London: Days when one is not exposed to sunlight can lead to seasonal affective disorder or SAD, which can leave you depressed and lethargic, say experts.
Once dismissed by medics, the condition is now recognised by psychiatrists and doctors and its symptoms also include insomnia and aching joints as a result of a change in season.
But experts believe that because the symptoms are similar to other illnesses, it is often undiagnosed, leaving sufferers struggling to cope, reported a newspaper.
"Light has many physiological effects on the body," says Russell Foster, a neuroscientist at Oxford University.
"Cells in the eyes register light so the brain knows when it is day or night. This triggers the release of certain hormones that regulate hunger and digestion, growth, mood and energy."
Darkness causes an increase in the production of the hormone melatonin, which helps us sleep.
There is also a reduction in serotonin, crucial for keeping us alert, and often called the feel-good hormone, which also regulates the digestive system. Light triggers the release of cortisol, which helps us wake up.
"If you drive to work in the dark, spend all day indoors in artificial light, and return in the dark, your internal body clock has nothing to lock onto and normal rhythms can be thrown," says Foster.
He recommends you should experience two hours of natural light a day, even if it`s via a large window.