Salt, Diet, and Exercise

An interview with Gabe Mirkin

Elvin Adams,
M.D., who
conducted this
interview, is a
physician in
private practice
in North
specializing in


Adams: I understand, Dr. Mirkin, that in addition to your very extensive medical practice, teaching, and writing, you are keenly interested in fitness and participate in sports yourself. Is there a special reason for this?

Mirkin: When 28 years old, I had a blood cholesterol level of 350 milligrams per cent, high blood pressure, chest pains, as well as a poor family history. That's when I started running. Al though begun as a means of preventing a heart attack, it became a habit, and I've been competing in marathons and other distance races ever since.

Adams: How much do you run each week?

Mirkin: Well, I'm running only about 40 miles a week now. When I ran competitively, I logged more than 100.

Adams: Would you discuss the various aspects of nutrition that are especially important in endurance athletics? What about minerals such as potassium, calcium, sodium, and magnesium? It's been my under standing that sodium is an important mineral. People who exercise perspire a lot. You hear about these people using salt tablets. Is sodium and extra salt important in exercise?

Mirkin: I don't think so. Sodium can be detrimental. It's very interesting that all through medical school I heard that you're supposed to give salt tablets to active people in hot climates. When I was a resident I remember seeing a football player dying of heat stroke and he was taking salt tablets. Even today physicians are stressing salt tab lets, although we now know better. Salt should not be taken in excess. Besides other harmful effects of excessive use of salt, it can cause high blood pressure in people susceptible to it. The current feeling now among most exercise physiologists is that it not only is not necessary but it may well have detrimental effects.

In 1967 a professor in mathematics named Tom Ostler came down to Washington to run in the national AAU championship 30-kilometer race. He was virtually unknown as a competitor. There were several national champions in the race. However, the day before the race the weather suddenly became hot and the 18-mile race was run in extreme heat. Tom Ostler won by more than a mile and a half against runners who were vastly superior to him. And I re member after the race going up to Tom and saying, "Tom, what's the reason for your fantastic success? No time before in your life were you near any of these big-name athletes?" He said, "Oh, that's easy. I never take salt."

I then stopped taking salt myself to see what would happen, and I went from the worst hot-weather runner in the world to at least a mediocre hot-weather runner. And then in 1971 there appeared an article by Dr. Borsier, a French sports physician, who did a study of soccer players in France. He found that they had low magnesium levels. To make the story short, the low magnesium levels were caused by salt. The point is that when you take excess salt you cause your body to lose larger amounts of both potassium and magnesium, which you need. So excess salt in hot weather is not beneficial. A word of caution if a person lives in a hot climate and has previously used salt, so that his body is not accustomed to retaining it, a sudden restriction could be serious. The ideal time to begin your salt restriction is in the winter, and then avoid adding any at the table.

Adams: You mentioned potassium and magnesium as being important in exercise. Would you comment a little further on this?

Mirkin: The metabolism of calcium, potassium, magnesium, and sodium are related. These are the four major minerals in our bodies, and it's not the total amount that's important, but their relationship to one another. In 1873 that's more than a hundred years ago a Ger man physiologist named Von Bunge showed that when excess salt is taken in the diet more potassium is lost. For a hundred years physicians failed to recognize the significance of this study. Von Bunge also showed that animals living only on fruits, which are a rich source of potassium and poor source of salt, required some salt. That's why cows, rabbits, and other animals that live only on vegetation need a salt supplement.

Adams: What relationship does magnesium have to running and strenuous exercise? How does exercise affect a person's magnesium level?

Mirkin: Well, many studies in different sports show that exercise depletes magnesium in the body, and unless you replace the lost magnesium, low blood levels of the mineral result. For example, studies on cross-country skiers, cross-country runners, and soccer players have all shown that these athletes run lower levels of magnesium than the general population.

Adams: I would think magnesium would be fairly hard to replace. Where does it go?

Mirkin: Well, this was a puzzle until very recently. The first implication that magnesium was really important in athletics was shown by Dr. Kenneth Cooper, the man who sold more than a million copies of his Aerobics. He found that during a marathon magnesium levels in the blood drop profoundly. He tried to explain this by loss in urine, but you don't urinate during a marathon. He tried to explain it by magnesium lost in the sweat, but there was no way he could correlate the amount in sweat with the large loss of magnesium from the blood. The answer didn't come until Dr. J. Carr Taylor, a physician who is also a marathon runner, found that the harder you run the more magnesium you lose in your stool. Further studies by Dr. Taylor have shown that the more you exercise the more magnesium you lose. For example, if you run 20 miles you lose twice as much magnesium, generally speaking, as you would lose running 10 miles. For years it has been known that constipation is unheard of in distance runners or distance skiers. People who are constipated are given epsom salts (magnesium sulphate). So runners are producing their own epsom salts.

Adams: What foods contain magnesium, and what foods would you recommend for a natural replacement of the magnesium that might be lost in exercise?

Mirkin: A general rule of thumb is that foods such as nuts, that are rich in vitamin E, are also rich in magnesium. So instead of learning which nuts are best, you can generally say that all nuts are rich sources of magnesium, and to keep up your magnesium and to keep your endurance you should eat a variety of nuts. We also need trace elements that would be supplied in a varied diet. Magnesium, potassium, and sodium are the major minerals, and we know we need these, but there are other elements that are essential in minute amounts, such as cobalt and manganese. To make sure that you get trace elements it is good to vary your diet.

Adams: So a variety of unrefined foods would ensure that a person would get at least some of the trace elements.

Mirkin: Certainly. I would suggest choosing fruits and vegetables of different types that come from different areas of the country.

Adams: This may be an advantage of modern marketing procedures, for our lettuce comes from California and our tomatoes come from Georgia.

Mirkin: Yes, it would. Studies are now showing that if your soil lacks an element, fruits or vegetables grown on it will not have that element in them. Fruits and vegetables will grow in soil that is deficient or thought to be deficient in certain trace elements not needed for normal plant metabolism. However, plants can sometimes appropriate from the soil minute amounts of elements that cannot be detected by laboratory tests.

Adams: Let's move on to vitamins. There's a lot being said about vita min C, and I'm wondering if this is important to persons who exercise.

Mirkin: I think vitamin C is important. How important it is or whether we need to supplement a balanced diet is a much-debated point. Dr. Ludwig Procope, a physician in sports medicine in Germany, says that an athlete needs four times the normal recommended daily allowances of vitamin C. Well, four times 45 milligrams, or 180 milligrams of vitamin C, is only two large oranges. So even though Dr. Procope steps out and says an athlete has in creased vitamin C requirements, that's no reason for you to take supplements, because if you're eating your fruit, which you need for minerals anyway, you've already satisfied your vitamin C requirements. It becomes ridiculous to supplement your diet when you can get all you want in just the fruits and vegetables that you're eating.

Adams: Have you had any experience taking supplemental vitamin C in your exercise program?

Mirkin: Certainly. Early in my running program I was more susceptible to fads and fallacies in athletics. As you know, athletes do all kinds of crazy things, hoping that these crazy things will make them perform better. One of the fallacies was that exercise requires more vitamin C, and therefore you must take larger amounts. Well, I took about a gram to a gram and a half, realizing that that's up to 30 times the recommended daily allowance. I was trying to run 100 miles a week at the time, and I found that every time I cut back on my vitamin C, I couldn't run as much. My workouts would drop back to 60 miles a week, or 70. And I was absolutely convinced that for endurance I needed vitamin C. In fact, I was misled enough to write it in an article. And I wrote that I can't run long distances unless I take vitamin C. Well, this went on for about a year and a half, when I injured my ankle and had a forced layoff of about a month and a half. When I resumed training I didn't pick up the vitamin C, and I found I could run just as well as ever. My race times were as good as ever, and my training was perfectly ad equate.

I accepted this, and didn't say much more till I read a report in one of the medical journals showing that babies born of mothers who take large doses of vitamin C develop scurvy, vitamin C deficiency. Let me say that again. If a baby in the mother's uterus is exposed to large amounts of vitamin C because the mother is taking doses of it, when the baby is born it will have a very large vitamin C requirement and get scurvy within six months. The point of these two anecdotes is that when you take large doses of vitamin C, your body re quires large doses of vitamin C.

Adams: So if you don't take large amounts of vitamin C, your requirements are really not very large?

Mirkin: No. The general recommendation of the United States National Nutrition Council is equal to less than one orange a day and is probably adequate under normal circumstances. In heavy exercise and infection requirements go up there's no question about it. But if the requirement went up—four times normal, it still wouldn't ordinarily be necessary to take supplements.

