Andrew Paul Smith

Psychological stress and susceptibility to the common cold.

BACKGROUND It is not known whether psychological stress suppresses host resistance to infection. To investigate this issue, we prospectively studied the relation between psychological stress and the frequency of documented clinical colds among subjects intentionally exposed to respiratory viruses. METHODS After completing questionnaires assessing degrees of psychological stress, 394 healthy subjects were given nasal drops containing one of five respiratory viruses (rhinovirus type 2, 9, or 14, respiratory syncytial virus, or coronavirus type 229E), and an additional 26 were given saline nasal drops. The subjects were then quarantined and monitored for the development of evidence of infection and symptoms. Clinical colds were defined as clinical symptoms in the presence of an infection verified by the isolation of virus or by an increase in the virus-specific antibody titer. RESULTS The rates of both respiratory infection (P less than 0.005) and clinical colds (P less than 0.02) increased in a dose-response manner with increases in the degree of psychological stress. Infection rates ranged from approximately 74 percent to approximately 90 percent, according to levels of psychological stress, and the incidence of clinical colds ranged from approximately 27 percent to 47 percent. These effects were not altered when we controlled for age, sex, education, allergic status, weight, the season, the number of subjects housed together, the infectious status of subjects sharing the same housing, and virus-specific antibody status at base line (before challenge). Moreover, the associations observed were similar for all five challenge viruses. Several potential stress-illness mediators, including smoking, alcohol consumption, exercise, diet, quality of sleep, white-cell counts, and total immunoglobulin levels, did not explain the association between stress and illness. Similarly, controls for personality variables (self-esteem, personal control, and introversion-extraversion) failed to alter our findings. CONCLUSIONS Psychological stress was associated in a dose-response manner with an increased risk of acute infectious respiratory illness, and this risk was attributable to increased rates of infection rather than to an increased frequency of symptoms after infection.

Negative life events, perceived stress, negative affect, and susceptibility to the common cold

After completing questionnaires assessing stressful life events, perceived stress, and negative affect, 394 healthy Ss were intentionally exposed to a common cold virus, quarantined, and monitored for the development of biologically verified++ clinical illness. Consistent with the hypothesis that psychological stress increases susceptibility to infectious agents, higher scores on each of the 3 stress scales were associated with greater risk of developing a cold. However, the relation between stressful life events and illness was mediated by a different biologic process than were relations between perceived stress and illness and negative affect and illness. That these scales have independently relations with illness and that these relations are mediated by different processes challenges the assumption that perceptions of stress and negative affect are necessary for stressful life events to influence disease risk.

Biological variation for N-Terminal Pro- and B-type natriuretic peptides and implications for therapeutic monitoring of patients with congestive heart failure

Given the limitations of low enrollments, this study suggests that a change of 130% for B-type natiuretic peptide (BNP) and 90% for N-terminal (NT)-proBNP are necessary before results of serially collected data can be considered statistically different. This study also shows that there are important differences in the performance of BNP versus NT-proBNP in monitoring patients with congestive heart failure that need to be further explored.

Smoking, alcohol consumption, and susceptibility to the common cold.

OBJECTIVES This study was conducted to test the supposition that both smoking and consuming alcohol suppress host resistance to viral infections. METHODS The relations between smoking, alcohol consumption, and the incidence of documented clinical colds were prospectively studied among 391 subjects intentionally exposed to one of five respiratory viruses and 26 subjects given saline. Clinical colds were defined as clinical symptoms verified by the isolation of virus or by an increase in virus-specific antibody titer. Analyses included control variables for demographics; body weight; virus; and environmental, immunological and psychological factors. RESULTS Smokers were at greater risk for developing colds than nonsmokers because smokers were more likely both to develop infections and to develop illness following infection. Greater numbers of alcoholic drinks (up to three or four per day) were associated with decreased risk for developing colds because drinking was associated with decreased illness following infection. However, the benefits of drinking occurred only among nonsmokers. CONCLUSIONS Susceptibility to colds was increased by smoking. Although alcohol consumption did not influence risk of clinical illness for smokers, moderate alcohol consumption was associated with decreased risk for nonsmokers.

Effects of Breakfast and Caffeine on Cognitive Performance, Mood and Cardiovascular Functioning

Two experiments examined the effect of breakfast (1.89 MJ) and caffeine (4 mg/kg) on cognitive performance, mood and cardiovascular functioning. In the first experiment, breakfast had no effect on performance of sustained attention tasks, but it increased pulse rate and influenced mood. The mood effects after breakfast differed between a cooked breakfast and a cereal/toast breakfast. In contrast to the effects of breakfast, this relatively high dose of caffeine improved performance of the sustained attention tasks, increased blood pressure and increased mental alertness. In the second experiment, effects of a breakfast and caffeine on mood and cardiovascular functions confirmed the results of the first study. The breakfast improved performance on free recall and recognition memory tasks, had no effect on a semantic memory task and impaired the accuracy of performing a logical reasoning task. In contrast to this, caffeine improved performance on the semantic memory, logical reasoning, free recall and recognition memory tasks. Overall, these results show that breakfast can improve performance in some but not all cognitive tasks and that these changes are very different from those observed after lunch, and those produced by caffeine.

