Sleep Experiment Shows the "Graveyard" Shift Is Aptly Named

By Rachel Cernansky | March 3, 2009 4:34 pm

sleep.jpgIt may be old news that people who work the night shift tend to have higher rates of certain medical conditions. But researchers say they have established a direct link between an abnormal sleep cycle and altered hormone levels, which can disrupt metabolism and increase the risk of heart disease, diabetes, and obesity. As soon as their circadian rhythms became separated from a day-night cycle, test subjects’ levels of key metabolic hormones went haywire—the most compelling evidence yet that shift work isn’t just an inconvenience, but an occupational hazard [Wired News].

The study, published in the Proceedings of the National Academy of Sciences, maps a clear path from work-sleep cycles to metabolic disregulation to disease [Wired News]. Scientists cannot yet explain the exact connection between metabolism and the circadian rhythm, the roughly 24-hour cycle that biological and behavioral processes are based on. But they believe the trigger to be a decrease in the hormone leptin, which the body uses to regulate appetite, that results when the circadian rhythm is disrupted.

In the study, the test subjects—five women and five men—were put on a 28-hour cycle, rather than the normal 24. They slept for 9 hours and 20 minutes every day and ate regularly, but were woken up each day four hours later than the previous day. Their blood pressure, heart rate, body temperature, oxygen consumption were measured throughout the day, and blood samples taken hourly while the subjects were awake. Production of leptin was found to have decreased, while glucose and insulin increased, as did blood pressure and cortisol, a hormone linked to stress. The blood sugar of three subjects, who were all previously healthy, even reached prediabetic levels.

Because the total amount of sleep time did not change, researchers concluded that these harmful effects stem from an off-kilter sleep cycle, and not from simply too little sleep…. The new research didn’t measure the quality of sleep, which may be responsible for some of the harmful effects of shift work, [sleep researcher Eve] Van Cauter says. “Shallow, fragmented sleep could be the mediator” [Science News]. Adds study coauthor Frank Scheer: “The surprising finding for us is that even so brief a misalignment caused quite impressive changes” [Wired News].

Related Content:
DISCOVER: 20 Things You Didn’t Know About… Sleep
DISCOVER: Mind Over Time asks whether we can alter circadian rhythms
DISCOVER: Night Owls vs. Early Birds
DISCOVER: 20 Things You Didn’t Know About… Fat

Image: Flickr / basykes

CATEGORIZED UNDER: Health & Medicine
  • Dr. Charles Martin

    Great article about useful research that will undoubtedly help millions. We must do all we can to stop the rising tide of type 2 diabetes, which is now epidemic. Sleep plays a critical role in diabetes care, and we have written extensively about this relationship at

    – Charles Martin, DDS
    Founder, Dentistry For Diabetics

  • Patrick Connor

    I agree with the blood glucose results since my blood work showed a level of 100 making me prediabetic even though my diet is mostly low glycemic foods. Do you have any recommendations for the best time to sleep when working 7p – 7a?

  • Hate Graveyards

    One thing a lot of people overlook regarding working graveyard shift, is the psychological issues that can come about.

    I got switched to the graveyard shift :(
    My wife works days at her job
    We no longer sleep together (rather obviously)
    And worse – after 24 wonderful years, my marriage is starting to suffer!!!

    For the guys out there: If your wife works a day job and you get put on the graveyard shift, do whatever you can to get off it! I have read that married couples often have problems when they work opposite shifts – and from first hand experience, I am in agreement!

  • may

    I love my new job… it’s everything I ever wanted: pay is good, coworkers are great, and the work itself is non-stressful and rewarding. The only problem I have is that I work graveyard. I strongly dislike working days at my company. Everyone is in a foul mood and many of my coworkers are just rude, there is too much chaos, and too much pressure. However, my neighborhood is loud, so I can’t sleep well during the day. I have had to put Aluminum foil on my windows to block out the sun. The weather is gorgeous and I’m 1 minute from the ocean. I live in a place where there is always something to do and yet I can never do anything! I have no life and it drives me crazy! So what to do – leave a job I like and have a life? Or keep the job and .. well, keep feeling this way… I am torn!


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