Predicting Light Treatment's Effectiveness on Reducing Depression and Cardiovascular Risk in Seasonal Affective Disorder

The winter subtype of seasonal affective disorder (SAD) is characterized by episodes of major depression in the fall and winter, with remission of these episodes in the spring and summer. SAD disrupts the lives of millions of Americans, who experience symptoms such as restless agitation, increased appetite and weight gain, and reduced energy and motivation. Bright light treatment, while shown to be effective in improving SAD in 75% of cases, only causes a full remission in 50% of cases. If doctors had a diagnostic tool to determine which patients would respond to bright light therapy, they could make better decisions about whether to prescribe bright light as treatment. This study will examine a possible diagnostic tool-a single, 1-hour bright light session-for predicting improvement in SAD symptoms over an extended course of bright light treatment. Additionally, because many symptoms of SAD (like weight gain and sedentary lifestyle) correspond to cardiovascular risk, this study will examine whether bright light treatment correlates with improved cardiovascular health.

Participants with SAD will be randomly assigned to first receive a 1-hour session of either bright light or the placebo, red light. Then all participants will switch and receive a 1-hour session of the other type of light. Red light has been accepted as a placebo in previous SAD studies because it does not suppress melatonin or shift circadian rhythms. Before and after each light session, participants will have their SAD symptoms evaluated in a clinical interview and self-report measure. After these two light sessions, all participants will receive instructions for administering bright light treatment on their own at home. For the next 6 weeks, participants will administer the bright light to themselves for 1 hour every morning. Every week they will undergo clinical interviews by phone and will mail in self-report measures, some completed daily and some weekly, to the researchers. The participants will have checkups and interviews in person on Weeks 4 and 6. At the two time periods, SAD symptoms and indicators of cardiovascular risk, such as appetite and sleep loss, will be evaluated. The participant responses to bright light and red light at the initial session will be compared with the participant responses to the subsequent 6-week treatment.