That will depend on personal. I have seen some of my family members just slept in less than 7 hours, and they have very busy every day. They still healthy, and they don't have any complaints with their body. I think if we are can manage our sleep to get quality and not quantity, we can feel fit and healthy, and we can also take care of our bodies. But many people will time that sleeping more than 8 hours will be better than sleep less than 7 hours because they don't think about the quality of sleep time.