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Harvard Commentaries
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Medical Myths Medical Myths
 

Should You Avoid Dairy Foods When You're Sick?


February 10, 2012

By Robert H. Shmerling M.D.

Beth Israel Deaconess Medical Center

Last week we had dinner with friends. Their young children were begging for ice cream for dessert. But their mom said:

"They can't have dairy. They had colds last week and they're just now getting back to normal."

So, the kids ordered cake and cookies. But I was puzzled. I couldn't think of a reason why dairy products should be avoided in kids who recently had a cold. And it was certainly nothing I'd ever learned in medical school.

It turns out that there is a rather widespread belief that dairy products trigger an increased production of mucus. And that might slow recovery or even cause another cold. It was easy to find evidence for this belief on the Web where authoritative advice promotes this idea. For example, I found this on a blog where someone asked about the effect of milk consumption on colds:

"Dairy products cause the body to make more mucus and so does a cold; so drinking milk will make the severity of your cold worse." (This was voted as the best answer).

Is it true that dairy products (including milk) should be avoided during or after a cold? If it is true, how does milk cause this problem? If it's not true, where did this myth come from? And, by the way, should medical facts be determined by an online vote?

The case against drinking milk with a cold

There are times when avoiding milk makes sense.

    • Lactose intolerance is a common condition in which a person lacks the enzyme (lactase) that digests the lactose in milk and other dairy products. People with lactose intolerance can avoid milk, choose lactose-free milk, or take enzyme supplements that help them digest it.
  • Some people, especially small children, are allergic to milk. When they drink it, they may wheeze, vomit, develop hives or experience abdominal pain. And increased mucus production can be a part of an allergic reaction. Clearly, people who are allergic to cow's milk should avoid it.

As for the connection between milk and colds, the logic goes something like this:

    • During colds, flus and other upper airway infections more phlegm is produced. Phlegm is the thick, mucus-containing fluid responsible for post-nasal drip and congestion in the ears and sinuses.
    • Some people report more phlegm or thicker phlegm when they drink milk.
  • Thicker phlegm might be irritating to the throat or make a cough worse.

People with asthma are sometimes told to avoid dairy products due to similar beliefs. I also found widespread recommendations for singers to avoid milk for similar reasons – increased phlegm is generally bad for someone who is dependent on a clear, controlled voice.

However, it's possible that some who describe thicker phlegm after drinking milk are actually allergic to milk.

The case for drinking milk if you want to

A remarkable set of studies published in 1990 found no clear connection between milk consumption and cold symptoms.

Australian researchers exposed study subjects to a rhinovirus (the cause of the common cold). They kept track of the dairy products the subjects ate and their symptoms over 10 days. Secretions from the nose were weighed (yes, they actually weighed tissues collected and sealed just after use).

The verdict? The amount of nasal secretions and symptoms of congestion had no relationship with milk or dairy intake. Later studies came to similar conclusions. Researchers involved in these studies concluded that the combination of saliva and a high-fat beverage (such as milk) may mimic mucus and that could lead to the false assumption that drinking milk during a cold is bad. Researchers have also been unable to confirm a connection between milk or dairy products and worsening asthma.

The publication of these studies in the early 1990s has apparently done little to eliminate the misconception that dairy should be avoided if you have a cold.

The bottom line

If you have a cold or are recovering from one, it’s okay to drink milk.

But if it gives you the sensation that you have more phlegm or that your congestion is worse, switch to skim milk, tea or other low-fat fluids.

Remember that fluid intake is important during an infection. The advice to "feed a cold, starve a fever" is as unfounded as the myth about milk intake.

In general, I don't go out of my way to give parental advice to friends. But, if they had asked, I would have told them that there's good evidence that the intake of milk or dairy products does not delay recovery from a cold or make symptoms worse. For kids who have just suffered through a bad cold, maybe ice cream is just what they deserve.

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Robert H. Shmerling, M.D. is associate physician at Beth Israel Deaconess Medical Center and associate professor at Harvard Medical School. He has been a practicing rheumatologist for over 20 years at Beth Israel Deaconess Medical Center. He is an active teacher in the Internal Medicine Residency Program, serving as the Robinson Firm Chief. He is also a teacher in the Rheumatology Fellowship Program.

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