EVERYONE NEEDS SLEEP.
The human body needs an average sleep of 10-12 hours of sleep, the reason our body's need so much sleep is because our body is rejuvenating itself at night and is fighting infections. It also might be caused be eating little he's eating habit is very bad for he's health, the body needs food,it's best to have 3 whole meals a day, even people on diets need food don't starve your body or yourself, people on diets need 15 very small servings of food to stay in shape.
As far as his working hours," 6am-12pm ", is normal,I'm in school and I have to get up at 5am and I come home around 12 or 1pm, so that's not the problem. For your friends sake ask him to at least get 11hours of sleep also if he doesn't prefer to eat 3 meals a day, ask him 2 eat 15 small nmeals a day it ends up being 4 meals instead, strange is it not?
But you can NOT change someone,it's up to them, one way or they other he will find out. =]
Health books/Library,My own facts,and my old school Eatonville Middle School.