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Popular belief that milk increases phlegm levels is ‘myth’, says child health expert

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The widely held and persistent belief that milk boosts phlegm production and worsens respiratory conditions from asthma to the common cold, is a myth, argues a children’s health expert.

There is no need to avoid giving milk to children with asthma, cystic fibrosis, or respiratory infections, according to Dr Ian Balfour-Lynn.

“The milk-mucus myth needs to be rebutted firmly by healthcare workers”

Ian Balfour-Lynn

The children’s respiratory consultant from London’s Royal Brompton Hospital called on health professionals to “firmly rebut” the “milk-mucus myth”.

He said the notion that milk might generate excess phlegm – while chicken soup might get rid of it–was started in 1204 by Moses Maimonides, Jewish spiritual leader and court physician, in a treatise on asthma.

The idea was perpetuated by children’s health guru, Dr Spock, in his highly influential book on baby and child care published in 1946.

However, there is not any evidence to back up these beliefs, argued Balfour-Lynn in the journal Archives of Disease in Childhood, citing studies dating back as far as 1948.

He acknowledged that a possible explanation for the link had been suggested, but said it was yet to be proven.

“It is the aggregates of milk emulsion that they are aware of lingering in the mouth after swallowing” 

Ian Balfour-Lynn

This theory involved a protein produced by the breakdown of certain types of milk, which is known to boost the activity of a gene that stimulates mucus production, said Dr Balfour-Lynn.

But he said this process happened in the bowel and could only affect the respiratory tract if bowel integrity was weakened by infection, allowing the milk protein to travel elsewhere in the body.

He said it was highly unlikely that the common cold would do this, although noting that it may be possible in people with cystic fibrosis, which is associated with gut inflammation.

The more likely explanation lies in how milk feels in the mouth, he said. Milk is an emulsion, while saliva contains compounds that make it stickier and which quickly interact, boosting its volume.

“This could well affect the sensory perception of milk mixed with saliva, both in terms of its thickness coating the mouth and the after feel–when small amounts of emulsion remain in the mouth after swallowing,” he said.

“This may explain why so many people think there is more mucus produced, when, in fact, it is the aggregates of milk emulsion that they are aware of lingering in the mouth after swallowing,” he added.

“There is no evidence (and indeed evidence to the contrary) that milk leads to excessive mucus secretion”

Ian Balfour-Lynn

He noted that milk was an important source of energy, calcium, and vitamins, and was critical for good bone health and warding off osteoporosis in later life.

The evidence showed that fractures were more common in children who did not drink milk, he highlighted.

He said milk consumption was particularly important in conditions like cystic fibrosis or asthma when sometimes repeated large doses of steroids, which sap bone strength, were part of the treatment.

“While certainly the texture of milk can make some people feel their mucus and saliva is thicker and harder to swallow, there is no evidence (and indeed evidence to the contrary) that milk leads to excessive mucus secretion,” he said.

“The milk-mucus myth needs to be rebutted firmly by healthcare workers,” stated Dr Balfour-Lynn.

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