Are you a lark, someone who likes being up and active in the early morning? Do you do your best work early in the day, and do you wind down in the evenings toward a relatively early bedtime? Or are you a night owl, someone who tends to wake later and perhaps gains energy and focus as the day progresses, someone who likes to work (and play) in the evening hours?
Whether you're inclined toward one direction or another -- or find yourself somewhere in the middle -- these tendencies feel deeply ingrained. Scientists have been exploring for some time the notion that the circadian rhythms that regulate the sleep-wake cycle and many other of the body's biological processes are influenced by our genes. Studies involving twins have provided evidence that our genes have a significant influence over sleep patterns and circadian rhythms. Scientists have in recent years identified a "wake up" gene that is believed to be responsible for activating the body's biological clock in the morning.
Now a team of researchers from the United States and Canada has identified a specific genetic variant that appears to determine whether a person will be an early bird, a night owl, or somewhere in the middle. The specific type of genetic variation an individual possesses may influence the tendency to rise earlier or later by as much as 60 minutes.
Another significant finding? This gene variant -- so common that it is present in most of the population -- may also determine the time of day a person is likely to die.
This information could have important implications for the treatment and monitoring of illness and disease, as well as for preventative medicine.
The study that resulted in this genetic discovery began a number of years ago. Researchers studying disrupted sleep patterns among older people were looking for pre-disease markers that could be associated with the eventual onset of Parkinson's disease and Alzheimer's disease. This study involved 1,200 healthy men and women aged 65. Their evaluation included annual neurological exams and psychiatric exams, as well as ongoing monitoring of sleep-wake cycles and activity levels using a wrist monitor. Participants to this study also had agreed to donate their brains to the research project upon their death, so that scientists could gather additional information related to sleep-wake cycles.
In the course of their research project, scientists learned that the same group of volunteers had also had their DNA genotyped -- a process of identifying differences in individual genetic makeup. With these data, researchers were able to compare data on patients' sleep-wake cycles with their genetic profiles, which led to their significant discovery.They found that variations to a gene called PER1 -- part of a group of genes that affects circadian rhythms -- are strongly linked to circadian timing, and to the tendency toward living as a night owl or a lark. Variations to this gene are so common, according to researchers, that nearly the entire population possesses one of several variants:
- 60 percent of the population has a variant called adenine (A)
- 40 percent of the population has a variant called guanine (G)
- 48 percent of the population will have a combination of A and G
- 36 percent of the population will have two As
- 16 percent of the population will have two Gs
According to the study results, people with the AA genotype -- the early birds -- tended to wake up 60 minutes earlier than those with the GG genotype. The third group -- AG -- tended to split the difference and wake right in the middle of this 60-minute timeframe.
How does this gene variant -- and its influence on circadian timing -- affect a likely time of death? Our circadian rhythms are at work in regulating a broad range of biological processes affecting our health and basic functioning. Research has shown that circadian clocks play a role in influencing the timing of major medical events such as heart attacks. Scientists describe what they call a circadian rhythm of death, which results in people generally being more likely to die in the earlier part of the day. The average time? 11 a.m.
Looking at the study population, researchers found that AA genotypes and AG genotypes tended to die around this most typical 11 a.m. time. The GG genotypes -- the night owls -- tended to die much later in the day, on average at around 6 p.m.
This is some fascinating and important research. There's more to study and to learn about how our individual genotype affects our circadian timing, but this knowledge could be applied in any number of ways to manage health and the treatment of disease. This information could be used to help people create sleep-healthy schedules, particularly for shift workers and people who travel frequently and experience jetlag -- that's everyone from a national sales rep to a major league ballplayer. Also, physicians could use this knowledge to create targeted treatment and prevention programs, using this information about when an individual is most vulnerable, to time procedures, medications, and exercise.
We all can do ourselves a favor by paying attention to our natural tendencies for sleeping and waking, and using this information in making our daily schedules work for our sleep and our health.
Michael J. Breus, PhD
The Sleep Doctor™
Everything you do, you do better with a good night's sleep™
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