Making Sense of Salt Sensing

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Sodium, or salt, content varies greatly in different foods. Last month in Philadelphia, many Experimental Biology conference attendees may have noticed something unique on restaurant menus: sodium warnings. These warnings caution diners about meals that have more than the recommended daily amount of sodium of 2,300 milligrams (mg). Wonder how the body regulates sodium levels? The answer: Special brain areas sense sodium content in the blood.

Most brain tissue has a barrier to keep it separated from the circulation. However, this blood-brain barrier is left incomplete—on purpose—near special areas of the brain called circumventricular organs. Without a barrier to the blood circulation, these regions can sense how much sodium is in the blood and then transmit signals to other brain regions to control our pulse rate, sympathetic nervous activity, blood vessel tone and how much sodium our kidneys get rid of. These changes are essential to control blood pressure.

Despite blood sodium being carefully controlled, changing the amount of salt we eat can cause small changes in the levels of sodium in our blood. When the body senses this reduction in blood sodium it causes a multi-step process that causes our body to hold on to more of the sodium that’s already there. And, it changes how much sodium the kidneys should get rid of.

Adults living in the U.S. tend to consume more sodium than the American Heart Association’s recommendation of no more than 1,500 mg of sodium per day and the Dietary Guidelines for Americans recommendation of no more than 2,300 mg of sodium per day for maintaining heart health. People with high blood pressureincluding about half of all adults in the U.S.—should be even more aware of these recommendations because too much salt may raise blood pressure. High blood pressure increases the risk of developing heart disease, which is the leading cause of death worldwide.

Although getting rid of the salt shaker might seem like an easy way to reduce sodium intake, only a small amount of sodium is added during home cooking and at the table. About 70% of sodium intake comes from restaurant, prepackaged and processed foods, including many products that don’t even taste salty. The takeaway from Philadelphia’s posted sodium warnings? Maybe cook at home more often than you take out.

Joseph C. Watso, PhD, is an instructor in the Department of Applied Clinical Research at the University of Texas Southwestern Medical Center and is affiliated with the Institute for Exercise and Environmental Medicine at Texas Health Presbyterian Hospital Dallas. Watso is interested in studying the role of lifestyle habits, such as diet and exercise, for optimizing health.

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