Text: Salome Kurth, Course co-lead with Gabriela von Arx
Sleep is an energy depot that we replenish every night. It promotes our well-being and our performance. Seasonal changes influence sleep through factors such as day length, light, or physical activity. Our physical and mental well-being depends on how well we harmonize with these changes.
The effect of light
Sleep patterns tend to be longer in winter than in summer, which may be due to shorter day length and higher melatonin levels in winter. Melatonin rhythms are strictly synchronized in summer due to the long light and short dark periods, whereas divergent melatonin patterns may occur in winter, suggesting that the winter season is more challenging for circadian rhythmicity (1). Morning light exposure is crucial in this regard. Research from the University of Basel shows that artificial light simulating dawn can improve subjective well-being, mood, and cognitive performance (2).
Different bedtimes
A study from the USA enrolled over 200 participants and showed that sleep duration and morning wake-up time in particular are changing, such that people tend to get up earlier in spring and sleep for a shorter time than in winter (3). There is evidence that in the winter months, in addition to sleep duration, sleep quality is also altered such that we sleep less deeply (4,5).
Changes in temperature
As outdoor temperatures increase, bedtimes and wake-up times occur somewhat later (3). However, indoor temperature can also influence our sleep: a cooler environment promotes better sleep, while an environment that is too warm can lead to restlessness and poor sleep (6).
Sleep changes due to humidity
Depending on geographic location, humidity may be higher in summer and lower in winter, which could result in restless sleep. Humidity that is too high or too low can lead to breathing problems and poorer sleep (7).
Changes due to activities
Our sleep is also influenced by leisure activities and hobbies. People are often more active in summer – and more exercise changes sleep, which is likely related to stress regulation, among other things (8). The sun is the strongest source of light and daylight via skin contact is important for vitamin D synthesis and bone health. So maintaining vitamin D levels even with less sunlight is a biological necessity for a sustainable and healthy life (9).
Rhythm of well-being
Winter depression (also known as “Seasonal Affective Disorder”) can lead to changes in sleep for some people, particularly showing a tendency to sleep disturbances and increased sleep duration. In some people, symptoms and excessive sleepiness (“hypersomnolence”) disappear during the remission phase in spring and summer. Overall, hypersomnolence in seasonal affective disorder appears to be a self-reported phenomenon for which further research is needed (10).
Biology in tune with dynamics
Understanding these dynamics is important to listening to your own body and ensuring you get adequate sleep to be refreshed and rested.
Each person can react differently, and although there are universal rules for sleep, we are always in a dynamic of seasonality and day-night rhythm – but moreover, we find ourselves in additional dynamics, such as the biological lifespan, social interactions, or that of the seasonal diet. The diversity of sleep, then, is a journey through the changes that each person experiences. The better we understand these influences, the more specifically we can implement adaptations to bring our biology in line with them.
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References
(1) Danilenko et al, 2019, Physiology and Behavior
(2) Gabel et al, 2013, Chronobiol Int
(3) Mattingly et al, 2021, NPJ digital medicine
(4) Kärki et al, 2022, Sleep Medicine
(5) Kohsaka et al, 1992, Experientia
(6) Lan et al, 2017, Energy and Buildings
(7) Li et al, 2022, Environ Sci Pollut Res Int
(8) De Nys et al, 2022, Psychoendocrinology
(9) Wirz-Justice et al, 2021, Biochem Pharmacology
(10) Wescott et al, 2020, Curr Opin Psychol
Bild: unsplash, Chris Lawton