For most people, the genetic picture is more muddled. While circadian disruptions like these - resulting from a single, misprinted gene - offer scientists a unique opportunity to study the genetic basis of sleep timing, they are rare. and feel sleepy by 7 or 8 in the evening. People with this condition are extreme morning larks - they wake up around 4:30 a.m. In 2001, for instance, scientists at the University of Utah identified a genetic mutation responsible for a disabling circadian disruption called familial advanced sleep phase syndrome. Similar genetic variants have been found in people. Jerry Feldman, then at SUNY Albany and now at UC Santa Cruz, found similar mutations in Neurospora crassa, a type of red bread mold. And, yet another abolished the circadian rhythm altogether. In the 1970s and 80s, CalTech scientists Seymour Benzer and Ronald Konopka identified a genetic mutation in fruit flies that compressed the circadian clock. Typos in the genetic code can speed up or slow down the clock other tweaks shift it earlier or later. Nearly all living things - from humans to fruit flies to bacteria - run on a roughly 24-hour internal clock. But, in a world built for morning larks, night owls and even middle-of-the-road chronotypes can experience disastrous health consequences. Access to electricity has pushed our sleep timing back and expanded the range of individuals’ sleep preferences. The Mozambique study, and others like it, show how malleable and adaptable our circadian rhythms are. In the last three decades, scientists have identified a slew of genes linked to chronotype, our individual internal clock that governs when we sleep and when we feel most alert. Even our preferred bedtime is rooted in our DNA. Our circadian rhythms - the roughly 24-hour cycles of sleep and wake - are baked into our genes. The study offers a microcosmic glimpse of the way our environment affects our sleep - for better or worse - and how sleep patterns have changed over the course of human history. “In understanding sleep patterns, you really need to consider the socio-cultural and environmental factors and context in which people are sleeping,” Knutson says. To Knutson, the study highlights the challenges of examining how a single factor - access to electricity - affects sleep. Surprisingly, it was the Tengua villagers who slept worse, likely because they slept on mats on the floor and slept with more family members to a room. Access to electricity may change when we go to bed but “it doesn’t necessarily have to lead to poor sleep quality,” the Northwestern Feinberg School of Medicine’s Knutson says. But they didn’t lose any sleep or sleep poorly as a result - their sleep timing simply shifted later. Indeed, Milange residents went to bed and woke up almost an hour later than people in Tengua. It stood to reason that more light at night could disrupt sleep patterns, says study author Kristen Knutson. Light sets our internal clocks, signaling that it’s time for activity. The residents were taking part in a study led by an international team of researchers examining how access to electricity affects sleep. Others lived and worked about 20 miles away in the small market town Milange, the only locale in the larger district with access to electricity. Those living in the rural village of Tengua spent long days in the fields where they grew maize and tended livestock. The wrist-worn devices recorded their movement, sleep, and light exposure as they went about their day. Lighting Up the Nightįor two weeks in 2016, residents of two towns in Mozambique donned activity trackers. But, work and school schedules haven’t really changed. In doing so, it’s pushed our sleep timing back and expanded the range of individuals’ sleep preferences. Access to electricity has offered new opportunities for things at night.
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