• Sleep efficiency (subjective and objective)
  
• neurobehavioral assessment battery
  

• psychomotor vigilance testing
  
• functional outcomes of sleepiness questionnaire
  

Melatonin is a hormone secreted predominantly during the sleep period, suspected to have a strong link to the circadian sleep-wake cycle. Melatonin is also available in a pill form and, when administered during the day, tends to have a sedative effect. Clinical trials that have examined the nocturnal effects of melatonin have focused on patients of any age who have insomnia, regardless of their endogenous melatonin levels. Data indicate, however, that individuals with low endogenous melatonin levels may be more responsive to exogenous melatonin. Generally, melatonin levels decrease with age; therefore, older individuals with insomnia represent an ideal population in which to study the effects of exogenous melatonin on sleep. This study will provide older adults with insomnia melatonin tablets to determine whether the tablets will increase their sleep.

Participation in this study will last 10 weeks and will comprise overnight visits at 2 timepoints, the beginning of Week 1 and the end of Week 6. At study entry, participants will be admitted to the General Clinical Research Center for a 3-night stay, beginning with an overnight urine screen to confirm low melatonin levels. Participants will also be asked to begin a sleep diary documenting their sleep quality and quantity; the diary will be used throughout the study. During Night 1 at the clinic, participants will have urine samples collected throughout the night. Night 2 will be an adaptation night to allow participants to get used to their surroundings. On Night 3, participants will have sensors attached to their bodies and a polysomnograph machine will be used to measure their sleep efficiency. Participants with sleep efficiencies of 80% or higher will complete their study participation. Participants with sleep efficiencies less than 80% will be randomly assigned to one of three study treatments daily for 6 weeks: high-dose melatonin (4.0 mg), low-dose melatonin (0.4 mg), or placebo. Participants will have study visits at Weeks 1, 3, and 6 to monitor for adverse events. After 6 weeks, participants will have 2 more overnight clinic visits that will be identical to Nights 2 and 3 from the beginning of the study. Sleep questionnaires, cognitive tests, and psychomotor tests will be used to assess participants at the beginning of the study, after 6 weeks, and at the end of the study. One month after the end of the study, participants will have a follow-up visit to be reassessed for adverse events.