Whether it’s a cup of coffee, tea or an energy drink, many people look for a caffeine fix to kick-start their day. During waking hours, the stimulant can help people feel more alert and boost concentration. But how does caffeine affect sleep?

According to a 2013 study in the Journal of Clinical Sleep Medicine, moderate consumption can increase the time it takes to fall asleep and negatively affect sleep quality.

But why? Below, we'll take a closer look at exactly how caffeine interacts with the brain and the implications for sleep.

How does caffeine affect the brain?