How much sleep do I need?

DEAR DOCTOR K:

I average about six hours of sleep each night. How much is enough, and how much do most people get?

DEAR READER:

Let’s start with how much is enough. Many large studies have found that people who average fewer than seven hours of sleep per night, or more than nine hours, have more health problems. That is, there is an association between “too little” or “too much” sleep and health problems.

However, these studies don’t prove 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 night 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 U.S. Centers for Disease Control and Prevention 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 that most people (65 percent) reported that they averaged at least seven hours of sleep per night. The bad news was that 35 percent did not. That amounts to about 84 million U.S. adults. About 12 percent reported sleeping fewer than five hours per night. About 23 percent reported sleeping fewer than six hours per night.

Interestingly, only about 4 percent reported averaging more than nine hours per night. So if sleeping that much is harmful, a relatively small fraction of people is affected.

Averaging fewer than seven hours of sleep each night was more likely in certain groups and certain geographic areas. For example, non-Hispanic blacks, American Indians/Alaska Natives, Native Hawaiians/Pacific Islanders and multiracial people were more likely than other groups to report too little sleep.

People in the upper Rocky Mountain and Midwest farm states got the most sleep. New York, Michigan, Illinois, Ohio, Kentucky, West Virginia, South Carolina, Georgia and Alabama got the least sleep.

When this most recent study was compared to past studies, it appeared that more Americans are sleeping longer hours than in years past. For example, in another large survey conducted in 2007-2008, only about 60 percent of people reported getting at least seven hours of sleep per night (compared with 65 percent in this study).

So, sleeping seven to nine hours per night may well be healthier than sleeping fewer than seven hours per night. But that is by no means proven. Also, if it is true, it is only true for the “average” person. There probably are people who are born to need more or less sleep than the average person.