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Summer is now over on the northern hemisphere - nature changes its colour, days become shorter and there are less hours of sunlight. Many people will experience less sunlight, especially all of us who spend most of our daytime at work.
Some of us may enjoy the changes in nature and the fresher climate but one thing is for sure: if we experience a lack of sunlight, we will experience a lack of health.
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There is also a powerful seasons cycle within the human body: during
fall we prepare for winter by eating more food, especially
energy-intense carbohydrates and fats. Through thousand's of years of
evolution this has been a healthy survival-mechanism as nutrition was
scarce during winter. This is obviously not the case today but still we
increase our energy intake to a large extent.
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On a physiological level, sunlight triggers hormonal functions in ways
that artificial light does not. When exposed to sunlight, a receptor in
our eyes triggers the production of the hormone cortisol that makes us
awake and alert. The exposure to sunlight also represses the production
of the hormone melatonin that makes us fatigued, in the need of sleep.
Put together, this hormonal dynamic is called the Circadian Cycle or
the Body Clock (see graph below).
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The next phase in this
cycle is winter, now our bodies puts extra focus on reducing energy
consumption, especially by making us tired and sleep more. Again
sunlight sets this seasonal clock. The less sunlight we are exposed to
during fall and winter, the more we experience carbohydrate cravings
and fatigue.
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Lack of sunlight exposure leads to a
de-synchronization of this rhythm, which is negative for our alertness
and immune system leading also to mood - and sleep disorders.
Research
also shows that the condition can be reversed: productivity increases
and sick-leave decreases when adding sunlight to work places.
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