Two cups (500ml) of milk per day is enough to maintain adequate vitamin D and iron levels in children aged between two and five, a Canadian study has claimed.

Researchers led by Dr Jonathon Maguire at St Michael’s Hospital in Ontario, Canada examined how the intake of cow’s milk affected body stores of iron and vitamin D in more than 1,300 children aged between two and five.

Iron is essential to make haemoglobin – the oxygen carrying component of red blood cells. While, vitamin D helps to control the amount of calcium and phosphate in the body, which are needed to keep bones and teeth healthy.  Vitamin D deficiency can cause rickets and poor growth in children.

The study, The Relationship between Cow’s Milk and Stores of Vitamin D and Iron in Early Childhood, found that two cups of cow’s milk per day maintained 25-hydroxyvitamin D (vitamin D) and had minimal negative effect on serum ferritin levels.

Serum ferritin levels correlate with total body iron stores.

Maintain vitamin D levels

A total of 1,311 children between the ages of two and five were recruited between December 2008 and December 2010 for the study.

Parents were asked to fill out a questionnaire about their children’s milk drinking habits and other factors that could affect iron and vitamin D stores. A blood sample was then taken from each child to determine body stores of iron and vitamin D.

Children that drank more cow’s milk had higher Vitamin D stores but lower iron stores, the research found.

 “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 with without greater benefit from vitamin D,” said Dr Jonathon Maguire, a paediatrician at St Michael’s Hospital and lead author of the study.

However, drinking just two cups of cow’s milk per day was found to maintain vitamin D levels, with little negative effect on iron stores.

“There is a trade-off between increasing 25-hydroxyvitamin D and decreasing serum ferritin with increasing milk intake. Two cups of cow’s milk per day appears sufficient to maintain healthy vitamin D and iron stores for most children,” said the published study.

Preserving iron stores

The study also revealed that children with darker skin pigmentation may not have enough vitamin D stores during the winter months.

 “Children with darker skin pigmentation not receiving vitamin D supplementation during the winter required 3 to 4 cups of cows’ milk per day to maintain 25-hydroxyvitamin D > 75 nmol/L.”

“Cow’s milk intake among children using a bottle did not increase 25-hydroxyvitamin D and resulted in more dramatic decreases in serum ferritin.”

In this situation, Maguire suggested that rather than consuming more cow’s milk, vitamin D supplementation may be a more appropriate way of increasing vitamin D stores while preserving iron stores.

By Mark Asltey