Nearly two thirds of exceptionally old people have good or very good sleep, working out to around 7.5 hours including naps, says a new study.

Surprisingly, the oldest adults aged 100 and above in the study conducted in China were 70 percent more likely to report good sleep quality than younger participants aged 65 to 79 years. Men were 23 percent more likely than women to report sleeping well.

The odds of reporting good sleep quality also were lower in people who often felt anxious, had at least one chronic disease or struggled with everyday tasks.

"Age and health conditions are the two most important factors associated with self-reported sleep quality and duration," said principal investigator and lead author of the study Danan Gu, faculty of the Nohad A. Toulan School of Urban Studies and Planning, Portland State University, Oregon.

The sample comprised 15,638 adults aged 65 and older, including 3,927 who were between 90 and 99 years of age, and 2,794 who were 100 years of age and older. Participants were spread across 22 provinces in mainland China.

According to the authors, China's population of more than 1.3 billion people includes the largest elderly population in the world, making the country a valuable resource for studying healthy longevity.

The World Bank estimates that China has nearly 40.5 million people who are 75 years of age and older.

Sleep quality was reported in response to the question "How do you rate your sleep quality recently?" Typical daily sleep duration was reported by answering the question, "How many hours on an average do you sleep every day including napping?"

Participants were 84 percent more likely to report sleeping well if they had adequate medical service, and they were 56 percent more likely to report good sleep quality if their family was in good economic condition.

Adults aged 80 and over tended to have a sleep duration that was either shorter or longer than adults aged 65 to 79, which was primarily due to deteriorating health, said a Portland State release.

These findings were published in SLEEP brought out by Associated Professional Sleep Societies LLC, a joint venture of the American Academy of Sleep Medicine and the Sleep Research Society.

Source : timesofindia.indiatimes.com