Workers punching in for the graveyard shift may be better off not eating high-iron foods at night so they don't disrupt the circadian clock in their livers.
Disrupted circadian clocks, researchers believe, are the reason that shift workers experience higher incidences of type 2 diabetes, obesity and cancer. The body's primary circadian clock, which regulates sleep and eating, is in the brain. But other body tissues also have circadian clocks, including the liver, which regulates blood glucose levels.
In a new study in Diabetes online, University of Utah researchers show that dietary iron plays an important role in the circadian clock of the liver. Judith A. Simcox, Ph.D., a University of Utah postdoctoral fellow in biochemistry, is the study's lead author.
"Iron is like the dial that sets the timing of the clock," Simcox says. "Discovering a factor, such as iron, that sets the circadian rhythm of the liver may have broad implications for people who do shift work."
Each of the body's circadian clocks operates on its own schedule to perform its necessary functions. The circadian clock in the brain, for example, is set by light, telling people to wake up in the morning and sleep when it's dark. Ideally all the body's clocks would work on their correct schedules. But, as anyone who has ever been on a graveyard or swing shift knows, working off-hours can cause one's circadian clocks to get out of synch and disrupt sleeping and eating patterns.
Numerous studies have found that shift workers experience higher incidences of obesity, diabetes and other metabolic disorders. The risk for cardiovascular disease, stroke and cancer also is higher among those workers. In 2007, a World Health Organization subcommittee declared that shift work is probably carcinogenic.
External Signals
The liver's circadian clock is set by food intake. As people sleep this clock helps maintain a constant blood glucose level, but then causes it to spike just before they wake up. When the clock in the liver gets out of synch with the one in the brain, it may contribute to metabolic diseases, according to Donald A. McClain, M.D., Ph.D., University of Utah professor of medicine (endocrinology) and biochemistry and senior author on the study.
McClain and Simcox wanted to identify external signals that set the circadian clock in the liver. They fed iron to mice as part of their natural eating cycle and observed that dietary iron increases the cellular concentration of heme, an oxygen-carrying iron compound found in hemoglobin. They found that when heme binds to a circadian protein–a substance whose function Simcox likens to that of a cog in a mechanical clock–the protein's activity increases and causes the liver to optimally control blood glucose levels.
Increased activity of a circadian protein is healthy when it occurs in the liver's natural clock cycle. But if this happens at a time that is out of synch with the circadian clock, such as during a graveyard shift, it could result in abnormal blood glucose levels.
"When a shift worker eats foods high in iron at night it could exacerbate the lack of synchronization between the clock in the liver and the main one in the brain," says McClain, who's also the University Health Sciences' associate vice president for clinical research and director of the Center for Clinical and Translational Science. "By tending to flatten the circadian variation of metabolism, high iron in tissues may also interfere with the normal day to night fluctuations associated with a healthy metabolic system."
More research is needed to see how the results of their study could affect dietary recommendations for everyone, and shift workers in particular. The investigators are quick to point out that too little iron is also unhealthy. Ultimately, they hope their studies define an optimal range of iron that is much narrower than the current "normal" range.
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Workers punching in for the graveyard shift may be better off not eating high-iron foods at night so they don't disrupt the circadian clock in their livers.
Disrupted circadian clocks, researchers believe, are the reason that shift workers experience higher incidences of type 2 diabetes, obesity and cancer. The body's primary circadian clock, which regulates sleep and eating, is in the brain. But other body tissues also have circadian clocks, including the liver, which regulates blood glucose levels.
In a new study in Diabetes online, University of Utah researchers show that dietary iron plays an important role in the circadian clock of the liver. Judith A. Simcox, Ph.D., a University of Utah postdoctoral fellow in biochemistry, is the study's lead author.
"Iron is like the dial that sets the timing of the clock," Simcox says. "Discovering a factor, such as iron, that sets the circadian rhythm of the liver may have broad implications for people who do shift work."
