In February 2005 the Center for Science in the Public Interest, a consumer advocacy group, sued the federal government for failure to act on the evidence that salt kills 150,000 Americans each year (Nutrition Action Newsletter, February 2005.) The average American consumes 4,000 milligrams a day. Government spokesmen recommend salt levels below 2,300 milligrams (one teaspoon) a day. The American Heart Association recommends 1,500 mg a day.
Excess salt intake raises blood pressure in some people by expanding blood volume. However, before you go out and try to avoid all salt, realize that your body needs some salt and severe salt restriction can be harmful. Severe salt restriction causes high blood pressure by causing the adrenal glands to release large amounts of aldosterone and the kidneys to release renin. Both hormones constrict arteries to cause high blood pressure. People on salt-wasting diuretics should also not try to restrict salt because they would then be at high risk for salt deficiency.
Athletes must be very cautions about salt restriction. Since sweat contains huge amounts of salt, athletes who restrict salt are in danger of developing fatigue, muscle damage and cramps caused by low salt levels. The most common cause of muscle cramps in exercisers is lack of salt.
The key to retaining water during exercise is to take in salt to replace the salt you lose in your sweat. Until recently, many scientists did not appreciated how important salt is to retaining fluid in your body. 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 exercisers lose far more water than salt, causing the concentration of salt in the blood to rise. A person will not feel thirsty until the concentration of salt in the blood rises high enough to trip off thirst osmoreceptors in the brain and it takes a loss of between two and four pints of fluid to do that.
Taking in fluid without also taking in adequate amounts of salt dilutes the bloodstream, so that the concentration of salt in the blood is lower than that in brain cells. This causes fluid to move from the low-salt blood into the high-salt brain causing the brain to swell which can cause seizures and death. Taking in extra salt during prolonged exercise increases thirst so you drink more fluids, and prevents blood salt levels from dropping so low that you become tired, develop muscle cramps, and can even die.
If you have high blood pressure and are not on diuretics that drain salt from your body, it is reasonable to restrict salt. If you are a regular exerciser and feel tired or become injured, have your doctor draw blood levels of salt. You may find that you need to increase your intake of salt, particularly during exercise in warm weather.
If you do not have high blood pressure, high cholesterol, diabetes or other risk factors for heart attacks and strokes, there is little evidence that you will benefit from severe salt restriction. However, future research may change this recommendation. Processed foods and fast-food restaurant fare contribute almost 80 percent of the salt to the American diet, and a healthful diet is low in these foods.
Dr. Gabe Mirkin has been a radio talk show host for 25 years and practicing physician for more than 40 years; he is board certified in four specialties, including sports medicine. Read or listen to hundreds of his fitness and health reports at http://www.DrMirkin.com
