A growing body of scientific evidence is drawing attention to the role of the body’s internal clock in brain health. A new study conducted in the United States indicates that individuals with weaker or more irregular circadian rhythms may face a substantially higher risk of developing dementia later in life.
The findings were published in Neurology, the medical journal of the American Academy of Neurology, and add to increasing concern that long-term disruption of biological rhythms could contribute to neurodegenerative disease.
Understanding the circadian system
Circadian rhythms are internal 24-hour cycles that regulate a wide range of physiological processes, including the sleep–wake cycle, hormone release, digestion and body temperature. These rhythms are coordinated by the brain and are strongly influenced by exposure to light, particularly natural daylight.
When circadian rhythms are robust, daily patterns of sleep and activity tend to remain stable, even in the face of seasonal changes or altered routines. In contrast, weaker or fragmented rhythms are more susceptible to disruption, leading to irregular sleep patterns and fluctuating activity levels.
Temporary disturbances such as jet lag or shift work are known to affect sleep quality and mood, but repeated or prolonged disruption has been associated with broader health consequences.
Age-related changes and neurological vulnerability
Circadian rhythms naturally weaken with age. Older adults often experience earlier bedtimes, earlier waking and more fragmented sleep. Previous research has suggested that these changes may be linked to an increased risk of neurodegenerative conditions, including dementia.
According to the study’s lead author, Wendy Wang, Assistant Professor of Epidemiology and Internal Medicine at UT Southwestern, alterations in circadian rhythms are a recognised feature of ageing and may represent a modifiable risk factor for cognitive decline.
Study design and key findings
The research followed more than 2,000 participants in the United States, with an average age of 79 years. None had dementia at the start of the study. Participants wore small activity-monitoring devices for approximately two weeks, allowing researchers to assess daily patterns of rest and activity and to measure the strength and regularity of their circadian rhythms.
Over a follow-up period of three years, 176 participants developed dementia. The researchers categorised individuals into three groups based on the robustness of their daily activity rhythms.
The analysis revealed that participants with the weakest circadian rhythms were nearly two and a half times more likely to develop dementia than those with the strongest rhythms. In addition, individuals whose peak activity occurred later in the day—after approximately 14:15—had a 45 per cent higher risk of dementia compared with those whose activity peaked earlier.
Researchers noted that delayed activity patterns may cause misalignment between the body’s internal clock and environmental cues such as daylight and darkness, potentially contributing to long-term neurological stress.
Implications for dementia prevention
Dementia represents a growing global health challenge. In 2019, an estimated 55 million people worldwide were living with the condition, including around 11 million in Europe, according to data from European health authorities. With ageing populations, this number is expected to rise sharply in the coming decades.
The authors of the study suggest that their findings may help guide future research into preventive strategies aimed at strengthening circadian rhythms. Interventions such as light therapy, melatonin use and lifestyle adjustments are already being explored in other contexts and may hold promise for reducing dementia risk.
Lifestyle measures and future research
Evidence from clinical and epidemiological studies indicates that maintaining regular sleep schedules, engaging in consistent physical activity and ensuring exposure to natural light—particularly in the morning—can support healthy circadian function. These approaches are considered non-invasive and accessible for most individuals.
The researchers emphasise that further studies are needed to determine whether actively improving circadian alignment can delay or prevent the onset of dementia. However, the findings underscore the growing recognition that the body’s internal clock may play a crucial role in long-term brain health.
As research continues, circadian rhythm regulation is increasingly being viewed not only as a matter of sleep quality, but as a potential pillar of dementia prevention strategies in ageing societies.