Australasian Science: Australia's authority on science since 1938

Rise and Shine, Soldier!

By Tim Hannan

Army research suggests that the timing of your caffeine hit is more important than the amount consumed.

CC0 Public Domain

The detrimental effects of insufficient sleep on cognition and performance are well established, and include lessening of attention, memory and problem-solving skills. It is also well-known to both scientists and the public that caffeine tends to reduce these cognitive and behavioural consequences of limited sleep, a finding that has led to caffeine becoming the world’s most popular stimulant.

However, in order both to maximise its efficacy and to reduce the overall intake, the timing and amount of caffeine consumed should be adapted to important sleep variables such as the amount of sleep loss and the length of time the person has been awake. While research has previously provided little guidance on how to make decisions about these matters, a series of recent studies by US Army researchers have now developed a specific algorithm for predicting the amount and timing of caffeine consumption to maximise performance.

Caffeine has long been known to benefit daily performance, especially after periods of reduced or inadequate sleep. Numerous neuropsychological studies have shown that caffeine enhances performance on a range of cognitive tasks, including on tests of attention, memory and executive (“frontal lobe”) functioning. The effect is particularly marked for individuals who experience prolonged periods of restricted sleep.

A significant proportion of this research has been conducted on military personnel who are required to perform effectively during extended periods of reduced sleep. It has been shown that while caffeine is effective at reducing the consequences of insufficient sleep, it is critical that the right amount be consumed, and at the right time.

To address this problem, a team of US researchers started with the well-supported theory that performance is affected both by the circadian cycle and by homeostatic processes. Put simply, general alertness is affected both by where one is in the regular daily sleep–wake cycle, and by the overall amount of sleep loss one has developed. To this they added modelling of the pharmacokinetic and pharmacodynamic processes of caffeine absorption, in order to correlate the effect of caffeine intake with the quality of performance on cognitive tasks.

The outcome of this work was a statistical model that predicts the duration and magnitude of the effect of caffeine intake on performance at different levels of sleep loss and circadian timing: an algorithm that aims to identify, for a given level of sleep loss and time of day, exactly how much caffeine will benefit performance.

The researchers then applied the model to data obtained from participants in a series of studies. They found that, compared with the standard “recommended” does of caffeine used in the previous research, significant benefits could be derived from employing the results of the statistical model.

On the one hand, if the standard amounts of caffeine were taken but adjusted for the timing of consumption, performance on the cognitive tasks improved by up to 64%. Alternatively, the same cognitive performance to what had been observed in the earlier studies could be achieved by adjusting the timing while reducing the amount of caffeine consumed by up to 65%. In short, these results suggest that statistical methods can be used to tailor the timing and amount of caffeine to an individual’s sleep–wake schedule, in order to maximise cognitive performance following sleep loss.

The authors acknowledge the limitations of using algorithms to predict responses to caffeine in individual cases. Such methods cannot account for individual differences in sensitivity to caffeine, and/or the development of tolerance of its effects: a highly sensitive individual who consumes the “recommended average” would suffer the detrimental effects on subsequent sleep, while a less sensitive individual may need more than the predicted amount to receive the beneficial effect. It is also known that people vary in both the response to sleep loss and the restorative effects of caffeine.

Nevertheless, these studies represent the first major attempt to develop a means of predicting how to maximise the use of caffeine to manage sleep loss, while also minimising overall intake. The authors have developed a web-based tool, “2B-Alert”, to facilitate real-time decisions about caffeine consumption although the practical utility of this is yet to be fully tested.


A/Prof Tim Hannan is Head of the School of Psychology at Charles Sturt University, and the Past President of the Australian Psychological Society.