Research from the Mayo Clinic has found that adults who have abnormal sleeping habits and the associated disruptions of their daytimes have a greater risk of developing dementia and mild cognitive impairment later on.
The researchers followed 1,282 normal women through their elderly years, and found that those women whose peak circadian rhythm activity occurred later than normal had an 83% increased risk of either contracting dementia or mild cognitive impairment later in life.
The women's peak circadian rhythm activity was measured using wrist actigraphy. Wrist actigraphy uses a small device worn on the wrist to measure a person's motor activity throughout the day and night. The highest level of motor activity during the day illustrates the person's peak circadian rhythm activity. Motor activity also peaks during the night, but its daytime peak is determined by one's sleep patterns.
A delayed peak circadian rhythm activity time is produced when a person typically goes to bed significantly later at night, and thus their energy levels are higher later in the day as compared to a person who goes to sleep earlier in the evening. The peak daytime activity time will typically occur earlier in the day and fall off through the day.
While some people are night-owls and tend to go to bed later, this research was focused on altered sleep-wake patterns, meaning one who must also sleep later into the morning in order to get enough sleep, or simply does not get enough sleep and awakens earlier in the day. The research focused upon the effects during the next day. The research also measured what is called disrupted daytime activity, meaning the person doesn't not have a typical daytime activity peak amplitude (volume).
In addition to the delayed and disrupted sleep-wake cycle, the research also found that those who have less daytime motor activity – also measured by wrist actigraphy – have a 57% increased risk of dementia or MCI. In addition, those with less energy ("robustness") during the day also have an 57% increased risk of dementia or MCI.
These parameters do not relate simply to when we go to bed, but also how well we sleep. A person who sleeps deeper will typically have higher motor activity levels during the day. As far as sleep duration, this is another matter altogether. There are other studies that show, surprisingly, that eight hours of sleep may not be the optimal amount of sleep after all.
Learn the facts about healthy sleep and how to sleep deeper using natural strategies.
Schlosser Covell GE, Dhawan PS, Lee Iannotti JK, Hoffman-Snyder CR, Wellik KE, Caselli RJ, Woodruff BK, Wingerchuk DM, Demaerschalk BM. Disrupted daytime activity and altered sleep-wake patterns may predict transition to mild cognitive impairment or dementia: a critically appraised topic. Neurologist. 2012 Nov;18(6):426-9. doi: 10.1097/NRL.0b013e318272f7ef.
Adams C. Natural Sleep Solutions for Insomnia: The Science of Sleep, Dreaming, and Nature's Sleep Remedies. Logical Books, 2012.