“If you’re taking an iron supplement or eating iron-rich foods and drinking milk at the same time, that might reduce absorption,” hematologist and delegate for the American Society of Hematology Dr. Amar Kelkar told the American Medical Association (AMA). This relationship between milk consumption and reduced iron absorption was examined in a 2009 study published in Childhood Obesity and Nutrition.
The researchers pointed out that cow’s milk, which contains low levels of iron, can interfere with all three steps involved in the body’s processing of the mineral: consumption, absorption, and excretion. Milk’s high casein content — the protein responsible for its white coloring — may be partly to blame. Also to blame may be the reduced levels of vitamin C in cow’s milk that occur as a result of pasteurization. This vitamin would otherwise boost absorption. Milk also contains high amounts of phosphorus — a mineral that has also been linked with hindering iron absorption. But phosphorus isn’t the only mineral that may be playing a role in milk’s obstruction of iron absorption.