ALERTNESS
There are a large number of studies showing that caffeine increases alertness. Effects of caffeine on alertness are often more easy to demonstrate in subjects in a state of low alertness. Thus caffeine can counteract the effects on alertness of benzodiazepine administration (1), the early morning (2), night-time working (3), a cold (4) or sleep loss (5). However, caffeine has also been shown to increase alertness in fully alert subjects (6). Effects of caffeine on alertness have been demonstrated both at high doses (1) as well as at more realistic lower doses (6). It has also been shown that the effects are due to caffeine itself rather than the combination of caffeine and the drink in which it is presented (7). These effects on alertness have important implications for certain practical situations as safety is often at risk when alertness is low. Improved alertness can be beneficial at different times of the day and night, and whilst undertaking different tasks. Driving is now somewhat essential for may people, and driver fatigue is a significant cause of road traffic accidents. In 2006 researchers investigated the effects of coffee and napping in relation to driver alertness, conducted on real nightime driver performance. The participants consumed 125ml coffee containing 200mg caffeine before driving 200 killometres between 6.00 and 7.20 pm, or 2.00 and 3.30 am. The authors concluded that coffee or napping at night statistically significantly reduces driving impairment without altering subsequent sleep. (8) It is accepted that fatigue related accidents raise a safety concern. Countermeasures to alleviate fatigue and to improve adaptation to shift work, such as napping, exposure to bright light, pharmacological interventions, caffeine and psychostimulants have been reviewed recently. (9) The authors of this review support the hypothesis that caffeine can help an individual to function more effectively when arousal levels are low.
References:
1. Johnson, L.C. et al. Psychopharmacology, 101, 160-167, 1990.
2. Smith, A.P. et al. Neuropsychobiology, 26, 198-204, 1992.
3. Smith, A.P. et al. Neuropsychobiology, 27, 217-223, 1993.
4. Smith, A.P. et al. Journal of Psychopharmacology, 11, 319-324, 1997
5. Bonnet, M.H. et al. Sleep, 18, 97-104, 1995.
6. Warburton, D.M. Psychopharmacology, 119, 66-70, 1995.
7. Smith, A.P. et al. Human Psychopharmacology, 14, 473-482, 1999.
8. Phillip,P. et al. Annals of Internal Medicine, 144, 2006.
9. Boivin, D. et al. Sleep Medicine, Online/In Press, May 2007.