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Maintaining Serotonin and Avoiding SAD - The Apeiron Life Perspective



What it is:

The joy of winter isn’t always immediately apparent, particularly for those who enjoy chasing the summer sun. Yet the season is covertly rejuvenating; it just requires some strategizing to get the most out of it. But much like the other seasons, which each offer their unique flavor of growth, there is something powerful about this time of year as it encourages both a reset and reassessment of what matters most.


When January rolls around and the dust settles on the prior holiday season, we are often met with a sense of space. That space can feel unsettling and even be mistaken for emptiness, especially if the holidays were filled with activity. The reality, however, is that the January interlude offers opportunity and possibility. It is a point from which we can pivot towards meaningful goals with fewer roadblocks.


Rather than emphasizing New Year’s resolutions or unsustainable expectations this month, consider setting yourself up for a successful year by optimizing your cognition in the months ahead. Doing so allows you to be guided more organically toward the things that matter with less brain fog, fatigue, and sluggishness to deter your focus.



The purported claims:

  • Optimize ambient lighting to promote alertness during the day and quiescence at night

  • Consider new ways of minimizing seasonal affective deficits

  • Learn about how the brain’s sleep-wake circuits are also involved in feeding behavior



What the science says:


Circadian rhythms and Seasonal Affective Disorder (SAD)

Humans are visual creatures who rely on the rod and cone cells in their retinas to make sense of shapes and colors in the environment. Alongside these optic powerhouses are intrinsically photosensitive retinal ganglion cells (ipRGCs) that guide our circadian rhythms. These cells are non-image-forming, meaning they do not contribute to our ability to see things. However, they are some of the body's most critical cells since they regulate much of our physiology downstream.


ipRGCs contain a photopigment called melanopsin, which is activated by short (blue) wavelengths of light. Blue light is emitted by the sun, as well as many electronic devices such as cell phones and tablets. When melanopsin is activated, it tells the brain's central clock that it is daytime and promotes a cascade of cognitive functions associated with alertness. This is a beneficial process if it is daytime, but less so if the light source is artificial and we are trying to fall asleep at night.


In the absence of blue light, melanopsin is no longer activated. When this happens, the brain's clock interprets this as the beginning of the biological night. At this point, the pineal gland synthesizes and secretes melatonin, releasing it into the bloodstream. This produces a suite of downstream effects. Melatonin dilates blood vessels, for example, which lowers blood pressure. It also binds to various parts of the brain to slow things down and promote sleepiness.


At higher latitudes where the winters bring with them significantly fewer daylight hours, some individuals can experience seasonal affective disorder (SAD), which produces a variety of mood-related symptoms, including lethargy, fatigue, weight gain, carbohydrate cravings, irritability, depression, and anxiety. The exact cause of SAD is unclear and is probably multifactorial. Short winter days may extend the time that melatonin remains in circulation, thus leading to grogginess in the morning. Our typical "get up and go" morning cortisol response may be delayed and dampen our alertness.


Many studies have demonstrated that morning light exposure — whether naturally or via a light box — can alleviate SAD symptoms and produce greater vitality and alertness. Other evidence suggests that SAD might develop, at least in part, due to a serotonin shortage that occurs during the wintertime. At least seven studies have shown that the administration of selective serotonin reuptake inhibitors (SSRIs) can help with SAD.


Many people with SAD tend to experience a delayed circadian phase during the winter months. This means that wake time and sleep time become delayed compared to other times of the year. Morning light exposure can help advance the body clock and improve sleep quality at night.


Those who experience winter lethargy may feel inclined to nap more frequently or spend more time in bed compared to other months of the year. This can negatively impact sleep by suppressing the brain's homeostatic sleep drive, which accumulates during the day and triggers the feeling of sleepiness at night. When this happens, sleep can become fragmented. Essentially, by blunting sleep pressure via excessive daytime napping, our brains no longer have enough of a drive to sleep throughout the night in one long bout. If sleep becomes more fragmented, it can then feel non-restorative. This can lead to next-day tiredness and perpetuate the cycle.


Some research suggests that maximizing daylight exposure during the middle of the day is associated with better sleep quality at night. Whereas morning light exposure helps to synchronize the circadian clock, light exposure about 6-8 hours after waking up may improve the subsequent night's sleep quality.


Maximizing the difference between light and dark during the day and night seems to be what matters most for regulating circadian rhythms and general sleep health. Studies show that exposure to blue-light-emitting devices at night is associated with disturbed sleep and worse mental health. However, this is considered particularly problematic among those who simultaneously are not experiencing sufficient daylight exposure during the first half of the day. Maximizing daylight exposure may protect against the adverse impacts of some artificial light at night. However, there is significant variability in sensitivity to light at night among different people, with some suffering sleep disruptions while others are relatively unaffected. Those who are sensitive should aim to keep lights very low for around one to two hours before bed (<10 lux), have complete darkness during sleep, and consider extra support, such as adequate blue light-blocking glasses with orange or red lenses when interacting with screens before bed.



