Here’s an important finding about sleep as we age. A review from the University of California, Berkeley suggests that some seniors lose the ability to get deep, restorative rest, and this contributes to medical conditions including depression and dementia.

People who wake up multiple times during the night can miss out on the deep stages of sleep and that can cause a vicious cycle.

Medical conditions and the treatments for them, can be the cause of sleep problems, but poor sleep can also contribute to disease. Researchers say that when it comes to dementia, deep sleep helps "clear" the brain of the amyloid-beta proteins that build up in people with the disease .Similar cycles may be at work with other diseases, too. And while the study authors don’t want people to panic if they are sleeping less than they used to – they advise consulting a doctor if you routinely sleep less than six hours a night, or lack long "consolidated" blocks of sleep.

A healthy diet and exercise are critically important especially because regular exercise contributes to better-quality sleep.

Bottom line: the researchers say sleep is a key factor in successful aging.