Did you know? Milk is an emulsion that gets stickier when it mixes with saliva
For centuries, people have thought that drinking milk or eating dairy products when they have a cold worsens symptoms by increasing mucus in the nose and throat.
Yet, despite what the public believed, there was never anything in the way of scientific evidence to back it up.
But now, research has shown for the first time that drinking milk does appear to make symptoms worse — at least in patients who already have excessive mucus secretion.
Doctors behind the study say the findings, published in the journal Laryngoscope, came as a complete surprise, as they were expecting to debunk the age-old link between dairy and phlegm.
‘I was sceptical and didn’t believe it was real,’ says Adam Frosh, consultant ear, nose and throat specialist at the Lister Hospital in Stevenage, Hertfordshire.
Indeed, a number of previous studies have suggested the link doesn’t exist. But, as Mr Frosh explains: ‘I have been asked about it by so many patients over the years that I felt I needed to look into it — if only to put the idea to rest.
‘The results were the opposite of what I was expecting.’
Mucus is produced by cells within the nose, sinuses and lungs, and consists of water, salt and proteins, which trap germs and dirt.
Antibacterial enzymes in mucus help to kill germs and protect us from infection.
Mucus is moved towards the back of the throat from the nasal passage by microscopic hairs, called cilia, where it is swallowed.
But too much mucus, usually triggered by infections or allergies, can mean it continually drips down the back of the throat (known as post-nasal drip). This excess can lead to a cough, sore throat and a husky voice.
Nearly 1,000 years ago, 12th-century Jewish physician Moses Maimonides wrote that milk caused ‘a stuffing in the head’.
A long history of speculation: Nearly 1,000 years ago, 12th-century Jewish physician Moses Maimonides wrote that milk caused ‘a stuffing in the head’
Since then, the idea has persisted and gained new ground in 1946, when U.S. paediatrician, Dr Benjamin Spock, whose book, The Common Sense Book Of Baby And Child Care, sold more than 50 million copies worldwide, advocated that children with chest problems avoid milk.
For the latest study, researchers recruited 26 men and 82 women at the Lister Hospital who had complained of increased mucus secretions. They were all put on a dairy-free diet, with no milk, cheese, or butter for six days.
From day three, half drank 350ml of full-fat cow’s milk a day for the remaining four days, while the rest drank 350ml of soya milk. Both milks were flavoured, so patients did not know which they were drinking.
Each patient kept a symptom diary and was asked to rate their mucus secretions on a scale of one (none at all) to 100 (‘overwhelming’ amounts).
All the volunteers experienced a reduction in mucus levels in the first two dairy-free days. But over the next four days, the symptoms of the group drinking soya milk continued to diminish, while those drinking cow’s milk saw them increase significantly.
At the start of the study, patients rated their mucus secretions at an average severity of 65 out of 100. After two dairy-free days, this had dropped to around 55 for both groups. By day seven, however, the ratings for the dairy group had risen back up to 63, while the rating for the soya milk group stayed about the same.
‘This was quite a big effect in a relatively short space of time,’ says Mr Frosh. ‘It’s reasonable to conclude that anyone who feels milk increases their mucus production should consider reducing their dairy intake, or try a dairy-free diet, to see if it improves their symptoms.’
One theory for milk’s apparent effect on mucus is that it contains beta-casein A1, a protein that activates the genes responsible for mucus production.
But this could only happen if the proteins escaped through the gut and entered the bloodstream, where they could activate the genes in question. This is unlikely to happen unless the gut is damaged or severely inflamed, as in the case of cystic fibrosis sufferers.
Dr Ian Balfour-Lynn, a specialist in children’s respiratory illness at the Royal Brompton Hospital in London, is convinced there is no scientific rationale for the milk-mucus link. In September, he published a review in the Archives of Disease in Childhood, in which he trawled through existing research and concluded the problem is not real.
And, he warned, if the parents of children with respiratory problems restrict their milk intake, they will risk depriving them of bone-building calcium.
‘There is absolutely no need to avoid giving this nutritious foodstuff to children with asthma, cystic fibrosis or chest infections,’ says Dr Balfour-Lynn.
‘The milk-mucus myth needs to be rebutted firmly.’
He believes sufferers imagine they have more mucus in their throat after drinking milk because of its viscosity.
Milk is an emulsion that gets stickier when it mixes with compounds in saliva.
‘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,’ says Dr Balfour-Lynn.
But Mr Frosh insists: ‘We owe it to patients not just to dismiss their claims. Now, we need bigger studies that monitor the levels and characteristics of these secretions.’