Most of us have used caffeine. And most of us have heard that caffeine consumed close to bedtime can worsen sleep quality. I tell my patients to not have caffeine within 8 hours of desired bedtime. This was what I was taught in sleep fellowship. Apparently, there are few studies that have determined that people should stop consuming caffeine within so many hours of bedtime.
This study sought to determine how caffeine affects sleep quality when taken at bedtime and at 3 and 6 hours prior to bedtime. It's a small study, with only 12 healthy, younger volunteers. The volunteers did not have insomnia but did consume caffeine regularly. Sleep was measured by subjective report and by objective home monitoring. The results showed that the 400mg of caffeine negatively impacted sleep quality when taken at bedtime and at 3 and 6 hours prior to bedtime. Interestingly, caffeine affected both subjective and objective sleep quality when it was taken at bedtime and 3 hours before bedtime. However, the study participants did not report reduced sleep quality when caffeine was consumed 6 hours prior to bedtime. But objective home measurement showed that the caffeine taken 6 hours prior to bedtime did negatively impact sleep. This lack of perceived disruption in sleep quality may explain why some patients ignore recommendations to eliminate caffeine consumption close to bedtime.