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Diurnal Drinking

Posted Jan 02 2010 10:09am

Casting a light on circadian disruptions.

Scientists and laypeople alike have known for years that the consumption of alcohol interferes with the body’s biological ability to synchronize its daily activities with light. Disruptions of the body clock due to alcohol increase the risk of cancer, depression, and other health problems. Furthermore, a recent animal study showed that the effect of alcohol on sleeping patterns could be detected several days after the last drinking event.

Alcohol’s chronobiological effects grow more profound as steady consumption continues. Previous research has demonstrated the disruptive function of alcohol on melatonin rhythms, body temperature and glucocorticoid release.  Disturbingly, recent research suggests that such disruptions along the hypothalamic-pituitary-adrenal axis may predispose alcoholics to relapse—a vicious hormonal feedback cycle. In a study on hamsters published in the American Journal of Physiology, researchers at Kent State University and the University of Tennessee describe “a feedback cycle of circadian rhythm deterioration and reinforcing alcohol self administration” mediated by glutamate and NMDA-driven “phase resetting of the circadian clock.”

The study separated drinking from non-drinking hamsters, and subjected both groups to light exposure in order to break up the regular diurnal wake/sleep cycle of the animals.  Hamsters that drank only water during the test woke up 72 minutes earlier than normal, while hamsters drinking 20% alcohol did not reset their internal clocks as acutely, waking up only 18 minutes earlier.

However, as Christine Guilfoy wrote for Medical News Today, “When the hamsters were withdrawn from alcohol for 2-3 days and then exposed to the same light treatment again, they woke up much earlier than the animals that had drunk only water. The hamsters that were withdrawn from alcohol woke up 126 minutes sooner compared to the water drinking control group, which advanced 66 minutes. This exaggerated response persisted even up to three days later, when the experiment ended.”

Bearing in mind that drawing conclusions about human brain behavior from animal studies is unavoidably speculative, what possibilities emerge from this study? From the short-term perspective, the researchers note that people who drink alcohol late at night are probably less likely to respond appropriately to light cues, and therefore less likely to keep their biological clocks synchronized over the next 24 hours. Moreover, this circadian disruption from drinking may continue for several days, like jet lag, even after a complete abstention from alcohol.

The researchers also discovered that the drinking animals had fewer bouts of activity during normally active hours, leading to the suggestions that heavy drinkers may be less active during normally active daytime hours, and more active late at night, when chronobiological systems are signaling for sleep. The result: chronic daytime sleepiness.

The major point of the study may be that “brain systems involved with circadian regulation are closely and reciprocally tied to those underlying alcohol abuse,” and that this connection has been underscored “by recent studies showing a link between circadian clock genes and an increased drive for alcohol consumption.”
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