The calcium in yogurt and other dairy products may affect your body's ability to absorb iron. This is a problem because iron is needed to make hemoglobin, a protein that allows your red blood cells to carry oxygen. If you are trying to maximize your iron absorption, you may need to avoid consuming yogurt or other calcium-rich foods at the same time you take iron supplements or eat high-iron foods, such as meats and leafy green vegetables.
Iron is absorbed by cells in the small intestine. These cells use a special protein that transports iron from the digestive tract into the intestinal cells. This process requires an acidic environment, so anything that reduces the amount of acid produced by the stomach -- such as antacids or medications for acid reflux -- can reduce iron absorption. Consuming calcium along with iron can also inhibit iron absorption. Dry beans, soy products and tea have a similar inhibitory effect on iron absorption.
Mechanism and Prevention
Calcium inhibits iron absorption because the protein that transports iron into intestinal cells can transport other molecules, too, including calcium. This means that calcium might "compete" with iron for transportation from the digestive tract into the body. However, the exact mechanism by which calcium inhibits iron absorption is not known. Even low amounts of calcium --- 200 mg --- can reduce your body's ability to absorb iron. If you are concerned about not getting enough iron in your diet, avoid eating yogurt and other calcium-rich foods along with iron-rich foods or near the time of taking an iron supplement.