Circadian Entropy, Causality in Research, and Chronotherapies for Mental Illness
Mental disorders are the leading cause of disability worldwide1. The most pressing ones are different by age:
The most common mental disorders in children are known as neurodevelopmental disorders and include:
Attention deficit and hyperactivity disorder (ADHD)
Autism spectrum disorder (ASD)
and Tourette’s syndrome (TS)
The most common mental disorders in adolescents and adults are known as affective disorders and include:
Bipolar disorder (BD)
Major depressive disorder (MDD)
Various anxiety disorders (AXD)
and various Eating disorders
The most common mental disorders in seniors are known as neurodegenerative disorders and include:
and Age-related neurodegeneration
Today’s question is: do the different mental illnesses share a common pathology?
This question arises when you look at the comorbidities among disorders. Many individuals with one will end up diagnosed with many across their lifespan. Plus, the experts keep rearranging the borders between all these conditions. Here's what the map currently looks like:
When looking at these data, one uniting factor emerges. At least, that's what researchers from the University of California think.
So according to this recently published review, the uniting factor among mental disorders may be circadian rhythmicity disruption (CRD) manifesting as sleep disruption.
What can we learn from this 2022 paper on Circadian Entropy and Mental Health Disorders?
Here are the most useful takeaways (IMHO):
To prevent the cascade of mental illness, we need to start with maternal rhythmicity. The progression through these overlapping mental illnesses may begin in the womb. It then seems to cascade through childhood, adolescence, adulthood, midlife, and seniority.
Aim interventions at people manifesting the "Evening" chronotype. Being an “Evening” chronotype correlates with being diagnosed with mental disorders in the future.
If you’d like to read this paper in it’s entirety, here’s the PDF:
Use of the term “circadian entropy” here is interesting.
Circadian refers to biological processes recurring naturally on a 24-hour basis.
Entropy refers to lack of order or predictability; or a gradual decline to disorder.
Researchers around the world are using a variety of similar terms to describe this topic. Here are some:
Circadian rhythm disruption
Circadian rhythmicity disruption
Desynchronization of circadian rhythms
When talking about these biological functions happening well, we see terms like:
Stable circadian rhythms
Strong circadian rhythms
Strengthened circadian rhythms
Entrained circadian rhythms
Synchronized circadian rhythms
and Circadian rhythmicity
Being aware of all these terms is helpful if you want to look up any conditions you might be curious about. Any of these make good search terms and give different kinds of information.
So, does circadian disruption cause mental health disorders?
Scientists are always cautious about throwing around the “cause.” Every statistics student learns the phrase “correlation does not equal causation”.
With circadian rhythmicity reasearch, we have a problem:
It would be
a double-blind study
that proved/disproved the thesis
that maternal circadian disruption caused lifelong mental illness!
So, we will likely never see the headline “circadian disruption causes mental illness.” It’s not the kind of thing we can ethically test using the scientific method. Instead, we can must draw our conclusions from related factors we can prove, such as:
- Artificial light at night (incandescent, LED, fluorescent, halogen, etc) causes circadian disruption because it is too bright.
- Artificial light during the day causes circadian disruption because it is too dim.
- Eating at night causes circadian disruption because the body NEEDS to fast in darkness.
- Circadian disruption is a common factor underlying every known mental disorder.
And on the flipside:
+ Natural light at night (starlight, moonlight, candlelight, firelight, etc) entrains circadian rhythms because it is perfectly dim.
+ Natural light during the day entrains circadian rhythms because it is perfectly bright.
+ Eating during the day entrains circadian rhythms because we need to eat in the light.
+ Stabilizing circadian rhythms treats and prevents symptoms of mental disorders that are otherwise untreatable, including manic episodes in bipolar disorder2 and sundowning episodes in dementia.
And so on!
Here is a simplified graphic showing the ins (afferents) and outs (efferents) of the suprachiasmatic nucleus (SCN)3. This is the brain’s main command center for circadian processes all throughout the body:
As we know, there are two primary time-givers for the human circadian system:
(Sun)light/darkness cycle (which is also a heat/coolness cycle) ←shown as the sun icon at the left of the above graphic
Eating/fasting schedule ← shown as the meal icon at the left of the above graphic
Besides our light and food consumption, everything else we do either supports or detracts from those primary signals (or, "zeitgebers")4. Proactive mental health practitioners are beginning to teach this circadian rhythmicity.
Chronotherapies for Mental Health
We see this proactive circadian approach with "bright light therapy", "enforced darkness regimes", and "chronotherapeutics". These interventions are emerging as a whole class of "chronotherapies." They are proving to be the only way to treat subsets of symptoms such as bipolar mania and sundowning. For those who have been following this newsletter for a while, this may not come as a surprise. After all, as Hatori, et al., so aptly stated in their 2017 paper “Global rise of potential health hazards caused by blue light-induced circadian disruption in modern aging societies”5: