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Can too little salt cause heart disease? - (5/21/2019)

By Dr. Ron Gasbarro

Tom had a new prescription for a blood pressure medication at a dose that was higher than previously prescribed. He said to the pharmacist, “Last year, my doctor told me that my blood pressure was too high, so she asked me to cut back on my salt intake. Last week, she informed me that not only was my blood pressure still too high but that my sodium level was too low. I thought the lower your salt levels are, the lower your blood pressure is and the less chance I have of getting heart disease.”  

The pharmacist agreed that clinical studies have consistently shown that too much salt (sodium) in the diet can drive up one’s blood pressure (BP). Even so, a new study has revealed that too little salt can have the same effect. Yes, high amounts of sodium cause problems in that they cause too much water to be retained throughout the body. More water means more blood to pump through to the same number of arteries, veins, and capillaries. This extra pressure – known as hypertension, because there is more tension placed on the circulatory system – results in damage to the major organs, culminating in situations such as kidney failure, stroke, and death. BP drugs are very effective in reducing this dangerous strain on the heart. 

However, very low blood sodium can result in heart disease, as evidenced by a recent study done at Boston University. The 16-year study, which followed over 2,600 people ages 30 to 64, found that those on a low-sodium diet had higher blood pressures than participants who consumed high amounts of sodium. Other large recent studies have revealed what researchers call a U-shaped relationship between sodium and cardiovascular risk – that means people with low-sodium diets and people with a very high sodium intake had higher risks of heart disease. Those with the lowest risk had sodium intakes somewhere in the middle, which is the range consumed by most Americans.

The pharmacist explained to Tom that the heart is a pump made up of muscle tissue. Like all muscles, the heart needs a source of energy and oxygen to function. The heart's pumping action is regulated by an electrical conduction system that coordinates the contraction of the four chambers of the heart. This electrical system uses electrolytes to conduct the electrical current needed to run the heart. The electrolyte sodium (Na+) is vital as to how efficiently the heart muscle contracts. Potassium (K+), another electrolyte, works in tandem with Na+ to make sure that the heart beats steadily. This is an exchange process known as the sodium-potassium (Na+/K+) pump. Imagine this pump as a gate that allows Na+ and K+ ions to pass into and out of the cell. The Na+/K+ pump relies on the exchange rate of three Na+ ions to two K+ ions. If a person’s K+ excessively outnumbers their Na+, as would occur in an extremely low amount of sodium, this pump would function irregularly or not at all. The heart would eventually cease to function, an event known as cardiac arrest.   

According to the pharmacist, low blood sodium, technically known as hyponatremia, can be caused by dehydration, changes in the adrenal glands which regulates the Na+/K+ balance, heart, kidney, and liver problems, or severe diarrhea or vomiting. Some medications, such as antidepressants, pain relievers, and water pills (diuretics) may also cause low sodium levels. The question that Tom needs to have answered is whether his low sodium levels are acute or chronic. In the meantime, he should continue to take his medications as prescribed and to get blood work done routinely so that any major problem can be directly addressed.  

Ron Gasbarro, PharmD, is a registered pharmacist, medical writer, and principal at Rx-Press.com. Read more at www.rx-press.com

 


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