Two Key Studies of Biological Explanations of Stress (DP IB Psychology)

Key study one: Kiecolt-Glaser et al. (1984)

Aim: 

• To investigate whether stress at exam time could lead to a reduction in immune system function

Participants: 

• A volunteer sample of 26 female and 49 male first-year medical students from the Ohio State University College of Medicine

Procedure: 

• This was a natural experiment with a repeated measures design

• A repeated measures design means that participants were tested twice for their levels of natural killer (NK) cells - a month before the exams and after they had sat their first two exams 

• A low level of NK cells indicates a reduction in immune system function

• Before their first blood test they were given a questionnaire and on the results of that divided into two groups: high stress and low stress

• They were also asked about loneliness, and split into two groups on that measure as well

Results:

• There was a significant decrease in NK cell activity between the blood test taken before the exams and the blood test taken during the stress of the exams 

• Participants in the high-stress group had lower levels of NK cells in both tests than those in the low-stress group

• This was also true of those in the high loneliness group, who had lower NK cell levels than those in the low loneliness group

• This finding means that stress experienced before the exams played a role in their immune systems' ability to cope with the stress of examinations 

• The findings also demonstrate the role of social support as a protective factor for health, as loneliness was a predictor of a low level of NK cells

Conclusion:

• Stress has a direct effect on the immune system by suppressing NK cell activity

Exam stress can lower your immune system

Evaluation of Kiecolt-Glaser et al. (1984)

Strengths

• The use of a repeated measures design eliminated the problem of participant variability, as each participant’s second blood test was compared against their first baseline measurement

• The results of this natural experiment have high ecological validity as it is a study that has taken place in real life and not under artificial conditions

Limitations

• Some of the medical student participants may have had better coping strategies than others, which would affect their stress response

• The participants were all young first-year medical students and younger people usually have better immune systems than older people, which limits the generalisability of the findings

Key study two: Fernald et al. (2008)

Aim: 

• To investigate the effect of continued stress on the cortisol levels of children with low-income, depressed mothers

Participants:

• 639 children (315 girls; 324 boys)

• Aged between 2 and 6 years old 

• The participants came from low-income areas of Mexico.

Procedure: 

• Households were identified in a house-to- house survey in low-income areas of urban Mexico 

• All participating households were visited without prior appointment by a team of health professionals

• The mothers of the children were interviewed in their homes, with each interview lasting one hour

• The mothers also completed a standardised depression scale

• The children were given cognitive tests to complete 

• The children’s saliva was sampled for cortisol levels three times: on arrival of the researchers (baseline test), 25 minutes after arrival and 50 minutes after arrival

Results:

• The researchers found that the children of mothers who had high levels of depression had low levels of cortisol at baseline

• Higher levels of maternal depression was also associated with less increase in children’s salivary cortisol in response to the arrival of the researchers and the cognitive testing

• Girls had some increase in cortisol levels in response to the researchers, but boys’ levels showed no change at all

• This result is in direct contrast to previous studies which suggested high child cortisol levels go hand in hand with high maternal depression

Conclusion:

• Among very low-income families, high maternal depressive symptoms are associated with a blunted cortisol response, particularly in boys

Evaluation of Fernald et al. (2008)

Strengths

• The findings (which were unprecedented) could lead to therapies and interventions being implemented for those affected by chronic stress

• The children’s cortisol levels were taken three times, allowing for objective measurement against a baseline, eliminating participant variability/individual differences 

Limitations

• The researchers did not use a control group of children from higher-income families, which limits the generalisability of the findings to just this small target group

• The study did not control for possible confounding variables, such as food eaten, health problems, exposure to fighting between parents or current post-traumatic stress disorder