Antidepressant effects of light therapy and “natural” treatments for winter depression

Abstract

Although bright light treatment may alleviate the symptoms of winter depression, it still remains to be clarified whether chronobiological mechanisms are involved in this antidepressant response. We studied the therapeutic action of bright light in 61 women with and 36 women without winter depression at the medical academic hospital near Novosibirsk (55 degrees North). Bright light was administered with cool-white incandescent lamp for seven days, two hours daily. The treatment started from either 8:00 (n = 29 patients and 16 controls) or 16:00 (n = 24 and 14, respectively) or 18:00 (n = 8 and 6, respectively). The subsets of bright light-treated subjects were then restudied in wintertime before and after one-week vacation in Firuza resort (south of Turkmeniya, 38 degrees North) (n = 19 and 0, respectively), in summertime (n = 42 and 18, respectively) and in the next winter before and after a week 30-min exposure in the morning hours to dim red light emitting “Light Cap” (n = 9 and 0, respectively). The results suggest that, in controls, mood slightly but statistically significantly improved after light treatment and in summer. In patients, the improvement of mood after one week of bright light was comparable with the effects of such “natural” treatments as trips south and transition from winter to summer seasons. Although next winter response to 0.5-h dim light was clinically significant, it was significantly worse compared to the previous response to 2-h bright light. Our therapeutic results indicate that, despite the different potential phase-shifting effect of bright light administered in the morning and in the second half of the day, the responses to all treatments are equally beneficial. This finding provides evidence against the view that circadian phase shifts are the key to the pathogenesis of winter depression and efficacy of light therapy. Although several different physiological effects of light therapy might be involved in the antidepressant response, none of them seems to be of more importance compared to psychological components of this response. Ours and earlier published reports on the independence of beneficial action of bright light from treatment timing support the suggestion that, in the open investigational trials, the placebo effect accounts for a large portion of the antidepressant response. We also reviewed several facts pointing to the close dependence of antidepressant effects of non-drug therapy upon patients' expectations and researchers' enthusiasm. In sum, unlike patients' chronobiology, their psychology seems to be most powerful mediator of the clinical response to bright light.