Eight hours is no longer considered the ideal amount of sleep one should receive each night, according to the largest study ever done on the subject.

UCSD professor Daniel Kripke, leader of the study, found that people who sleep only six or seven hours each night live longer than those who sleep eight or nine.

“”Our main findings were that people who sleep seven, six or five hours a night have nothing to worry about, as long as they are not too tired to work or drive,”” Kripke said.

The study surveyed the sleeping habits of 1.1 million adults between the ages of 30 and 102, controlling demographics, habits, health factors and the use of medication. These findings were published in the Feb. 15 issue of the Arichives of General Psychiatry, a journal of the American Medical Association.

The six-year study concluded that the best survival rate was found among those who slept seven hours per night. Those who slept eight or more hours per night had a significantly higher mortality rate, which increases with the amount of sleep over seven hours. Those who slept nine or 10 hours had a mortality rate similar to that of people with moderate obesity.

However, the study did not establish a distinct causality between mortality rates and sleeping longer.

“”It is impossible to be certain of causality with this kind of study,”” Kripke said.

Kripke said he would like to see more research done on the topic.

“”I hope that one day, someone will restrict long sleepers’ intake to see the health effects. Such studies would be needed to determine direct causality,”” Kripke said. “”We are not ready to say that anyone should set their alarms early.””

Many sleep experts have been highly critical of the study and its findings. The National Sleep Foundation, a nonprofit organization interested in promoting healthy sleeping habits, responded critically to the study, especially to the assertion that the risks associated with sleeping pills are far more dangerous than the risks associated with insomnia. The study showed a 25 percent increase in death risk with daily sleeping pill use.

The foundation said that the sleeping pills available during 1982-1988, the time the study was conducted, are different from those available today. The foundation said that this would cause unnecessary alarm among sleeping pill users.

Kripke struck back at his critics by stating they have a conflict of interest.

“”Much criticism is coming from people who receive money from the sleeping pill industry, which are worried that this study won’t help their profits,”” Kripke said.

He also saw hope in the future.

“”We appreciate all of the students who help us with our research and we look forward to seeing a new generation of researchers who will answer all of the unanswered sleep research questions,”” he said.