First published Winter 2018


Expert says there is “no evidence” that dairy increases mucus production from the lungs


An expert in children’s respiratory diseases says that there is no need for children with asthma, cystic fibrosis, or the common cold to avoid dairy products. In a research review published in Archives of Disease in Childhood, Dr Ian Balfour-Lyn, a consultant at London’s Royal Brompton Hospital, argues it is a myth that milk boosts phlegm production and worsens respiratory conditions, and says parents shouldn’t avoid giving “this nutritious and bone-strengthening foodstuff to children with asthma, cystic fibrosis, or respiratory infections”.1 

He writes that the notion that milk might generate excess phlegm (and that chicken soup alleviates it) began in 1204, with a treatise on asthma by Moses Maimonides, who was a court physician. This belief, he says, was later perpetuated by children’s health guru Dr Spock in his 1946 best seller Baby and Child Care.

Weakened bowel integrity

Citing studies back to 1948, Balfour-Lyn says there is no evidence to support the belief, although one (yet to be proved) possible explanation involves 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”.

But this, he writes, happens in the bowel and could only affect the respiratory tract if the integrity of the bowel was weakened by infection, allowing the milk protein to travel elsewhere in the body. He says whilst it is highly unlikely that a cold would do this, it may be possible with cystic fibrosis, which is associated with gut inflammation.

Mouth-feel may also offer an explanation. Milk is an emulsion, whilst saliva contains compounds that make it stickier and which quickly interact with the emulsion, boosting its volume. He writes: “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.” Balfour-Lyn says that as there is no evidence (but is evidence to the contrary) that milk leads to excessive mucus secretion, “the milk-mucus myth needs to be rebutted firmly by healthcare workers”.

...this could only affect the respiratory tract if the integrity of the bowel was weakened by infection, allowing the milk protein to travel...

Post-nasal drip

Eliminating dairy is often used to tackle the annoying problem of a persistently runny nose, or for post-nasal drip, which is when excess mucus drips down the back of the throat. However, Balfour-Lyn specifically refers to mucus production in the lungs of children; rather than in the upper airways. 

Speaking to Optimum Nutrition, he said there was a need for further study into the role of dairy and mucus production. “But [it is] very difficult to measure mucus production in lower airways. I also think that however much scientific evidence is produced, people still prefer to stick to their beliefs.”

He had no doubt that some people have genuine milk allergies, but the studies he reviewed specifically looked at increased mucus production in the lungs. “Milk has not been shown to increase mucus production in the lungs,” he said. “I worry that loads of parents stop milk for no good reason and then run [the] risk of low calcium in a growing child.”

Calcium intake, he says, is particularly important with cystic fibrosis or asthma “when sometimes repeated large doses of steroids, which sap bone strength, are part of the treatment”.

Registered nutritional therapist Kate Delmar-Morgan, who specialises in working with children, said: “I concur with Dr Balfour-Lyn in that children should not be taken off dairy unless there is a very good reason, since it is a crucial source of calcium required for growing bones.

“The mucus issue is a confusing one since the scientific literature does not support the theory that dairy increases mucus production. However, clinical evidence shows there have been cases where reducing or avoiding dairy for a short time during colds or infections may help some of the symptoms.”

Gut inflammation

Delmar-Morgan highlighted the problem of gut inflammation raised by Balfour-Lyn. “There may be other reasons why a child’s gut is inflamed (apart from cystic fibrosis) and, as suggested, certain milk proteins may migrate from the gut and cause unwanted reactions elsewhere.”

She added that antibiotics prescribed for bacterial infections may also have a negative effect on a child’s gut immunity, perpetuating a cycle of illness.

“The way I try to support children is to encourage immune-supporting foods. General recommendations for this are to provide brightly-coloured fruits and vegetables including lovely orange vegetables such as sweet potatoes, pumpkin and carrots; good sources of protein such as seafood, meat, seeds, beans, peas and lentils; plus good wholesome wholegrains.

Because vitamin D is also essential to bone development in children, she said it was important to ensure exposure to sunshine — although “obviously not in the middle of the day, in the summer”.

If your child has continuing colds and infections then seek the help of a GP or registered nutritional therapist who will be able to offer more specific nutrition advice.


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