The Straight Dope on Salt
Last year my father-in-law and his wife visited my wife and me at our home in California. My wife cooked up lots of good food for all of us. But her dad has high blood pressure and is scrupulous in his avoidance of salt. So he asked her to cook without it, and advised us to avoid excess salt in our own diet
I was tempted to disabuse the man of the widely held but false notion that high levels of salt consumption cause hypertension, but I held my tongue, because that’s what one does with one’s father-in-law. But I certainly went right on eating a high-salt diet after he returned home.
The research-supported truth is that salt avoidance is beneficial only for the roughly 30 percent of already-hypertensive individuals who are “salt sensitive.” In the rest of us, salt intake does not have a significant effect on blood pressure. A recent review of 114 studies performed by researchers from the University of Copenhagen and published in the Journal of the American Medical Association found that even an extreme reduction in salt intake would barely lower blood pressure to a measurable degree in those with normal blood pressure.
Salt and the Endurance Athlete
Endurance athletes have a more favorable view toward salt than the average person does. That’s because we know that we lose a lot of salt every day through exercise-induced sweating, and we’re used to consuming salt in sports drinks during exercise to compensate for those losses. Failure to do so, we’ve been taught, will cause internal fluid imbalances and muscle cramps.
Or are these notions false too? The answer is yes and no. There is surprisingly little scientific evidence that salt consumption during exercise provides any benefit. However, the practice does no harm and is advisable whenever large volumes of sweat are lost and large volumes of fluid are consumed during very prolonged exercise.
The notion that sodium depletion during exercise causes muscle cramps is clearly false. A 2005 study found no difference in blood sodium levels between athletes who suffered muscle cramps and athletes who did not during an Ironman triathlon. Some exercise physiologists now believe that exercise-induced muscle cramps represent a type of tendon fatigue that occurs during unaccustomed levels of exertion. The fact that some athletes are especially prone to muscle cramps while others are not also suggests that sodium depletion is not the cause.
However, there is some evidence that consuming fluid and salt during prolonged exercise may at least delay cramping in those who are susceptible. In a study from the University of North Carolina, cramp-susceptible athletes were able to exercise twice as long before experiencing cramps when they consumed a sports drink during activity than they when they did not drink.
Gatorade teaches athletes that the addition of sodium to a sports drink improves hydration by increasing the rate at which fluid is absorbed into the blood stream and by slowing the decline in blood volume. But most research supports neither of these claims. A study from the University of Iowa found that sports drinks with different levels of osmolality, both with and without salt, were all absorbed at the same rate during exercise and none reduced blood volume decline more than another. Studies from the University of Cape Town, South Africa, and the University of Auckland, New Zealand, found that sodium supplementation during an Ironman triathlon had no effect on blood sodium concentration or blood plasma volume.
Timing of Intake
Interestingly, the studies showing the greatest beneficial impact of salt on exercise have involved sodium loading before exercise instead of sodium intake during exercise. Another group of New Zealand researchers found that when runners consumed a highly concentrated sodium beverage prior running to exhaustion at 70 percent of VO2max in a hot environment, they maintained a higher blood volume, lower core body temperature and lower level of perceived exertion than when they consumed a low-sodium beverage before running. It’s tough to know what to make of this result, though, since no fluid was consumed during the runs.
No study has found that consuming salt during endurance exercise has a detrimental effect on performance. Couple that fact with the mountains of anecdotal evidence from real athletes who say that salt intake is beneficial to them in extreme endurance events such 100-mile runs and you get the following sensible prescription: Consume salt in the normal amounts contained in sports drinks and energy gels during prolonged endurance exercise, but don’t knock yourself out to get more salt in the form of salt tablets or salty foods.
Nor do you need to add salt to your diet. However, you just might do it unconsciously anyway. A 1999 Israeli study found that exercise increased the preference for salty foods. So that’s why you crave potato chips after a long weekend endurance session!