In “How Much Sleep Do We Really Need?” the National Sleep Foundation says:
You hear the advice that people need eight hours of sleep, but does that apply to every person? What about children, teens and older people? Many people seem to get by on less than eight so… … The first thing experts will tell you about sleep is that there is no “magic number.” Not only do different age groups need different amounts of sleep, but sleep needs are also individual. Just like any other characteristics you are born with, the amount of sleep you need to function best may be different for you than for someone who is of the same age and gender. While you may be at your absolute best sleeping seven hours a night, someone else may clearly need nine hours to have a happy, productive life. In fact, a 2005 study confirmed the fact that sleep needs vary across populations, and the study calls for further research to identify traits within genes that may provide a “map” to explain how sleep needs differ among individuals.
Another reason there is “no magic number” for your sleep results from two different factors that researchers are learning about: a person’s basal sleep need – the amount of sleep our bodies need on a regular basis for optimal performance – and sleep debt, the accumulated sleep that is lost to poor sleep habits, sickness, awakenings due to environmental factors or other causes. … Though scientists are still learning about the concept of basal sleep need, one thing sleep research certainly has shown is that sleeping too little can not only inhibit your productivity and ability to remember and consolidate information, but lack of sleep can also lead to serious health consequences and jeopardize your safety and the safety of individuals around you.This article was found in a quick, hit-and-run search. More research necessary, but the above fits my experience, my observations, and my broader context of knowledge (e.g., there is variation among all people in all our aspects: hair color, hair thickness, height, visual acuity, weight, temperature) whereas the “everyone needs eight hours” nonsense does not.