Light treatment is best prescribed by psychiatrists who have experience in its use and can appropriately evaluate the indication for light therapy and monitor the response to treatment. Some individuals buy light boxes using the Internet or from stores and carry out the treatment without prior consultation and adequate supervision. Patients should be discouraged from treating themselves without medical supervision. However, patients can be encouraged to participate in establishing an optimal light protocol. For patients with SAD, light therapy should be regarded as the first-line treatment, but other treatments including antidepressants, stress management, exercise and psychotherapy may also be useful (Lam et al., 1999b).
The biological mechanisms of SAD and light therapy are not clear. Various studies suggested the involvement of serotonergic, dopaminergic and noradrenergic pathways; the hypothalamic-pituitary-adrenal and hypothalamic-pituitary-thyroid axes; and changes in circadian rhythm and melatonin(Drug information on melatonin) secretion in the neurobiology of seasonal changes in mood and behavior and effects of light therapy (Enns et al., 1999; Magnusson and Boivin, 2003; Oren and Rosenthal, 1992; Rosenthal and Matthews, 1999). For example, Lambert et al. (2002) reported that the rate of production of serotonin by the brain was directly related to the prevailing duration of bright sunlight and rose rapidly with increased luminosity.
A psychobiological response to seasonal changes is a result of interacting environmental and genetic factors (Lam et al., 1999b; Sher, 2001). Genetic factors can interact with environmental factors in different ways, and two such mechanisms have been described: genetic control of sensitivity to the environment and genetic control of exposure to the environment (Kendler, 1998). Genetic control of sensitivity to the environment suggests that genes, in part, render individuals relatively vulnerable to the effects of seasonal and lighting conditions. For example, the effect of light deprivation may be substantially greater in those at high genetic risk for seasonal changes in mood and behavior (Sher, 2003). Genetic control of exposure to the environment suggests that genetic factors influence the probability that individuals will select themselves into certain environments. For example, the genetic risk factors for seasonality may express themselves by influencing the probability that individuals will spend more time indoors (Sher, 2003).Nonseasonal Depression
Use of light treatment for nonseasonal depressive disorders is growing (Kripke, 1998; Lam et al., 1999a, 1997; Tuunainen et al., 2004). There may be a role for light therapy in treating nonseasonal depression, especially in cases where antidepressants are not tolerated or where the patient preference is for nonpharmacological treatment. A recent Cochrane report suggested that bright light therapy offers a modest, though promising, antidepressant effect (Tuunainen et al., 2004). Treatment is particularly effective when administered in the morning during the first week and as an adjunct to sleep deprivation. Light therapy may be useful as an augmentation strategy for antidepressant nonresponders (Levitt et al., 1991).
A recent study found that there were seasonal influences on morning cortisol levels in patients with major depression (Sher et al., 2004). It is interesting to speculate that the hypothalamic-pituitary-adrenal system is involved in the biological mechanisms of light therapy in nonseasonal depression.
Recent reports suggest that bright light therapy has an antidepressant effect on patients with antepartum depression (Epperson et al., 2004; Oren et al., 2002). Evening bright light for two premenstrual weeks decreases depression and tension in patients with premenstrual dysphoric disorder (Lam et al., 1999a). Light treatment appears to decrease depressive symptoms in patients with nonseasonal bipolar disorder (Bauer, 1993).Light and Healthy People
Exposure to bright light is important for psychological well-being of healthy people (Bauer et al., 1994; Lambert et al., 2002; Partonen et al., 1998). In the modern industrial world, many people spend a lot of time indoors. They are light-deprived and have a sedentary lifestyle. Combined exposure to bright light and physical exercise can be especially effective for improving mood- and health-related quality of life (Partonen et al., 1998). Various outdoor activities may provide opportunities to improve psychological and physical health.Conclusion
The increased clinical and research interest in light treatment appears well justified. There is sufficient research evidence to support the efficacy of light therapy in SAD. Light therapy has a promising potential role in the treatment of nonseasonal depressive disorders. We are in the early chapters of our understanding of how light affects humans.