Retinal neurons and light exposure as the key to (re)setting your circadian rhythms - by Sixtine Ayem de Lagaerd

Retinal neurons and light exposure as the key to (re)setting your circadian rhythms - by Sixtine Ayem de Lagaerd

Circadian rhythms are the patterns of physiological and metabolic activity which follow a 24 hour cycle. This 24 hour cycle is roughly synchronised with the rising and the setting of the Sun. They explain why we feel sleepy at night and awaken in the morning; why our body’s temperature fluctuates throughout the day. Patterns of melatonin release are also run by these circadian rhythms. Melatonin is a hormone that is released at night when we sleep - helping us fall asleep, and remain asleep. Although much has yet to be elucidated, science has shown that disrupted circadian rhythms can be strongly associated with adverse health outcomes. On a more positive note, we have also found that focusing on setting them back on track can be a powerful, meaningful, and accessible way to improve one’s health. 

Sunlight is the most potent source of entrainment (adjustment) of our circadian rhythms and is therefore essential to setting healthy sleeping patterns. 

In the retina of our eyes exist photoreceptor cells - their function is to send signals to the brain when they are exposed to photons (visible light). The electrical signal that they transmit travels to the master clock of the brain (and therefore of the body). This structure is called the suprachiasmatic nucleus (SCN). You can think of this clock as the CEO of the circadian rhythms of the whole body. And yes, light has a very important weight in helping this clock decide how to set the time. 

We run into problems when the natural design of the body is disrupted by the demands of our modern, post-industrial lives. Since most of us work indoors and use artificial light after sunset, our clocks don’t receive the strong synchronizing signals that they would expect from sunlight, and the lack of sunlight at night. 

If you have issues finding a healthy sleep-wake pattern, getting outside when the sun is rising - when it is at a low angle relative to the Earth, is the best stimulus for setting your circadian clock. This is because the retinal neurons that set your clock respond best to blue-yellow contrast, which is abundant in low solar angle  - early morning - sunlight. This is true even through thick cloud covers. However, due to circadian shifts in retinal sensitivity, once night time arrives, melatonin production can be easily suppressed by viewing lights that are too bright. This can alter your circadian clock. Thus, It is best to avoid bright lights between 10pm and 4am. 

Author: Sixtine Aymen de Lagaerd.

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