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ST. LOUIS (KSDK) - It's one of those things most mothers always make sure their kids do every day.

Drink their milk at every meal!

But a new study published in the journal Pediatrics is questioning the practice of making sure kids get three glasses a day.

After following 1,300 preschoolers, scientists found three glasses a day can help kids get enough vitamin D, but the levels of iron in their bodies dropped.

This is such a interesting finding we asked St. Louis Children's Hospital pediatrician Dr. Kathleen Berchelmann to come on First @ 4 and give us some guidance.

Click the video player above to hear what Dr. Berchelmann had to say.