Matching Light to Internal Clock Fights Depression
By AliciaMarie Belchak

NEW YORK (Reuters Health) - Bright light treatments may help lift people from the depths of severe winter depression, but new research suggests that timing these treatments to the body's internal clock may improve light's antidepressant affect. The results of the study suggest that light has its most antidepressant effect if used early in the morning. Light therapy, a treatment for seasonal affective disorder (SAD), can alter the body's internal clock, researchers report in the January 15th issue of the Archives of General Psychiatry. Therapy sessions timed to match an individual's circadian rhythm, or internal clock, can be twice as effective as those applied later in the morning or in the evening, said co-author Dr. Michael Terman, of Columbia University's College of Physicians and Surgeons and the New York State Psychiatric Institute. ``There's a direct neural connection from the retina in the eyes to the site of the biological clock in the (brain). The biological clock resets depending upon the pattern of daily light exposure,'' Terman told Reuters Health.

As many as half the people in the middle and extreme latitudes of the earth feel at least mildly depressed with seasonal changes. In the US, 6% of these experience the more severe symptoms of depression known as seasonal affective disorder (SAD). Light therapy, however, can trick the brain into thinking it is spring or summer instead of fall or winter. In the study, Terman, his wife Dr. Jiuan Su Terman, and colleagues monitored the melatonin levels of 42 patients with SAD, both during depression and during light therapy. ``Melatonin is the hormone in the animal kingdom that (alerts) the nervous system the season of the year,'' Terman pointed out. ``As night length grows longer the melatonin secretory episode also grows longer, and that's what puts our brain and body into a winter state.''
The investigating team found that 30 minutes of intense, bright light (with no ultraviolet radiation) about 2 to 3 hours after the midpoint of sleep produced the best antidepressant results.

In fact, light timed to this point in the circadian cycle actually doubled the effectiveness of the therapy as compared to sessions in the evening, a time when melatonin begins to be released. SAD patients who underwent the early morning light therapy sessions had an 80% chance of sending their depression completely into remission, explained Terman. ``There's an optimum circadian time, internal time, for the administration of light therapy in order to achieve the antidepressant affect for SAD,'' Terman told Reuters Health. ``The pattern of light exposure is the critical event to that synchronizes the internal clock to the external world.''
Light therapy is best done under the care of a doctor, and it can help relieve the effects of the more common and milder winter blues at home, Terman noted.
``There are too many ways you can do it wrong, and you really need to have an expert observer to help you find the optimum dosing combination for you as an individual,'' said Terman. SOURCE: Archives of General Psychiatry; 2001;