DEAR READERILet's start with how much is enough Many large studies have found that Too li people who average fewer than seven hours of sleep per night or more than nine hours, have more health problems. That is, there is sleep an association between too little "or" too much "sleep and health problems However, these studies do not prowe that too little or too much sleep is the cause of their worse health. Instead, something else may be. causing too little or too much sleep, and also causing health problems For example, people who sleep more than nine hours per might tend to have higher rates of obesity, heart disease and depression But it could be that their primary problem is depression, not excessive. sleep. People with depression often spend more time sleeping And they often eat too much and exercise too little, and thereby become obese. Obesity, poor diet and inadequate exercise all raise the risk of heart disease. Most experts are more convinced of the adverse effects. of sleeping fewer than seven hours per night. How many people are, like you, averaging fewer than seven hours per night? A recent study published by the US Centers for Disease Control and Preven tion sheds light on that question. The study involved nearly half a million people from all 50 states and the District of Columbia, The good news was thatmost people (65%) reported that they averaged at least seven hours of sleep per night. The bad news was that 35% did not. That amounts to about 84