Dietary supplements are big business in the United States. The U.S. Department of Health and Human Services reports that approximately 53 percent of the adult population takes at least one nutritional supplement. Calcium is the leading mineral supplement taken by Americans. Many people also take iron supplements to prevent or treat iron-deficiency anemia. You should not take calcium and iron supplements together, because mixing the minerals may reduce the absorption of iron from your intestines.
Iron absorption occurs in your small intestine. Cells called enterocytes, which line your small intestine, absorb iron and transfer it to your bloodstream. Iron absorption from your intestines is inefficient, however, with approximately 10 to 15 percent of the iron you consume entering your bloodstream, reports the National Institutes of Health. Because of the poor efficiency of intestinal iron absorption, it may be challenging to rebuild your iron stores once a deficiency develops. It is important that you take steps to optimize your iron absorption to overcome this problem.
Calcium may interfere with the absorption of iron from supplements or your diet. Although the mechanism by which calcium inhibits intestinal absorption of iron remains unclear, the threshold at which interference begins is approximately 300 mg of calcium. Most calcium supplements contain significantly more than this amount. If you are taking iron and calcium supplements, talk with your doctor about dosages, when to take each supplement and potential interactions with foods and medications. Taking your calcium supplement at bedtime and your iron supplement during the day may be a simple way to derive maximum benefit from both products.
Meeting Your Calcium Needs
If your doctor recommends an iron supplement, and you also take calcium, ask whether you need the supplemental calcium or if your dietary intake is sufficient. Although calcium is an essential nutrient for bone and muscle health, a balanced diet with the recommended intake from each of the major food groups supplies most people with an adequate amount of dietary calcium. If you have difficulty tolerating milk products — a major source of calcium — an over-the-counter enzyme to aid with the digestion of milk sugar may enable you to include these foods in your diet without digestive-system upset.
Vitamin C and meat enhance the absorption of iron from plant sources, so-called nonheme iron. A glass of orange juice, along with a serving of lean meat and spinach, for example, may enhance iron absorption from the spinach. Avoid drinking tea or eating whole-grain foods when you take your iron supplement, because these foods may interfere with iron absorption. Optimal calcium absorption requires an adequate amount of vitamin D in your system. Include vitamin D-rich foods in your nutrition plan, such as fortified milk, eggs, tuna, sardines, mackerel and liver. Avoid an overabundance of salt and protein in your diet to help preserve your body's calcium stores.
- "Dietary Supplement Use Among U.S. Adults Has Increased Since NHANES III (1988–1994)"; Jaime Gahche, M.P.H., et al.; April 2011
- National Institutes of Health, Office of Dietary Supplements: Iron
- National Institutes of Health, Office of Dietary Supplements: Calcium
- "American Journal of Clinical Nutrition"; Does Calcium Interfere with Iron Absorption?; Leif Hallberg, M.D., Ph.D.; July 1998
- "American Journal of Clinical Nutrition"; Inhibitory Effects of Dietary Calcium on the Initial Uptake and Subsequent Retention of Heme and Nonheme Iron in Humans: Comparisons Using an Intestinal Lavage Method; Zamzam K. Roughead, Ph.D., R.D., et al.; September 2005