system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do doctors recommend 8 hours of sleep, and not 7h30 or 9h

From what I understand, it’s best to wake up at the end of a cycle, and each cycle is 90 minutes, right?
gpt
The 8hrs of sleep thing was taken from (I believe) a small number of studies. People were asked how much sleep they need a night. Some said 6, some said 8, some said 10, etc, so they just averaged it out to 8 for everyone. It’s kinda like how some people need more or less than 2000 calories to be healthy. It all just depends on the person and their genetics.