There is no specific number of hours each one person needs. 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. Some people may be at their 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. Two studies suggest that healthy adults have a basal sleep need of seven to eight hours every night, but where things get complicated is the interaction between the basal need and sleep debt. For instance, you might meet your basal sleep need on any single night or a few nights in a row, but still have an unresolved sleep debt that may make you feel more sleepy and less alert at times, particularly in conjunction with circadian dips, those times in the 24-hour cycle when we are biologically programmed to be more sleepy and less alert, such as overnight hours and mid-afternoon. You may feel overwhelmingly sleepy quite suddenly at these times, shortly before bedtime or feel sleepy upon awakening. The good news is that some research suggests that the accumulated sleep debt can be worked down or "paid off."
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.
For example, short sleep duration is linked with:
•Increased risk of motor vehicle accidents
•Increase in body mass index – a greater likelihood of obesity due to an increased appetite caused by sleep deprivation
•Increased risk of diabetes and heart problems
•Increased risk for psychiatric conditions including depression and substance abuse
•Decreased ability to pay attention, react to signals or remember new information