Drinking two cups of milk a day is enough to give most young children enough vitamin D and iron, a Canadian study suggests.

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.

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.

Drinking too much milk

The researchers suspect that the more milk children drink, the less iron-containing foods they eat.

They also found that drinking from a bottle seemed to result in more dramatic decreases in iron stores. No one knows why, Maguire speculated that parents could be underreporting milk intake from bottles and again the child ends up eating less iron-rich food.

Nancy Martin’s daughter used to love drinking six child-size glasses of milk a day. It was a doctor that pointed out it was too much.

"It wasn't until the doctor, I think at her two-year checkup sort of said, ‘She's quite pale and you're saying she's drinking a lot of milk, she's a picky eater, does she sleep a lot? And I said yeah, that's her, and they said, ‘Oh it sounds like she could be anemic."

The family now encourages her to eat more meat, beans and legumes that are rich in iron. "It's still a struggle," her mother said.

Conversely, Aviva Allen, a nutritionist in Toronto, has a four-year-old son and an 18-month-old son who don’t drink cow’s milk because lactose intolerance is common in their family.

Alternative milks such as almond milk, rice milk and hemp milk are often fortified with calcium, Allen said. She also suggests supplements for vitamin D in the winter.

"There aren't any nutrients that are in cow's milk that you can't find in other places," Allen said.

"If you have a glass of milk and there's two to three hundred milligrams of calcium in that one cup it's an easy way to be sure that your child is intaking the proper amount. So if you going to choose other plant sources then you just need to be more on top of it."

Plant sources of calcium include nuts and seeds, beans like white and navy beans, leafy green vegetables like kale, collard greens and broccoli.

For plant-based sources of iron, Allen suggested prunes, dried apricots, beans and lentils and dark, leafy greens.

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

The research was funded by the Canadian Institutes of Health Research Institute and St. Michael's Hospital Foundation.

LOOK: If your little one has a hard time sitting still at the dinner table, here are some tips to get them to stay put and eat healthy.

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  • Let Kids Help You Prep

    Let your kids help you in the kitchen. Talk to them about what's in food and why it's good for our bodies. Involve kids in menu planning, shopping, and meal prep, and they'll be more likely to eat what's being served.

  • Offer A Variety Of Foods

    Offer a variety of vegetables, fruits, whole grains and legumes at the dinner table. Even if your child eats only two bites, he or she will understand that these foods make up a nutritious diet. When he starts wanting more than two bites, expand your offerings to include different foods.

  • Same Foods, Different Shapes

    Slice and dice foods in different ways. Try raw carrot sticks one day and cooked carrot coins another.

  • Have Patience

    This is the toughest one of all. Giving in to your child's demands only makes things harder in the long run. Many kids won't accept a new food until it's been offered at least 10 times, according to the Canadian Academy of Pediatrics.

  • Take Small Steps

    Some kids are overwhelmed by large quantities of food on their plates. If you're introducing your child to a a new dish, keep the portions small.

  • Two-Bite Rule

    One way to help them develop new taste buds? Insist kids eat at least two bites of everything on their plate before leaving the table.

  • Don't Take Personal Orders

    Don't make special orders or substitutes for everyone's special preferences. (Unless there are allergies of course). At first, your child may refuse to eat. Stay calm, stand firm, and ignore tantrums. Your child will not go hungry from skipping a meal. Yes, you heard that right: your child will not go hungry from skipping a meal. They'll come to the next meal with a healthy appetite, and (most importantly) an understanding that a tantrum won't break you.

  • Stay Cool

    When your child rejects a food, stay calm and reaffirm the boundaries you've established (two bites before leaving the table). Don't let your child engage you in a power struggle.

  • Don't Forbid Foods They Like

    You know how this works: you always want what you can't have. And if you don't give your kids candy at home -- they most likely have other ways of finding it. Allow your kids to choose a special food from time to time and let them eat it guilt free. Teach your kids the difference between everyday foods and occasional foods.

  • The Power Of Stickers

    Most kids like being recognized for work they do. Stickers often have the power to encourage younger kids, especially if they can help pick them out. Use stickers as a reward for trying a new food, finishing a meal, or choosing a healthy option.

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