The Circadian Rhythm and Mental Health

You probably know that sunshine can boost vitamin D levels. But did you know that getting enough sunshine, especially in the morning, can also help with sleep and mental health?

It seems simple, but many of our schedules don’t automatically make time for it: a morning walk through the grass in the sunshine, 15 minutes on the patio while eating your breakfast, or even (for those who live in areas where it’s frequently still dark or cloudy in the morning) using an indoor UV sun-mimicking lamp. Now that it’s wintertime, it’s even more challenging for many who live in cold and cloudy climates to get the sunshine their bodies need.

Sunrise, sunset

Yes, sunshine is our primary natural “source” of vitamin D. (The UV-B rays of the sun actually activate a complicated chain of events in the skin that causes our bodies to produce vitamin D. While you make the most vitamin D when you’re outside when the sun is highest in the sky, early morning sunshine is considered the best for skin health, including reducing the risk of the damage that can lead to sunburn and skin cancer.) But getting out in the early morning rays is about more than just vitamin D production.  

And conversely, those recommendations to avoid artificial light and especially screens late at night is about more than just melatonin production (though that is hugely important).

Our bodies and minds are made to operate on a “clock,” meaning that we operate on 24-hour cycles that are set by exposure to the cycle of day and night, sunshine and darkness.

Here are a few of the systems and tissues in the body that function on a circadian rhythm—many of them even independently from the brain and central nervous system:

• The suprachiasmatic nucleus. (Now wasn’t that fun to say?) This one’s a big one, the “master clock” in the brain. It’s activated by blue light, the type that we see from daytime sunlight. Over the span of a 24-hour cycle, the expression of different genes change, creating a cascade of effects that help us to be awake and alert during the day, and restful and (hopefully) asleep during the night.
• The stomach. Its circadian rhythm seems to be set primarily by intake of food.
• The skin. What?! I know. Things like cell reproduction in the top layer of the skin happen in conjunction with the light and dark cycles of the day.
• The liver. Even though it doesn’t have any direct contact with light, it turns on and off according to the light and dark cycle, so that it’s ready to start digesting food and turning glucose (sugar) into energy during the day.
• The skeletal muscles. Their circadian clock is based around how much we’re using them – how much we’re moving.
• The adrenal glands. This is really important because the hormones they secrete help regulate your metabolism, immune system, blood pressure, response to stress, and more. For obvious reasons, we don’t want them to be producing lots of adrenaline in the middle of the night.
• …And literally every cell of the body. Yep, they all have their own individual little watches keeping time, but they can be overruled and have their watches synchronized by the major clocks above.

How does this apply to mental health?

I think we’ve established that our bodies operate in a rhythm, a daily 24-hour cycle that is fueled by the sunlight. So what does this have to do with our mental health?

The connection between sleep disturbance, circadian rhythm dysfunction, and depression is well-established. Sometimes sleep disturbances happen as a result of mental illness; other times they may cause it, and perhaps most of the time, it’s going both ways.

People with major depressive disorder have different body rhythms than people who don’t have the diagnosis. For example, our body temperature changes on a 24-hour cycle, with lower core temperatures at night. For someone with MDD, their body temperature doesn’t decrease as much. Their melatonin and cortisol levels don’t change as much in the course of the day, so they might not produce enough melatonin for quality sleep or enough cortisol to get through the activities of the day. The degree of misalignment between the internal clock and the timing of actually being able to fall asleep seems to correlate with the degree of severity of symptoms of depression.

Plus, there’s all sorts of other impacts that sleep disturbance can have on mental health. Insomnia increases levels of inflammation in the body, which (as we’ve discussed in other posts) can be correlated with depressive disorders. In the long term, sleep deprivation can also decrease the production of some really important brain proteins that support brain growth, elasticity, and resilience. There’s even a weakening of the blood-brain barrier, the “wall” that keeps stuff from the rest of the body away from the fragile tissue of the brain. This can let in all kinds of neurotoxic substances, leading to more inflammation.