Now there are several cautions against taking vitamin C. There are side effects. For one, vitamin C has an anti-vitamin D effect. That means that when you take more vitamin C, your body requires vitamin D. Another side effect is that vitamin C may decrease availability of the B vitamins, particularly Be and B12.

When you give a person large doses of vitamin C, the vitamin B complex levels, particularly Be and 612, go down.

People with gout, which is not an uncommon disease, develop kidney stones. The mechanism for this is that large doses of vitamin C make the urine more acid, and an acid medium makes kidney stones form from uric acid. So people with gout should never, never take large doses of vitamin C, because you can die from a kidney stone, or you certainly can get very sick. So it is unwise for a person with gout to take vitamin C supplement.




Adams: Would you comment on the value of vitamin E or vitamin E supplementation in exercise?

Mirkin: In the late 1920's, when vita min E was first discovered, it was unbelievable how many exciting things it was reported to do. It was supposed to rejuvenate your sex drive, to keep you from growing old, to prevent heart at tacks, to stop pain in the legs. Vitamin E does have an anti-oxidant effect. That means that it may help oxygen binding and may make the tissue run more smoothly, whatever that means. There is one very important claim that appears to really work. Air pollutants are oxidants, and vitamin E is a potent anti-oxidant. The next question is, if you take large doses of vitamin E during an air-pollution alert, will this help protect you against air pollution? The answer now appears to be Yes. The basic studies go as follows: when you mix vitamin E with the various air pollutants, the air pollutants are broken down. When you raise the blood level of vita min E the air pollutants are less likely to affect lung tissue. A study done on asthmatic children exercising in air pollution shows that the asthmatics who took vitamin E were affected less than asthmatics not taking vitamin E.

Adams: You mentioned the relationship between vitamins and how supplementing one creates a need for more of another, or abnormally depletes the body of another vita min. I think that not only applies to vitamin C and vitamin D and the B vitamins but probably there's an inter-relationship between all the vitamins. What is the best approach to a person who wants to make sure that he has the right balance of vitamins in his diet? Is there any one formulation that one could take?

Mirkin: That's an absolutely excel lent point, but we don't know that much. The answers aren't all in. If they were there wouldn't be so many arguments.

We know that the absolute level of minerals is not important, it's the ratio of potassium to magnesium, the ratio of sodium to potassium, the ratio of calcium to magnesium that counts. We know that the absolute value of vitamins is not important. It's the ratio of vitamin B to vitamin C. It's the ratio of D to C. And since our knowledge is so limited, you're really unwise to take vitamins. How many vitamins do we not know about that you're not getting? What imbalance are you causing by supplementing your vitamins? We know that longevity is not associated with vitamins. The Hunzukuts and the Vilcabambans and other peoples known to live to be a hundred never take vitamins. They're very poor. They never had a pill in their whole lives.

What we do know is that vitamin-rich supplements and excesses are associated with short lives and heart disease and atherosclerosis. Because of our limited knowledge, you shouldn't be taking excesses of anything. Now let me just add another point. We know that potassium and magnesium are very important to exercise and endurance athletics. So what happens? Many companies and many enterprising people produce drinks with potassium or magnesium supplementation. These drinks are all junk, because one important drink doesn't contain any magnesium at all. Another important drink doesn't have an adequate ratio between sodium and potassium. Another drink has too much potassium. Another drink has sacharine, which is not so healthful. Do you know that you get a better balance of minerals in an orange than you do in any artificial drink? There are no trace elements in artificial drinks. I think artificial drinks are ridiculous.

Adams: What kind of diet do you recommend for the athlete?

Mirkin: Number one, eat as varied a diet as possible, and limit it. Excess is not associated with either endurance or longevity. Number two, protein deficiency. Eating less than what we say in this country is our minimal daily requirement, is associated with longevity. The Hunzukuts and others we mentioned are protein deficient by our standards and many live to be a hundred. You'll find more and more en durance athletes turning away from meat to a basic, staple diet that doesn't include a lot of protein. It's amazing how many articles on vegetarianism can now be found in swimming, cycling, running, and rowing journals. Pick up a kayaking journal, for instance, and there's an article entitled "How I Switched to Vegetarianism." My recommendation is fruits, vegetables, nuts, and maybe dairy products. Stay away from meat—and don't waste money on supplements.

Adams: Thank you. Your advice should help us all understand how to keep on the middle road to better health.

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Elvin Adams,
M.D., who
conducted this
interview, is a
physician in
private practice
in North
specializing in

March 1977

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