It's a question I get all the time: how much cow's milk should my child drink?

It's a question I get all the time: how much cow's milk should my child drink?

Cow's milk can be part of a healthy diet for children; about 70 percent of children drink it on a daily basis. Milk has protein and calcium--and it's fortified with Vitamin D, a vitamin that is very important not only for healthy bone growth, but for the prevention of some chronic diseases, including autoimmune, respiratory and heart diseases. In fact, the Committee on Nutrition of the American Academy of Pediatrics (AAP) says that children who don't drink at least 1000 mL (about four cups) of milk daily should take extra Vitamin D. 

That sounds like kids should be drinking at least four cups of milk a day--but that may not be such a good idea. 

Fortified milk may be high in calcium and vitamin D, but it's low in iron. Not only is it low in iron, but drinking a lot of it interferes with the body's absorption of iron and can even cause small amounts of bleeding in the intestine, further lowering the amount of iron in the body. And when children drink a lot of milk, it can fill them up and make it less likely that they will eat enough of other healthy iron-containing foods like meat or dark leafy vegetables (I see this often in my practice). In fact, drinking a lot of cow's milk is a common cause of iron deficiency. That's why the American Academy of Pediatrics Bright Futures guidelines recommend that children should only drink two cups a day.

So which is right? Two cups or four cups? A study just released in the journal Pediatrics helps doctors and parents answer this question. Researchers in Canada studied more than a thousand children ages two to five, looking at their diets, their lifestyles, and their vitamin D and ferritin (a test that measures iron) levels. 

Their answer to the question: two cups is right--with some caveats.

The biggest caveats have to do with the fact that Vitamin D is a sunshine vitamin--our bodies literally make it with help from the sun. If you have dark skin, you don't absorb those important rays as well--and during the winter, when we all tend to stay inside more, we get less exposure to sunshine. The researchers found that dark-skinned children who didn't get extra Vitamin D during the winter would need 3-4 cups of milk to get enough Vitamin D--but when they got that much, their iron levels went down. So supplementation is probably the better way to go.

Another interesting caveat had to do with bottles. Kids who drank milk from bottles didn't seem to get the same bump in Vitamin D from drinking more--and were more likely to have iron deficiency. The researchers weren't sure why this is, but said maybe parents don't realize how much milk their kids drink when they use a bottle--and kids who take milk from bottles might drink other things like juice from it too, and be otherwise more likely to fill up on fluids instead of eating a healthy diet.

So--here are the bottom lines for parents when it comes to cow's milk:

• Give your child two cups a day.
• Have your child play outside whenever possible, not only for Vitamin D levels but for overall health.
• If your child is dark-skinned, or you spend very little time outdoors, talk to your doctor about taking a Vitamin D supplement, especially in the winter.
• Ditch the bottle as soon as possible (by a year--sooner if you can).

Cow's milk isn't absolutely necessary for a healthy diet--there are other ways to get the nutrition it offers. If your child isn't drinking cow's milk for whatever reason, talk to your doctor about the best way to be sure that he or she is getting enough calcium, vitamin D and protein.

For more information on healthy diets for children, visit the Nutrition page of the AAP's healthychildren.org website and KidsEatRight.org, which has great (and practical) information from the American Academy of Nutrition and Dietetics.