The effect of caffeine on memory
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).
Consistent with earlier indications that moderate caffeine consumption may protect against memory decline, a study of genetically engineered mice has found that when the old mice began to show memory impairment, those given caffeine for 2 months performed as well as normal aged mice on cognitive tests, while those given plain drinking water continued to do poorly. The Alzheimer's mice received the equivalent of five 8-oz. cups of regular coffee a day (or two cups of Starbucks coffee, or 14 cups of tea). Moreover, the brains of the caffeinated mice showed nearly a 50% reduction in levels of beta amyloid. The effect appears to be through suppression of both β-secretase and presenilin 1 /g-secretase expression. Caffeine had this effect only on those with Alzheimer’s; normal mice given caffeine through adulthood showed no cognitive benefit.
Arendash, G.W. et al. 2009. Caffeine Reverses Cognitive Impairment and Decreases Brain Amyloid-β Levels in Aged Alzheimer's Disease Mice. Journal of Alzheimer's Disease, 17 (3), 661-680.
Cao, C. et al. 2009. Caffeine Suppresses Amyloid-β Levels in Plasma and Brain of Alzheimer's Disease Transgenic Mice. Journal of Alzheimer's Disease, 17 (3), 681-697.
A large, long-running Finnish study has found that those who were coffee drinkers at midlife had lower risk for dementia and Alzheimer’s later in life compared to those drinking no or only little coffee midlife. The lowest risk was found among moderate coffee drinkers (drinking 3-5 cups of coffee/day). Tea drinking was relatively uncommon and was not associated with dementia.
Eskelinen, M.H. et al. 2009. Midlife Coffee and Tea Drinking and the Risk of Late-Life Dementia: A Population-based CAIDE Study. Journal of Alzheimer's Disease, 16(1).
A study of over 2000 older Norwegians (aged 70-74) has found that those who consumed chocolate, wine, or tea had significantly better cognitive performance and lower risk of poor cognitive performance than those who did not. Those who consumed all 3 studied items had the best performance and the lowest risks for poor test performance. The associations between intake of these foodstuffs and cognition were dose dependent, with maximum effect at intakes of around 10 grams a day for chocolate and around 75–100 ml a day for wine, but approximately linear for tea. The effect was most pronounced for wine and modestly weaker for chocolate intake. The finding is consistent with research indicating that those who consume lots of flavonoids have a lower incidence of dementia.
 Nurk, E., Refsum H., Drevon C. A., Tell G. S., Nygaard H. A., Engedal K., et al.
(2009). Intake of flavonoid-rich wine, tea, and chocolate by elderly men and women is associated with better cognitive test performance.
The Journal of Nutrition. 139(1), 120 - 127.
A recent study of 40 older adults (over 65) confirmed the popular belief in the value of caffeine in helping overcome a decline in mental sharpness later in the afternoon. All the participants (like three-quarters of all people in that age group, studies suggest) described themselves as "morning people". Testing confirmed that they were less alert later in the day. Given coffee, but not told whether it was "real" coffee or decaffeinated, those who drank the regular coffee did not experience mental declines in the afternoon tests. Note that participants were already regular coffee drinkers (and were asked to abstain before arriving for the test).
 Ryan, L., Hatfield C., & Hofstetter M.
(2002). Caffeine reduces time-of-day effects on memory performance in older adults.
Psychological Science: A Journal of the American Psychological Society / APS. 13(1), 68 - 71.
Do caffeine and glucose help concentration? A recent study found that volunteers who drank a mixture containing caffeine and glucose (as well as trace levels of guarana, ginkgo and ginseng) showed clear improvements in memory and attention. Those who consumed the individual ingredients, or a placebo, did not show such improvements.
Scholey, A. & Kennedy, D. 2003. Report at the British Psychological Society Annual Conference in Bournemouth 13-15 March.
Two recent studies suggest that caffeine is most effective in boosting your energy and alertness in small doses, and more effective for males.
A study involving 80 college students (34 men and 46 women) between the ages of 18 and 40, has found that those given a caffeinated energy drink reported feeling more stimulated and less tired than those given a decaffeinated soda or no drink. However, although reaction times were faster for those consuming caffeine than those given a placebo drink or no drink, reaction times slowed for increasing doses of caffeine, suggesting that smaller amounts of caffeine are more effective.
The three caffeine groups were given caffeine levels of either 1.8 ml/kg, 3.6 ml/kg or 5.4 ml/kg. The computerized "go/no-go" test which tested their reaction times was given half an hour after consuming the drinks.
In another study, 52 children aged 12-17 drank flattened Sprite containing caffeine at four concentrations: 0, 50 mg, 100 mg or 200 mg. Changes in blood pressure and heart rate were then checked every 10 minutes for one hour, at which point they were given a questionnaire and an opportunity to eat all they wanted of certain types of junk food.
Interestingly, there were significant gender differences, with boys drinking high-caffeine Sprite showing greater increases in diastolic blood pressure (the lower number) than boys drinking the low-caffeine Sprite, but girls being unaffected. Boys were also more inclined to report consuming caffeine for energy or “the rush”, than girls were.
