When you sleep well, you’re making a long-term investment in the health of your memory as you age. That’s one important takeaway from a significant new study on the relationship of sleep to cognitive function. Scientists at Baylor and Emory universities reviewed a wide body of research—roughly 200 studies conducted over more than 50 years—that examined the role that sleep plays in memory and other cognitive processes. Their analysis found that making high-quality sleep a priority during youth and middle age may help guard against age-related cognitive decline, including problems with memory, many years later.
Both sleep and memory change with age. Understanding these changes—as well as how these two vital processes interact over time—can put a focus on how we might best use our sleep for overall health and for memory in particular.
The phrase “sleep like a baby” exists for good reason. When we’re young, sleep often comes easily. Generally, during our younger years we sleep more soundly, experience fewer awakenings, and spend more time in the most restorative and rejuvenating phases of sleep: deep sleep and REM sleep. Very young children, of course, spend a great deal of time asleep. Newborns typically sleep 16 to 20 hours of every 24-hour day. Throughout childhood and adolescence, the need for sleep is higher than for adults. So is the amount of time spent in deep sleep, or slow-wave sleep. As we age throughout adulthood, we spend gradually less time in slow-wave sleep, and also in REM sleep, in favor of more time spent in the lighter stages of sleep.
One study of age-related changes to sleep showed that young adult men spent about 20 percent of their overall nightly sleep time in slow-wave sleep, compared with only 5 percent for middle-aged men. The age-related reductions in slow-wave sleep seen in this study came with corresponding increases to time spent in sleep stages 1 and 2, both phases of light sleep. Between middle age and old age, the study showed no significant change to amounts of slow-wave sleep. However, sleep became significantly more fragmented. Each additional decade of age brought an average 28 minutes of additional time spent awake at night. During these years, both light sleep and REM sleep declined.
What impact could these age-related sleep changes have on memory? We’re increasingly aware that slow-wave sleep provides important benefits to memory function, including helping with acquisition and consolidation of memories. REM sleep, too, has been shown to be important for the creation and consolidation of certain forms of memory, including procedural memories and memories that are emotionally charged and complex. The age-related drop in slow-wave sleep and REM sleep likely play a role in diminishing the brain’s memory function compared to our younger selves. It’s also clear that overall sleep quality and sleep quantity matter for memory function. The tendency to sleep less with age, as well as to experience more fragmented sleep, may all contribute to age-related declines in memory function. Sleep disorders that may have a negative influence on memory, such as insomnia and obstructive sleep apnea, also become more likely with age.
Studies have linked age-related changes to sleep with memory changes. In particular, research has shown a link between reduced slow-wave sleep and having trouble holding on to memories. Sleep fragmentation has also been associated with age-related memory problems. With age, changes and disruptions to the body’s internal clock become more likely and more pronounced. Research indicates these disruptions may contribute to problems with memory.
Some research indicates that the memory benefits of sleep may be the largest when you’re young, which is another reason to make the investment now in sleeping well. Research indicates that with age, memory consolidation becomes less dependent on sleep, and that older adults may develop some resistance to the memory-impairing effects of sleep deprivation and sleep fragmentation. This doesn’t mean sleep isn’t a priority for older adults. But it does indicate that the earlier years of life may be key to building a healthier brain later in life. One of the highlights from the very recent study out of Baylor? Some of the studies that were analyzed showed that experiencing high-quality sleep during middle age predicted stronger cognitive function decades later.
Is sleep the only factor in age-related memory decline? Not at all. Physiological changes including slower neural growth, decreased blood flow to the brain, and deterioration within the brain combine with stress, poor diet, and lack of physical activity to influence deterioration of memory over a lifetime. But sleep is one important factor that you can easily influence. How?
First, commit to a healthy sleep routine. That means creating a sleep schedule that is consistent, and involves time for seven to eight hours of sleep on a nightly basis. Second, change behaviors that undermine your sleep. Whether it’s cocktails every night, or staring at a brightly lit computer screen until bedtime, lifestyle choices make a critical difference to how well you sleep. Make sleep-friendly choices in your everyday behavior and you’ll reap the benefits of sound sleep at night. Third, don’t ignore sleep problems. If you’re not sleeping well, or if you’re feeling tired during the day despite a full night’s sleep, discuss these issues with your physician. Don’t be reluctant to ask for a referral to a sleep specialist. Treating sleep problems now may help you avoid memory difficulties down the road.
Memory is our link to the world, and to our sense of self. It provides us with a dynamic living record of our personal histories, a map to the way the world works, and a sense of time and place that grounds us and gives us meaning. For all these reasons, memory is well worth caring for and protecting. Sleeping well can help you do just that.