It's probably not mineral levels that tire the athlete who's training


All athletes have days and months when they become too tired to train effectively. Years ago, doctors thought that potassium and magnesium deficiencies caused chronic fatigue in athletes. Now we know that low body levels of these minerals are almost never the cause.

As you become more fit, your blood volume can increase by as much as 20 percent. Your blood levels of potassium drop because the blood volume expands, diluting the minerals. This has no adverse affects and can increase your endurance.

Dehydration is a common cause of tiredness during prolonged exercise. Since you have more fluid in your body when you are fit, it will take longer for you to become dehydrated. Even if you are dehydrated, the kidneys and sweat glands are so effective in preserving potassium that a potassium deficiency rarely occurs in healthy people unless they vomit frequently or have diarrhea, take diuretics or cortisones, or eat a lot of licorice.

More than 50 years ago, doctors noted that blood magnesium levels dropped immediately after exercise, so they often diagnosed magnesium deficiency as a cause of chronic fatigue in athletes. But recent data show that during exercise, magnesium is not lost; it moves temporarily from the blood fluid into red blood cells and muscle cells. Within a couple of hours, the magnesium moves back into the blood fluid.

Mineral supplements will not cure chronic fatigue. The most com

mon causes of chronic tiredness in athletes are overtraining or infection.

I'm a 36-year-old competitive runner, and I have stopped having periods. Should I be concerned?

A recent report from Stanford University shows that virtually all women who stop menstruating can develop osteoporosis, even if they are serious exercisers or competitive athletes.

Neither exercise nor excessive thinness cause irregular periods. Dr. David Cummings of the University of Alberta has shown that so-called athletic amenorrhea is caused by not eating enough food. It is not caused by exercise.

Women should menstruate every 25 to 35 days and should have two hormones called estrogen and progesterone. When the interval between periods is more than 35 days or fewer than 25, a woman is almost always deficient in one or both of these hormones. Estrogen stimulates the uterus to grow. Progesterone stops the stimulation. Women who lack progesterone have a uterus that is stimulated all the time. This can lead to uncontrolled growth, which is cancer. Those who lack both estrogen and progesterone are at increased risk of suffering from osteoporosis.

The vast majority of women who develop irregular periods when they exercise will not have a serious cause and will have their periods return to normal if they eat more food. If increasing your food intake does not restore your regular menstrual interval, you should see your doctor. Ignoring irregular periods will lead to

a marked weakening of bones, no matter how much you exercise.

Do you recommend taking fish oil pills to prevent heart attacks?

You get the maximum protection against heart attacks by eating fish two or three times a week. Eating fish more often than that or taking fish oil pills does not offer you further protection and may even harm you.

A heart attack is caused by two events. First, fatty plaques accumulate in your arteries and partially obstruct the flow of blood. Second, a clot forms and cannot pass through the narrowed arteries, obstructing the blood flow to the heart completely.

The oils in fish do not prevent plaques from forming, but they do help prevent clotting. You get the maximum benefit from these oils by eating fish two or three times a week.

Taking fish oil pills has not been shown to prevent heart attacks. The Food and Drug Administration has written letters to manufacturers of fish oil pills telling them that it is illegal for them to claim that fish oil pills prevent heart attacks.

A recent study from Tufts University showed that people who were on a low-fat diet and ate fish every day had markedly reduced ability to kill germs. Other studies show that eating a lot of fish harms your immunity by preventing natural killer cells from killing germs after they enter your body.

Dr. Mirkin is a practicing physician in Silver Spring specializing in sports medicine and nutrition.

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