Evidence that the universe is expanding, at least when it comes to beverages, is plentiful in the dairy aisle. Where once there was milk, now there is soy milk, almond milk, rice milk, hemp milk, flax milk, goat milk and oat milk. And coconut milk. Also cashew milk. And apparently hazelnut milk. 

The dizzying expansion of plant milks follows mounting concerns about the potential negative health consequences of hormones and antibiotics given to cows, for us and the bovines, as well as rising rates of dairy allergies among children. Add a dash of helicopter parenting to these concerns, and, boom, you’ve got a new industry. 

GettyImages-75540976 The milk section at a Safeway store in Livermore, California. A new study found a height difference between children who drank cow’s milk compared with children who drank non–cow’s milk. Justin Sullivan/Getty Images

Cow’s milk has long been part of the American diet. Its potential health benefits were first popularized in the early 20th century, and by the 1950s, children were drinking multiple glasses per day. But now, the iconic image of a full glass of milk beside a dinner plate is fading. Whereas the average American once drank 30 gallons per year, current statistics put the average at 18 gallons per year, according to the United States Department of Agriculture. 

And so it makes sense that researchers would investigate whether alternative “milks” have any impact, positive or negative, on children’s health. A new study from pediatricians at St. Michael’s Hospital in Toronto shows they might. 

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For the study, newly published in the Journal of Clinical Nutrition, pediatricians examined data from a large, ongoing research project called TARGet Kids! (The Applied Research Group for Kids). The researchers concentrated on children who consumed about 8 ounces of non-cow’s milk per day in order to check for height differences among this group compared with children who drank the same amount of cow’s milk per day. More than 5,000 children were included in the analysis. 

The study found a difference, albeit a tiny one. For each cup of non-cow’s milk consumed (that group included plant-milk and goat-milk drinkers), children were, on average, 0.2 inches shorter. More broadly, 3-year-olds who drank plant or goat milk were about half an inch shorter than 3-year-olds who drank cow’s milk. 

Although the difference is slight, it is in keeping with the percentile lines marked on the World Health Organization growth chart. Lead study author Jonathon Maguire, a pediatrician at St. Michael’s Hospital, explains that the height difference between the groups would place the non-cow’s milk drinkers in the 15th percentile for height, compared with the 50th percentile for the cow’s milk drinkers. Interestingly, children who drank both types of milk were still shorter than average, indicating that the increased height is likely tied to the amount of cow’s milk consumed. 

“This study does fit with prior research showing cow’s milk is associated with taller stature over time,” says Mark DeBoer, a pediatric endocrinologist at the University of Virginia, who was not involved with the research. DeBoer also highlights potential limitations of the findings. For example, if the children who drank non-cow’s milk were doing so due to allergies, those allergies could be responsible for growth differences by diminishing the absorption of nutrients.

Anthropologist and biologist Andrea Wiley, who has written an entire book about milk, emphasizes the same point. “Drinking cow’s milk is so normative in Americans that kids who drink non-dairy milk likely have other things going on,” she says. Those other things could include allergies and steroid medications to treat the allergies that could also inhibit overall growth. She also cautions against lumping all non-dairy milks together. “Some, like soy, are high in protein and fortified with calcium and vitamins A and D,” she says. “Almond and rice milk are much lower in protein and may not be fortified.” 

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Alternatively, hormones given to cows prior to milking could increase childhood growth. “The study is consistent with the potential that there’s something about cow’s milk that adds to growth over time,” says DeBoer. Only a large, randomized study comparing milk from cows given growth hormones compared with milk from cows that weren’t would confirm that theory, says DeBoer. 

Maguire emphasizes that the study does not indicate that drinking non-cow’s milk caused lower height, only that the two are associated. But, he says, because plant milks are not regulated in the same way as cow’s milk, the possible health effects are important to know. “The message for parents is to pay careful attention to the nutritional contents of these products,” says Maguire, “to make sure they contain the necessary protein, fat and micronutrients to support optimal growth.”