Those participants who ingested the most caffeine also ate more high-sugar snack foods in the laboratory, and reported higher protein and fat consumption outside the lab.
 Howard, M. A., & Marczinski C. A.
(2010). Acute Effects of a Glucose Energy Drink on Behavioral Control.
Experimental and Clinical Psychopharmacology. 18(6), 553 - 561.
 Temple, J. L., Dewey A. M., & Briatico L. N.
(2010). Effects of Acute Caffeine Administration on Adolescents.
Experimental and Clinical Psychopharmacology. 18(6), 510 - 520.
A recent study indicates that the alertness benefits of caffeine may simply reflect the reversal of the fatiguing effects of caffeine withdrawal.
A study involving 379 individuals who abstained from caffeine for 16 hours has revealed little variance in levels of alertness after receiving caffeine. Those who were medium/high caffeine consumers reported a decrease in alertness and an increase in headache if given the placebo, neither of which were reported by those who received caffeine. However, their post-caffeine levels of alertness were no higher than the non/low consumers who received a placebo, suggesting caffeine only brings coffee drinkers back up to 'normal'. In other words, the stimulatory effects of caffeine appears to be an illusion generated by the reversal of the fatiguing effects of acute caffeine withdrawal.
 Rogers, P. J., Hohoff C., Heatherley S. V., Mullings E. L., Maxfield P. J., Evershed R. P., et al.
(2010). Association of the Anxiogenic and Alerting Effects of Caffeine with ADORA2A and ADORA1 Polymorphisms and Habitual Level of Caffeine Consumption.
A special supplement in the Journal of Alzheimer's Disease focuses on the effects of caffeine on dementia and age-related cognitive decline. Here are the highlights:
A mouse study has found memory restoration and lower levels of amyloid-beta in Alzheimer’s mice following only 1-2 months of caffeine treatment. The researchers talk of “ a surprising ability of moderate caffeine intake to protect against or treat AD”, and define moderate intake as around 5 cups of coffee a day(!).
A review of studies into the relation between caffeine intake, diabetes, cognition and dementia, concludes that indications that coffee/caffeine consumption is associated with a decreased risk of Type 2 diabetes and possibly also with a decreased dementia risk, cannot yet be confirmed with any certainty.
A study involving 351 older adults without dementia found the association between caffeine intake and cognitive performance disappeared once socioeconomic status was taken into account.
A study involving 641 older adults found caffeine consumption was significantly associated with less cognitive decline for women only. Supporting this, white matter lesions were significantly fewer in women consuming more than 3 units of caffeine per day (after adjustment for age) than in women consuming less.
A Portuguese study involving 648 older adults found that caffeine intake was associated with a lower risk of cognitive decline in women, but not significantly in men.
A review of published studies examining the relation between caffeine intake and cognitive decline or dementia shows a trend towards a protective effect of caffeine, but because of the limited number of epidemiological studies, and the methodological differences between them, is unable to come up with a definitive conclusion.
A review of published epidemiological studies looking at the association between caffeine intake and Parkinson’s Disease confirms that higher caffeine intake is associated with a lower risk of developing Parkinson’s Disease (though this association may be stronger for men than women). Other studies provide evidence of caffeine’s potential in treatment, improving both the motor deficits and non-motor symptoms of Parkinson’s.
Arendash, G.W. & Cao, C. Caffeine and Coffee as Therapeutics Against Alzheimer’s Disease. Journal of Alzheimer's Disease, 20 (Supp 1), 117-126.Biessels, G.J. Caffeine, Diabetes, Cognition, and Dementia. Journal of Alzheimer's Disease, 20 (Supp 1), 143-150.Kyle, J., Fox, H.C. & Whalley, L.J. Caffeine, Cognition, and Socioeconomic Status. Journal of Alzheimer's Disease, 20 (Supp 1), 151-159.Ritchie, K. et al. Caffeine, Cognitive Functioning, and White Matter Lesions in the Elderly: Establishing Causality from Epidemiological Evidence. Journal of Alzheimer's Disease, 20 (Supp 1), 161-161Santos, C. et al. Caffeine Intake is Associated with a Lower Risk of Cognitive Decline: A Cohort Study from Portugal. Journal of Alzheimer's Disease, 20 (Supp 1), 175-185.Santos, C. et al. Caffeine Intake and Dementia: Systematic Review and Meta-Analysis. Journal of Alzheimer's Disease, 20 (Supp 1), 187-204.Costa, J. et al. Caffeine Exposure and the Risk of Parkinson’s Disease: A Systematic Review and Meta-Analysis of Observational Studies. Journal of Alzheimer's Disease, 20 (Supp 1), 221-238.Prediger, R.D.S. Effects of Caffeine in Parkinson’s Disease: From Neuroprotection to the Management of Motor and Non-Motor Symptoms. Journal of Alzheimer's Disease, 20 (Supp 1), 205-220.
Full text available at http://iospress.metapress.com/content/t13614762731/. http://www.eurekalert.org/pub_releases/2010-05/ip-nec051710.php
Dr McPherson's practical, research-based books are instantly available as digital downloads from the Mempowered store (all formats), Kindle Store, Kobo Store, and iTunes. They are also available in paperback.