Each of the body's circadian clocks operates on its own schedule to perform its necessary functions. The circadian clock in the brain, for example, is set by light, telling people to wake up in the morning and sleep when it's dark. Ideally all the body's clocks would work on their correct schedules. But, as anyone who has ever been on a graveyard or swing shift knows, working off-hours can cause one's circadian clocks to get out of synch and disrupt sleeping and eating patterns.
Numerous studies have found that shift workers experience higher incidences of obesity, diabetes and other metabolic disorders. The risk for cardiovascular disease, stroke and cancer also is higher among those workers. In 2007, a World Health Organization subcommittee declared that shift work is probably carcinogenic.
External Signals
The liver's circadian clock is set by food intake. As people sleep this clock helps maintain a constant blood glucose level, but then causes it to spike just before they wake up. When the clock in the liver gets out of synch with the one in the brain, it may contribute to metabolic diseases, according to Donald A. McClain, M.D., Ph.D., University of Utah professor of medicine (endocrinology) and biochemistry and senior author on the study.
McClain and Simcox wanted to identify external signals that set the circadian clock in the liver. They fed iron to mice as part of their natural eating cycle and observed that dietary iron increases the cellular concentration of heme, an oxygen-carrying iron compound found in hemoglobin. They found that when heme binds to a circadian protein–a substance whose function Simcox likens to that of a cog in a mechanical clock–the protein's activity increases and causes the liver to optimally control blood glucose levels.
Increased activity of a circadian protein is healthy when it occurs in the liver's natural clock cycle. But if this happens at a time that is out of synch with the circadian clock, such as during a graveyard shift, it could result in abnormal blood glucose levels.
"When a shift worker eats foods high in iron at night it could exacerbate the lack of synchronization between the clock in the liver and the main one in the brain," says McClain, who's also the University Health Sciences' associate vice president for clinical research and director of the Center for Clinical and Translational Science. "By tending to flatten the circadian variation of metabolism, high iron in tissues may also interfere with the normal day to night fluctuations associated with a healthy metabolic system."
More research is needed to see how the results of their study could affect dietary recommendations for everyone, and shift workers in particular. The investigators are quick to point out that too little iron is also unhealthy. Ultimately, they hope their studies define an optimal range of iron that is much narrower than the current "normal" range.
Explore further: Biological clock disruptions increase breast cancer risk, study finds
Medical Xpress on facebook
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Biological clock disruptions increase breast cancer risk, study finds
Oct 17, 2014
The disruption of a person's circadian rhythm—their 24-hour biological clock—has been linked to an increased risk of breast cancer, according to new University of Georgia research. The culprit, in this study in particular, ...
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Oct 16, 2014
Organisms ranging from bacteria to humans have circadian clocks to help them synchronize their biological activities to the time of day. A study published by Cell Press October 16th in Cell now reveals that gut microbes in mic ...
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May 03, 2012
International travellers, shift workers and even people suffering from obesity-related conditions stand to benefit from a key discovery about the functioning of the body's internal clock.
The circadian clock is like an orchestra with many conductors
Mar 27, 2014
You've switched to the night shift and your weight skyrockets, or you wake at 7 a.m. on weekdays but sleep until noon on weekends—a social jet lag that can fog your Saturday and Sunday.
Nutrition influences metabolism through circadian rhythms
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A high-fat diet affects the molecular mechanism controlling the internal body clock that regulates metabolic functions in the liver, UC Irvine scientists have found. Disruption of these circadian rhythms may contribute to ...
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18 hours ago
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Getting enough magnesium in the diet may reduce the risk of diabetes, especially for those who already show signs of heading that way.
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Oct 16, 2014
I exercise, stay slim and think I am reasonably careful about my diet. Subtract the dark-chocolate habit and minus the Cheetos cravings, I make fairly good choices. So I was shocked to learn that my fasting blood sugars were ...
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Oct 14, 2014
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User comments
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