If you're someone who usually has a lot of trouble getting to bed at night and feels sleep-deprived during the day, it may not be just that you're gulping down too many espressos or are addicted to Jimmy Fallon's monologues. You may be part of the minority with an abnormality in your circadian rhythm — that is, the neural master body clock that regulates your periods of alertness and sleepiness. Normally, that rhythm, which is partly genetic but also influenced by environmental signals such as light and darkness, runs pretty close to the 24-hour cycle of the Earth's rotation.
For years, researchers have been amassing evidence that abnormal circadian rhythms have some pretty worrisome effects. Not only can they result in poor sleep, but also are related to health problems such as obesity, diabetes, depression, bipolar disorder and seasonal affective disorder, according to the National Institutes of Health. And to make matters worse, a new study in Proceedings of the National Academy of Sciences says that evolution actually tends to weed out individuals with genetic mutations that throw their master body clocks out of kilter.
If you've got a circadian rhythm abnormality, this all might seem like pretty depressing news. But don't worry! There's also an upside, according to one of the scientists involved in the study: If you've got ambitions of joining NASA and exploring or even terraforming another planet, you may be unusually well qualified. But more on that later — first, let's dig into the findings of that new research.
In the recent study, a team of researchers from Holland, Germany and Great Britain studied two groups of mice — one with a normal, roughly 24-hour circadian rhythm, and another group with a genetic quirk called the tau mutation, which shortened their cycle by up to four hours. They released the rodents in equal numbers to outdoor pens with free access to food, and then watched the animal populations over the next 14 months.
The scientists found that over the course of the study as the animals reproduced, mice with the abnormal circadian rhythm gradually became less and less common. By the end, they decreased from 50 percent of the population to just about 20 percent. Additionally, their lifespans were shorter than the normal mice as well.
"Collectively, these disappearance rates suggest that natural selection operates to eliminate genotypes expressing a circadian oscillation that is not in resonance with the period of the earth's rotation," wrote the scientists.
Kamiel Spoelstra, a postdoctoral researcher in animal ecology at the Netherlands Institute of Ecology, and one of the study's authors, says via email that it's not clear precisely why the mutant mice with shorter circadian rhythms fared so poorly. Hamsters with the same genetic mutation tend to develop renal and cardiac disease, he notes. But regardless, he says that having an out-of-sync internal master clock probably has a similar effect on humans.
"If your endogenous circadian rhythm substantially deviates from the overt light/dark cycle, you basically suffer from a permanent jet lag," Spoelstra explains. "You need to keep shifting your rhythm in order to keep in pace. It may well be comparable with the negative effects of shift work, which has been linked to an increase in cancer and diabetes risk."
The Silver Lining Brings Us to Space
But as we alluded to previously, there's one advantage to having an off-kilter circadian rhythm. But to take advantage of it, you'll need to join NASA, which is planning a manned expedition in the 2030s to Mars, where a Martian day lasts longer than one here on Earth. However, those circadian rhythms would have to be slightly longer rather than shorter, meaning Mars would be more hospitable to those who are night owls here on Earth (by a slight degree).
"Astronauts with an abnormally slow rhythm — and therefore longer than 24 hour, so an abnormally long circadian period — are best suited, as the day on Mars is longer than 24 hour," says Spoelstra. "It's not unlikely that astronauts with a rhythm of around 24 hours and 39 minutes — the Martian day length — can be found, as there's most likely considerable natural variation in circadian period in the population."
Those astronauts presumably would be healthier and better-rested than counterparts with normal (for Earth) circadian rhythms. We don't know if NASA will begin searching for such candidates, but the space agency already is studying how space affects astronauts' sleep patterns, by having space travelers wear Fitbit-like monitors to track their rest.
Sorry, morning people. Looks like you early birds will have to keep getting that worm here on Earth.