NEW YORK (Reuters Health) – Seven hours of sleep per night appears to be ideal from the standpoint of mortality risk, according to results of the Cancer Prevention Study II. An hour or more than this results in "distinctly and significantly increased" risk of mortality.
Dr. Daniel F. Kripke, of the University of California in San Diego, and colleagues analyzed data from more than 1.1 million respondents to a health questionnaire received in 1982. The respondents–primarily friends and relatives of American Cancer Society volunteers–were on average 57 to 58 years old at the time of the survey; all were over 30.
Six-year follow-up data were available for 98% of the subjects. Of these patients, 9.4% of the men and 5.1% of the women died, Dr. Kripke's group reports in the Archives of General Psychiatry for February.
The researchers controlled for 32 sources of comorbidity, more than previous studies have done. This included demographic risk factors; health habits, such as exercise, and smoking; health history, including cardiovascular disease, cancer, diabetes and stroke; and medication use.
"The modal reported sleep duration was 8 hours among both women and men," they write. However, the lowest mortality was observed in those who slept 7 hours per night. "The increased risk exceeded 15% for those reporting more than 8.5 hours sleep or less than 3.5 or 4.5 hours," the analysts write.
For those who slept 10 or more hours per night, the adjusted hazard ratio was 1.34 for men to 1.41 for women. The increased risk was primarily due to cerebrovascular deaths.
Insomnia, on the other hand, resulted in adjusted hazard ratios ranging from 0.81 to 0.94. The risk associated with the use of prescription sleeping pills was greater than any risk associated with insomnia, the authors note.
"Although there may be risks in depression, anxiety, heart disease, cancer, lack of exercise, sleep apnea, and other conditions in which insomnia is often present, patients with insomnia without underlying comorbidities can be reassured that there appears to be no survival risk, as long as the patients refrain from long-term use of sleeping pills," they conclude.
"Sleep is not bad for you and insomnia is not good," Drs. Daniel J. Buysse and Mary Ganguli, of the Western Psychiatric Institute and Clinic in Pittsburgh, comment in an accompanying editorial.
They point out that Dr. Kripke's team reported results in terms of hazard ratios rather than actual mortality risk. Although 1 extra hour of sleep carries a 100% increase in the hazard ratio, this is just a 1% absolute increase mortality risk, they add.
Arch Gen Psychiatry 2002;59:131-138.
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