Add one more insult to the injury of working the night shift: Drinking coffee during work hours may just keep you awake during the day.
"Caffeine is the most widely used stimulant to counteract sleepiness, yet it has detrimental effects on the sleep of night-shift workers who must slumber during the day, just as their biological clock sends a strong wake-up signal," said Julie Carrier, a University of Montreal psychology professor. "The older you get, the more affected your sleep will be by coffee."
Carrier bases the claim on a small lab study, however, so more research would be needed to verify the results with a larger group and in a real-world setting.
The study involved 24 people split into two age groups: 20 to 30 years old, and 45 to 60. The participants spent two sleepless nights in lab rooms. Then, they were given either a caffeine pill or a placebo, so that they did not know if they'd had caffeine or not. Three hours later they were allowed to sleep.
All subjects who consumed caffeine pills had their sleep negatively affected, especially older participants who slept 50 percent less than usual. In both age groups, caffeine decreased sleep efficiency, sleep duration, slow-wave sleep (SWS) and REM sleep, the researchers said in a statement.
"We all know someone who claims to sleep like a baby after drinking an espresso, Carrier points out. "Although they may not notice it, their sleep will not be as deep and will likely be more perturbed."
Night-shift work is bad for health, other studies have found. The new study suggests everyone over age 40, and particularly night-shift workers, should reduce caffeine consumption.
The study, funded by the Canadian Institutes of Health Research and other institutions, is detailed in the journal Sleep Medicine.
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