Young children who drink cow’s milk increase their stores of vitamin D, but decrease their iron levels.
According to the study, “The Relationship Between Cow’s Milk and Stores of Vitamin D and Iron in Early Childhood,” in the January 2013 issue of Pediatrics (published online Dec. 17, 2012), two cups of cow’s milk per day is sufficient to maintain adequate vitamin D levels for most children, while also maintaining sufficient iron stores.
Researchers looked at more than 1,300 children aged 2 to 5, assessing the amount of milk they drank per day as well as vitamin D and iron supplementation, time spent outdoors, skin pigmentation, body mass index and bottle use, all of which can modify the effects of milk consumption on vitamin D and iron levels. Blood samples were taken from the children to determine these levels. The authors found there is a trade-off for milk consumption in this age group: It raises vitamin D stores but lessens iron stores.
They concluded that two cups of milk per day is sufficient to maintain adequate vitamin D levels in most children, while having minimal impact on iron stores. The authors also noted that vitamin D supplementation is important for certain children based on the season, their skin pigmentation, and amount of time spent playing outdoors.