The Myth of Milk and Mucus: Coughs, Colds, and Asthma
Does drinking milk cause you to produce more mucus and make conditions like coughs, colds, and asthma worse? Surprisingly, the answer is both yes and no—and largely the answer depends on whether you personally believe it does or not.
It seems to be well known that drinking milk will make you more "stuffed up." Drink milk when you have a cold, they say, and you’ll be blowing your nose all day and night. Worse, it’ll stop you getting rid of that chest infection that’s been plaguing you for weeks. And if you’ve ever suffered from asthma, forget it. Milk, for you, is definitely off the menu.
Milk does not cause you to produce more mucus
Except that "they," whoever they are, are wrong. In a quite disgusting experiment conducted by the Department of Community Medicine at the University of Adelaide, Australia, researchers infected over 50 people with the common cold and then collected and weighed the snot of those people for the next 10 days.
Some of the subjects didn’t drink any milk for the duration of the experiment. Some of them drank more than 10 glasses of milk a day. Some didn’t believe in the theory that milk produces mucus; others believed it with a righteous passion.
But when the researchers gathered in all the data, they found that there was no difference. Drinking milk had zero effect on the quantity of mucus produced.
The Power of Belief: The Nocebo and Placebo Effects
The placebo effect is what happens when you believe a pill, potion, tincture, or snake oil will work. If someone believes that what they are taking (or doing) will help them recover from illness, there is a greater chance of them getting better.
The nocebo effect is the opposite. There is a rumour that one gentleman in the 1970s was told by his doctor that he had a terminal illness and had just a couple of months to live. He did indeed die within that time, but the autopsy showed no signs of disease, and it was eventually concluded that he had died because his doctor said he would. Possibly this is just a rumour—certainly I’ve been unable to find any reputable records that confirm the story—but I’ll be treating any doctorly advice with some scepticism nonetheless.
What the experiment above, with the milk and the common cold, did find was that a very small, statistically insignificant percentage of those people who believed in the theory coughed a bit more after they drank some milk.
It’s not Asthma: It’s a Milk Allergy
So where did the belief come from, and why is it so common? Well, in a review of all the scientific studies on milk and mucus by the Allergy Department at the University Hospital of Zurich in Switzerland, it was found that in some people who have an allergy to cows’ milk, their symptoms after drinking milk were very similar to asthma.
Now. Although lactose intolerance is fairly common, and especially the milder forms, having a true milk allergy is relatively rare. However, the symptoms of a mild allergy and an intolerance can possibly be remarkably similar. This does not mean that lactose intolerant people will experience asthma-like symptoms by drinking milk, but what it could mean is that people with a mild lactose intolerance may associate other symptoms with drinking milk, and thus have a more deep-rooted belief that milk causes mucus—and from the Australian experiment above, we know that simply having a belief in this can cause someone to cough more.
Does this Mean It’s All in your Head?
No, certainly not. It is all a lot more complicated than that.
In people with a milk allergy (even a mild one), or for people who have a lactose intolerance, drinking milk will mean that the efforts of your immune system will be diverted to dealing with the problems that milk causes when you ingest it. This means that if your immune system is busy dealing with that problem, it won't be dealing with your cold—or at least not as well as it could—which might make your cold symptoms worse, or make your cold last longer.
But even just the non-physical aspects of drinking milk can cause problems for some people. Stress and depression cause your immune system to work less well. And conversely, relaxation and happiness cause your immune system to work better. And it doesn’t take a lot to upset your stress-happiness, and therefore your immune system balance. So if you have just drunk a glass of milk, and if you believe that it will make you feel worse—maybe because you have a mild lactose intolerance that you haven’t had checked out properly—there will be two stresses at work in your body: an upset digestion from drinking milk, and a belief that you did something that will make you feel worse. In response, your immune system will be just that bit less able to cope efficiently.
So What are you Saying? Should I Drink Milk or Not?
Do you want to drink milk? Do you believe it will make you feel better or worse? Have you been tested for a milk allergy? Are you lactose intolerant?
Milk will not make you produce more mucus. However, for some people—lactose intolerant people—it can give you other symptoms that can make you feel a bit miserable and ill and thus lower your immune response and maybe lessen your ability to fight off infections. And for others, simply believing that milk causes mucus will make you cough. For anyone with a milk allergy, obviously dairy products should be avoided and you should talk to your doctor. But for most people, you can drink milk until... well, until the cows come home, and it won’t make a speck of difference to your cold or chest infection.