Experts generally recommend seven to nine hours a night for healthy adults.  The latest research says Americans are on average sleeping less than they did in the past.

Several sleep studies have found that seven hours is the optimal amount of sleep, not eight.  Many doctors question that conclusion.

More research has shown that skimping on a full night's sleep, even by 20 minutes, impairs performance and memory the next day.  And getting too much sleep, not just too little of it is associated with health problems including diabetes, obesity and cardiovascular disease and with higher rates of death.

Sleep experts say that seven hours might be better than eight to function the next day.