Light therapy in mood disorders: A brief history with physiological insights

Abstract

The mother of today's Bright Light Therapy (BLT), Heliotherapy, has been the longest used form of phototherapy and the only one until the mid-nineteenth century. Sun therapies were applied in ancient Chinese, Hindu and Egyptian medicine over 15 centuries BC. Since the invention of the electric light bulb and the progress of medicine, heliotherapy shifted to: ultra-violet (UV) phototherapy, which is still used today in dermatology, immunology or neonatology; and to light therapy (UV filtered light) in the treatment of neurological, endocrinological and psychiatric affections. BLT is today the gold standard treatment of the Seasonal Affective Disorder, and is recommended in various others affective disorders. Recent findings as the Zeitgeber Theory involving the Central Biological Clock, and the implication of photo transductor melanopsin in the regulation of the circadian clock are guiding chrono-biologists to understand the physiological insights underlying BLT's action on affective disorders. Those researches combined with ongoing clinical trials could guide us toward an optimal use in mood disorders of this millennial therapeutic resource.