2023-06-29 10:43:08
The natural light provided by the sun is the key to the evolution of all life on earth, that of plants, animals and people. Without it, the human body, which regenerates itself thanks to it, would be like a battery without an energy source to charge it. Here’s an overview of the problems posed by too much artificial light, the health benefits of natural light and advice on how to make the most of it.
Benefactor sun: from ancient Egypt to chrono-medicine
From ancient Egypt to pre-Columbian America, passing through the Romans and the Greeks, the various secular traditions attributed curative virtues to the light and erected, for example, sun-drenched places dedicated to healing the sick.
Descartes, great thinker of the 17th century, described in his famous Discourse on Method the pineal gland as the “seat of the soul », perhaps sensing the importance of this tiny gland in our relationship to the world, without however having the biological knowledge to be able to explain it. Science demonstrates today how the one we more readily call the “epiphysis” adapts to the quality and quantity of light received by the body to convert the amino acid tryptophan into melatonin and watch over our biological clock.
These are the photoreceptors of the eye which are the main way of entry, with the skin, of the light of day and as such play a vital role in the balance of the body. New research(1) has shown that photosensitive cells, located at the heart of our retina, can detect the intensity of light (which has specific wavelengths depending on the time of day: dawn, high day, dusk), including when the eyelids are closed, and transmit the information to the hypothalamus, which allows the latter to orchestrate the stimulation of the various systems of the body (nervous, hormonal, immune, cellular…) which depend on the circadian rhythm. « In mammals, the light-dark cycle is the most powerful synchronizer of the internal clock. recall the members of the consensus group Chronobiology and Sleep of the French Society for Sleep Research and Medicine (2).
Read also Sunlight: a real medicine?
Lack of natural light and excess of artificial light: factors of breakdown of the biological clock
Our contemporary lifestyles lock us up, for a large part of the day, in closed and artificially lit spaces : homes, offices, transport, classrooms or sports halls, restaurants, shopping centres, etc. We are no longer exposed, or very little, to daylight, which has consequences both physiological (low energy, sleep problems, cardiovascular problems, glycemic dysregulation, etc.) psychological (mood disorders, depression, etc.). Moreover, when we go out in the open air or take a sunbath, it is, most of the time, “protected” by sunglasses: nbone cells are then deprived of signals essential to their proper functioning, generating circadian cycle disorders with cascading physiological effects. We also often go out protected by sunscreen, yet sunscreens reduce the synthesis of vitamin D by 98% from an SPF 15. It should also be remembered that 80% of the French population is deficient in vitamin D.
On the other hand, we bathe in artificial light. This one, with an incomplete chromatic spectrum unlike natural light, deceives the messenger photoreceptors located in our retina, putting us in a way permanently jet lag. This artificial lifestyle disrupts in particular melatonin (sleep hormone)released later, altering the quality of sleep as well as cell recovery and regeneration.
It is therefore useful to repeat it: our internal biological clock synchronizes harmoniously only with exposure to natural light without which it cannot function properly. However, a repeated disturbance of the circadian rhythm is a factor of irritability, sleep disturbances and hormonal disorders, fatigue, depression(3), and increases the risk of cardiovascular diseases and obesity(4). This is why working staggered hours eventually leads to so many health problems. In children, a lack of exposure to light is associated with increasingly widespread attention deficit and hyperactivity problems.
In addition, it should be noted that the ability to benefit from the benefits of light is reduced with advancing age, mainly due to eye pathologies such as glaucoma or cataracts. Chronic inflammation, favored by circadian rhythm disorders(5), is also a disorder often associated with these two pathologies.
Read also “Artificial light knocks out 200 million year old instincts” -Johan Eklöf
Mood, sleep, energy… What are the effects of exposure to daylight?
Who hasn’t felt, following a day in the fresh air and natural light, a real benefit – mood, “good fatigue” – auguring a good night’s sleep? We experience this intimately on a daily basis: daylight, with its full spectrum (from red-orange to blue-violet via green), influences us in depth.
