The less you are sleeping the more at risk you are of becoming or staying obese and that is why people that have sleep related problems usually gain weight more so than someone who gets a good nights sleep. It is a like a circle effect too because the less sleep you get the better chance for weight gain and the less energy you will have so the less active you will be probably haveing less exercise.
Anything less than 7 for an adult is not good…go to sleep!! Not to mention that lack of sleep causes other problems like poor memory and poor coordination.