How Shift Work Can Hurt Us

A new sleep study explains why sleeping at odd hours can be harmful to your health.

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Previous studies have shown that working the graveyard shift places you at a greater risk for heart attacks and may even shorten your life span.

Scientists know that part of the reason may be work that alters natural sleep-wake cycles impacts circadian rhythms, interfering with your body's physiological rhythms. Researchers at the University of Surrey, England sought to explain just how these shifts occur at the molecular level.

"We know that shift work is associated with negative health consequences such as cardiovascular problems and that we don't feel well when we're jet-lagged. This [study] shows how important that rhythmicity is for our body and how much of an impact it can have on us when this natural cycle is altered," Derk-Jan Dijk, a senior author of the study on sleep, told the Telegraph.

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The study involved 22 subjects, 11 men and 11 women, who were placed under observation at a clinical research center.

Circadian rhythms are controlled by our master clock in a region of the brain called the hypothalamus. Your body temperature, hormone levels and even your mood are affected by this body clock. But there isn't just one clock. Different organs throughout the body, from the heart to the kidneys have their own clock and perform different functions accordingly. These rhythms go awry when sleep patterns change.

"It's chrono-chaos. It's like living in a house. There's a clock in every room in the house and in all of those rooms those clocks are now disrupted, which of course leads to chaos in the household," Dijk told the BBC.

For three days, researchers forced study participants off of their normal sleep-wake cycle, delaying sleep by four hours each night — four, then eight, then 12 hours — until in the final cycle, subjects were sleeping during the day and awake at night. The researchers regularly took blood samples and analyzed them and found that the timing of sleep directly impacted genes and biological processes that are tightly bound to circadian rhythms and gene expression. Both genes that are more active during the day and those that are more active at night were affected.

During the three-day period, the body's internal clock, which can be studied by observing melatonin levels which follow a 24-hour pattern, remained on track.

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The blood samples offered other clues to changes in biological processes. Part of the role of genes is to create codes which guide cells in producing proteins and other molecules. More than 6 percent of the participants' gene transcripts followed a 24-hour rhythm, which is in line with previous research. After three days, only 1 percent of the participants' genes demonstrated this cyclical pattern.

"So what we're starting to see is that some aspects of rhythmicity in some parts of the brain are still intact, but in other parts of the body the rhythmicity is disrupted," Dijk told The Scientist.

This disruption in rhythmicity could explain some of the negative health outcomes researchers have found in shift workers and other daytime sleepers.

The study was published by the journal PNAS (Proceedings of the National Academy of Science) on Monday.

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