Two cups per day, that's the short answer.
"We started to research the question because professional recommendations around milk intake were unclear and doctors and parents were seeking answers," said Dr. Jonathon Maguire, a paediatrician at St. Michael's Hospital and the lead author of the study.
Dr. Maguire and his team studied the effect of cow's milk on body stores of iron and vitamin D – two very important nutrients in milk – in more than 1,300 children aged two to five years.
The results of the study were published online in Pediatrics journal.
Children who drank more cow's milk had higher Vitamin D stores but iron stores were lower.
"We saw that two cups of cow's milk per day was enough to maintain adequate vitamin D levels for most children, while also maintaining iron stores. With additional cow's milk, there was a further reduction in iron stores without greater benefit from vitamin D," Dr. Maguire said.
The researchers studied healthy children during their routine appointments with the doctor between 2008 and 2010. Parents were asked to complete an questionnaire about their children's milk consumption habits and other factors that could affect iron and Vitamin D stores. A blood sample was taken from every child to evaluate body stores of iron and Vitamin D.
The study also inferred that children with darker skin pigmentation may not have enough vitamin D stores during the winter months. Dr. Maguire suggested wintertime vitamin D supplementation may be a more appropriate way of increasing vitamin D stores than consuming more milk to increase these levels, because that would help in preserving iron stores.
"Vitamin D deficiency in children has been linked to bone health issues and iron deficiency has been linked to anemia and delays in cognitive development," Dr. Maguire said. "Being able to answer parent's questions about healthy cow's milk intake is important to avoiding these potentially serious complications of low vitamin D and iron stores."
The Canadian Paediatric Society recommends that cow's milk be started only to children older than one year of age.
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