Updated May 22, 2008

Choosing a Multivitamin

by Marie Spano, M.S., R.D.

For more information about these vitamins, check out the chart "Vitamins."

Minerals
Minerals help regulate several body processes such as fluid balance, muscle contractions, and nerve impulses. Some minerals help make up the structural integrity of bones and teeth.

Calcium. Calcium is best known for its role in keeping bones and teeth strong. However, it also plays a vital role in muscle contractions, blood vessel contraction and expansion, the secretion of hormones and enzymes, and sending messages through the nervous system.

The amount of calcium absorbed decreases as the amount of calcium consumed at one time increases. Therefore, it is best to take 500 mg or less at one time.

Chromium. Chromium is involved in the metabolism of fat, protein, and carbohydrate. In addition, it can enhance the action of insulin. In fact, chromium deficiency can impair the body's ability to use glucose. Consequently, there has been a considerable amount of interest in the possibility that supplemental chromium may help minimize the impaired glucose tolerance associated with Type 2 diabetes. However, there have been no large, randomized, controlled clinical trials carried out in the United States to support this hypothesis. In fact, a review of 15 trials revealed that all but one showed chromium supplementation had no effect on glucose or insulin concentrations in people with or without diabetes.

Both the safety and efficacy of chromium supplementation for people with diabetes is considered controversial. In addition, researchers are still trying to elucidate which form of chromium has the best absorbability. At this point, therefore, most health organizations recommend taking a daily supplement that has no more than 100% DV or speaking to your physician before taking more.

Copper. Copper plays a role in the functioning of several enzymes, helps the body make hemoglobin (which transports oxygen throughout the body), and helps the body produce energy in the cells. A very high intake of zinc can interfere with the absorption of copper.

Iron. Iron is essential for both the functioning and synthesis of hemoglobin. It is also involved in DNA synthesis, immune functioning, brain development, and the synthesis of neurotransmitters and collagen.

Check with your physician prior to supplementing with greater than the RDA for iron. If you take antacids or other calcium-containing supplements, take your iron supplement one to two hours before or after. Take iron two hours before or after any antibiotics.

Magnesium. Magnesium is part of over 300 enzymes that regulate bodily functions, including energy production, muscle contraction, and the manufacturing of body proteins. Magnesium is also a structural component of bones. Single-dose multivitamin–multimineral supplements do not contain 100% DV of magnesium because that quantity of magnesium will not fit into one pill.

There is some indication that Americans may not get a sufficient amount of magnesium from their food. Making a conscious effort to eat more high-fiber foods, which are often rich in magnesium, may remedy this problem. Good dietary sources of magnesium include legumes (dried beans and peas), nuts, whole grains, and green vegetables.

Magnesium-based supplements have been marketed to people with diabetes as a result of research indicating that higher magnesium intake is associated with lower fasting insulin concentrations in both adults and obese children. Lower fasting insulin levels may correspond with greater insulin sensitivity and possibly even a decreased risk of developing Type 2 diabetes. In addition, low magnesium levels have been noted to occur in approximately 25% to 38% of people with Type 2 diabetes. However, clinical studies in which magnesium supplements were given to people with Type 2 diabetes in an effort to decrease their fasting blood glucose levels and improve insulin sensitivity have yielded mixed results.

Marie Spano is a registered dietitian and exercise physiologist. She is a freelance writer, consultant, and speaker in the nutrition, fitness, and health industries. In addition, she is a spokesperson for the International Society of Sports Nutrition.

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