Ask Dr. K: No one theory on yawning

DEAR DOCTOR K: I get plenty of sleep. So why do I yawn all the time?

DEAR READER: We all yawn frequently, more often in the early morning and late evening. Does it mean we’re tired? Bored? Short on oxygen? As common as it is, we know little for certain about yawning.

We do know that yawning does not always indicate a need for sleep. It is true that people often yawn as they get ready to retire for the night. But we also yawn when we wake up and at other times during the day.

Past theories about why we yawn centered on the assumption that it was a reflex in response to low oxygen or high carbon dioxide levels. That’s because breathing takes in oxygen and removes carbon dioxide. When you yawn, you take in more air than with a normal breath. So it’s a reasonable theory that we yawn because we need more oxygen, or less carbon dioxide.

But this theory lost favor after a study in which volunteers subjected to high oxygen levels did not yawn less, and after high carbon dioxide exposure did not yawn more.

Another theory of yawning is that it protects against a condition called atelectasis, which is the collapse of some of the lung’s air sacs. Yawning opens up tiny airways and prevents them from collapsing. This could explain why yawning seems to occur when your breathing is shallow, such as when you’re tired or bored.

Also, yawning may be a sign of disease. Although rarely the first sign, excessive yawning has been observed among people with multiple sclerosis, ALS (Lou Gehrig’s disease) and Parkinson’s disease.

To be clear, yawning is not usually a sign of disease. It’s usually just a sign that you’re human.