Caffeine has been shown to minimise the effects of sleep loss on performance and alertness. However, caffeine may also have negative repercussions for recovery sleep, particularly during the daytime.
Finally, non-restorative sleep was associated with an interaction between increased caffeine consumption and sleep duration.
Greater effects with difficulty falling asleep not falling asleep.
Additionally, while this study found higher amounts of caffeine consumed related to decreased time in bed there was no association between subjective sleep quality and the amount of caffeine consumed. This could be due to the fact daily caffeine consumption was, on average, low to moderate or it could be because caffeine was not consumed close to bed time.
Sleep Tip #85: Love Your Coffee But Not Before Going To Bed