As well as less creepy things, like when you wake up in the morning
PROBLEM: The 24-hour day is inscribed in our biology -- our bodies contain inner circadian clocks that keep time and regulate the rhythms of various functions and behaviors. In part, this clock can be affected by the environment, such as when we travel to a different time zone and adjust to new hours of darkness and light. But other aspects of our circadian rhythm, such as what time of day we're most alert, appear to have a genetic component.
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METHODOLOGY: Researchers at Beth Israel Deaconess Medical Center in Boston borrowed data that had been collected 15 years ago from a sleep study at Rush University in Chicago. Unintentionally, that study turned out to be perfect for this new research. First, its subjects had worn a device, called an actigraph, that provided detailed information about their sleep-wake patterns. Second, the subjects were all over the age of 65 when the study was originally done. So by the time the Harvard researchers got to them, many had passed away. They had all also agreed to donate their brains to science. Because of this, the researchers knew their precise times of death. Finally, in the course of the many physical and psychological evaluations undergone by the subjects, they had also had their DNA sequenced.
Using all of this information, the researchers at Beth Israel were able to compare the differing circadian cycles of 537 of the original participants with variations in their genetic makeup. They then replicated their findings with a second group of 38 younger individuals who had been part of a different study at Brigham and Women's Hospital.
RESULTS: The researchers isolated a single nucleotide that appeared to be responsible for significant differences in wake-sleep behavior. Those with an A-A genotype tended to wake up a full hour earlier than those with a G-G genotype. Those with a combination -- A-G -- would wake up almost exactly in-between the other two groups.
This gene, according to the researchers, affects virtually all of us. We have about a 36 percent chance of being A-A, or early risers, a 16 percent chance of being G-G, or late sleepers, and a 48 percent chance of falling in the middle.
Looking back at the participants' time of death, the differences became more extreme. Consistent with most of the population, the A-A and A-G genotypes died in the late morning, just before 11 a.m. The G-G genotypes died just before 6 p.m., representing a 6 hour variation. Intriguingly, the authors hypothesize that the social commitments that would usually normalize people of varying circadian rhythms became irrelevant as the subjects approached death, allowing them to drift toward their natural states.
IMPLICATIONS: More relevant than allowing us to channel our inner Nate Silver and predicting the time of people's death, understanding people's individualized rhythms can allow us to reschedule things like school and work hours to help people function at peak efficiency. From a medical perspective, diseases that have been shown to correspond to our circadian cycles, like stroke, epilepsy, and tumor growth, may turn out to involve this same gene.
The full study, "A Common Polymorphism Near PER1 and the Timing of Human Behavioral Rhythms" is published in the journal Annals of Neurology .
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