Michael Terman

The circadian timing system modulates the activity of every cell in our body. Timed light exposure is nature’s way of keeping the activity of these cells in check.

We are confronting three main factors that can underlie depression: an internal clock that runs slower than 24 hours, late evening light exposure that adds physiological time and further slows the process, and a dark bedroom that disallows the morning light signal essential for achieving synchrony with local solar time.

Our inner clock, whose timing cycle does not necessarily match day and night outdoors, needs to stay in sync with rest-activity cycles dictated by family and work life, this is both very disorienting and a trigger for mood slumps and depression.

Since the inner clock relies on sunlight to stay in sync, winter sunrise is later and winter nights are longer, melatonin can overshoot into the day, causing grogginess or 'brain fog,' for several hours.