Strong coffee first thing in the morning after a lousy night's sleep might seem like a good idea, but it actually isn't, researchers say. The reason? The combination reduces glucose tolerance, so it's a much better idea to have breakfast first, then coffee, the team reports in the British Journal of Nutrition. Each of the 29 participants in the randomized crossover study consumed a sugary drink in the morning after experiencing (randomly, on separate occasions) each of three sets of experimental conditions: a typical night's sleep, a disrupted night's sleep, and a disrupted night's sleep followed by a strong black coffee. The sugary drink was intended to simulate the calorie intake of a typical breakfast. As measured by oral glucose tolerance tests, mean peak glucose and mean peak insulin were significantly higher in participants after the fragmented-sleep-plus-coffee experience, vs fragmented sleep only. "The present study demonstrates that one night of hourly sleep fragmentation had no effect on next-day insulin sensitivity or glucose tolerance, relative to a habitual night of sleep, in young, healthy men and women," Harry A. Smith, a PhD student at the Centre for Nutrition, Exercise and Metabolism at the University of Bath, in the U.K., and colleagues write. "However, consumption of caffeinated coffee after sleep fragmentation increased glucose incremental area under the curve by approximately 50%." In an email to Reuters Health, Smith cautioned, "The findings of this acute study would not apply to someone routinely doing this, as it is more likely that there would be a shift in their circadian rhythms (i.e., body clock) to adapt to this routine." It has been well established that sleep deprivation or broken or fragmented sleep can impair glucose clearance and insulin sensitivity. Further, the researchers note, a single serving of caffeinated coffee has been shown to "acutely impair postprandial glucose metabolism in both normal-weight and overweight individuals." The participants' mean age was 21, they had no diagnosed metabolic disease, and all slept in their own beds for the experimental conditions. Sleep fragmentation was caused by audible alarms every hour on the hour throughout the night, followed by multiple text messages from a researcher that required simple responses before the participant could fall asleep again. Under the fragmented-sleep-plus-coffee portion of the study, participants drank a cup of instant coffee containing about 300 mg of caffeine about an hour after waking up. The sugary drink consumed in each part of the study contained about 75g of glucose. Dr. Robert Gabbay, chief scientific and medical officer for the American Diabetes Association, told Reuters Health by e-mail, "Sleep deprivation is important and worsens diabetes control and the resistance to the effects of insulin." Caffeine is known to raise blood sugar in some individuals, he continued, whether they do or do not have diabetes. Research data generally suggest that coffee consumption lowers the risk of diabetes, probably because "in part, caffeine and coffee have a number of other effects beyond the one studied here," such as coffee drinkers being more active in the morning. Dr. Gabbay, who was not involved in the study, concluded, "Caffeine's effects on blood glucose are complex, but this study represents some interesting new data, the clinical significance of which is somewhat unclear." —Scott Baltic Source
