Effects of upper respiratory tract illnesses in a working population.

The aim of the present study was to assess the impact of upper respiratory tract illnesses on efficiency at work. This was done using the 'after-effect' technique with measurements being taken before and after work and the difference between these giving an indication of efficiency over the day. All of the volunteers (N = 48) were tested when healthy to provide baseline data for simple reaction time and mood. When volunteers developed an upper respiratory tract illness (URTI) they (N = 16) repeated the procedure. Those who remained healthy over a three month period (N = 32) were recalled as healthy controls. In addition to the performance test and mood ratings the volunteers kept a sleep log and also rated how demanding the day had been and how much effort they had put in. The results showed that those with URTIs had slower reaction times and a more negative mood both before and after work. Illness did not have an effect on ratings of demand and effort. Those who were ill reported greater sleep disturbance but this could not account for the impaired performance or negative mood states. These results suggest that upper respiratory illnesses may impair performance and well-being at work.

Caffeine and central noradrenaline: effects on mood, cognitive performance, eye movements and cardiovascular function.

There have been numerous studies on the effects of caffeine on behaviour and cardiovascular function. It is now important to clarify the mechanisms that underlie such effects, and the main objective of the present study was to investigate whether changes in central noradrenaline underlie some of the behavioural and cardiovascular effects of caffeine. This was examined using a clonidine challenge paradigm. Twenty-four healthy volunteers were assigned to one of four conditions: (i) clonidine/caffeine; (ii) clonidine/placebo; (iii) placebo/caffeine: (iv) placebo/placebo. Baseline measurements of mood, cognitive performance, saccadic eye movements and cardiovascular function were recorded. Subsequently, volunteers were given either clonidine (200 microg) or placebo and consumed coffee containing caffeine (1.5 mg/kg) or placebo. The test battery was then repeated 30 min, 150 min and 270 min later. A second cup of coffee (with the same amount of caffeine as the first) was consumed 120 min after the first cup. The results showed that clonidine reduced alertness, impaired many aspects of performance and slowed saccadic eye movements; caffeine removed many of these impairments. Both clonidine and caffeine influenced blood pressure (clonidine reduced it, caffeine raised it) but the effects appeared to be independent, suggesting that separate mechanisms were involved. In addition, there were some behavioural effects of caffeine that were independent of the clonidine effect (e.g. effects on speed of encoding of new information) and these may reflect other neurotransmitter systems (e.g cholinergic effects). Overall, the results suggest that caffeine counteracts reductions in the turnover of central noradrenaline. This mechanism may underlie the beneficial effects of caffeine seen in low alertness states.

Effects of caffeine on mood and performance: a study of realistic consumption.

RATIONALE: There is a vast literature on the behavioural effects of caffeine. Many of the studies have involved single administration of a large dose of caffeine that is not representative of the way in which caffeine is usually ingested. Further information is required, therefore, on the behavioural effects of realistic patterns of consumption. OBJECTIVES: The present study aimed to determine whether a realistic drinking regime (multiple small doses - 4 x 65 mg over a 5-h period) produced the same effects as a single large dose (200 mg). The smaller doses were selected so that the amount of caffeine present in the body after 5 h would be equivalent to that found with the single dose. METHODS: A double-blind, placebo-controlled, within-subjects experiment was, therefore, carried out. The participants ( n=24) attended for four sessions. Each session started with a baseline measurement of mood and performance at 0930 hours. On two of the sessions, coffee was then consumed at 1000, 1100, 1200 and 1300 hours. In one of these sessions 65 mg caffeine was added to the de-caffeinated coffee. In the other two sessions, the participants consumed coffee at 1300 hours and 200 mg caffeine was added in one of the sessions. The volunteers completed the battery of tests again at 1500 hours. RESULTS: The results showed that in both consumption regimes caffeine led to increased alertness and anxiety and improved performance on simple and choice reactive tasks, a cognitive vigilance task, a task requiring sustained response and a dual task involving tracking and target detection. CONCLUSIONS: These results suggest that previous findings from studies using a large single dose may be applicable to normal patterns of caffeine consumption.

Factors associated with caffeine consumption.

The main aim of this research was to identify factors that were related to caffeine consumption. From this investigation it can be concluded that coffee is the main source of caffeine and that consumption varies with time of day. Individuals may be utilising the arousing effects of caffeine by consuming it at times when arousal is low for instance to counteract sleep inertia or a post-lunch dip in alertness. There is, however, very little evidence to suggest that psychological characteristics such as personality traits or psychosocial factors are important in influencing caffeine consumption, although smoking was found to be related to the amount of caffeine consumed.

The Scale of Occupational Stress: A further analysis of the impact of demographic factors and type of job

Reports the results and analysis of a workplace stress survey. It identifes the factors associated with preceptions of stress at work. Presented in PDF, requires Adobe Acrobat.

Caffeine levels in saliva: associations with psychosocial factors and behavioural effects.

The present study had two main aims. The first was to examine associations between psychosocial factors, health-related behaviours, regular level of caffeine consumption, time of day and levels of caffeine in saliva following acute caffeine challenges. The second aim was to determine whether individual differences in changes in performance following ingestion of caffeine were related to levels of caffeine in saliva. One hundred and forty-four young adults participated in the study. Questionnaires were administered prior to the study to measure psychosocial characteristics, health-related behaviours and habitual levels of caffeine consumption. Two double-blind acute caffeine challenges were then carried out 1 week apart. Volunteers were given either placebo or 1.5 or 3 mg/kg of caffeine on each occasion. The challenges were carried out at 8 : 00, 11 : 00, 14 : 00 or 18 : 00 h so that the impact of time of day could be assessed. In the week between the two challenges the volunteers consumed either caffeinated or decaffeinated products. This allowed investigation of the effects of caffeine withdrawal on caffeine metabolism. Prior to each caffeine challenge volunteers performed a range of tasks, and a baseline saliva sample was taken. The tasks were repeated 1 h after ingestion of the caffeine, with saliva samples being taken at the start and end of the 1 h test battery. The results showed that the level of caffeine in the saliva was a good indicator of the dose of caffeine consumed and of compliance with the withdrawal manipulation. Caffeine levels were not influenced by time of day, habitual caffeine consumption, psychosocial factors or health-related behaviours. Individual differences in caffeine levels in saliva were not related to the individual variation in the effects of caffeine on performance. Copyright 2001 John Wiley & Sons, Ltd.

The effects of caffeine on simulated driving, subjective alertness and sustained attention.

There is evidence that caffeine increases alertness and reduces fatigue. This may be especially so in low arousal situations (e.g. working at night or for prolonged hours). Caffeine has also been found to improve performance on vigilance tasks and simple tasks requiring sustained response. Again, these effects are often clearest when alertness is reduced, although there is evidence that benefits may still occur when the individual is unimpaired. Most studies to date have investigated the behavioural effects of caffeine in laboratory experiments using artificial tasks. In the current study 3 mg/kg caffeine was found to improve steering accuracy in a 1 h simulated drive. Measures of mood and performance on a sustained attention task also showed the benefits of caffeine. These findings suggest that laboratory results reflect a general benefit of caffeine that may also be observed in real-life situations. Other evidence examining the effects of caffeine on performance efficiency over the working day has shown the benefits of caffeine consumption on measures of sustained attention and alertness. This study also provided evidence suggesting that caffeine is often consumed when alertness is low to maximise alertness and performance efficiency. The implications of these findings for road safety are also considered. Copyright 2001 John Wiley & Sons, Ltd.