2 cups of milk per day best for toddlers, study finds

Some pediatricians are advising that parents only give their toddlers two cups of milk a day, because too much of it could deplete them of necessary nutrients.

A new study, published online on Dec. 17 in Pediatrics, found that 2.1 cups of milk a day gave young children the sufficient amount of vitamin D without lowering levels of iron, a potential side effect of drinking too much milk.

"For each additional cup of milk, it reduces the iron stores by a little bit," said study author Dr. Jonathon Maguire, a pediatrician at St. Michael's Hospital and the Hospital for Sick Children in Toronto, said to CBC News. "But in children who are at risk for iron deficiency for example, that little bit actually is very important."

The American Heart Association recommends fat-free and low-fat dairy foods should be part of a balanced diet, including two cups of milk or its equivalent for children 1 through 8 and three cups of milk or its equivalent for children 9 through 18. The 2010 Dietary Guidelines put out by the United States Department of Agriculture recommends three cups of milk for adolescents between 9 and 18, 2.5 cups for children 4 to 8 and two cups for children 2 to 3.

Milk and other dairy products have been known to increase protein, calcium, magnesium, folate, B1, B2, B6, B12, and vitamins A, D, and E intake, according to WebMD. However, they can increase the amount of calories a person eats.

Cow's milk can cause iron deficiency because it contains less iron than other foods it may replace, and also makes it harder for the body to absorb iron from other foods. Cow's milk can also make the intestines lose a small amount of blood, further depleting iron. The National Institutes of Health said that the resulting condition, iron deficiency anemia, is more common in infants younger than 12 months who drink cow's milk and young children who drink a lot of cow's milk instead of eating foods with more iron. Dr. Emilia Baczek, a pediatric nutritionist at La Rabida Children's Hospital in Chicago, told HealthDay that the calcium in milk is what affects iron levels.

"The calcium makes iron absorption a little bit harder," Baczek said. "Toddlers often aren't getting enough iron in their diet in the first place."

Researchers looked at blood samples from 1,311 children between the ages of two to five who went to the dotor for a routine visit. They were asked how many cups of cow's milk their child drank daily or if they used a bottle.

On average, children drank 1.9 cups of milk a day. Each cup of milk increased their vitamin D levels by 6.5 percent, but lowered their iron levels by 3.6 percent. Drinking from a bottle did not increase vitamin D levels, but lowered iron levels.

Baczek said the two-cups-per-day recommendation was a good call.

"It's enough to promote adequate vitamin D with minimal decreases in [iron]," she said.