A persistent myth about milk — that drinking it can lead to the production of more gooey mucus in your body’s airways — is completely false, a new review finds. The myth is so persistent that some parents have stopped giving milk to children with chronic respiratory conditions, such as asthma and cystic fibrosis, out of concern that drinking milk might make it harder for their children to breathe. But the milk-mucus connection is simply a myth, said review author Dr. Ian Balfour-Lynn, a pediatric pulmonologist at Royal Brompton Hospital in London. And when people take this myth as true medical advice, it could have serious consequences: Not giving milk to children can make it challenging for them to get enough calcium, vitamins and calories, Balfour-Lynn said. Children who don’t drink enough milk are also more prone to fractures and shorter stature, studies show. It’s unclear exactly when the milk myth got started. It’s possible that it came from Moses Maimonides, a philosopher and doctor who wrote that milk causes “a stuffing in the head.” Moreover, traditional Chinese medical texts have linked dairy consumption with “a humidifying effect and thicker phlegm,” Balfour-Lynn wrote in the review, which was published online yesterday in the journal Archives of Disease in Childhood.
Even the influential “Baby and Child Care” book, of which more than 50 million copies have been sold since its publication in 1946, repeats this claim. A 2011 edition of the book states that “dairy products may cause more mucus complications and more discomfort with upper respiratory infections,” Balfour-Lynn found while researching the myth. Given the myth’s reach, it’s no surprise that in a study of 345 randomly selected shoppers in Australia, 51 (46 percent) of the 111 whole-milk drinkers “agreed” that milk causes mucus, according to research published in 2003 in the journal Appetite. However, the type of milk appeared to influence the shoppers’ decision: Just 30 (25 percent) of the 121 reduced-fat-milk drinkers and only 12 (11 percent) of the 113 soy-milk drinkers agreed with this statement, the study found. The myth may persist because of milk’s unique properties. Milk is an emulsion, meaning it has droplets of one liquid suspended in another liquid. In milk’s case, fat droplets are suspended in water. When a person drinks milk, the milk mixes with their saliva.