Monday January 13 2014
Participants were given a dose of 200mg caffeine pills
With exams on the horizon for many students, the somewhat dubious claim made by The Independent is that the "Secret to passing exams is [a] large espresso after revision".
But while the study it reports on did find an association between caffeine intake and enhanced memory, the effect was inconsistent.
The study, which involved 160 people between the ages of 18 and 30, showed that giving a dose of 200mg caffeine pills (roughly equivalent to two mugs of instant coffee) enhanced their ability to distinguish between subtly different objects one day after studying them.
However, no enhancing effects were found when recalling which objects were identical to the day before and which were new, so the memory enhancement effect was not consistent across the elements tested.
This may be a sign that caffeine enhances memory in a very specific way. Alternatively, the one significant result may be a chance finding and there really is no effect.
The study did not address whether caffeine has any effect upon children's learning or retention at school, or whether caffeine could have any effect upon older adults with diseases affecting their memory, such as Alzheimer's disease.
These results need to be replicated in further research, as the effect observed may be a chance finding.
If you do have a big exam coming up, we would recommend that you stick to plain old tap water instead. As the lead author of the study warns, "Caffeine can have side effects like jitteriness and anxiety in some people. The benefits have to be weighed against the risks".
Where did the story come from?
The study was carried out by researchers from Johns Hopkins University and the University of California. The researchers were funded by the US National Institute on Aging, the US National Science Foundation, and Johns Hopkins University.
It was published in the peer-reviewed journal Nature Neuroscience.
The media generally reported the story accurately, although many of the headlines hyped the strength of the evidence provided in the study. For example, the Sunday Mirror's claim that "Scientists reveal caffeine provides huge boost to your short-term memory" is groundless.
However, BBC News did include a particularly useful quote from the main study author, Professor Michael Yassa, who cautioned that the findings "do not mean people should rush out and drink lots of coffee, eat lots of chocolate, or take lots of caffeine pills".
The negative effects associated with caffeine, such as irritability and insomnia, also need to be considered in weighing up the potential benefits and harms. The amount and quality of sleep we get can also influence learning and memory, so there may be some trade-offs in terms of the potential benefits of caffeine.
What kind of research was this?
This was a double-blind randomised controlled trial looking at the effect of caffeine on memory.
The researchers say that some studies have shown caffeine enhances short-term cognitive (brain) performance, but most long-term studies found little or no effect.
However, these studies gave people caffeine before they tried to learn or memorise objects or tasks. This means the other effects of caffeine, such as increased wakefulness or arousal, may impact learning in ways other than enhancing memory, and could cloud the findings specifically on memory.
The difference with the new research was that it gave people caffeine after the learning phase in an effort to investigate any potential effects it had on memory in isolation. That is, whether caffeine intake after a specific cognitive task helps "fix" the resulting piece of information in the memory.
What did the research involve?
The researchers showed 160 healthy participants individual pictures of objects to study. Half the group was randomly selected to receive 200mg of caffeine and the other half was given a placebo pill.
The participants were tested on their recollection of the objects 24 hours later. This test included objects they had seen the previous day (targets), some new objects (foils), and some objects that were visually similar but subtly different to the original objects (lures).
Examples given of "targets" and the corresponding "lures" included images of saxophones and seahorses. For each image, the participants were instructed to decide whether the image was "old", "new" or "similar".
Saliva samples were taken immediately after the participants studied the objects, and again one, two, three and 24 hours after they received the caffeine or placebo so that the researchers could study how the caffeine was broken down in the body.
Participants were described as "caffeine-naïve", suggesting they didn't usually have a caffeine intake in their diets, but this was not described explicitly. Those who consumed more than 500mg caffeine a week were excluded from the study.
The study was described as double-blind, meaning neither the participants nor the people assessing their memory knew which group (caffeine or placebo) they had been randomly assigned to.
The main analysis compared how well the two groups identified:
- targets – identical objects they had seen the previous day
- foils – new objects they had not seen the previous day
- lures – similar, but not identical, objects to the previous day
What were the basic results?
Participants who received caffeine were more likely to correctly identify the lure objects compared with participants who received the placebo.
There were no differences between those who received caffeine and those who received placebo in the recognition of target or foil objects.
To rule out any effects of caffeine on memory retrieval, the authors conducted a second delayed caffeine experiment. They gave participants caffeine one hour before the memory test (still 24 hours after the initial study session).
The authors observed no significant memory enhancement in those given caffeine compared with placebo. They interpreted this as suggesting that caffeine does not affect any other aspect of memory retention performance.
They also studied different doses of caffeine to see what was best for memory and if there was a dose-response relationship. They found:
- the dose-response relationship did not appear to be linear – that is, higher caffeine doses did not improve memory in a simple relationship
- 200mg was better than placebo and 100mg, but it was no different to 300mg
- the dose-response curve was described as an "inverted U", meaning the optimum dose was in the middle of the 100, 200 and 300mg range tested, with a diminishing effect at the higher and lower doses
The researchers concluded that at least 200mg was required to observe the enhancing effect of caffeine on memory.
How did the researchers interpret the results?
The authors concluded that the lack of difference in identifying identical objects (hits) and recognising when the objects were new (foils) meant that basic recognition memory was unaltered by caffeine.
The slightly better performance in the caffeine group when identifying lures was interpreted as meaning that, "Caffeine enhanced consolidation of the initial study session such that discrimination during retrieval was improved".
This study showed that giving a 200mg dose of caffeine to people who don't usually consume it enhanced their ability to distinguish between subtly different objects one day after studying them. However, no effects were found when identifying identical or new objects, so the memory enhancement effect was not consistent.
It is unclear what benefit this very specific effect would lead to in a real-life situation, such as an exam, if replicated in a wider population.
The result may also be a chance error and caffeine actually has no effect on memory. We will only be able to know if the effects are real if the study is repeated more times in different and larger populations.
This study also has a number of other limitations to consider when interpreting its findings:
- The study sample was relatively small, with 160 participants.
- The study sample was relatively young (mean age 20 years) and excluded those aged under 18 or over 30. It therefore does not address whether caffeine has any effect on a child's ability to learn or remember, or whether caffeine may have any effect on older adults with diseases affecting memory, such as Alzheimer's.
- The study subjects were aware they were participating in a study of caffeine. However, a survey of the participants suggested they didn't know which group they had been assigned to (caffeine or placebo), indicating the blinding element of the trial was effective and unlikely to bias the results.
- The sample sizes were small in the experiments comparing different caffeine doses (sometimes just 10 people), increasing the chance that no differences would be found between groups, even if real differences existed. These findings should therefore be treated with a pinch of salt.
- Participants with high caffeine consumption of more than 500mg per week were excluded from the study. The potential additional memory enhancing effects may be different or absent in people already consuming high levels of caffeine.
The bottom line is that the study results need to be replicated, as the effect observed may be a chance finding.
Readers should not rush out and consume large amounts of caffeine in the hope it will boost their memory based on the results of this study. Until further studies prove these findings, there is currently no sure-fire short-cut to revision other than hitting the books on a regular basis.
Analysis by Bazian. Edited by NHS Choices. Follow Behind the Headlines on Twitter.