Preschoolers who drink three or more cups of milk a day may get a small height boost, but they’re also more likely to be overweight or obese, according to a new U.S. study.

The results, based on nearly 9,000 children, support current recommendations that preschoolers consume two one-cup servings of milk a day, the authors say.

“Overall, we were most struck by the heavier BMI (body mass index) among four-year-old children drinking high volumes of milk,” said Dr. Mark DeBoer, a pediatrician at the University of Virginia in Charlottesville who led the study.

“Given the country's current obesity epidemic, we felt as though the data supported the current recommendations of the American Academy of Pediatrics, recommending that children drink two servings of milk daily - but restrain them from drinking higher volumes because of the potential for unhealthy weight gain,” he told Reuters Health by email.

DeBoer said earlier research in other age ranges had noted a connection between higher amounts of milk intake and taller stature. But, his team writes in Archives of Disease in Childhood, studies have found mixed results when it comes to milk and excess weight gain.

Data for the new study came from the Early Childhood Longitudinal Survey, a U.S. study that began when the kids were born in 2001.

The researchers examined the milk-consumption patterns of 8,950 children during their first four years, based on interviews with parents. They were also able to follow up with 7,000 of those kids at age five.

They found that 53 percent of children who drank milk consumed two or three one-cup servings daily.

Four-year-olds who drank more than the recommended two servings of milk per day were 16 percent more likely to be overweight than the kids who drank less.

The study team also found that on average, kids who drank two, three and four or more servings of milk per day were about a centimeter taller than kids who drank one serving or less.

By age five, the weight differences were no longer statistically significant and drinking more milk was only associated with being slightly taller.

“As pediatricians, we had noticed that some families do not appear to restrain their children's milk intake, and we were wondering whether high amounts of milk intake would be associated with higher body mass index,” DeBoer said. “In that sense, we were not surprised when we noted that children at four years old who drank a larger number of servings of milk daily also had a higher BMI.”

There are several possible explanations for the results, particularly given that milk is high in growth factors that may or may not contribute to getting taller, DeBoer noted. It’s also possible, he said, “that the heavier weight status associated with more milk intake could push children toward earlier growth.”

Because the study is based on observation, it cannot draw conclusions about cause and effect, he cautioned.

Dr. Jonathon Maguire, a pediatrician and researcher at St. Michael’s Hospital in Toronto, said studies based on observing people over time, like the one DeBoer’s team used, are very important.

“We learn from those children about what's healthy and what's potentially not healthy, and this study is a nice example of that,” said Maguire, who wasn’t involved in the new study.

The findings are also compatible with Maguire’s own research showing that around two cups of milk per day balances vitamin D and iron stores nicely, he said. (See Reuters Health article of December 19, 2012 here: reut.rs/1B0ahPC.)

“And what this study emphasizes is that around two cups is a nice balance between linear growth in terms of stature and avoiding problems like obesity and overweight,” he said.

Milk is a staple of the Western diet, MacGuire said, “It's a very important source of calories and essential fats, but too much of a good thing may not be a good thing and that's what this study is supporting,” he said.