There's a dangerous connection between sodium and high blood pressure, but not enough people heed doctors' warnings.
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It's one of the first things people are told to do when they're diagnosed with high blood pressure: Cut back on salt. But not enough Americans are taking that advice, a new study shows. Researchers found that between 1999 and 2012, daily sodium intake increased by more than 14% in people with high blood pressure.

The study, which will be presented at the American College of Cardiology's annual scientific session, revealed that people with high blood pressure consumed more than twice their recommended daily amount in 2012—a whopping 3,350 milligrams per day on average.

According to United States dietary guidelines, people who have or are at high risk for high blood pressure should have no more than 1,500 milligrams a day. That’s significantly less than the 2,300-milligram daily limit set for most people with normal blood pressure (the amount in one teaspoon of table salt), because studies have shown that sodium and high blood pressure are inextricably, and dangerously, linked.

The exact mechanism for this link is unknown, says study author Elena Dolmatova, MD, a resident at Rutgers New Jersey Medical School. But scientists do have a few theories. One is that salt attracts water to the blood stream, increasing blood volume and therefore increasing pressure within the blood vessels. This increased pressure then creates strain on the heart and the entire cardiovascular system.

A few studies have also linked sodium consumption with secretion of a hormone called endogenous ouabain, which exhibits a “vasotonic effect” and causes blood vessels to contract, says Dr. Dolmatova.

Still other research has implicated a hormone called angiotensin II, which also constricts blood vessels. In people with normally functioning hormone systems, the body decreases its levels of angiotensin II in response to increased sodium consumption. But it’s believed that for people with certain genetic alterations, this doesn’t happen the way it should.

Regardless of how sodium contributes to high blood pressure, the important thing is that it does. And because people with high blood pressure already have a higher risk of developing cardiovascular problems, lowering sodium intake is especially important for them.

In fact, the people with the lowest sodium intake in the new study tended to be the same ones who’d had a heart attack or stroke, were taking blood pressure medications, or who had diabetes, obesity, or heart failure. In other words, it took a drug prescription or a serious health issue—not just a diagnosis of high blood pressure—to get people to take the dangers of sodium seriously.

That shouldn’t be the case, says Dr. Dolmatova, because often this simple dietary change can help people avoid complications or medications with unwanted side effects. “People shouldn't wait until they have a heart attack before taking action to limit sodium," she says.

Dr. Dolmatova says it’s possible that some doctors are quick to prescribe medications before promoting lifestyle modifications, which may explain part of the increased rise in sodium intake. It’s also likely that increased access to restaurant and processed food plays a role. “People tend to pay more attention to calorie content of the food that they buy, and usually disregard sodium content,” she says.

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But the truth is that most Americans (with the exception of people with rare low­–blood pressure disorders) should be paying attention to their sodium intake, says Dr. Dolmatova—especially because most of us exceed even the higher maximum amount recommended for healthy people.

And even though salt is ubiquitous in American diets today, cutting back can be relatively simple: Eat less processed food, buy low-sodium or sodium-free products like soups and condiments, avoid the obviously salty restaurant items (hello, cheese fries), and use less salt when cooking your own meals at home. Watch out for these sneaky sources of sodium, too.