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Finding the Sweet Spot: Milk Intake, Vitamin D and Iron
Cow’s milk is an important source of vitamin D for young children. But too much cow’s milk can cause iron deficiency. How much milk is enough? How much is too much? Vitamin D and iron are two important nutrients that affect a child’s general health, growth and development. A recent Canadian study addressed the question of how best to balance the good effect milk has on Vitamin D levels and the bad effects it has on iron, and came up with the answer.
Young Bones Need Vitamin D, Developing Brains Need Iron
Vitamin D is necessary for absorption and maintenance of calcium and phosphorus in bones, and a deficiency of vitamin D can lead to rickets, the softening and bowing of some bones. Vitamin D may also play a role in the prevention of some chronic diseases, including those of the immune, respiratory, and cardiovascular systems. While there are a few food sources of Vitamin D including oily fish, beef liver, cheese, egg yolks, and some mushrooms, for most toddlers and young children vitamin D fortified milk is the primary nutritional source.
Vitamin D is measured by a blood test, 25 hydroxyvitamin D. In the U.S. the recommended 25 hydroxyvitamin D level is above 50 nmol/L, whereas the Canadian Pediatric Society has suggested a higher level of >75 nmol/L using data for adults.
Iron is necessary to prevent the most common kind of anemia, iron deficiency anemia. But even before anemia develops, low iron stores can cause problems with early brain development. Low iron has been associated with permanent impairments in thinking and reasoning skills, as well as movement and coordination. Iron stores are measured by a blood test called serum ferritin. Normal values vary by age and sex. Nutritional sources of iron include meat, shellfish, legumes, iron-rich fruits and vegetables, and iron-fortified cereals. When eaten at the same time as iron-containing foods, fruits rich in vitamin C help iron absorption.
Cow’s milk, a major dietary component for young children, presents a nutritional dilemma. Although cow’s milk is an important source of Vitamin D, it is low in iron and it can cause iron deficiency in young children. Cow’s milk decreases the absorption of iron from other foods and can also irritate the lining of the intestine, causing small amounts of bleeding and the gradual loss of iron in the stool. It can also contribute to iron deficiency because when kids drink a lot of cow’s milk they often don’t eat other iron rich foods.
The study looked at the milk drinking habits of 1311 two- to five-year-olds for two years to determine how cow’s milk intake affected their vitamin D and ferritin levels, and what other factors in a child’s health history impacted these nutrients. Children were excluded if they had chronic illnesses, were born prematurely before 32 weeks, or were on medications which would affect their vitamin or iron metabolism.