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Why sunlight first thing in the morning?Updated 7 months ago

☀️ We need exposure to the sun as it is literally the ‘guiding light’ for the human diurnal circadian rhythm. This is the near-24-hour body clock that makes us wake in the day and sleep at night. This rhythm is intrinsic to almost every physiological process in the body (which is why you feel utterly rubbish when you’re jet lagged). And how do you think we keep our circadian rhythm in sync? We do it by exposing ourselves to the sun. Through our eyes, and our skin. 


Sunlight activates the suprachiasmatic nucleus (SCN) in the hypothalamus - the central pacemaker of the circadian timing system. Exposure to sunlight is the most potent cue for entraining our circadian rhythms - helping to synchronise our internal clock with the external world. Information received by light will be used by the SCN to guide a cascade of hormonal changes that control feelings such as alertness versus tiredness, and hunger versus satiety. A lot of these feelings are driven by melatonin cortisol and leptin, which are the master circadian hormones that impact all of your other hormones downstream.


Evidence has shown that outdoor exposure to sunlight first thing in the morning is going to be the most powerful trigger for setting your circadian rhythm, making you feel alert and energised for the day, and improving sleep. This is because viewing sunlight stimulates a rise in cortisol in the morning - making you feel alert and stimulating metabolic processes during the day, while also setting a biological timer for sleep that evening. The research on exactly how much morning sunlight exposure we need is still insubstantial as there are varying factors depending on the individual, environment and seasons, but it’s recommended to aim for at least 5 minutes (in direct sun), ideally 30 minutes.


The reason why sunlight is the only light that we can use to guide a healthy circadian rhythm is because it is (the only natural source of light that we’ve evolved with and it is) ‘full-spectrum’. By that, I mean that it provides every colour of light at some point throughout the day. And if you think of yourself as a painting, you will use every different frequency/colour of that sunlight for a different purpose in the body - again, only if you are actually exposed to it, without glass, contacts, or sunscreen getting in the way.


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