — assigning thousands of people to a particular level of salt intake over many years to figure out how their diet relates to their risk of developing cardiovascular disease and death — is much more difficult and expensive.
The controversy here lies in the question of whether the temporary boosts in blood pressure we've seen from the studies we have actually end up taking a toll on the heart and overall health in the long term.
To truly answer this question, some argue we'd need a big, randomized trial that looks at various levels of sodium restriction and the impact on cardiovascular disease and mortality in about 20,000 patients for five years. As yet, no one has funded such a study.
The randomized trials we do have aren't very telling about long-term health outcomes. One 2014 meta-analysis, which examined all the best research on sodium intake, concluded, "There was weak evidence of benefit for cardiovascular events, but these findings were inconclusive and were driven by a single trial among retirement home residents, which reduced salt intake in the kitchens of the homes." Another, published in 2011, concluded, "We do not know if low salt diets improve or worsen health outcomes," and "more research on reduced salt intake is required."
So how much salt should you eat?
For any given individual, how much salt is too much varies quite a bit. In general, the Centers for Disease Control and Prevention says one teaspoon (or 2,300 mg) a day seems to be just right for most people. Two teaspoons or more of salt each day (what's considered a high-sodium diet) is probably harmful, while a very low-sodium diet (much less than one teaspoon per day) may also be harmful.
Several years ago, the Institute of Medicine — an independent nonprofit organization that provides medical advice — convened an expert panel to review all the evidence on dietary sodium and health outcomes.
In 2013, the panelists published a report in which they agreed that it made sense to aim to reduce sodium intake around the world, but they also said they couldn't find any evidence that a very low-sodium diet (less than 2,300 mg/day) was helpful to anyone, not even those high-risk groups.
"The only conclusion we could draw is that there haven’t been enough studies to make any recommendation for lowering your sodium intake below 2,300 mg per day [or about a teaspoon]," said Maria Oria, an Institute of Medicine scientist who worked on the report. The IOM said that based on the best available evidence, about 2,300 mg per day seemed fine for most people, and the newest US dietary guidelines suggest Americans eat no more than that.
This is something every expert I spoke to for this story agreed on. "There’s no evidence lowering sodium below 2,300 mg will do you any good," said sodium expert and Albert Einstein College of Medicine professor Michael Alderman.
He pointed out that there’s never been a nutrient with a linear relationship to health that ends in zero. In other words, the health benefits of nutrients tend to exist in a J-shape: if sodium intake were plotted on the x-axis, and cardiovascular disease were plotted on the y-axis, you'd see the healthiest people fall somewhere in the middle.
Emory University's Andreas Kalogeropoulos , the author of a recent sodium study in JAMA Internal Medicine, looked at the effects of salt intake on mortality, cardiovascular disease, and heart failure in older people (ages 71 to 80). (This was an observational study based on data gathered for another purpose, not a big experiment.) Like other researchers, he also found the extremes weren't beneficial.
"There seems to be a ‘sweet spot’ of salt intake restriction, after which it is difficult to observe extra benefit with more restriction," he said. "On the other hand, in all studies, including ours, high salt intake (say, two teaspoons of salt or more daily) was harmful."
The easiest way to control salt intake
Start by making fresh fruits and vegetables central to your diet. "If it’s fresh," said UT Southwestern blood-pressure researcher Norman Kaplan, "you don’t have to worry about the sodium. The fact that nothing in nature is high in salt should tell people something."
Exercise more caution when eating prepared foods or in restaurants. As the handy Vox chart at the top of the story shows, restaurant dishes often contain an excessive amount of sodium.
Even worse than restaurant meals are packaged foods. Luncheon meats, canned foods, and condiments can contain particularly egregious amounts of sodium. (One serving of ham has about half a day's worth of sodium, while three tablespoons of soy sauce or two cups of canned chicken soup deliver enough for an entire day.)
All told, about 80 percent of the sodium you eat comes from salt that's added during food processing. So the easiest way to cut back is to avoid prepackaged foods (and restaurant meals) wherever possible.
This may not be easy when many of us rely on quick, ready-made foods. That's why some public health officials continue to call on governments and industry to find ways to cut added sodium during food processing.
People like Alderman think this could create unintended consequences, which we saw when the low-fat craze led food manufacturers to pack sugar into their foods to compensate for lost flavor.