The sleep of participants was monitored during a night in a sleep lab. Then they stayed awake in the lab for 25 hours. While awake they were given caffeine capsules. Then their sleep was monitored again as they slept during the day.
Results show that daytime sleep was worse after taking caffeine. Measures such as sleep efficiency and sleep duration were lower.
So does this mean that people who work the night shift should avoid caffeine? Not necessarily.
The participants were given caffeine late during the night. They took a 100-mg dose three hours before attempting to sleep during the day; they were given another 100-mg dose only one hour before daytime sleep.
The stimulating effect of caffeine can last for hours. So it’s no surprise that their sleep was affected.
But an AASM task force report concluded that your sleep is unlikely to be disrupted if you take caffeine at least eight hours earlier. And other studies show that caffeine helps improve the performance and alertness of night-shift workers.
A study in the journal Sleep in 2006 found that combining caffeine with an evening nap provided the greatest benefit. Before a simulated night shift, participants were given a nap opportunity at 7:30 p.m. Their average nap duration ranged from 73 to 99 minutes.
At about 10:30 p.m. they were given 4 mg/kg of caffeine. The authors reported that this dose has been shown to be effective without interfering with daytime sleep.
A 4 mg/kg dose means that you take 4 mg of caffeine for each kg of body weight. So the dose would be about 272 mg if you weigh 150 pounds, 318 mg if you weigh 175 pounds, and 363 mg if you weigh 200 pounds.
A second part of the study involved actual night-shift workers who took 300 mg of caffeine at the start of each night shift. It also found that caffeine and napping improved performance and reduced sleepiness.
On Tuesday the Sleep Education Blog reported that another option for night-shift workers is to follow a “compromise” sleep schedule.