Through its rays, light somehow nourishes us, like an essential nutrient, just as it gives life and makes all plants grow. These are enriched with nutrients in the light, are colored with pigments often beneficial to human health. (chlorophyll, carotenoids, anthocyanins, polyphenols, etc.). Natural light, as a catalyst, has a beneficial impact on both humans and plants: our skin, exposed to the sun, produces vital vitamin D, while plants, exposed to UV, produce their protective antioxidants. Antioxidants from the plant kingdom, products of photosynthesis, are also essential to human health.
The biological clock, like a conductor, harmonizes our internal physiology by synchronizing it with external time, the light perceived by the retina acting as the main indicator. Thus, each morning, the operation of going from sleep to wakefulness, directed by the adrenal glands, is carried out thanks to the photosensitive cells of the eye.
On this synchronization with the day-night rhythm everything depends the subtle hormonal ballet that governs the body and its balances : secretion of melatonin from around 9 p.m. until early morning encouraging sleep and cell repair (melatonin is a powerful antioxidant), secretion of cortisol the day (with a peak between 6 a.m. and 8 a.m.) raising the body’s temperature, providing energy, alertness, memory…
It is therefore no coincidence that waking up is more laborious in winter when you get up before the sun rises or in summer when you sleep with the shutters hermetically closed! For a serene awakening, there is no physiological need for coffee. Going for a short walk outside or opening your windows wide at the first light of day is much more necessary for your physical and mental start-up.
Read also Chronobiology: body clocks
You encounter Difficulty falling asleep at night? Start by trying to wake up at the same time as the day and take advantage of its light: the problem will no longer arise, or much less. This is particularly true for adolescentsmost often under-exposed to the light of daybreak and locked up too early in classrooms, which causes a biological shift in the natural phase of falling asleep.
How does daylight influence our mood? Sunbathing, winter and summer, prevents SAD in particular (seasonal affective disorder), or seasonal affective disorder (SAD). Light therapy lamps have been shown to prevent the harms of lack of exposure to natural light, including SAD, but also have a positive effect on depression altogether (6). Chromotherapy, or therapy using the different colors that make up natural lightis used, less in France it is true, to treat all sorts of pathologies, including chronic stress, which we now know how much it is a precursor to many ailments.
If it is crucial to be exposed to light during the day, it is equally important to do not expose yourself to light at night : be sure to sleep in the full black (aside from power strips, lighted chargers or backlit clock radios!), studies prove that nighttime exposure to even minimal light harms heart health and increases insulin resistance! If we know that prolonged exposure to blue light from screens in the evening, by tricking our brain, delays the production of melatonin and reduces the quality of sleep, it also has an impact on morale. Especially between 11 p.m. and 4 a.m. exposure to blue light negatively affects parts of the brain that regulate emotions and mood (7). Perhaps in a related way, but without knowing exactly why, it seems that exposure to sunlight favorably influences the composition of our microbiota!
Read also Protect yourself from blue light
Expose yourself to natural light in practice
To take full advantage of the benefits of natural light, let’s start by stepping outside, without sunglasses (except in the high mountains or at sea due to the strong reverberation) which block a whole part of the light spectrum and as such “decoy” our retinal receptors. Since it is not a question here of looking at the sun, but of “taking it”, there is no need to protect your eyes.
When and how long during the day should you be exposed to light? Experts recommend exposing yourself to natural light at least three times a day – in the morning when the sun has just risen, in the middle of the day and at the end of the day, regarding 30 minutes before the sun sets – for at least 5 minutes, or 15 to 20 minutes a day in total. You thus clearly indicate to your body what time of day we are so that it adjusts. The advice is all the more relevant when you want to recover from jet lag! We will obviously take care not to look directly at the sun, especially when its light is intense like in the middle of the day, otherwise we will damage our retina!
Finally, how to compensate for the lack of daylight in winter or in environments where access to natural light is limited? If you have no choice but to stay locked up and cannot invest in a light therapy lamp, bring at least full spectrum light bulbswhich is not the case with most household bulbs, let alone neon lights.
Read also Luminotherapy. At the dawn of a new medicine
Under no circumstances is the information and advice offered on the Alternative Santé site likely to replace a consultation or a diagnosis formulated by a doctor or a health professional, who are the only ones able to adequately assess your state of health.
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