Stress and the immune system

A: Investigate how the stress of important exams affected the immune system

P: Natural experiment, repeated measures. Blood samples of 75 medical students were taken 1 month before their exam and another on the morning of  their exam. Also gave them a questionnaire to find out about stress and loneliness. Blood smaples were analysed to assess the levels of T lymphocyte activity

F: In comparison with the first blood sample, T cell activity was significantly reduced in the second sample. Most reduced in those who had reported experiencing other stressful events in their life and those who reported loneliness

Co: Stress clearly has an immunosuppressant effect, reducing the functioning of the immune system. Long term stressors may make individuals more vulnerable to the added effect of short term stressors

Cr: The study had a low representativeness becasue the participants were all medical students, so thier stress levels may be different to that of a general member of public. Also, the findings didn't identify if they actually became ill due to the lower T cell levels

A: Investigate how the stress of caring for a relative with Alzheimer's disease affected would healing due to reduced effectiveness of the immune system

P: Natural experiment, independent measures design. 13 women who cared for relatives with Alzheimer's and a control group of 13 with no caring responsibilities had small wounds created in them and the healing of the individuals was monitored

F: Wounds of those in the highly stressed group (carers) took on average 9 days longer to heal than those in the low stress group

Co: Stress reduces the functioning of the immune system, meaning the production of interlukin B (a protein secreted by white blood cells in order in help repair tissue) is damaged

Cr: Individual differences could have affected this study, for example people may not be stressed as easily as others. Also, the study only focused on women, so it may not be very representative

A:  Investigate the stress of hostile relationships on the susceptibility to infectious diseases

P: Couples were given questionnaires in order to assess the level of negative interactions in their relationship in the last month. The participants were then exposed to the cold virus. 

F: The couples who had reported more negative interactions were more likely to actually develop the cold after being exposed to it

Co: Suggests the immune system may not have been functioning properly. This supports the idea that stress is related to immunosuppression.

Cr: Social desirability bias could have affected the results of the questionnaire because couples may not wish to admit they were having problems