Dairy

If you are sick, you should stay away from dairy products (milk makes you phlegmy)

We have tried to debunk this myth before, but even our supporters have trouble believing that milk does not give them a lot more mucus. A pharmacist friend named Sonak, who considers himself a huge fan of medical myth-busting, just cannot believe that milk does not increase his phlegm and congestion when he’s sick. “I can feel it!” he insists. He thinks it is one myth where we are wrong. So we’ll look at the science again. If milk is going to make you more congested when you are sick, then we would hate to recommend the wrong thing.

Sonak has plenty of supporters on this one. Drinking milk or consuming other dairy products has long been thought to be associated with increased respiratory problems, congestion, or even with asthma. It has been a traditional Chinese medicine tenet to cut down on how much dairy you are taking in if you have too much mucus in your system. A twelfth-century physician, Moses Maimonides, recommended that people with breathing or congestion problems needed to eliminate milk and dairy from their diets. Even Dr. Spock said that children should not have milk when they have colds! Many of today’s doctors recommend the exact same thing; in a study of 330 parents, almost 60 percent believed that milk would increase their child’s mucus production, and almost a third of them got this information from their doctor.

Scientists have recently developed a hypothesis to help explain how milk might increase mucus production. We thought Sonak would be interested in this new theory. In the scheme of how allergies usually work, it did not make sense that milk would give you more congestion instead of, for example, giving you a rash or irritating your digestive tract. Scientists found that when milk is broken down by your body one of the chemicals it becomes is beta-casomorphin-7. The reason you might care about beta-casomorphin-7 if you think milk makes you phlegmy is that this chemical stimulates mucus production from certain glands that line the inside of your gut, specifically the colon. The scientists proposed that maybe this same chemical makes the glands inside your respiratory tract produce more mucus too. It is not yet time to say that Sonak is right and we are wrong. There are a number of reasons why we are not yet convinced by the science. First, there is no evidence that this chemical from milk stimulates the glands in your respiratory tract and makes them produce more mucus. Second, even if it is stimulating glands in your gut, there is no evidence that this would have an impact on your respiratory tract. The chemical would need to get to your respiratory tract, and that’s a separate set of pipes from your digestive tract. The two only intersect in the back of your throat. If milk is going down the respiratory set of pipes, you have more problems than just mucus—you will choke! For this chemical that is made in your digestive tract to have an effect in your lungs, it would need to be absorbed into the bloodstream in a way that also causes inflammation in your lungs. There is no evidence that this happens.

In contrast to this unproven idea, there are a lot of scientific studies that seem to prove that there is no link between drinking milk and becoming phlegmy. When tested carefully in human beings, there is no evidence that milk or dairy increases your mucus production. In one test of this idea, scientists took 125 volunteers and randomly assigned them to get cow’s milk or a soy drink, both of which were flavored with cocoa and peppermint in a way that made it impossible for the volunteers to know which drink they were getting. The scientists asked all of the participants to rank how much of a mucus effect they had after drinking either product and to describe what their symptoms were. When people did not know whether they were getting dairy milk or a soy drink, they could not tell any difference between how the drinks affected them. There was no difference in having a “coating over the mouth,” “swallowing a lot,” or having “thicker saliva” whether you drank milk or soy. However, if you believed beforehand that milk gave you more mucus, then you reported more of these problems for either of the beverages.

In another great study of this myth, scientists took sixty volunteers and tried to make them sick with the common cold virus by sticking it directly in their nose. Then they carefully recorded the volunteers’ breathing symptoms and their milk and dairy intake over the next ten days. Even better, they actually measured the weight of the sick people’s snot to see how much mucus they were making! (Take a moment to be glad that you don’t have a job measuring people’s mucus weight.) Fifty-one of those volunteers got sick, but how much dairy they were taking in did not have any impact on how they felt. Drinking more milk was not associated with any increase in problems with coughing, congestion, or a runny nose, nor did drinking more milk change the weight of their nasal secretions. In other studies that look at adults with asthma, researchers also found that there was no effect on their breathing, coughing, or wheezing from drinking either whole or skim milk. It was the same as drinking water. This was also true in a study looking at patients with eczema and asthma. If they did not have any actual milk allergy, the milk did not do anything to flare up their asthma or their eczema. These are very careful studies, testing this idea in human beings, and showing no impact from milk.

Are we saying that milk causing more mucus is all in your head? Not entirely. People who believe that milk causes more mucus seem to be sensitive to the sensation that milk creates in the mouth. Though milk does not actually increase the amount of mucus your body makes or change how congested you are, you might feel something different in your mouth when you drink it. Experts tell us that milk spreads out in tiny droplets over the saliva in your mouth. The official name for this process is called “droplet flocculation.” The feeling of those tiny droplets in your mouth might be mistaken for having more mucus, especially among people who are very sensitive to this sensation. You also might be interested to know that drinking any fluid—water and milk alike—increases the amount of saliva that you have, though studies show neither makes your saliva thicker.

Even if you think something is happening and feel something different, this does not make it real! The studies have showed that people who are “sensitive” to milk’s effects can be fooled in the same way by soy drinks. Milk does not make your cold or breathing worse.