TORONTO -- Can there be too much of a good thing when you are talking about little kids and cow's milk? A new study suggests there can.
The study, by scientists in Toronto, says children between the ages of two and five should be drinking half a litre, or approximately two eight-ounce cups of milk a day.
Less than that and kids may not be getting enough vitamin D, the study suggests. But more than that, and the stores of iron in their blood -- which are essential for a developing brain -- may start to slip below acceptable levels.
The study was led by Dr. Jonathon Maguire, a pediatrician and researcher at St. Michael's Hospital in Toronto. It is published in this week's issue of the journal Pediatrics.
"Cow's milk is a very important staple in our western diet for children. I don't want to underestimate the importance of cow's milk," Maguire said in an interview about the study.
"Our question was really: Well, how much?"
It's a query pediatricians face all the time, Maguire said. They haven't had a good answer to give because expert groups are divided on the issue.
Some organizations have argued young children should consume a litre of milk a day to get the vitamin D they need to build strong bones and avoid rickets, a formerly common bone-softening condition. (Milk is fortified with vitamin D.)
But other groups have warned that children's consumption of cow's milk should be curtailed because some studies have shown kids who drink a lot of milk can have low levels of iron in their blood.
Low iron can lead to anemia, where the body produces too few of the red blood cells that transport oxygen throughout the body.
"It looks like in children who have iron deficiency severe enough to cause them... to have anemia, those children have difficulties with their cognitive development. Over time, they're not quite as bright as other children," Maguire said.
Iron deficiency in young children isn't uncommon in Canada. While it's just a guesstimate -- Maguire said recent studies haven't been done -- it is believed between 10 per cent and 20 per cent of young children in Canada may have low iron stores.
Given the confusing advice and the fact milk consumption by preschoolers seems to involve a trade-off between vitamin D and iron, Maguire and some colleagues decided to try to find the sweet spot.
They enrolled 1,311 healthy Toronto children aged two to five in a study, evaluating samples of their blood for vitamin D and iron stores and gathering information from parents about the amount of milk the kids drank.
The researchers found about 500 millilitres of milk a day for most children was the right amount to have adequate levels of vitamin D and iron.
There was an exception: During winter, children with dark skin didn't hit the vitamin D target with 500 ml daily. The study suggests in winter, children with dark skin may need a vitamin D supplement as well as milk.
The study was funded by The Canadian Institutes of Health Research and the St. Michael's Hospital Foundation.
-- The Canadian Press