Decrease of psychomotor performance in subjects with latent 'asymptomatic' toxoplasmosis

Toxoplasma gondii is known to induce specific behavioural changes in its intermediate hosts. This is usually considered to be an evolutionary adaptation aimed to increase the probability of transmission of the parasite into its definitive host, the cat, by predation. In rodents an increase of reaction time as well as many other specific behavioural patterns have been observed. Here we report the results of our double blind study showing the significantly longer reaction times of 60 subjects with latent toxoplasmosis in comparison with those of 56 controls. Moreover, the existence of a positive correlation between length of infection and mean reaction time suggested that slow and cumulative effects of latent toxoplasmosis rather than a one-step (and possibly transient) effect of acute toxoplasmosis disease are responsible for the decrease of psychomotor performance of infected subjects. To our knowledge, this is the first study confirming the existence of such parasite-induced changes in human behaviour that could be considered in evolutionary history of the human species as adaptive from the point of view of parasite transmission.

Job strain, effort--reward imbalance, and stress at work: competing or complementary models?

Background: The Demand Control Model (DCM) and the Effort - Reward Imbalance Model (ERI) offer putative explanations of the relationship between stressful working conditions, job strain, and psychological and physical ill health. Aims: The aims of this study are to: (a) compare the predictive powers of the two models for explaining perceived job stress and mental distress amongst workers as a whole, (b) identify whether a model which combines dimensions of the DCM and ERI might have more predictive power than either of them separately, and (c) ascertain whether the models make distinct contributions to explaining stress at work in specific occupational settings. Methods: Statistical analysis was carried out on data collected from a cross-sectional postal survey of a random sample (n=7,069), of the adult population in an urban area in Southern England. The analysis focused on the 4,135 respondents who were in paid employment. Results: There was little support for combining the models as the combined model was dominated by the predictive power of dimensions from the ERI. However, the results also showed that the models or dimensions of the models made distinct contributions to explaining perceived work stress in different types of occupation. Conclusions: There is little evidence to support a combined model of work characteristics. The ERI appears to be the stronger of the two models although the DCM has explanatory value for specific occupations.

Occupational stress, job characteristics, coping, and the mental health of nurses

OBJECTIVES  This study investigated the relationships between job characteristics and coping in predicting levels of anxiety and depression in nurses. The study was based on current theories of occupational stress, and predictors included job demands, social support, decision authority and skill discretion control, effort, over-commitment, rewards, and ways of coping. It was predicted that job demands, extrinsic effort, over-commitment, and negative coping behaviours would be positively associated with depression and anxiety, and social support, rewards, decision authority, skill discretion control, and positive coping would be negatively associated with depression and anxiety. METHODS  Participants were 870 nurses, who responded to a bulk mail sent randomly to 4,000 nurses from the south of England. RESULTS  The results showed that job demands, extrinsic effort, and over-commitment were associated with higher levels of anxiety and depression. Social support, rewards, and skill discretion were negatively associated with mental health problems. Few interactions were found between the variables. Coping behaviours significantly added to the explanation of variance in anxiety and depression outcomes, over and above the use of demand-control-support, and effort-reward factors alone. CONCLUSION  The results from the study demonstrated the importance of coping factors in work-stress research, in accordance with the multi-factorial premise of transactional stress models. It is argued that multi-factor research is needed to help develop effective organizational interventions.

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 μg) 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 repeated doses of caffeine on mood and performance of alert and fatigued volunteers

Evidence for behavioural effects of caffeine is well documented in the literature. It is associated with increased subjective alertness, improved reaction time and enhanced encoding of new information. These effects are most prominent in low arousal situations. However, there is an ongoing debate as to whether such changes are in fact improvements or merely a reversal of the negative effects of a period of caffeine withdrawal (e.g. overnight abstinence). To avoid such a confound this study included multiple doses of caffeine which were administered under double-blind conditions to participants who had ingested their normal daily quota of caffeine. In the present study participants were fatigued by carrying out a prolonged testing schedule in the evening. Sixty volunteers, all regular caffeine consumers, took part in the study. They attended for three sessions on separate days. They were instructed to consume normal amounts of caffeinated beverages. Consumption was measured by a diary and saliva samples were taken and caffeine assays conducted. A baseline test session was carried out at 18.00h and following this a double blind placebo controlled caffeine challenge (1.5mg/kg) conducted. The test battery was repeated twice approximately 30 minutes after the caffeine challenge. Following this another drink was administered and the test battery repeated twice more. On one test session volunteers had placebo in both drinks, in another they had caffeine in both drinks and another caffeine in the first and placebo in the second. Order of conditions was balanced across subjects. The results showed that caffeine led to a more positive mood and improved performance on a number of tasks. Different effects of caffeine were seen depending on the person’s level of arousal. Linear effects of caffeine dose were also observed. This is evidence against the argument that behavioural changes due to caffeine are merely the reversal of negative effects of a long period of caffeine abstinence. The findings are discussed in relation to both noradrenergic and cholinergic neurotransmitter systems.