Diet and Supplementation

Where sunlight is limited at higher latitudes, vitamin D supplementation can be helpful. One study found that after four weeks of supplementation, SAD mood symptoms decreased, correlating with a rise in Vitamin D serum levels by 74%. Vitamin D is a hormone involved in many functions, including immunity, bone health, and mood. A meta-analysis found that blood serum levels of less than 30 ng/mL were associated with increased mortality. Therefore, strive to maintain levels above this minimum for total-body health.


It may also be helpful to keep an eye on dietary sources of tryptophan during the winter months. Tryptophan is an amino acid and building block for serotonin, which converts to melatonin after additional biosynthesis. Given that serotonin levels can decrease during winter, a tryptophan boost may be beneficial. Some evidence suggests that tryptophan supplementation may work synergistically with morning sunlight in alleviating seasonal mood symptoms.



The Future of SAD Therapies

Some pioneering work has found that carefully controlled light flashes during sleep can advance circadian rhythms. This may be useful for those who experience a delayed body clock during the winter months, although further research needs to be done to determine optimal protocols.


It may be the case that SAD subtypes exist, requiring assorted treatments. One study assessed the brains of those with SAD and found differences in activity compared to healthy controls via electroencephalography (EEG). However, whether there are different brain pattern subtypes remains to be determined.


SAD occurs in approximately 30% of those with adult attention deficit hyperactivity disorder (ADHD). Many people with ADHD are also evening chronotypes, meaning that their natural body clock runs a bit later year-round. Genetic markers may indicate which individuals would benefit from an attempted circadian phase advance or nutrition and lifestyle interventions.


Exercise and food timing are potent modulators of our internal clocks, and there is strong evidence to suggest that shifting the timing of our activity and meals earlier can help to advance a delayed body clock. This can be utilized during travel to minimize the effects of jetlag and, more broadly, when seasonal changes negatively affect mood.


Diet quality is crucial during the winter months. Where seasonal mood changes promote cravings for carbohydrate or sugar-laden foods, these can throw off internal rhythms and even alter sleep-wake patterns.


Diets high in processed foods might lead to sleep disturbances by causing spikes in blood sugar that activate the brain’s orexin system. Orexin neurons promote wakefulness and also feeding behavior. Frequent consumption of sugary foods can sometimes cause insulin to over-compensate, thus artificially causing a drop in blood glucose that is too low. This can activate orexin neurons in the hypothalamus (the brain’s feeding center), which promotes unnecessary further eating. Because those orexin neurons are also involved in wakefulness, this can make it difficult to fall and stay asleep. Keeping blood sugar levels stable by avoiding highly processed or sugary foods can prevent this.



Our take:

Humans evolved to be active, outdoor mammals. While we spend more time indoors than our ancestors once did, we haven’t yet evolved to cope with the combination of days spent indoors and excessive light at night. Plus, extreme levels of sedentary activity and unhealthy eating patterns exacerbate these health problems.


So, aim to make a daily habit of spending as much time outdoors as possible. Ideally, this includes at least ten minutes first thing in the morning, at lunchtime, and around sunset. During these three critical periods, the light wavelengths and angle of the sun in the sky send important information to the brain about where it is in time, supporting alertness when we want it and sleepiness when we don’t.



Will this benefit me?

So much of the circadian influence on cognition happens below our level of consciousness. Going through the motions to get outside at critical points throughout the day - even if it involves wrapping up and bracing against the cold - supports every other aspect of our physiology alongside the all-important pillars of mood and productivity many strive for.



Still curious to try it? If you do, here’s what to keep an eye on:

Get the most out of circadian-drive boosts in cognition by incorporating some of these suggestions into your daily routine. Akin to brushing your teeth — generally considered a daily non-negotiable — commit to daily practices of strategic light and dark exposure and watch how well your year unfolds.



References and Additional Materials:

Photosensitive retinal ganglion cells and SAD - https://pubmed.ncbi.nlm.nih.gov/23286902/

Moving time zones with light flashes - https://pubmed.ncbi.nlm.nih.gov/37660233/

Light therapy nursing homes - https://pubmed.ncbi.nlm.nih.gov/36410392/

Different profiles of SAD - https://pubmed.ncbi.nlm.nih.gov/36244199/

Review of treatments for SAD - https://pubmed.ncbi.nlm.nih.gov/30048159/

Inter-individual sensitivity to light at night - https://pubmed.ncbi.nlm.nih.gov/31138694/

Morning cortisol blunted in SAD - https://pubmed.ncbi.nlm.nih.gov/21145663/

Daytime light and sleep quality - https://pubmed.ncbi.nlm.nih.gov/35730553/

Light flashes and circadian advancing - https://pubmed.ncbi.nlm.nih.gov/37660233/

Glucose excursions and sleep - https://pubmed.ncbi.nlm.nih.gov/37156196/

Sleep, rhythms, and mechanistic insights - https://pubmed.ncbi.nlm.nih.gov/37236066/



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