The study conducted by Professor Renata Riha, from the Department of Sleep Medicine at the University of Edinburgh is published in the Institute for Scientific Information on Coffee.
‘Early in the day, coffee consumption can improve alertness and concentration in individuals with disturbed sleep patterns. People can benefit by drinking low caffeine drinks or decaffeinated coffee during the afternoon and evening.’
Coffee is particularly preferred by those experiencing restricted sleep and those adjusting to new sleep/wake cycles, such as shiftworkers, for increasing wakefulness and concentration. In those affected by limited sleep, regular coffee can effectively improve short-term cognitive impairment brought about by sleep loss.
This was reported in a study that compared decaffeinated coffee to regular coffee and found that consuming 300mg of caffeine (or three cups of coffee) per day can improve vigilance, alertness, reaction-time, accuracy and working memory in the first three days of poor sleep.
Based on a study of emergency medical teams, those working nightshifts can benefit from consuming caffeine as it improves psychomotor performance and vigilance. However, the researchers of this study state that it can later affect sleep quality and duration.
How Does Coffee Improve Alertness?
The main psychoactive compound found in coffee is caffeine, and its effect on alertness is associated with adenosine (a compound found in the body). Adenosine triggers the feelings of tiredness by binding to the adenosine receptors. Adenosine and caffeine have similar structures and caffeine blocks the action of adenosine by binding to the adenosine receptors thereby replacing the feelings of tiredness with feelings of alertness.
As part of a healthy balanced diet and an active lifestyle, moderate caffeine consumption of around 400mg caffeine per day (the equivalent of up to five cups of coffee) can be safely enjoyed.
Women who are pregnant and breastfeeding should limit their caffeine intake to 200mg per day.
Effect of Coffee on Sleep
The action of caffeine on adenosine receptors impact sleep as research suggests that coffee consumption can increase the time taken by an individual to fall asleep and reduce the total sleep time and sleep quality. Specifically, caffeine decreases a deep phase of sleep known as ‘slow-wave’ and can increase wakefulness and arousal from sleep.
The effect of caffeine on sleep depends on the amount of caffeine consumed in the hours before bed and the amount of caffeine consumed over the day. Sleep also depends on the individual susceptibilities and consumption habits.
Genetic makeup can also help determine the response to caffeine, specifically mutation in the gene adenosine A2A receptor gene, ADORA2A. Hence, the same amount of caffeine may affect two individuals differently.
Melatonin is a hormone that promotes sleep, and it was found that coffee consumption in the evening can delay the circadian melatonin rhythm.
The study, which lasted for 49 days, found that individuals who consumed 200mg of caffeine three hours before their usual bedtime experienced a delay to their circadian melatonin rhythm of approximately 40 minutes.
A study conducted in 2020 suggested that consuming 300mg caffeine per day helps preserve attention and cognitive function in the first three-to-four days of restricted sleep in genetically caffeine-sensitive individuals. However, by the fifth and final day, no difference was seen. This study suggests that regular coffee is beneficial in short term period, but it is not a substitute for sufficient sleep.
When Is Coffee Consumption Useful?
Coffee consumption is useful in situations like driving and on occasions where sleep may be compromised, such as those experiencing jet lag, shift workers,especially night shift workers.
Individuals that consume coffee later in the day can benefit by swapping with low caffeine content drinks or decaffeinated coffee during the afternoon and evening. It is important to find the balance between enjoying coffee while limiting consumption close to bedtime for those that are sensitive to the stimulating effects of caffeine.
The author of the study Professor Renata Riha said, “Caffeine is consumed daily by roughly 80% of the world’s population, often for its benefits in promoting wakefulness and concentration. Its effects can last for several hours, depending on how quickly or slowly it is metabolized by the body. Those who find that drinking coffee later in the day disrupts their sleep patterns may wish to swap to low caffeine drinks, or decaffeinated coffee during the afternoon and evening.”
- Coffee and Sleep in Everyday Lives, Institute for Scientific Information (ISIC)