Researchers from Rush University Medical Center, Brigham and Women's Hospital and Harvard Medical School say they discovered that low doses of caffeine throughout the day are more effective than the traditional method of having a large dose in the morning.
The research, funded by the United States Air Force Office of Scientific Research, wanted to examine how military pilots dealt with night work and duty hours that went longer than 16 hours. The study kept the subjects awake for 28 hours and then allowed them to sleep for 14 hours.
Subjects who took the low-dose caffeine performed better on cognitive tests. They also exhibited fewer accidental sleep onsets compared to placebo subjects.
The Early Show medical correspondent Dr. Emily Senay notes after the study was over, subjects got a full night's rest. It did not interfere with their ability to fall asleep or their ability to stay asleep. And they stopped the caffeine about an hour-and-a-half before they were to go to bed.
The study discovered that caffeine works by thwarting one of two interacting physiological systems that govern the human sleep-wake cycle. Senay notes the caffeine taken in a large amount in the morning may be useless in keeping a person alert for the entire day.
She says, "Theoretically, if you get a good eight hours of rest a night and stay awake for 16 hours, you shouldn't need caffeine to stay awake and alert. But most of us don't have that. When we get up in the morning, we need it, to sort of wake up. As the day goes on, we get drowsier and drowsier. When we really need the caffeine, it's not in our system, which is later in the day."
The researchers reported in the journal Sleep that shift workers, medical residents, truck drivers and others who need to stay awake are better served by low doses of caffeine to get a bigger boost from their tea or coffee.
Senay points out, "The source is very important because different products have different amounts of caffeine, and it can be incredibly variable. Coffee, generally speaking has 95 to 135 milligrams per eight ounces. Tea has 15 to 50, depending how long you steep it for. Soda -- the source of caffeine for teens and a lot of adults -- 35 to 55, and even chocolate has caffeine."