Seasonality in affective disorders.

Humans retain neurobiological responses to circadian day-night cycles and seasonal changes in daylength in spite of a life-style usually independent of dawn-dusk signals. Seasonality has been documented in many functions, from mood to hormones to gene expression. Research on seasonal affective disorder initiated the first use of timed bright light as therapy, a treatment since extended to non-seasonal major depression and sleep-wake cycle disturbances in many psychiatric and medical illnesses. The growing recognition that sufficient light is important for psychological and somatic well-being is leading to the development of novel lighting solutions in architecture as well as focus on a more conscious exposure to natural daylight.