Based on a study conducted by the American Cancer Society between 1982 and 1988, the report examined the sleeping habits of 1.1 million American men and women over a six-year period. The report found that women who slept between eight and 10 hours per night had a 13%, 23% and 41% greater risk of dying than those who slept seven hours each night.
For men sleeping between eight and 10 hours each night, the greater risk of death increased 12%, 17% and 34%. Sleeping as little as five hours a night, however, increased the risk of death only 5% for women and 11% for men.
However, the authors of this sleep report, led by psychiatry professors at the University of California at San Diego, acknowledged that they did not focus on why more sleep negatively affects human life spans. One researcher speculated that people who sleep longer may suffer from sleep apnea, a condition in which people stop breathing during sleep, unconsciously waking them up throughout the night and thereby disrupting their sleep patterns.