Scientists from the Royal Brompton Hospital have finally answered the question
Drinking milk doesn’t increase phlegm after all, according to new research.
The findings suggest the widely-held belief that a glass of the white stuff boosted mucus production and worsened respiratory conditions – from asthma to the common cold – is a myth.
Now, researchers say parents should not stop giving their child milk as the calcium it contains is vital for bone health and growth.
Dr Ian Balfour-Lynn, of the Royal Brompton Hospital in London, said: “Our department has repeatedly been told by parents that drinking milk increases mucus production from the lungs, and so they stop their child having milk.
“This is particularly so in patients with conditions associated with excess mucus, for example, cystic fibrosis and primary ciliary dyskinesia, but also includes children with infant wheeze or asthma.
“Indeed, many people believe milk should be avoided with any respiratory illness, even a common cold.”
He added the myth 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 written for a relative.
Children’s health guru Dr Spock perpetuated it in his highly influential book on baby and child care published in 1946 which sold over 50 million copies by the time of his death in 1998.
But since 1948 research showed this was not the case but the myth persisted.
One unproven theory was that a protein derived from the breakdown of certain types of milk triggers that gene that increases mucus secretion.
Dr Balfour-Lynn said this all happens in the bowel, and could only affect the respiratory tract if the integrity of the bowel was weakened by infection, so allowing the milk protein to travel elsewhere in the body.
It’s highly unlikely that the common cold would do this, although it may be possible in people with cystic fibrosis, which is associated with gut inflammation
Instead the myth could be down to how milk feels in the mouth.
Milk is an emulsion, while saliva contains compounds that make it stickier and which quickly interact with the emulsion, boosting its volume.
He said: “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 emulsions remain in the mouth after swallowing.
“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 aware of lingering in their mouth and throat.”
He added: “Many asthmatics perceive their asthma is worsened by drinking milk, and dairy is often avoided.
“While allergy or lactose intolerance is often thought to be the issue, in reality, respiratory symptoms as the sole manifestation of food allergy is uncommon.
“Milk is the principle source of calcium for children and adults as well as a good source of several vitamins.
“Adequate calcium intake is critical for the development of normal bone health and prevention of future osteoporosis.”
He cited research that showed children who avoided milk were shorter and had reduced bone mineral density.
They were also at greater risk of childhood fractures which was “particularly important for children with respiratory disease who may require frequent courses of oral corticosteroids.
Milk was also an important energy source for children and “omitting this important calorie source is particularly deleterious for young children with cystic fibrosis with their increased energy requirements.”
He concluded: “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.
“Milk is an important source of calories, calcium and vitamins for children. The milk-mucus myth needs to be rebutted firmly by healthcare workers.”
The study was published in the journal Archives of Disease in Childhood.