Others dealing with depression may have the opposite experience, where rather than insomnia, they find themselves sleeping too much. This is also potentially linked to circadian rhythm dysfunction, imbalance of melatonin and cortisol, and poor-quality sleep (which is very common in depressive disorders).

So what can we do about it?

Nothing in biology is ever quite as simple as the word “reset” makes it sound. Recalibrating or resynchronizing your body’s clocks is not as quick and easy as resetting your Wi-Fi router. But there are some fairly simple steps we can take to try to get back on track, improve our sleep, and improve our mental health.

Many of these tips won’t be new to you, but hopefully you now have a deeper appreciation for their importance, and for specifically how they might improve not just your sleep, but pretty much everything else that happens in your body, as well.

• Get some sunshine as early in the day as possible. Whether you’re sitting in a sunroom, walking in the park, or even sitting by a UV lamp in a living room in northern Alaska, the goal is to get exposure to that morning sun to almost literally wake up your cells, from your eyes to your skin to your liver.
• Move your body. Combine this morning sunshine exposure with morning movement, when possible. Remember the importance of movement in calibrating the circadian “clocks” of the muscles. Morning exercise is also likely a lot better for supporting good sleep rather than doing high-intensity exercise late in the afternoon or evening, when we could make falling asleep more difficult for ourselves. Walking, yoga, and stretching are great anytime of day.
• Eat in the morning. I’m a big proponent of breakfast within roughly two hours of getting up in the morning. We are all busy people with a lot to do, but I think most of us will do those things much more effectively and efficiently if we’re properly nourished in the morning.
  I often get push-back on this one because of intermittent fasting. I know a lot of people like the idea of an intermittent fasting schedule shifted later in the day to allow eating dinner socially. Eating meals with others is really important to me, too. But from a circadian rhythm perspective, the goal of intermittent fasting is not just to limit the number of hours that you can eat, but rather, to place your eating window in the optimal time frame to align with the “clocks” in your digestive system. So maybe this means that your eating window, if you do intermittent fasting, is a little wider. Maybe it’s worth experimenting with.

• Eat your polyphenols. Along with all the other things they do for us, the anti-inflammatory colorful compounds in things like green tea, citrus zest, and red grapes have also been shown to help re-align the circadian rhythm. So cool.
• Dim the lights and avoid screens during your evening wind-down time. Research shows that melatonin production is delayed substantially by being in room light – maybe even up to an hour and a half, according to some research. That is potentially problematic when you’re trying to fall asleep, but I would argue perhaps more sneakily problematic when we’re thinking about sleeping well and waking up feeling well-rested.
• Keep to a schedule. A lot of our evening and nighttime habits might feel relaxing, but they might also lead us to stay up later than we intend to and then end up eating later at night than we intend to. (And often also consuming things that aren’t really helpful for supporting good sleep, like alcohol and sugar.) Conversely, we might sometimes stay up late trying to “get things done,” which raises our nighttime stress and cortisol levels. I’m speaking to myself here as much as to anyone else: Just go to bed.

Remember: it's all about starting small, incremental, gentle. Be kind to yourself. Choose one thing you can do today. Notice how little changes can have big impacts, especially when they are done mindfully and with self-compassion.
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Sources:

• https://www.embopress.org/doi/full/10.15252/embr.202152412
• https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7182033/
• https://pubmed.ncbi.nlm.nih.gov/19524304/
• https://academic.oup.com/jcem/article/96/3/E463/2597236?login=false
• https://pubmed.ncbi.nlm.nih.gov/22542179/
• https://www.cell.com/cell/fulltext/S0092-8674(19)30507-0

Erica Golden, RDN, LD, IFNCP

Integrative and functional registered dietitian nutritionist. 
Food therapist.
Nutritional psychiatrist.
Lover of all things biology.

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