A recent study led by the University of Colorado Boulder and the Medical Research Council’s Laboratory of Molecular Biology in Cambridge, England reveals that drinking caffeine in the evening delays the internal biological clock that regulates our sleep-wake patterns. The researchers showed that consuming quantities of caffeine equal to those in a double espresso, or an equivalent amount, before going to bed induced a delay of 40 minutes in the approximately 24-hour human circadian clock.

Caffeine Hazards: Insights Into Human Physiology

It has been known that caffeine affects circadian rhythms of primitive species, such as algae and the fruit fly. The team demonstrated, for the first time, how caffeine alters ‘cellular timekeeping’ of human cells, remarked 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.

Wright commented that the study, published in Science Translational Medicine, had managed to uncover new and exciting aspects of how the most widely used psychoactive drug in the world influenced human physiology.

Caffeine Hazards: Investigating Various Influences Of Caffeine

Five participants – two women and three men – were recruited for a double-blind, placebo-controlled 49-day protocol via CU-Boulder’s Sleep and Chronobiology Laboratory. The participants were tested under four scenarios: low light and a placebo pill, low light and caffeine equal to a 200 mg pill (depending on the participants weight), bright light and a placebo pill, and bright light with the caffeine pill.

Samples of saliva were taken and tested periodically for levels of melatonin – the hormone produced naturally by the pineal gland when stimulated by the ‘master clock’ found in the brain. The master clock is re-set when exposed to light, and regulates biological clocks found in the human body. Normally, increased melatonin signals the onset of ‘biological nighttime’, and decreased levels indicate ‘biological daytime’.

Those given the caffeine pill under low-light had an approximately 40-miunte delay in the nighttime circadian rhythms, as compared to those taking the pill under bright light. The degree of delay from the dose was about half of the delay experienced by the participants after a three-hour exposure to bright light at the start of their usual bedtime.

Moreover, bright light alone, and coupled with a dose of caffeine triggered delays in circadian phases – 85 minutes and 105 minutes respectively. No significant differences were seen between the low light/caffeine combination and the bright light/placebo combination.

Bringing In Reporter Genes

In order to measure caffeine-induced changes, researchers also used ‘reporter genes’ that made cells ‘glow’ when their biological clock genes were expressed. Results suggest that caffeine blocks cell receptors of adenosine, a neurotransmitter that generally promotes sleep and represses arousal.

According to Wright, these results might explain why drinking caffeine at night turns people into ‘night owls’ – going to bed late and waking up late. This might also lead to the development of treatments for certain circadian sleep-wake disorders. Also, travelers could benefit from the study as well; properly timed consumption of caffeine could help regulate their circadian clocks according to the direction (time-zone) they are flying in.