- Caffeine has both good and bad effects, both of which may impact on cognitive performance.
- Coffee contains active ingredients other than caffeine which may, directly or indirectly, impact on cognitive performance.
- Caffeine appears to be of greater potential significance to older adults.
- However, those with hypertension, diabetes, impaired glucose tolerance, or high homocysteine levels, would be wiser to avoid coffee, even if decaffeinated.
- Caffeine's main impact is on attention.
It seems clear that caffeine improves alertness and reaction time, but evidence is inconclusive for its effect on higher memory and reasoning processes. It is possible that caffeine may in fact impede memory, where the information is complex or ambiguous.
Caffeine can be helpful in ameliorating the effects of time of day and sleep deprivation on cognitive performance. In normal circumstances (i.e., not prolonged sleep deprivation, or extreme stress), caffeine seems to be more helpful to older adults, in helping them overcome time-of-day effects.
Recent research has demonstrated that caffeine affects blood flow in the brain. It is not yet clear what the implications of this may be.
Caffeine has been implicated in raising blood pressure. High blood pressure is undoubtedly a risk factor for cognitive decline and dementia for those over 60. However, recent studies suggest that, while it is clear that coffee raises blood pressure, it is not clear that caffeine is the culprit.
Brewed coffee raises homocysteine levels. High homocysteine levels in older adults increase the risk of cognitive decline and dementia. Recent research suggests however that caffeine is not the sole ingredient in coffee responsible for the homocysteine-raising effect.
Evidence for the effect of caffeine on glucose regulation is inconclusive as yet, but there is some suggestion that caffeine may be a risk factor for impaired glucose tolerance. Impaired glucose tolerance is a risk factor for cardiovascular disease (and thus, by implication, cognitive decline, since research now indicates that “what is good for the heart is good for the brain”). More direct evidence also suggests that impaired glucose tolerance in older adults is associated with memory problems.
While people clearly build up a tolerance to some of the effects of caffeine, it is not yet clear what the long-term effects of regular caffeine use are. Nor can we say, as yet, what factors are important in determining those long-term effects, although we can speculate that gender, metabolic factors, cardiovascular health, alcohol and tobacco use are all possible influences.
Conclusion: Clearly, caffeine has both good and bad effects, both of which may impact on cognitive performance. Moreover, the main vehicle for caffeine — coffee — contains active ingredients other than caffeine which may, directly or indirectly, impact on cognitive performance. Caffeine does appear to be of greater potential significance to older adults. Overall, the evidence suggests that, while caffeine may help older adults in the later part of the day, those with hypertension, diabetes, impaired glucose tolerance, or high homocysteine levels, would be wiser to avoid coffee, even if decaffeinated. In general, while caffeine may help you overcome factors that lower your cognitive performance, it does not seem that caffeine has any significant direct effect on memory, although it may well help you pay attention.
This is a summary of research into the effects of caffeine on memory. You can download the full report (in pdf format).