People who had cataract surgery have a lower incidence of dementia

I just got my regular newsletter from the University of Washington's Alzheimer's Disease Research Center with a surprising research finding.  People who had cataract surgery had a 30% lower risk of developing dementia.  Obvious question: why would that be?

The findings come from the Adult Changes in Thought Study that's been going on since 1994.  The study tracks thousands of older people known not to have dementia and follows them until they do develop dementia.  Obviously many never will, but they'd like to know about the lifestyle differences between those who do and don't develop dementia.

So why would people have a lower incidence of dementia if they had cataract surgery?  An article in Science Daily provided some speculation.  The article noted that the research report did not provide any answers, but some people have proposed some.

One idea is that, after cataract surgery, people get higher quality sensory input, and that's somehow good for brain health.  

Another idea is that after cataract surgery people are getting more blue light.  Cataracts cause the light getting to the retina to be more yellow, filtering out blue light.  Blue light may stimulate some cells in the eye associated with cognition.  The new, bluer light might stimulate those cells somehow.  This affects the sleep cycle that depends on blue light to tell the body that it's day.  So it might promote better regulation of the circadian rhythm and better sleep.  If you read Beating the Dementia Monster, you know that sleep is extremely important in how Alzheimer's disease does or does not develop.  

So get outside during the day when there's lots of blue in the sky and blue in the light.  You're teaching your brain what time of the day is daylight.  But don't expose yourself to light containing a lot of blue in the evening, such as cool fluorescent and LED light.  This goes double for light from computer and phone screens.  It's been super-juiced with blue.  (I've calibrated the colors on my computer screens to be warmer -- more yellow, less blue.)

I'll add my own speculation which I think is consistent with these ideas.  We have associated hearing loss with dementia, likely because hearing loss interferes with communication with other people.  As we said in Beating the Dementia Monster, social connection is very important to brain health.  Impairing social connection, such as through hearing loss, raises the risk of Alzheimer's disease.  Maybe the same thing applies here -- untreated cataracts interfere with social connection.

Another thing we noted in Beating the Dementia Monster is a correlation between glaucoma and dementia.  People are often diagnosed with glaucoma very near the time they are diagnosed with cognitive impairment.  In my case, only a few months separated my two diagnoses.  I don't know what the connection would be, but an ophthalmologist once pointed out to me that the biggest sensory input to the brain is from they eyes, and we've said before that some consider the eyes to be an extension of the brain.