Nehligh's 2010 review
Nehlig (2010) wrote a systematic review article called "Is caffeine a cognitive enhancer?" (link to publisher, no PDF).
On page S89 to S90 Nehlig reviews the evidence of caffeine as a cognitive enhancer within the context of a history of caffeine consumption:
In
caffeine non-deprived young (20–25 years) and older subjects (50–65
years), 250 mg caffeine slightly offset the decline in performance
found in the placebo group on a digit span memory test. However,
caffeine did not improve performance in the immediate word recall
task in either age group [11]. Caffeine (12.5–100 mg) given after
overnight abstinence improved cognitive performance in a relatively
difficult and stressful task involving rapid visual information
processing and using a high load of working memory in 11 males and 12
females, aged 18–56 years. The effect was more marked in individuals
with a high habitual caffeine intake [78]. In 68 volunteers
consuming a regular daily amount of caffeine, 2 mg/kg caffeine
improved the speed of encoding new information in a categorical search
task [79]. Likewise, in a study comparing 24 non-consumers (20
mg/day) to 24 consumers of caffeine (217 mg/day), there was no
baseline difference between group performances. Caffeine improved
numeric working memory reaction time and sentence verification
accuracy; alertness was also increased, but in general caffeine tended
to improve more the performance in non consumers [80].
In adult
subjects, a higher habitual caffeine intake with no additional
caffeine administration on the day of testing was positively related
to better performance on incidental verbal learning and visuospatial
learning tasks [15]. There was also an association between estimated
caffeine intake and performance in a choice reaction time task, and in
delayed recall of a verbal word learning task [81]. In the former
study, older sub- jects appeared to benefit more from higher caffeine
intake [15], while this was not the case in the latter study [81].
Also, in real life activities, regular caffeine consumption might
benefit cognitive functioning in a non-working population [82].
Smith's 2002 review
Another good review is provided by Smith (2002, PDF).
The main claim relevant to the present question argues that coffee remains beneficial despite habituation:
It has been claimed that the positive effects of caffeine really reflect
removal of negative effects of caffeine withdrawal. This view cannot
account for effects observed in non-consumers or nondeprived
individuals. In addition, there is little evidence of caffeine
withdrawal impairing tasks which show improvements following ingestion
of caffeine.
The article is worth reading if you want to read about the relevant empirical evidence and some of the limitations of existing research.
References:
- [11] Rees K, Allen D, Lader M (1999) The influences of age and
caffeine on psychomotor and cognitive function. Psychophar-
macology (Berl) 145, 181-188.
- [78] Smit HJ, Rogers PJ (2000) Effects of low doses of caffeine
on cognitive performance, mood and thirst in low and higher
caffeine consumers. Psychopharmacology (Berl) 152, 167-
173.
- [80] Haskell CF, Kennedy DO, Wesnes KA, Scholey AB (2005)
Cognitive and mood improvements of caffeine in habitual con-
sumers and habitual non-consumers of caffeine. Psychophar-
macology (Berl) 179, 813-825.
- [81] Hameleers PA, Van Boxtel MP, Hogervorst E, Riedel WJ,
Houx PJ, Buntinx F, Jolles J (2000) Habitual caffeine con-
sumption and its relation to memory, attention, planning
capacity and psychomotor performance across multiple age
groups. Hum Psychopharmacol 15, 573-581.
- [82] Smith AP (2009) Caffeine, cognitive failures and health in a
non-working community sample. Hum Psychopharmacol 24,
29-34.
- Smith, A. (2002). Effects of caffeine on human behavior. Food and chemical toxicology, 40, 1243-1255. PDF
