Amy Wolfson knows sleep. An energetic woman with short, curly brown hair, the professor of psychology at the College of the Holy Cross serves on the board of the National Sleep Foundation, is the author of The Woman's Book of Sleep, and has spent much of her career studying sleep. When I met her in her office on the verdant campus on a hill overlooking Worcester, Massachusetts, she told me sleep is undervalued in American culture. "We spend at least a third of our lives asleep," she said, "but often we don't get enough sleep, and I'm interested in the ramifications of that."
Sleep disruption is a well-known side effect of caffeine use, but it is highly variable. Some people can drink coffee until the moment they turn in and sleep like babies. Others need to stop drinking caffeine by noon, or they will lie abed, gnashing their teeth, hearts thumping in their chests, thoughts racing. This brings us back to one of caffeine's conundrums: It is a fantastic drug for treating the symptom of sleepiness, but it can lead to increased sleepiness by interfering with sleep.
"Sleep researchers have been . . . I would almost use the word 'guilty,' of sometimes giving a confused message with regard to caffeine," Wolfson told me. "Caffeine is sometimes recommended as a sleep countermeasure, recommended for the military, recommended for pilots, recommended for train drivers, et cetera. I have colleagues that have devoted their careers to looking at countermeasures to sleepiness that aren't sleep.
From Caffeinated: How Our Daily Habit Helps, Hurts, and Hooks Us by Murray Carpenter. Reprinted by arrangement with Plume, a member of Penguin Group (USA) LLC, a Penguin Random House Company. Copyright © Murray Carpenter, 2015. Available on Amazon.
"And then at the same time, you have the insomnia researchers that have for decades said, 'Oh, caffeine is a bad thing. For three to five hours before you are going to try to fall asleep, make sure you have caffeine out of your system.' For individuals who suffer from insomnia, they are given lectures in cognitive behavioral treatment programs to stay away from caffeine. So we have had a kind of love-hate relationship with caffeine. At least in the field of sleep research."
Wolfson told me she is especially interested in adolescents' caffeine use and the relationship between caffeine and a population of sleepy teens, which researchers are starting to scrutinize. In 2006, Maryland researchers found an association between caffeine use and adolescents who have trouble sleeping and feel tired in the morning. Wolfson and a colleague found a similar trend when they surveyed high school students about caffeine use. The students in a high-caffeine group – who took caffeine from coffee, energy drinks, and sodas – reported more daytime sleepiness, expected more energy enhancement from caffeine, and said they used it to get through the day.
Looking at younger caffeine consumers, a team of Nebraska researchers surveyed 228 parents and found that their five- to seven-year-old children drank approximately 52 milligrams of caffeine daily, and eight- to twelve-year-old children drank 109 milligrams daily. Those children who used the most caffeine slept fewer hours.
Wolfson believes the emergence of the new generation of energy drinks is related to a population of sleepy teens, and that excessive caffeine use by young people is part of a larger problem.
"I don't think that every person who stops at Starbucks on their way to work or Dunkin' Donuts, or, as we do in my house, brew our Peet's Coffee every morning, is necessarily sleep deprived," she said. "But there may be a group that is getting an inadequate amount of sleep, and probably a higher percentage of adolescents than adults, who are going to be at risk for gravitating toward those products."
Caffeine's sleep-disrupting properties are so reliable that researchers sometimes use it to induce insomnia in healthy subjects. And it does not take a whopping dose to affect sleep. Swiss scientist Hans-Peter Landolt used an electroencephalogram to measure brain wave activity in healthy subjects who took two hundred milligrams of caffeine (less than three SCADs) in the morning. By that night's bedtime, the morning caffeine was still affecting the subjects. The effects were small, and not severely sleep disruptive, but they were there. Bedtime reactions to caffeine may also hinge on stress—among people who are not insomniacs, caffeine has a stronger effect on those who are vulnerable to stress-induced sleep disturbance.