Milk is a staple in the diets of most toddlers, but for some children, it isn't an ideal food choice. Toddlers who drink milk to the exclusion of iron-rich foods, are allergic to milk or have lactose intolerance might develop symptoms that could lead to irritability or lethargy. It might not be immediately clear that milk is causing behavior problems in your toddler, but doing blood work, trying an elimination diet or allergy testing can help pinpoint whether milk is causing behavioral changes.
Cow's Milk Allergy
Around 2 percent of children are allergic to cow's milk, according to pediatrician and author Dr. William Sears, although most outgrow their allergy by age 2 to 3. Symptoms of milk allergy can vary, but most toddlers with milk allergy often experience rashes, wheezing, hives, runny nose or behavioral changes such as night waking or irritability. A toddler with a milk allergy might be able to tolerate dairy in other forms, such as cheese or yogurt, since heating milk makes the proteins in milk less allergenic, Dr. Sears reports.
Young children need to be able to digest milk, since it's their primary food source. After infancy, other foods take on more importance. For around 65 percent of the world's population, according the Genetics Home Reference website, the ability to digest milk wanes with age. Lactose intolerance -- the ability to break down the milk sugar lactose and absorb it from the intestines -- generally doesn't develop until age 2 or later, when the intestines produce less lactase, the enzyme that breaks down lactose. Symptoms of lactose intolerance, which can cause chronic discomfort that leads to behavior changes, include abdominal cramping, diarrhea, nausea and sometimes vomiting.
Toddlers who drink a lot of milk often fill themselves up and then refuse foods high in iron. Cow's milk also interferes with absorption of iron from other foods. As many as 15 percent of children aged 1 to 3 have iron-deficiency anemia, family physician Dr. Louis Kazal reports in an October 2002 "American Family Physician" article. Low iron levels can cause behavior changes such as irritability, lethargy or weakness. Children with anemia may also be more fearful and clingy than other children. Reducing cow's milk intake to no more than 24 ounces per day can help prevent iron-deficiency anemia in toddlers.
Testing for Milk Problems
Trying an elimination diet can help determine whether milk is the offending substance when your toddler exhibits behavior changes. If you suspect your toddler has a milk allergy, allergy testing can confirm your suspicions if eliminating milk decreases symptoms. A simple blood test can diagnose iron-deficiency anemia.