Use and effects of food and drinks in relation to daily rhythms of mood and cognitive performance. Effects of caffeine, lunch and alcohol on human performance, mood and cardiovascular function.

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There have been many studies of the effects of caffeine (for a review, see Lieberman, 1992), lunch (for a review, see Smith & Kendrick, 1992), and alcohol (for a review, see Finnigan & Hammersley, 1992) on human performance and mood. However, these factors have usually been considered in isolation, which is not representative of what happens in real life. There have, however, been a few studies which have looked at the interactions between them. For example, Smith et al. (1990) examined the effects of caffeine on the post-lunch dip in sustained attention and showed that caffeine removed the post-lunch impairment. Millar et al. (1992) have demonstrated that consumption of lunch can reduce the negative effect of alcohol observed in some aspects of performance. In contrast to this, previous research (e.g. Oborne & Rogers, 1983) suggests that caffeine does not remove the detrimental effects of alcohol. The main aim of the present study was to examine the separate and combined effects of caffeine, lunch and alcohol to provide further insight into their modes of action and to allow comparison of the magnitude of the effects of the different factors. Previous research has also shown that there are individual differences in the effects of caffeine, alcohol and lunch. In the case of caffeine it appears to be impulsivity which predicts the size of the effect. In contrast to this, anxious subjects tend to show a smaller post-lunch dip than non-anxious subjects. There are also individual differences in the effects of alcohol, with extravert, anxious subjects showing the greatest impairments after alcohol. These personality effects were examined in the present study but the findings are not reported here.