Sure, I'd agree with the "more stressed and less health conscious" bit. But, the article does give some good reasons to suggest that either midlife insomnia is a very early symptom of dementia, or that sleep deprivation itself leads to dementia.
Nonetheless, we are talking about people who have pre-existing insomnia before being diagnosed with dementia. According to the Mayo Clinic[0], the most common causes of insomnia are:
* Stress.
* Disrupted circadian rhythms due to shift work or frequent travel.
* Poor sleep habits.
* Eating too much late in the day.
Further down the list are:
* Anxiety disorders.
* Medications.
* Other medical conditions.
* Sleep disorders.
* Caffeine, nicotine, and alcohol.
* Age (older people sleep less than younger people).
Of these, anxiety disorders; sleep disorders; and caffeine, nicotine, and alcohol seem the most interesting to me. Anxiety disorders probably have an effect much like that of chronic stress, except that simple chronic stress generally goes away eventually. Sleep disorders seem interesting because we have some evidence that sleep serves a function related to brain health, but, really, we don't know exactly what sleep does for us. And, alcohol, nicotine, and caffeine are interesting because the former two carry their own, independent health risks.
Caffeine is interesting because, of course, it is active in the central nervous system, and it actually shows some limited evidence for a protective effect against Alzheimer's disease. [1]
Cross referencing that with the list of things they control for ("age (timescale), sex, ethnicity, education, marital status, alcohol consumption, physical activity, smoking status, fruit and vegetable consumption, BMI, hypertension, diabetes, cardiovascular disease, GHQ depression, and CNS medications"), we can (lightly) cross age, nicotine, and alcohol off the list of interesting things.
All this makes me wonder if either insomnia is an early dementia symptom, as they suggest, or if one of the causes of insomnia is the instigating factor. And, it seems to me the most interesting causal factors for insomnia left on the board are anxiety and stress.
Oh, and guess what? Anxiety, stress, and PTSD have been independently linked to the development of dementia! [2]
To me, that's interesting because anxiety is known to impair both working memory and cognitive processes[3], things which are both impaired in dementia.
I don't mean to suggest that anxiety and stress cause dementia all by themselves, but I do think this might point to a more significant role for anxiety and stress than is typically considered these days.
Anyway, these are just some idle thoughts from someone who is neither a doctor, neuroscientist, nor biological researcher of any kind. If anyone has anything else to add, or would care to riff off this, I'd love to see it.
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[0]: https://www.mayoclinic.org/diseases-conditions/insomnia/symp...
[1]: https://content.iospress.com/download/journal-of-alzheimers-...
[2]: https://www.alzheimers.org.uk/blog/there-link-between-stress...
[3]: https://www.psychologytoday.com/us/blog/anxiety-fear-and-hat...