Bright side of the night – 2.4.1

Why do we need the night?

Circadian rhythm

Circadian rhythms are physical, mental, and behavioral changes that follow a 24-hour cycle. These natural processes respond primarily to light and dark and affect most living things, including animals, plants, and microbes. Biology distinguishes between different circadian rhythms, such as diurnal rhythms as the circadian rhythm synced with day and night and ultradian rhythms, with a shorter period and higher frequency than circadian rhythms. People in highly developed economies spend far more than half of their lives inside buildings and therefore receive little sunlight. At the same time, they are exposed to a lot of artificial light in the evening and night hours. This imbalance has a negative influence on the day-night rhythm to which the body’s internal clock has always adjusted.

The magic of melatonin

The circadian rhythm and thus the functions of the body are controlled by melatonin. The pineal gland releases the hormone in the hours of darkness in the evening and at night. Melatonin is important for a balanced immune system and healthy sleep and is also thought to have a cancer-inhibiting effect. Daylight and nocturnal artificial light in the short wavelength range below 480 nm inhibits melatonin synthesis, and thus can suppress the release of melatonin for more than 90 minutes. Even very low levels of luminous intensity suffice to lower the melatonin level in the blood. This shifts the day further into the night and shortens the period of sleep.

Sleep – regeneration & recovery

As diurnal creatures, we humans need the night to sleep, to recover, rest and regenerate. To ensure adequate, regenerative sleep from around 10:00 pm, it is recommended to stop exposing oneself to artificial light after 8:00 pm. Lighting, especially screens, that we use in our homes nowadays continue to have an impact on the human body for approximately 90 minutes after the last exposure.

Chronobiology, owls and larks

Chronobiology is the study of circadian rhythms. This branch of biology looks at the temporal organization of physiological processes and behavior patterns in organisms. The field’s importance increases as modern lifestyles deviate more and more from the framework conditions set by the biological clock. It is assumed that it wasn’t before the invention of artificial light—which allows humans to postpone sleep—that many different chronotypes developed. Today, we categorize people in owls (extreme: sleep at midnight, get up at 10 a.m.) and larks (extreme: get up between 5 and 6 a.m.). Interestingly, modern economic and social life has been organized almost exclusively geared to larks. Hence, millions of people live and work contrary to their chronotype. Owls or people with an owl tendency tend to be tired when getting up and are less productive during the day. In the long run, working against one’s biorhythm can lead to a range of health consequences.

The short-wave radiation from the displays of smartphones, tablets and e-readers and also from computer screens suppresses the release of the sleep hormone melatonin and thus also the ability to sleep. This can be remedied with the help of the software f.lux(r).

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*Sleeping Woman. Image by IceRedfield ̶ Pixabay.*

*Screen emitting blue light. Image by flasherie ̶ Pixabay.*

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Images

Numerous images on the Circadian Clock can be licenced on Alamy.