Research funded by the Canadian Institutes of Health Research Institute suggests drinking two cups of milk a day is enough to give most young children enough vitamin D and iron.

In Monday's issue of the journal Pediatrics, Toronto researchers said there's a trade-off from drinking milk for those aged two to five: it raises vitamin D stores but lessens iron stores.

"For each additional cup of milk, it reduces the iron stores by a little bit," said study author Dr. Jonathon Maguire of St. Michael's Hospital and the Hospital for Sick Children in Toronto. "But in children who are at risk for iron deficiency for example, that little bit actually is very important."

In children with very low iron stores, the brain doesn’t develop in the same way as in their peers who weren't iron deficient. In the long term, that can lead to difficulties with school performance, behaviour, Maguire said.

The Candian CBC reported “For the study, researchers analyzed blood samples from 1,311 healthy children aged two to five during routine visits to the doctor. Parents were asked how many 250-mL cups of cow's milk their child drinks a day or if the child currently uses a bottle. The average daily milk intake in the study was 460 mL.

Each cup of cow's milk increased vitamin D by 6.5 per cent on average and decreased iron stores by 3.6 per cent on average.

Gender, season, vitamin D supplementation, skin pigmentation and drinking from a bottle were all factors in the trade-off, the researchers said.

For children with darker skin pigmentation who absorb less vitamin D from the sun, Maguire suggested taking vitamin D supplements, which fits with current recommendations from the Canadian and U.S. pediatric societies.”

Alternative milks children could use to supplement their cow’s milk intake include: almond milk, rice milk and hemp milk are often fortified with calcium.

The Canadian Pediatric Society and American Academy of Pediatrics recommend that children under the age of one not drink cow's milk.