I have seen it claimed that yawning lowers intraocular pressure. Is that true?

I'm not asking about a single spontaneous yawn. I want to know if frequent yawning on purpose can help me maintain my IOP at a lower level, as this person recommended.

He recommended yawning regularly throughout each day. Furthermore, the person said, "you should be feeling lightheaded" as a consequence of yawning. Is that good?

Yawning and intraocular pressure is an interesting topic. As far as I know, we don't have any evidence that yawning can be useful for maintaining low IOP. I'm seeing some misleading information posted online, so I would like to urge the FitEyes community to investigate it, but don't accept the claims without evidence. So far, we don't even have anecdotal evidence in support of the idea that yawning lowers IOP.

Yawning and Lightheadedness

In regard to this claim:

You should be feeling lightheaded

Lightheadedness could be a sign of reduced blood circulation to the brain (which indicates reduced blood flow to the optic nerve).

Scientists have found evidence that yawning increases blood flow to the face and neck, but I find no direct evidence that it increases blood circulation to the brain. (I just performed a pubmed search.)

I do, however, have evidence that excessive yawning reduces CO2 (end tidal carbon dioxide, as measured by a capnograph). My experimental methodology is valid. The cerebral blood flow response to changes in CO2 can be reliably estimated from the noninvasive measurement of end tidal carbon dioxide. (pubmed)

It is well-established that reduced CO2 leads to reduced blood circulation to the brain. I'm not suggesting an occasional yawn would have a negative consequence, but I think we need more information before we can recommend frequent, habitual yawning on purpose.

Here's what I wrote recently on this topic:

The level of carbon dioxide ("CO2") and nitric oxide ("NO") strongly influence both blood flow (in the eye, brain and elsewhere) and cerebral spinal fluid pressure ("CSFP"). In fact, CSFP is proportional to CO2. Carbon dioxide levels sufficient to affect CSFP can be induced by changes in breathing, including yawning.

I did some self-experimentation with capnography and found that repeated yawning reduced my CO2 by enough to reduce my cerebral blood flow by 42 percent! This is why I've been saying you will not find me practicing habitual yawning. I did the experiment and I found results that steered me away from frequent yawning.

In fact, one of the papers on yawning noted that it "also sends cerebrospinal fluid downward, away from the brain." This is consistent with my research. It is also the opposite of what glaucoma patients should probably be doing habitually. CSFP balances IOP. Low CSFP has similar consequences on the optic nerve as elevated IOP. I believe that glaucoma patients should aim for lower IOP while seeking to normalize CSFP. You can normalize CSFP with proper breathing, but frequent yawning is counter productive to that goal.

I also disagree that you want to provoke lightheadedness with any frequency.

Yawning and Brain Temperature

Ten facts about yawning

A blog article claimed to offer ten "facts" about the benefits of yawning. I am not providing the URL because there is not much of substance in the article. It's best to educate ourselves with better sources of information. However, this did catch my attention:

3. Modern research suggests that yawns are to cool down the brain...

According to a recent report by National Geographic, an open-mouthed yawn causes sinus walls “to expand and contract like a bellows, pumping air onto the brain, which lowers its temperature.”

Apart from the decidedly unscientific wording of this statement, this general idea is gaining traction in scientific circles. It is one of several theories about yawning. However, so far we cannot say that brain cooling is the reason for yawning. Stating that as a fact is premature based on what is now known. Scientists who do not buy into the brain cooling theory note that yawning is only minimally effective in reducing brain temperature, there is a significant delay between the yawn and cooling, and both fetuses and cold-blooded animals yawn.

But let's speculate. What happens to your hands or feet when the blood circulation is reduced? The temperature decreases. Therefore, I would not be surprised to discover that the mechanism behind reduced brain temperature from yawning is due to decreased blood circulation. That could also explain the delay between the yawn and cooling.

When it comes to brain temperature, I don't think we know enough to make a conclusion about yawning. But we do, in my opinion, know enough about breathing physiology, CO2, CSFP and cerebral blood circulation to recommend against excessive habitual yawning.

I find this interesting:

In 1986, Provine, the pioneer of yawning research wrote that "Yawning may have the dubious distinction of being the least understood, common human behavior."

Today, more than 20 years later, scientists are still unable to offer a definitive explanation for yawning.

