There are three base Stats in the game: Hunger, Thirst, and Sleep Deprivation. These requirements are fulfilled when a Survivor eats, drinks, or sleeps. If a survivor doesn't eat in a week, they will die. If they don't drink in two days, they will die, and if they don't sleep for a week, they (as you guessed it) die. Food can be easily grown and is rather plentiful in buildings, and wells can be made to create an infinite water source. This removes the worries of food and water later on in the game. There is also a fourth stat, Blood Glucose Levels, exclusive to Alice Ivers. If she doesn't get any insulin for a week, she'll perish.
A Lung Cancer stat bar will appear for any character that smokes a cigarette, and will increase for every cigarette smoked.