If you’ve ever worked a swing shift (4pm to 12am) or graveyard shift (12am to 8am), you’re painfully aware of impact they have on your sleeping and eating patterns as a result of the disruption of the body’s circadian clock.
The primary circadian clock, which is responsible for these functions, is located in the brain. Circadian clocks are also located in other body tissues, including the liver, where the clock is charged with regulating blood glucose levels.
A new study from University of Utah researchers, published in Diabetes News Journal online, reveals that dietary iron plays an important role in the liver’s circadian clock.
Study leader Judith A. Simcox, Ph.D., a University of Utah postdoctoral fellow in biochemistry, describes iron as being like the dial that sets the timing of the clock. “Discovering a factor, such as iron, that sets the circadian rhythm of the liver may have broad implications for people who do shift work,” she comments.
Food intake sets the liver’s circadian clock. During sleep, this clock helps maintain a constant blood glucose level, but causes it to spike just before you wake up. When the clock in the liver gets out of synch with the clock in the brain, this may contribute to metabolic diseases, says senior author of the study, Donald A. McClain, M.D., Ph.D., University of Utah professor of medicine (endocrinology) and biochemistry.
In order to identify external signals that set the circadian clock in the liver, McClain and Simcox fed iron to mice as part of their natural eating cycle. They noted that dietary iron increases the cellular concentration of haem, an oxygen-carrying iron compound found in haemoglobin. When haem 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.
While increased activity of a circadian protein is healthy when it occurs in the liver’s natural clock cycle, when it occurs at a time that is out of synch with the circadian clock – such as during a graveyard shift – this may lead to abnormal blood glucose levels.
Eating iron-rich food at night could exacerbate the lack of synchronisation between the clock in the liver and the main clock in the brain. 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.
Numerous studies have found shift workers experience higher incidences of obesity, diabetes and other metabolic disorders. Their risk for cardiovascular disease, stroke and cancer also is higher. In 2007, a World Health Organization subcommittee declared shift work is probably carcinogenic.
More research is needed to see how the results of this study could affect dietary recommendations for everyone, but especially for shift workers. 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.
Written for the Australian Traditional-Medicine Society (ATMS) by Rosemary Ann Ogilvie from materials released by the University of Utah