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Salt and High Blood Pressure

by Dr. Gabe Mirkin, M.D.

Salt Restriction Fails to Lower High Blood Pressure in Most People

Gary Taubes wrote an article in the New York Times, stating correctly that there is no good evidence that restricting salt intake reduces high blood pressure significantly or prevents heart attacks (June 2, 2012). If you read my newsletters or listened to my radio show, you know that I have been saying this for more than thirty years. High blood pressure is best managed by eating large amounts of fruits and vegetables; losing excess weight; eating less saturated fat, particularly in red meat; and exercising every day.

Most doctors who believe that a low-salt diet lowers high blood pressure base their argument on the INTERSALT project, published in 1988, which showed that populations that have very high salt levels in their urine also had a high incidence of high blood pressure; and on the 2001 DASH-Sodium study, a 30-day trial of salt restriction (N Engl J Med, January 4, 2001, 201;344:3-10). The DASH study showed that eating significantly less salt can lower high blood pressure a little bit, but it did not show that salt restriction prevents heart attacks or strokes.

THE DATA: Research shows that restricting salt can lower high blood pressure slightly, but there is insufficient evidence that it prevents heart attacks, strokes or premature death (Cochrane Database of Systematic Reviews Published Online: October 5, 2011).

Excess salt intake can cause your body to retain excess water which can raise your blood pressure temporarily. However, middle-aged people who start an exercise program lose their tendency to develop high blood pressure when they take in extra salt (Journal of Human Hypertension, May 2006).

Researchers at Albert Einstein College of Medicine showed that people on low-salt diets are actually more likely to suffer heart attacks than those on high salt diets (Journal of General Internal Medicine, June 2008). They analyzed data from the Third National Health and Nutrition Examination Survey (NHANES III) of American adults. Dr. Hillel W. Cohen, lead author of the study, stated, "Our findings suggest that for the general adult population, higher sodium is very unlikely to be independently associated with higher risk of death from heart attacks.

Salt Restriction Can Cause High Blood Pressure in Exercisers

Serious exercisers can be harmed by the broad recommendations for all people to restrict salt intake. If you do not exercise, you are not likely to sweat very much and you do not need very much salt. On the other hand, if you exercise vigorously, you sweat and lose a lot of salt. When you don't have enough salt, your adrenal glands put out large amounts of aldosterone, which constricts arteries and raises blood pressure; and your kidneys put out large amounts of renin that also constricts arteries and raises blood pressure (Clinical Autonomic Research. 2002;12(5):353-357). Furthermore, without the extra salt that you need, you will not recover from your hard bouts of exercise and you will be more likely to be injured or tired all the time.


Dr. James Gamble spent World War II studying the mineral needs of soldiers fighting the Japanese in the Pacific. He concluded that the only mineral soldiers and athletes need in large amounts is sodium, common table salt. They do not need extra potassium, magnesium, calcium or trace minerals. To this day, nobody has improved on his data and recommendations. His lectures on this topic were presented to Harvard Medical students right up to the time of his retirement in the 1960s {Gamble JL, Extracellular Fluid, A Lecture Syllabus, Harvard University Press. Cambridge, Massachusetts 1958}.


If you are a serious exerciser and you suddenly are not recovering from your workouts as fast as you usually do, a common cause is loss of salt. Symptoms of salt deficiency include muscle weakness, soreness and cramps, loss of strength and tiredness. Get a blood test for sodium on the day after a hard workout. If your blood sodium is below 132 mmol/L, you need more salt.


Not taking in salt when you exercise for more than two hours can prevent you from retaining the water that you drink. It can also block thirst, so you may not know that you are dehydrated. Thirst is a late sign of dehydration. You lose water during exercise primarily through sweating, and sweat contains a far lower concentration of salt than blood. So during exercise, you lose more water than salt, causing the concentration of salt in the blood to rise. You will not feel thirsty until the concentration of salt in the blood rises high enough to trip off thirst osmoreceptors in your brain, and it takes a loss of two to four pints of fluid to do that.


You need to take salt to retain the fluid you drink while exercising. If you lose two pints of fluid, you can replace it with two pints of water if you also take salt, but if you don't take salt, it can take four pints of fluid to replace two pints of sweat because the water you drink will pass out through your kidneys. In one study, female competitive distance runners took in drinks with different concentration of salt during a four-hour run (British Journal of Sports Medicine. 2003;37(4). Ninety-two percent of those who took in plain water with no additional salt developed low blood levels of salt.


A study from Spain shows that being fit does not reduce the concentration of salt in sweat (European Journal of Applied Physiology, November 2011). A person who exercises in the heat can lose far more than 4000mg of salt. So in spite of the fact that most serious exercisers get a lot of salt from the large amounts of foods that they eat, they can still become salt deficient.


Taking salt just before competition improves performance (Medicine and Science in Sports and Exercise, January 2007; Clinical Journal of Sport Medicine, January 2007). Athletes who took extra salt had larger blood volume and greater endurance. Salt makes you thirsty earlier so you drink more, and salt in your body holds water so you have more water available to meet your needs.


You can keep yourself fresh during extended exercise by eating foods with salt and drinking frequently, before you feel hungry or thirsty. Once you are weakened by loss of fluid or salt, it becomes very difficult to regain your strength. When an athlete competes in events lasting more than three hours, he or she should replace salt (sodium) at the rate of 700 mg/hour.

Commercial sports drinks help to increase endurance with their caffeine, sugar and salt content, and, to a lesser degree, protein (The Physician and Sportsmedicine, April 2010). Most sports drinks do not contain adequate amounts of salt for long-term exercise, because very salty drinks taste awful. When we cycle for more than three hours on very hot days, we eat salted potato chips and drink ordinary soda.


The North American diet contains up to 10 times your minimal salt requirements. Salt is added to almost all prepared foods, so if you doubled or tripled your salt losses through sweating, you would still not be deficient because you are already taking in far more salt than you need.


Taking in large amounts of fluid without also taking in salt dilutes the bloodstream, so that the concentration of salt in the blood is lower than that in brain cells. This can cause fluid to move from the low-salt blood into the high-salt brain causing the brain to swell which can cause seizures and death.

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