Published on: December 28, 2017
by Women’s Brain Health Initiative:
A good night’s sleep is one of life’s greatest pleasures for many people, and for good reason—it leaves you feeling fantastic in the morning. That refreshed and energized feeling you have isn’t the only reason to love sleep, though; sleep is critically important for the healthy functioning of every part of your body, including your brain. Yet, many older adults experience insufficient and/or disrupted sleep. As many as 50-60% of adults 60 years old and older report having sleep difficulties. And research suggests that poor sleep is having a huge negative impact on their brain health.
The impact of poor sleep
A study by Lim et al., published in Sleep in 2013, looked at the effects of sleep fragmentation on a group of 737 older adults (who did not initially have dementia) over a period of up to six years. The researchers found that higher levels of sleep fragmentation were linked with higher rates of cognitive decline and an increased risk of developing Alzheimer’s disease.
Sleep fragmentation also affects the size of the brain; individuals experiencing the most fragmented sleep were found to have the smallest brain volume in their frontal lobes, an area important for higher thought.
Other studies looking specifically at respiratory disturbance during sleep (such as sleep apnea) have found that the presence of sleep-disordered breathing is linked to an earlier age of onset for cognitive decline, and that sleep-disordered breathing can lead to dementia. Each time someone with sleep apnea stops breathing, they experience a decrease in blood oxygenation. This intermittent hypoxia (i.e., oxygen deficiency) has a significant negative impact on the brain since neurons in the brain have a high demand for oxygen. Hypoxia has been found to increase production of amyloid beta (Aβ), which is one of the changes found in the brains of people with Alzheimer’s disease.
Sleep-disordered breathing doesn’t just affect healthy brains though, it also appears to accelerate the progress of cognitive decline in existing dementia patients. A study by Aoki et al. and published in the Journal of Sleep Research in 2014 examined how the cognitive function of 111 people already diagnosed with dementia was impacted by respiratory disturbance during sleep. These researchers found a strong association between the severity of sleep-disordered breathing and the severity of dementia. An interesting additional finding was related to age; participants younger than 80 years old were more susceptible to cognitive dysfunction associated with sleep-disordered breathing than those over 80 years of age.
Learning more about poor sleep and cognition
A new study recently launched at Western University in London, Ontario will examine the effects of sleep, and sleep deprivation, on the brain. “The ability to function on just a few hours of sleep is a socially-acceptable point of pride for many people, symbolic of their ability to push through fatigue to get lots accomplished,” pointed out the lead researcher for the study, neuroscientist Dr. Adrian Owen. “Yet those people fail to realize that sleep is essential for health and productivity.”
Although we do know that skimping on sleep isn’t wise, there is much we still don’t know about the specifics of how sleep impacts brain health. This study seeks to drastically expand our knowledge by studying a large number of people—hundreds of thousands of participants from around the world. Some of the questions the study will explore include: how much sleep is enough, what are the short- and long-term effects of insufficient sleep on brain health, and is the impact of sleep deprivation the same across all age groups?
Study participants will track their sleep over a 3-day period and play a series of scientifically-valid tests of brain function online. If they are interested, participants can check in after three days, and see how their sleep and cognitive performance compare with other volunteers’. Researchers will then analyze the collective data and share the results within approximately six months.
“Some early participants have completed the brain-game tests and been monitored with functional MRI scans when well rested and after a sleepless night. Since that type of extensive testing is impossible to do with large numbers of people, we designed the current online study to draw out equivalent information on an exponentially larger scale,” explained Dr. Owen. “The Internet allows us this unprecedented opportunity to involve the public in scientific research.” If you would like to participate in this study, visit http://worldslargestsleepstudy.com and click on “Enroll Now.”
The effects of too much sleep
So, brain health is negatively impacted by insufficient or disrupted sleep, but getting too much sleep can be a problem as well. Researchers from Madrid, Spain and New York, USA conducted a three-year study of more than 2,700 people in their 60s and 70s. Participants’ brain function was tested using the mini-mental state examination (MMSE) at the beginning of the study and again at the end. In between, they kept a detailed diary of their sleeping patterns.
Participants were grouped into three categories, “normal” sleepers who got six to eight hours of sleep each night, “long” sleepers who got more than nine hours of sleep a night, and “short” sleepers who slept five hours or less each night. Although all three groups got lower scores at the end of the study than at the beginning, the long sleepers experienced the most decline in their cognitive test scores. These study results were published in the Journal of Psychiatric Research in December 2013.
A more recent study—by Westwood et al. and published in Neurology in 2017—found that prolonged sleep may predict dementia risk. The researchers examined data from the Framingham Heart Study and discovered that individuals who consistently slept 9+ hours a night had double the risk of developing dementia in 10 years compared to those who slept less. They also found that the long sleepers had smaller brain volumes. These results only show a link between sleep duration and dementia risk, though, not cause and effect; more research is needed to determine whether dementia might be caused by excessive sleep, or if excessive sleep is a symptom of dementia. For now, the researchers were able to conclude that prolonged sleep duration may be an early indicator of neurodegeneration, and thus might be a useful clinical tool doctors could use to identify who is at higher risk of developing dementia.
The effect of sleeping position
Length and quality of sleep aren’t all that matters; it looks like sleeping position might be important, too. Researchers from Stony Brook University in the USA (Lee et al.) have discovered that sleeping on your side, rather than your back or stomach, may help reduce the risk of developing Alzheimer’s and other neurological diseases. The brain has a complex system for clearing wastes and other harmful substances—including amyloid beta (Aβ) and tau proteins, both associated with Alzheimer’s disease—called the glymphatic pathway. This pathway works most efficiently while we are at rest, i.e., during sleep or anesthesia. The researchers used magnetic resonance imaging (MRI) to observe the glymphatic pathway in anesthetized rats when placed in different sleeping positions. They also used radiotracers to study the influence of body position on the clearance of Aβ. They found that waste removal, including Aβ, was most efficient in the lateral (side) position. It is important to remember that these findings, which were published in the August 5, 2015 issue of the Journal of Neuroscience, have not been tested in humans yet.
Women and men differ when it comes to sleep
Making the study of this subject even more complex is the fact that women and men are different in many ways when it comes to sleep. An article exploring sex and gender differences in sleep health was published in 2014 in the Journal of Women’s Health. Some of the differences noted include:
The researchers, Mallampalli et al., emphasized, “There is a great need for scientists and clinicians to consider sex and gender differences in their sleep research to account for the unique biology of women.” They also note that differences may not only be driven by biological factors but also by differences in the way women and men report their symptoms.
Pink Noise is a Potential Tool for Improving Sleep and Memory
Researchers at Northwestern University have found that gentle sound stimulation synchronized to the rhythm of brain waves significantly improved deep sleep in older adults and improved their scores on a memory test. Thirteen people, aged 60 to 84 years, took part in the study, the results of which were published in March 2017 in Frontiers in Human Neuroscience. Each participant listened to one night of acoustic stimulation (pulses of pink noise delivered during the rising portion of each slow brain wave oscillation) and one night of “sham stimulation” (no noise). Participants took a memory test at night and again in the morning, for both the real and sham stimulations. The test assessed their ability to recall words.
The acoustic stimulation enhanced deep sleep for participants, an important benefit since deep sleep tends to decrease substantially starting in middle age yet it is critical for memory consolidation. The acoustic stimulation also improved memory recall ability. While recall ability after the sham stimulation improved by a few percent, the average improvement after the pink-noise stimulation was three times higher, leading the researchers to believe that this method could be a useful intervention for longer-term use in the home.
Source: MIND OVER MATTER – V5
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