"Sleep Age" Infers Lonq-Term Health.

• Position: LONGEVITY

Numbers tell a story. From your credit score to your age, metrics predict a variety of outcomes, whether it is your likelihood to get a loan or your risk for heart disease. Now, Stanford University Department of Medicine researchers have described another telling metric, one that can predict mortality. It is called sleep age.

Sleep age is a projected age that correlates to one's health based on his or her quality of sleep. So, for instance, if you analyze the sleep characteristics of dozens of 55-year-olds and average them out, you will have an idea of what sleep looks like at that age. For instance, someone who is 55 and sleeps soundly through the night with good quality REM cycles could, theoretically, have a sleep age of 45.

Emmanuel Mignot, professor of sleep medicine, and his colleagues analyzed some 12,000 studies, each of which focused on the characteristics of a person's sleep, such as chin and leg movement, breathing, and heartbeat. Their goal was to develop a system that assigns one's sleep age and, using machine learning, identifies the variations in sleep most closely linked to mortality.

Generally speaking, people sleep differently at different ages, with changes in sleep quality being one of the first and most well-documented signs of aging and poor health. "When you sleep, you're disconnected from sensory inputs. You're ideally not being bothered by the noisy external world or bright lights," notes Mignot.

"During sleep, it's not just the brain that's going through an automatic program, but heart rate and breathing also change, and variations in these can be early predictors of a health disturbance. We spend about one-third of our lives sleeping, so it's a substantial component of our general well-being. It's well known that, in pretty much any disorder, sleep is one of the first things that is disturbed. For example, about five or 10 years before other symptoms appear in Parkinson's disease patients, a specific sleep disturbance occurs during which the patient violently acts out dreams, shouts, or punches into a wall."

As for the study, "our main finding was that sleep fragmentation--when people wake up multiple times throughout the night for less than a minute without remembering it--was the strongest predictor of mortality. Though we see a link in the data, how it contributes to mortality is unknown. This is different from a person realizing they were waking up, which happens during sleep disorders such as insomnia...