Nasal breathing

While I cannot recommend habitual yawning, I can recommend habitual nasal breathing (including while sleeping). Studies by Mariak et al. and Harris et al. have both found a direct reduction in human brain temperature following nasal air flow. So if you want to do something positive to help regulate your brain temperature, I can recommend nasal breathing.

Based on some of the studies I have read, yawning itself may not be directly responsible for the claimed benefits of yawning. Instead, in my opinion, the benefits come from stretching and exhaling slowly after the yawn. The following paper is one source of my view on this matter:

Inhibition of muscle sympathetic nerve activity during yawning - PubMed
https://pubmed.ncbi.nlm.nih.gov/8902321/

Therefore, I do recommend that if you happen to yawn naturally, make sure the exhalation afterward is prolonged.

I can also suggest that any benefits you think may come from habitual yawning can more beneficially be obtained from habitual good breathing practices and stretching.

Yawning and brain hypoxia

For the past several centuries, a commonly held notion associated with yawning was that it is triggered when blood or brain oxygenation is insufficient, that is, when oxygen (O2) levels decrease and carbon dioxide (CO2) concentration rises. Yawning was thought to remove “bad air” from the lungs and increase O2 circulation in the brain.

However, this false belief has been discarded in wake of the results of a newer study in which the yawning frequency was unaffected in subjects who breathed air mixtures containing either higher than normal CO2 or even pure O2 (source).

Let's not make the mistake of starting another incorrect notion about yawning without having good evidence for it.

Yawning and arousal

Yawning facilitates a heightened state of arousal as evidenced by a significant change in various physiological parameters, including changes in neurotransmitter and endocrine levels, increased heart rate and more. (sources below)

In fact, the effect of yawning on physiological parameters of arousal is similar to caffeine. (see Barry et al. below)

This arousal theory of yawning does make sense to me. If it is correct, it would seem to indicate that yawning will not reduce intraocular pressure. Let's see if we can gather some data to go from theory to reality. I won't personally be doing the yawning experiments (I don't want the low CO2), but for those of you who wish to try it and measure your IOP with your tonometer, let us know what you find. Please be rigorous in your IOP data recording. We need exact IOP values, exact times, etc.

Conclusion

I support a rational and factual discussion of yawning and intraocular pressure.

An occasional natural yawn is almost certainly fine (especially when followed by a prolonged relaxing exhalation). But excessive yawning probably is not. I remain to be convinced that habitual frequent yawning is highly effective at managing IOP. Even if it is, the risks of reduced blood flow to the brain and reduced CFSP need to be factor into the equation. Let's get the facts before we recommend something.

Sources on yawning and arousal:

• Corey TP, Shoup-Knox ML, Gordis EB, Gallup GG., Jr Changes in physiology before, during, and after yawning. Front Evol Neurosci. 2011;3:7.
• Barry RJ, Rushby JA, Wallace MJ, Clarke AR, Johnstone SJ, Zlojutro I. Caffeine effects on resting-state arousal. Clin Neurophysiol. 2005;116:2693–700.
• Provine RR, Hamernik HB. Yawning: Effects of stimulus interest. Bull Psychon Soc. 1986;24:437–8.
• Kasuya Y, Murakami T, Oshima T, Dohi S. Does yawning represent a transient arousal-shift during intravenous

Yesterday a FitEyes members reported, via the email discussion group, that yawning does not lower their intraocular pressure. He said:

I yawn but IOP doesn't drop. I checked IOP before and after yawning using my tonometer.

This is our first anecdotal evidence, and it is not in favor of the idea that yawning lowers IOP.

Furthermore, the person who originally proposed that yawning can lower IOP actually does not have a tonometer. Based on his emails to the FitEyes email discussion group, he has never tested tested before and after yawning. His IOP is checked only once every three months at his ophthalmologists office. He said:

Personally I do try it out consciously while waiting for my Appointment in my Opthalmologist's waiting room.

This appears to be his basis for the idea. He also stated some serious misunderstandings regarding the medical facts about intraocular pressure.

Does Frequent Yawning Help to Maintain Low Intraocular Pressure?

It appears we have a half-baked idea coming from a person who misunderstands basic medical facts. He proposed this idea as if it is fact, but he had no evidence supporting it.