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.