“Caffeine typically blocks adenosine receptors, which is a neurotransmitter that builds through the day to increase sleep pressure by the evening,” Aarti Grover, MD, medical director of the Center for Sleep Medicine at Tufts Medical Center, tells SELF. “Also, caffeine can delay production of melatonin—typically produced three to four hours before natural bedtime—which can also make it harder to fall asleep at the usual time.”
But 217 milligrams is the average amount of caffeine in pre-workout. “The amount of caffeine in pre-workout can vary wildly—100 milligrams to 400 milligrams—so that amount really matters, particularly if you are also consuming caffeine elsewhere,” W. Christopher Winter, MD, a neurologist and sleep medicine physician with Charlottesville Neurology and Sleep Medicine and host of the Sleep Unplugged podcast, tells SELF.
“Caffeine has a half-life of roughly five to seven hours in most adults, but there’s wide variability based on genetics, habitual intake, and liver metabolism,” Scott Keatley, RD, cofounder of Keatley Medical Nutrition Therapy, tells SELF. So, if someone takes a typical pre-workout dose at 2 p.m., they still may have at least 75 milligrams of caffeine active in their system at 9 p.m., he points out. “That’s enough to reduce sleep latency, fragment sleep, or blunt deep sleep,” Keatley says.
Caitlyn Mooney, MD, assistant professor in the department of sports medicine at Vanderbilt University Medical Center, agrees that caffeine is likely the big issue here. “Caffeine is known to block signals that impact sleep onset, shifts our circadian rhythm, and increases our flight or fight reaction…. This can make it harder to fall asleep, stay asleep, and our sleep will be less restorative,” she tells SELF. “Even if one falls asleep okay, they may have poorer-quality sleep, which may still affect their longer-term performance.”
