With SAD, the lack of sunlight causes the brain to work overtime producing melatonin, the hormone that regulates your body clock and sleep patterns and a hormone that has been linked to depression.

During the shorter days of the winter months, your body may produce melatonin either earlier or later in the day than usual.

The brain produces less and less melatonin, a hormone that regulates sleep at night and alertness during the day.

Most adults start to produce melatonin at about 10pm.

When dusk falls, the hypothalamus alerts the pineal gland to start producing melatonin.

Lowering the lights signals your brain to produce melatonin, the hormone that brings on sleep.

Because the body produces less melatonin as we age, these medications may help get the brain back on track.

The suprachiasmatic nucleus (SCN) regulates melatonin and temperature and typically produces melatonin at night.

Although we can quickly reset our watches, our body clock takes many days to adjust, and so instructs the pineal to produce melatonin at the wrong time of day, causing jet-lag.

It produces melatonin, a hormone crucial in regulating sleep.