According to Men’s Health,
A new study, caffeine loses its effectiveness when you are continually short on sleep. Researchers aren’t totally sure why the effects of caffeine are stunted after you’re short on sleep for a few days but they think it may have something to do with how caffeine works. When caffeine binds to the receptors in your brain for a sleep inducing chemical called adenosine, it makes you feel more alert but when you’re continually sleep deprived your body produces more adenosine. Lead study author Tracy Jill Doty, Ph.D., research scientist at Walter Reed Army Institute of Research, says it’s possible that these extra molecules are pushing the caffeine away from the receptors, preventing their stimulating effects. Doty did note that more research needs to be done to determine whether increasing the caffeine dosage can help.
Hmmm…and all this time I thought caffeine helped to keep you awake. But it doesn’t work if you’re lacking sleep.