People with unstable “internal clocks” have a higher risk of developing dementia, according to a study conducted by a team of scientists in the United States.

Circadian rhythms are the body’s “internal clocks” that regulate the sleep–wake cycle, body temperature, and digestion.

In people with stable circadian rhythms, the internal clock closely matches the 24-hour day. Such individuals tend to maintain a clear and regular schedule of activity and rest, even when their workload or the season changes, Euronews reports.

By contrast, when circadian rhythms are weak, changes in lighting conditions and daily routines can throw the body’s clock off course.

With age, circadian rhythms weaken or at least change: older adults generally go to bed and wake up earlier, and their sleep becomes more fragmented.

The study involved more than 2,000 people in the United States with an average age of 79. None of the participants had dementia at the start of the study. Doctors monitored their daily activity patterns over a three-year period.

During that time, 176 participants developed dementia.

Researchers divided the participants into three groups based on the strength and type of their circadian rhythms.

They found that the risk of developing dementia among people in the group with the weakest rhythms was almost 2.5 times higher than in the group with the most stable daily schedules.

In addition, individuals whose activity peaked later in the day — after 2 p.m. — had a 45% higher risk of developing dementia than “early birds.”

Summarizing the findings, the researchers concluded that preventing dementia and other neurodegenerative diseases requires a regular sleep schedule, the use of melatonin, physical exercise, and exposure to natural light, especially in the morning.