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We ask the experts to settle common questions we've all wondered about.

Question

Can milk or dairy products increase phlegm production and exacerbate breathing or congestion problems?

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Answer

It is a widely held belief that drinking milk increases phlegm production. Phlegm is a thick, sticky substance made up of mucus. It is produced by your respiratory system and tends to drip down the back of your throat when you have a cold. Some people shun milk and other dairy products because they are firmly convinced it increases phlegm. And individuals with asthma are sometimes advised by some alternative medicine practitioners to avoid so-called "mucus-forming" foods, particularly dairy products.

One concern for those who avoid dairy products is that they are losing a key source of calcium as well as other essential nutrients. So, is this avoidance really necessary?

According to a study published in the American Review of Respiratory Disease where people were inoculated with the common cold virus, milk intake was not associated with increased nasal secretions, symptoms of cough, or congestion. Various investigations have also shown no relationship between milk intake and the occurrence or exacerbation of asthma symptoms. In rare cases asthma can occur in individuals with an allergy to cow's milk, but this is not typical for people with asthma.

Interestingly, people who were convinced that a relationship exists between milk consumption and mucus formation reported more respiratory symptoms, thicker saliva and increased swallowing after drinking milk, compared to people not convinced of this relationship. And they also reported these effects with a soy-based drink that was used as a placebo in this experiment.

While dairy doesn't cause your body to make more phlegm, it may make the existing phlegm thicker and more irritating to your throat. This may make breathing more difficult and aggravate a cough. It is thought to be the fat content of the dairy products that has this thickening effect, which explains why a soy-based drink with similar fat content would have the same result.

Overall, there is no need for most people to avoid milk products due to fear of increased phlegm and mucus formation. The best way to counteract the thickening of phlegm is to drink plenty of water, which will help thin the mucus and allow it to move more easily.

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Liora Zilnik is a registered dietitian at Bridgepoint Hospital in Toronto.

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