EFFECTS OF WORK STRESS ON BEHAVIORAL OUTCOMES :Caffeine Ingestion

Caffeine is the most widely consumed pharmacologically active substance in the world. The evidence on its possible implications for human health, that is, whether it has chronic physiological effects on habitual consumers, is as yet inconclusive (Benowitz, 1990). It has long been suspected that repeated exposure to caffeine may produce tolerance to its physiological effects (James, 1994). The consumption of caffeine is known to improve physical performance and endurance during prolonged activity at sub-maximal intensity (Nehling & Debry, 1994). Caffeine’s physiological effects are linked to the antagonism of adenosine receptors and to the increased production of plasma catecholamines (Nehling & Debry, 1994).
The study of the relationship between work-related stress and caffeine ingestion is confounded
by the high correlation between coffee consumption and smoking (Conway et al., 1981). A meta-analysis of six epidemiological studies (Swanson et al., 1994) has shown that about 86% of smokers consumed coffee while only 77% of the non-smokers did so.Three major mechanisms have been suggested to account for this close association between caffeine intake and smoking: (a) conditioning effect, (b) reciprocal interaction; that is, caffeine intake increases arousal while nicotine intake decreases it, and (c) the possibility of a third variable affecting both. Stress, and particularly work-related stress, is a possible third variable influencing both caffeine and nicotine intake (Swanson et al., 1994).
Caffeine consumption is often regarded as reinforcing and augmenting the psychological and physiological effects of stress (France&Ditto, 1992; Lane et al., 1990). This synergetic relationship has been explained as due to the effects of both on the elevation of blood catecholamines (Lane et al., 1990). Experimental laboratory studies have found that as opposed to a placebo drink, consumption of high levels of caffeine interacts with stress in worsening the effects of stress on psychological and physiological strain (France & Ditto, 1992; Lane & Williams, 1987).