There seems to be a lot of confusion as to whether milk and dairy products increase phlegm production, and whether we, as CF patients, should avoid it. Some people are certain that milk proteins trigger a mucus response in them that causes congestion, exacerbations, and overall malaise. Others consume large amounts of milk and dairy and have never noticed a single difference in the amount or thickness of their mucus compared to no-dairy days. I happen to fall in the latter category, but nonetheless, everyone’s experiences are different, so maybe I’m the odd one out. I decided to look into what the science really says about the relationship between milk and mucus.
Since the average person really only feels congested when they are sick with a virus, a lot of the research I found was directed at cold and flu symptoms. Popular medical websites seem to promote the hypothesis that phlegm can be made to feel worse with ingestion of dairy products such as milk, ice cream, and cheese. But they don’t go so far as to say milk causes mucus production. Mayo Clinic responds to the question this way: Although drinking milk may make phlegm thicker and more irritating to your throat than it would normally be, milk doesn’t cause your body to make more phlegm. In fact, frozen dairy products can soothe a sore throat and provide calories when you otherwise may not eat.
They cite two studies for this. The first, a 2012 paper published in Canadian Family Physician, a small journal with a low impact factor, had to do with restricting milk in children with asthma for reasons of mucus production. They found no reason to do so. The second source is titled, Does Milk Increase Mucus: Medical Hypothesis, published in 2010. To summarize, a certain exorphin (morphine-like peptide) called Beta-casomorphin-7 is produced in the blood stream when drinking A1 (i.e. regular) milk; if in a petri dish, this exorphin added to respiratory cells stimulated the kind of mucus from respiratory tract glands, it would support the explanation why certain subgroups with already inflamed respiratory tissue would feel an increase in mucus. Not entirely helpful, as it’s only a hypothesis, but interesting nonetheless.
Moving on, WebMD also supports that there is a correlation reported with milk and mucus production, but it isn’t explicitly causal. They refer to their expert, Neil L. Kao, MD, associate professor of medicine at the University of South Carolina School of Medicine. Kao says [the reason people may make the association is] due to gustatory rhinitis, a reflex reaction that’s triggered by eating. Gustatory rhinitis is also why your nose runs when you eat hot peppers. Milk proteins cause the same type of response in some people. But although you may feel like you have more phlegm, you’re not going to worsen a cold by drinking a glass of milk. (Gustatory means having to do with taste, and rhinitis, nasal inflammation).
So those are the pretty, packaged up explanations that you can get in the form of 1-2 sentences on generic health websites; but I want more than that. I want to get to the meat of the research, and find studies that actually apply to the question. The CFF makes no mention of dairy-phlegm problems, and I can’t find anything specifically having to do with the kind of sticky mucus that we produce. But I did find one lead: a doctor who was faced with a similar query from a friend and decided to look into it himself. He pointed to a series of studies done in the 1990’s which almost unequivocally abolished the milk-mucus myth. He asserts that some researchers have posited the cause of this sensation is the lipids from high-fat drinks combining with saliva could be responsible for a sort of mucus mimic in your throat, which feels hard to swallow. Another interesting point he makes is that you don’t have to be lactose intolerant to have an allergy to milk, in fact, “it’s possible that some who describe thicker phlegm after drinking milk are actually allergic to milk.”
In the studies he refers to, scientists injected rhinovirus into the participants, monitored their milk intake (0-11 glasses/day), then collected and weighed their nasal secretions, determining there was no reason to link milk consumption to mucus production. Similar studies were able to repeat these results. What was especially interesting to me was that subjects who had a pre-conceived belief in the milk-mucus relationship reported more mucus than their non-believing counterparts, even when the secretion weight was found to be the same. And in a follow up randomized double blind trial, researchers found that the same sensations of mucus production were reported whether the subject was getting cow’s milk, or a soy placebo, concluding that the 169 participants could not distinguish between the two.  This is fascinating to me.
The next two studies I compared had to do with asthma in children. The first one, a single blind, pilot study published in a small British journal, contradicted the ones I previously researched by concluding that after eight weeks, the elimination of eggs and dairy products from a child’s diet could reduce atopic symptoms and improve lung function in children with asthma. The findings were based on blood analysis for food-based antibodies, and on peak expiratory flow tests of the 22 children involved. In the second study, which was a cohort study looking at close to 3,000 participants of preschool age published in Thorax (a leading respiratory medicine journal) found that children who consumed full-fat milk and butter between ages 2-3 had a significantly reduced rate for developing asthma. Now, that doesn’t really have anything to do with mucus production, but it is important since many asthma patients are told to avoid milk for this purpose.
Finally, in a review of the literature published in the Journal of the American College of Nutrition, the authors unambiguously proclaim that “milk consumption does not lead to mucus production or the occurrence of asthma.” That’s actually the title.
So, there you have it. Plain results from an undisputed consensus. I realize some people who read this will still think, “I don’t care what they say, I know my body, and eliminating dairy was the best thing I did for my health.” And that’s OK. In CF, optimal nutrition is imperative to lung health, so if you can maintain weight, energy levels, and lung function without the calories and fat from milk products, more power to you. Many people can’t though, and I would argue that even if you do still believe the myth that milk increases the amount or thickness of the mucus in your respiratory tract, the benefits of the extra calories, calcium, vitamin D, and protein outweigh the uncomfortable, but relatively harmless sensation of throat phlegm, especially in growing children and teens.