To Your Health

Q. I sometimes feel I'm doing myself more harm than good by taking the recommended 1,500 mg of calcium a day along with 600 mg of magnesium. All that calcium makes me constipated. How can I tell if I have the right balance of calcium and magnesium for me?

A. Calcium and magnesium are so essential to our bodies that whole books are dedicated to their function. Unfortunately, accurate measurement of calcium and magnesium levels (and balance) in the body is extremely difficult. Calcium and magnesium absorption is affected not only by calcium and magnesium intake but also by the intake of other nutrients such as fiber, protein, potassium, phosphorus, and other minerals. Once inside the body, there are several hormones that minute-by-minute interact with one another to dictate what happens to calcium and magnesium. To make matters more interesting, the effect of these nutrients and hormones on calcium/magnesium balance varies with age and sex.

Currently, probably because of its association to osteoporosis, calcium is in the limelight. Although 99% of calcium is found in your bones, the other 1% that circulates in your blood is equally important to maintaining good health. Every cell in the body needs calcium, which is essential for proper blood clotting, heart rhythm, nerve impulse transmission, and both muscle contraction and relaxation. Many enzymes rely on calcium as a "second messenger" to control what happens in the body.

About 50% of magnesium in your body is also in your bones. Most of the remainder is dissolved in the fluid inside each cell and about 1% is in the interstitial fluid that bathes your cells. Magnesium is required to relax muscles (especially the heart and lungs), and to maintain normal blood pressure and blood sugar. The public is generally more aware of the nutritional importance of calcium and sodium and pays less attention to the signs, symptoms, and treatment of magnesium deficiency.

Extensive metabolic balance studies done by the U.S. Department of Agriculture Research Service indicate that on average the best ratio of dietary calcium to magnesium is 2-to-1. However, these studies generally assumed that magnesium intake was approximately 600 mg per day. Dietary surveys taken in the last decade have found that the diet of most Americans provides less than 300 mg per day, and thus magnesium intake tends to be inadequate in relation to calcium. The imbalance between calcium and magnesium has worsened mostly because our calcium intakes have risen while magnesium intakes have not.

Blood calcium level is tightly regulated and is a poor reflector of calcium status. The calcium in the interstitial fluid, the calcium that interacts with magnesium, is best estimated as "ionized calcium." When ionized calcium rises, nerve cell activity is reduced, and this can lead to decreased intestinal motility (the constipation mentioned), as well as lethargy and mental confusion. Your physician can order a test for ionized calcium, along with a test for your red-cell magnesium, to help her or him decide if your calcium and magnesium are out of balance. It is entirely possible that your calcium and magnesium supplement should be closer to a ratio of 1-to-1 instead of the usual 2-to-1 or your present 2.5-to-1 ratio.

Although only 4 to 5% of your body weight is composed of minerals, they are all vital to our physical and mental well being. Calcium and magnesium (and their balance) are among the minerals most crucial to good health.