These feelings of depression are aroused more prominently in winters. But for some people, those feelings can manifest into something even more extreme: an illness called seasonal affective disorder, or SAD.

SAD is diagnosed more often in women than in men. And SAD occurs more frequently in younger adults than in older adults.

Lonliness is a public health issue, in UK 60% of 18 to 34 year olds say they often feel sad. in the US 46% of people feel sad and lonely.

When the brain’s pineal gland starts pumping out melatonin, we get sleepy. During winter, animals secrete melatonin for longer periods than they do at other times of the year. And also people do, too — but only those who suffer from seasonal affective disorder. Winter depression is still a mystery to scientists who study it.

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