The widely held belief that drinking milk promotes excessive mucus production in the lungs needs to be rebutted, a UK paediatric respiratory specialist says.
Dr Ian Balfour-Lynn, of the Royal Brompton Hospital in London, says his department’s staff are constantly told by parents that they have stopped their child having milk because it causes mucus.
“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,” he writes in the Archives of Diseases in Childhood.
“Indeed, many people believe milk should be avoided with any respiratory illness, even a common cold.”
But Dr Balfour-Lynn writes that while the texture of milk can make some people feel their mucus and saliva is thicker and harder to swallow, there is no evidence that milk promotes mucus and in fact some evidence to the contrary.
The notion that milk causes mucus dates back the 13th century and the claim has been maintained down the ages, including being repeated in recent times in the influential Dr Spock Baby and Child Care book that sold 50 million copies.
There is even a published, unproven hypothesis which holds that protein derived from the breakdown of certain types of milk upregulates MUC5AC gene expression, increasing mucus secretion in the colon.
The earliest attempt to obtain real evidence of a milk-mucus link was in 1948 where a published US study of 647 patients found no difference in self-reported throat mucus between those who drank 0-5, glasses of milk per week and those who drank 6-9 or more than 10. In the same study, nose and throat examinations of 157 subjects showed no excess mucus in those who drank milk and who did not.
Dr Balfour Lynn cites a second study, funded by the Australian Dairy Research Council, which found no correlation between milk/dairy intake and symptoms of respiratory tract congestion or weight of nasal secretions produced in 60 adults with rhinovirus.
And although many people with asthma avoid milk because they perceive it exacerbates their symptoms, double-blind milk challenges did not cause bronchoconstriction or respiratory symptoms in two studies of non-milk allergic asthmatic adults.
Nevertheless, surveys have shown people believe that consuming milk causes them to produce more mucus.
In one Australians survey of 345 random shoppers 46% of whole milk drinkers, 25% of reduced fat milk drinkers and 11% soy milk drinkers ‘agreed’ that milk causes mucus.
The author suggests this could because the texture of milk – an emulsion – can make the saliva feel thicker or the inside of the mouth is covered with a coating. Perceptions after drinking milk also include difficulty in swallowing.
But milk should not be avoided in children because it is an important source of calcium and vitamins that are important for children with asthma who may be at risk of bone loss from steroid treatment. Milk is also an energy source that may be crucial to ensure adequate nutrition in children with cystic fibrosis who are at risk of weight loss, he adds.
“The milk-myth needs to be rebutted firmly by healthcare workers,” concludes Dr Balfour-Lynn, who declares no conflict of interest.