Excerpt from The Magnesium Factor by Drs Mildred Seelig and Andrea Rosanoff. pp.95-96
If the body’s cells are low in magnesium stress, such as exercise, can be dangerous because it causes the release of adrenaline and a sudden shift in magnesium from the cells to the blood, further lowering magnesium in cells to dangerously inadequate levels. The heart is particularly vulnerable to exercise stress-induced magnesium loss because the magnesium in heart cells is rapidly exchangeable. This means that the heart can take up magnesium quickly, which is a protective capacity. But it can also rapidly release it, so this capacity is a double-edge sword.
When the cells of coronary arteries become deficient in magnesium, a situation that is accompanied by a shifting of calcium into the cells, they constrict, thereby interfering with blood bringing oxygen to the cells. Even though an exercising, magnesium-low person may be free of ischemic heart disease (see page 6), temporary constriction of the coronary arteries can create the risk of a heart attack or cardiac arrhythmia that can cause cardiac arrest. If the body’s cells contain adequate magnesium, a sudden shift of magnesium is not dangerous. The body cells can cope with the ‘emergency’ of exercise and not become too low in magnesium.
If a person’s magnesium status is low, excessive strenuous sport or other physical activity can intensify the consequences of a marginal magnesium deficiency. Thus, if magnesium status is low to begin with, exercise or training can use up the available magnesium while increasing the body’s need for it. If there are not adequate body stores to back up the initial burst or long-term usage of magnesium, signs of the magnesium deficiency can become manifest. This can happen in the fit as well as the unfit, the thin as well as the obese.
The intense physical exertion of training worsens nutritional deficits, which, if severe, can then become obvious. In someone with a magnesium deficit – even a borderline one, but especially a more severe deficiency – an intense bout of physical exercise or an extended period of intense training can be dangerous regardless of the individual’s aerobic fitness or muscle strength.
Both athletes and sedentary people who want to begin an exercise program should therefore make sure that their magnesium status is up to par before beginning their program. The rise in adrenaline that comes with a rise in activity level can evoke signs of serious magnesium inadequacy in a person whose magnesium status is borderline, and this can be very dangerous. If the magnesium status is low enough, such a burst of exercise can cause cardiac arrhythmia and even bring on sudden death.
These facts explain why some athletes who are lean and in shape but also low in magnesium can experience sudden, unexpected cardiac arrest and death, while some people who are fat but have adequate magnesium can safely engage in regular exercise.