[Phototherapy of jet lag, night work and sleep disorders]

Jet lag, complaints associated with night work, and certain sleep disorders may be caused by misalignment between the endogenous circadian rhythm and the sleep/wake cycle. The authors discuss how light influences and regulates the circadian rhythm. The endogenous circadian rhythm is generated by the suprachiasmatic nucleus, and the effect of light is mediated to this nucleus directly via the retinohypothalamic tract. The effect is dependent on the timing of the light exposure relative to the nadir of the endogenous rhythm, which usually is located at about 5:00 AM. Exposure to bright light before nadir induces a phase delay, whereas a phase advance is obtained with exposure to light after nadir. The paper describes how bright light treatment can be used to reduce the effects of jet lag and of night work, sleep phase disturbances and early morning awakenings. Melatonin administration is an alternative treatment for the same type of disorders, and is also discussed in the article.