In our busy 24-hour world, Americans are devoting far less time to sleep. In 1910, Americans slept an average of nine hours per night. In 1975, that number fell to 7.5 hours. It dropped to 6.8 hours in 2005. According to the National Heart, Lung and Blood Institute, one in six people in the United States averages less than six hours of sleep per night.
Insufficient sleep has been associated with depression, irritability, behavior problems in children and friction in relationships. Relatively minor decreases in sleep time decrease performance on tests that measure memory, concentration and the ability to complete simple tasks and also increase risk of accidents, including car crashes and work injuries. We are now learning that there are also consequences to our physical as well as mental health from getting too little sleep.
• Heart disease: In 2011, researchers at the University of Chicago scanned for calcium deposits in the coronary arteries, a marker for hardening of the arteries, in 495 middle-aged adults who had no calcium at the initial evaluation. Sleep times were measured, and calcification scans were repeated five years later.
Of those averaging less than five hours of sleep per night, 27 percent showed new calcifications. Eleven percent of those with five to seven hours of sleep showed new calcifications, while only 6 percent of those who slept more than seven hours per night showed new calcifications. The results suggest that people with short sleep times are considerably more likely to develop hardening of the arteries over time. Another large study of middle-aged women showed that heart attacks were 45 percent more likely to occur in those who slept less than five hours per night versus those who slept longer.
• Obesity: Studies show adults who average less than seven hours of sleep per night are 1.5 times more likely to be obese, and children with short sleep times are almost twice as likely. Evidence indicates that inadequate sleep results in an imbalance in the levels of hormones that control appetite, resulting in increased hunger. Lack of sleep also can slow the rate of metabolism, so people who sleep fewer hours burn fewer calories. So far, studies have not proven that lack of sleep causes weight gain, only that the two are strongly associated. The growing epidemic of obesity in America has paralleled the decrease in average number of hours of sleep per night.
• Hypertension: In a 2006 study, middle-aged adults who slept less than six hours per night were twice as likely to have high blood pressure (hypertension), compared with those who slept seven to eight hours. Our blood pressure normally falls during sleep, and it may be that prolonging the higher blood pressure while awake could contribute to hypertension.
• Diabetes: A study limiting sleep in healthy individuals to four hours per night for six nights resulted in impaired glucose tolerance, a precursor to diabetes. Other studies have shown that people who sleep five or fewer hours per night are 2.5 times more likely to be diabetic, and those who sleep six or less hours are 1.7 times more likely. While it has not been proven that short sleep times cause or worsen diabetes, it seems it is associated with increased diabetes risk.
Much of the research to date is based on the participants self-reporting their average sleep times, rather than actually measuring time of sleep. However, the relationship between short sleep times and increased risk of obesity, diabetes, hypertension and heart disease is strong enough that everyone should make a goal of getting seven to eight hours of sleep high on their priority list, along with exercise, a healthy diet and smoking cessation. Skimping on sleep may seem necessary in our fast-paced world, but it is certainly not wise. For more information about how sleep issues relate to your health, visit www.sleepfoundation.org.