Discussion of causes and consequences of sleepiness among college students, 2014

Dear editor I was recently directed to, “Causes and consequences of sleepiness among college students”, from Hershner and Chervin.1 As a psychologist who specializes in treating college student sleep problems, I was very pleased to see this article. Overall, it is a gem: thorough, well-conceived, and thoughtful. However, I have concerns about two sections. First, on page 74, Hershner and Chervin1 write, “How much sleep a young adult needs is not clearly known, but is thought to be 8 hours.” They then cite Wehr et al2 as well as Van Dongen et al.3 These choices are surprising as reference for the assertion that young adults need approximately 8 hours of sleep. The Wehr et al article makes no such assertion. No mention of demographics is given whatsoever of the 15 subjects included in their study, so it is surprising to make an assertion about sleep need for any particular age group based on their work. Van Dongen et al3 seems to come closer. While the authors do not assert an 8-hour sleep need, they use 8 hours as a baseline for sleep for their subjects. However, this group of 48 subjects are aged 21–38, and no further information is given about their demographics. While it is possible that the average age of participants could be vaguely similar to college-aged students, it is a stretch to assume that this population represents college-aged students without more information. There is a great deal of research regarding young adults, late adolescents, and sleep need. I expected references to Mary Carskadon’s work, 4,5 to the 2010 Wolfson article6 looking at emerging adults’ sleep, as well as Galambos et al7 focusing on the four university years and how students in different years sleep. Research with adolescents has shown a sleep need of 9 ¼ hours, and most college students are nearer to adolescence than they are to adulthood.4,5 While it is true there is no clear agreed-upon sleep need for college students, it seems important to reference those who are doing important work in the area of sleep need. My second concern is on page 76. Hershner and Chervin1 include a brief, much needed section about caffeine and energy drinks. I believe there are two flaws in this section. The first one is the attention to energy drinks. While somewhat varied in caffeine amounts, energy drinks are actually much more consistently caffeinated than coffee. While a handful of energy drinks break the rule, most of them are caffeinated at the rate of 10 mg/fluid ounce. Coffee, on the other hand has no limitations placed on it. While the US Food and Drug Administration tries to keep a control on energy drinks and energy shots (10 mg/fluid ounce, and 100 mg/fluid ounce, respectively), there are no limits on the caffeine in coffee. In my opinion, the argument against energy drinks is not as important as an argument against the very common, very strong coffee that is now sold everywhere. This leads to the second difficulty with the caffeine section. Hershner and Chervin1 refer to the Walsh et al article8 and cite their finding that, “caffeine, equivalent to 2–4 cups of coffee taken at night can increase sleep latency on average from 6.3 to 12.1 minutes […]”. Looking at the Walsh article, each of their experiments includes participants drinking 300 mL (about 10 ounces) coffee with 4 mg of caffeine per kilogram of body weight. To put this in American college student terms, a 120 pound person would be drinking 217 mg of caffeine; a 180 pound person would be drinking 326 mg of caffeine in that experiment. Walsh et al were presumably giving participants a dose equivalent to 2–4 cups of coffee as it was brewed in 1990, in one 10 ounce cup. Because coffee was brewed with less caffeine at the time of Walsh et al’s article8 200–320 mg of caffeine was consistent with 2–4 cups of regular coffee. It was commonly described at that time that a standard cup of coffee was 8 ounces and would have about 80–100 mg of caffeine (10 mg/ounce). Due to changes in the coffee market, caffeine in coffee has changed since 1990. The prevalence of coffee brewed very strongly has never been as it is today. In addition, the size of the average “cup” of coffee has nearly doubled since 1990; it certainly is not eight ounces anymore. At most coffee stores it is difficult to find an 8-ounce cup of coffee. Among the college students I meet with, the most common sized coffee purchase seems to be 16 ounces or larger. The issue here is that 1990 coffee is not the same as 2016 coffee in size or strength. When Hershner and Chervin1 write that “caffeine, equivalent to 2–4 cups of coffee taken at night can increase sleep latency on average from 6.3 to 12.1 minutes”, they miss the point that cups of coffee today are not what they were 25 years ago. A more clear way of saying this is that 200–300 mg of caffeine can increase sleep latency, which is about equivalent to 12–16 ounces of today’s premium coffee (Table 1). Table 1 Amount of caffeine in popular commercial coffee I greatly appreciate Hershner and Chervin’s1 article. I believe it provides a thorough and thoughtful review of a tremendous amount of information related to college students and their sleep. My hope is that in the future, articles that discuss caffeine and caffeinated beverages and products could cite the likely amount of caffeine rather than the number of “cups”, and then encourage caffeine users to be curious about how much caffeine is contained in what they are drinking.