Investing in good-quality sleep during early- and middle-adulthood may be key for a good memory later in life, according to a new study published in the journal Perspectives on Psychological Science.
The link between sleep and cognitive functioning has been extensively researched, with a large body of evidence indicating that the quantity and quality of our sleep can have profound effects on learning and memory. Research suggests that sleep helps learning and memory in two distinct ways. First, a sleep-deprived person cannot focus attention optimally and therefore cannot learn efficiently. Second, sleep itself has a role in the consolidation of memory, which is essential for learning new information.
While much research has focused on the short-term effects of sleep and sleep deprivation on memory and learning, in recent years scientists have become increasingly interested in the role of sleep across the lifespan.
The benefits of sleep during early adulthood are remarkable and unmistakable. One example is that a particular kind of “deep sleep” called “slow-(brain)-wave-sleep” helps memory by taking pieces of a day’s experiences, replaying them and strengthening them for better recollection.
By the time we reach middle age, more sleep during the day — such as an afternoon nap — also becomes important for strengthening memory and protecting against its decline — as long as those naps don’t cut into nighttime sleep. But as we grow older, we tend to wake up more at night and have less deep sleep and dream sleep — both of which are important for overall brain functioning.
Those findings raise an “alluring question,” said Michael K. Scullin, Ph.D., director of Baylor’s Sleep Neuroscience and Cognition Laboratory, who led the new study.
“If sleep benefits memory and thinking in young adults but is changed in quantity and quality with age, then the question is whether improving sleep might delay — or reverse — age-related changes in memory and thinking,” said Scullin, assistant professor of psychology and neuroscience in Baylor’s College of Arts & Sciences.
Good sleep quality early, not later, in life helps protect against age-related cognitive declines
Scullin’s team conducted a comprehensive review of more than 200 studies dating back more than half a century, which analyzed the association between sleep and cognitive functioning. Study participants were divided into three age groups: young (ages 18-29), middle age (ages 30-60) and old (ages 60 and older).
The researchers assessed self-reported data on how many hours, on average, the participants sleep each night, how long it takes them to go to sleep, the frequency at which they awake during the night, and how tired they feel during the day.
Results of the analysis revealed that young and middle-aged participants tend to get more sleep and better quality sleep than older adults, and this appears to benefit their cognitive functioning later in life. “We came across studies that showed that sleeping well in middle age predicted better mental functioning 28 years later,” notes Scullin.
Good sleep quality among participants in their 70s, 80s and 90s, however, appeared to have little effect on their memory, the analysis revealed.
“We interpret the literature as suggesting that maintaining good sleep quality, at least in young adulthood and middle age, promotes better cognitive functioning and serves to protect against age-related cognitive declines,” say the authors.
“It’s the difference between investing up front rather than trying to compensate later,” adds Scullin.
People sometimes disparage sleep as ‘lost’ time,” he said. But even if the link between sleep and memory lessens with age, sleeping well in later life can still promote better physical and mental health, and reduce the risk and severity of an array of other disorders, said Scullin. For instance, sleep deficiency is associated with increased risks of heart disease, kidney disease, hypertension, diabetes, stroke and obesity. Sleep is also involved in healing, growth, hormonal balance and maintaining a strong immune system.