Abstract
Recent development of the research on the chronobiology has revealed that clock mechanism may cause some types of disorders, such as sleep-wake rhyihm disorders and seasonal affective disorders (SAD). Bright light therapy has been demonstrated to be effective in treatment of these rhyihm disorders. In human, bright light has been shown to advance the phase of the endogenous rhythms, when the subjects are exposed to light early in the morning. Such phase advance of the rhythm may cause amelioration of rhyihm disorders. Besides light therapy both methylcobalamin (vitamin B_<12>) and melatonin are reported to be beneficial in some cases of sleep-wake rhythm disorders, although their effectiveness has not been well established yet. One possible action of methylcobalamin responsible for sleep-wake rhythm disorder is to increase sensitivity to light. This was suggested by the fact that subjects given methylcobalamin showed more suppression of melatonin release by bright light immediately after wake up during night sleep compared to subjects without methylcobalamin. Melatonin has three different modes of action which are beneficial to amelioration of sleep-wake rhythm disorders. First, it shifts the phase of the rhythm according to the time of melatonin intake, in other words, evening melatonin advances and morning melatonin delays the phase. Second, melatonin accelerate sleep itself. Third, it decreases body temperature, resulting in deeper sleep. Longitudinal follow up study of seasonal affective disorder revealed various types of course. About half of patients with SAD examined maintained consistently regular course of autumn or winter time episodes. Such patients with regular course often showed atypical symptoms, such as hypersomnia, hyperphagia, carbohydrate craving, weight gain and so on. Furthermore, it was very interesting that patients with atypical symptoms responded better to bright light therapy than those without atypical symptoms. The author postulates that patients who show three major characteristics, atypical symptom, good response to light therapy and consistent seasonality, are composing the core group of SAD.
