Five Hours Sleep Enough for a Longer Life

Students worried about not getting the recommended 8 hours of sleep before their next-day midterm can now relax. The common idea that 8 hours of sleep nightly is necessary for health may not be true. Psychiatry professor Daniel F. Kripke led a study found that  women who sleep between 5 and 6.5 hours are more likely to live longer.

In its research, the team followed up on a study first conducted from 1995 to 1999 to determine if there is a correlation between sleep duration and mortality rates. The researchers used a wrist activity monitor to measure the sleep duration of 444 women, age 50 to 81, living in San Diego.

Kripke’s team analyzed the findings this year to examine the women who were still alive after 14 years. Of the original participants, 358 were located. Of these, the 209 women who slept on average, between 5 and 6.5 hours had the highest survival rates while the 101 women who slept 6.5 or more hours had the second highest survival rates.

The 43 women who slept less than 5 hours were most likely to suffer from fatal health issues. The other 86 women had died and the group did not have information on the causes of death.

“[Women who are] over age 60 do not have to worry about sleep apnea — the suspension of external breathing — either, in terms of survival,” Kripke said.

This information confirms other studies on sleep, which have found that self-reported sleep durations shorter than 6.5 hours or longer than 7.5 hours are associated with increased mortality risk.

Kripke’s study also found the number of hours associated with a low-mortality risk. In addition, the team found that high melatonin — also known as the “hormone of darkness” because it is secreted both in day and night — is also related to high mortality.

“[It] is interesting because it tends to disprove the idea a lot of people have that melatonin supplementation is good,” Kripke said.

Though the study was only conducted on women, Kripke said it would be worthy to conduct a men’s sleep study as well. In previous studies on sleep duration, the results have been very similar for men and women.