It is now clear that chronobiology is increasingly important in defining human health. But be careful: the biological clock that marks the times of the organism is particularly sensitive and must be protected, also because its alterations would not only affect sleep rhythms but could also be associated (therefore without a well-defined cause-effect relationship) with processes of cognitive decline.
This is according to a study that shows how people whose daily rhythms were weaker, more fragmented or tended to concentrate activities towards the end of the day would have a much higher risk of developing dementia. The findings suggest that staying in sync with natural sleep and activity cycles may play a key role in brain health as we age. The scientific investigation appeared in Neurology, the journal of the American Academy of Neurology,
Elderly people under control
The research followed 2,183 adults with an average age of 79, who did not suffer from dementia at the start of the study. Each participant wore a small heart rate monitor attached to their chest for an average of 12 days. These devices monitored periods of rest and activity, allowing the researchers to analyze circadian rhythms. The participants were then followed for approximately three years. During this period, 176 people were diagnosed with serious cognitive impairment.
To understand the role of the biological clock, scientists coordinated by Wendy Wang at the UT Southwestern Medical Center in Dallas examined heart rate monitor data using various indicators of the intensity of the circadian rhythm. A key measure was relative amplitude, which reflects the difference between the times of day when a person is most active and least active. Higher relative amplitude indicated a stronger and clearly defined daily rhythm. Participants were divided into three groups based on the intensity of the rhythm. Comparing the stronger and weaker groups, 31 of 728 people in the high-pace group developed dementia, while 106 of 727 people in the low-pace group did not.
After accounting for factors such as age, blood pressure and heart disease, the researchers found that subjects in the slowest rhythm group had an almost two-and-a-half times higher risk of dementia. Each standard deviation drop in relative amplitude was related to a 54% increase in dementia risk. Regarding the time of peak activity in the day, people whose activity peaked in the afternoon, i.e. after 2.15pm, showed a higher risk than those whose activity peaked earlier, around 1pm and 2pm. A later peak activity could reflect a discrepancy between the internal biological clock and environmental signals such as daylight and darkness.
What can be done
Circadian rhythm refers to the body’s natural time system. It controls the 24-hour sleep-wake cycle and helps regulate key functions such as hormone release, digestion and body temperature. This internal biological clock is driven by the brain and responds to environmental signals, especially light. When circadian rhythms regulate the situation appropriately, the organism remains closely aligned to the daily cycle of light and dark. This leads to consistent sleep and activity patterns, even when times or seasons change. Alterations in circadian rhythms can also alter bodily processes such as inflammation and interfere with sleep, potentially increasing amyloid plaques linked to dementia or reducing amyloid clearance from the brain.
In short: weaker rhythms make the biological clock more sensitive to interruptions. People with less stable rhythms are more likely to change their sleep and activity schedules due to changes in routine or daylight.
“Our study measured these rest-activity rhythms and found that people with weaker, more fragmented rhythms, and people with activity levels that peaked later in the day, had a higher risk of dementia. Future studies should examine the potential role of circadian rhythm interventions, such as phototherapy or lifestyle changes, to determine whether they can help reduce the risk of dementia.”
is Wang’s comment.
