New Research: Late-Night Caffeine Disrupts Natural Sleep-Circadian Rhythms

Most of us have likely observed what happens when we have a cup of coffee with dinner, but new research suggests that imbibing caffeine can have more deleterious effects on our sleep cycle than we may have thought.

A study led by the University of Colorado Boulder and the Medical Research Council’s Laboratory of Molecular Biology in Cambridge, England has shown for the first time that caffeine delays our internal circadian clock that lets us know when to get sleepy, and when to be awake.

Though you may not have to worry if you’re having a normal cup of coffee. Researchers discovered that the amount of caffeine in a double espresso consumed three hours before bedtime can delay our sleep cycle by 40 minutes.

They found in the study that our ‘cellular timekeeping’ is affected by drinking caffeine in the later part of the day. Research conducted previously showed these effects on other creatures like algae and fruit flies, but now it is clear that human cells are affected by caffeine as well.

CU-Boulder Professor Kenneth Wright, who co-led the study with John O’Neill of the Medical Research Council’s Laboratory of Molecular Biology (LMB) in Cambridge, commented:

“This is the first study to show that caffeine, the mostly widely used psychoactive drug in the world, has an influence on the human circadian clock. It also provides new and exciting insights into the effects of caffeine on human physiology.”

A paper discussing these findings will be published in the Sept 16 issue of Science Translational Medicine.

Study Details

Five human participants, 3 female, and 2 male, were tested under 4 conditions:

• Low light and a placebo pill
• Low light and the equivalent of a 200-milligram caffeine pill dependent on the subject’s weight
• Bright light and a placebo pill
• Bright light and the caffeine pill in a double-blind peer-reviewed study

Saliva samples were then taken to track melatonin hormones, which help us regulate our biorhythms for sleep and wakefulness. When we produce melatonin, it is an indication that the pituitary gland is working properly to set our “master clock.” Normally, melatonin levels in the blood increase to signal the onset of biological nighttime during each 24-hour period and decrease at the start of biological daytime.

Those who took the caffeine pill under low-light conditions were found to have a roughly 40-minute delay in their nightly circadian rhythm compared to those who took the placebo pill under low light conditions, said Wright.

Additionally, researchers used “reporter” genes that made cells glow when the clock genes were expressed to measure changes caused by caffeine. It was apparent that the group consuming caffeine suffered from blocked cell receptors of the neurotransmitter adenosine, which normally promotes sleep and suppresses arousal.

If you must drink coffee or other caffeinated drinks, it looks like it would be best to do so in the mornings, to make sure your normal sleep cycles are not impaired. And don’t forget: there ARE numerous coffee health benefits to be aware of.