There are various strengths and limitations of this research, and it is important to evaluate how these affect the studies and the conclusions that they have drawn about the relationship between stress and the immune system. Firstly, the findings have important implications on how the improper functioning of the immune system could affect our bodies. Stress-related illness can be reduced when our knowledge of how it effects the immune system is fully understood. For instance when treating people with infections, or particularly those who are recovering from surgery, it is useful to know that reducing stress could speed up recovery. Therefore in medical terms, understanding the relationship between stress and the immune system is quite significant, and the research highly important. However individual differences and psychological factors are not accounted for in the various studies which suggest stress causes immune suppression. Self-perception of what is stressful and what isn’t could majorly change results, for example in Kiecolt-Glaser et al (1995) some of the participants could have perceived stress differently, therefore this would have had different effects on the immune system and the wounds could have healed at different rates. It is also important to take into account that the participants of the control group were only matched to the carers in age and family income, overlooking that, firstly, they may be exposed to stress conditions that deviate from this specific example, and secondly, that personality, self-perception and culture should have been monitored as well. As only females took part in this experiment, it is fair to suggest that it’s conclusions are not necessarily representable to males. Another factor that can be evaluated in this study is how lifestyle could affect immune functioning. More of the carers were married and were non-smokers, both of these relating to lower stress, social support and non-smoking being related to better immune functioning. This suggests that the carers’s primary stress came from being a caregiver for a relative with Alzheimer’s disease. Although this adds strength the Kiecolt-Glaser et al study we can also suggest that lifestyle would have a negative affect on the immune system. For instance smoking, drinking, poor diet and lack of exercise would increase risk of physical illness, and often enhance immune suppression caused by stress. These limitations can be applied to all of the research concerning stress and the immune system, and they suggest that as these other factors have not been accounted for, that the strength of the evidence that says stress causes suppression on the immune system is somewhat lessened.
It is also fair to say that measures of immune functioning change depending on the type of stressor, duration and timing, shown in a study by Segerstrom and Miller (2004). They conducted a meta-analysis into the precise effects of stressors on the immune system, and found that different types of stressors affect the immune system in different ways according to their nature and duration. So, although stress may have an affect on the immune system, in some cases it would have an insignificant amount. We can also conclude that the research which provides us with evidence that stress effects the immune system negatively may not be representative of all types of stressors, or the duration or timing at which they occur, it is a reductionist argument that this research presents. The insignificance of minor stress on the immune system links in with the research of Bachen, Cohen and Marland (1997) who found that even in stressed individuals, the functioning of the immune system is still within a normal range. Susceptibility to disease therefore is not increased, so we are able to conclude that although stress does affect the balance of the immune system, it does not so in a significant way that would be harmful to health. Robles et al (2005) even found in their study that chronic stress enhanced some aspects of immune functioning.
These contrasting ideas reflect that the immune system is very complex, and that the assessments that have been made in research are often too simplistic to be able to say it is stress that has an affect on the immune system. For instance in Riley’s study lymphocyte levels were used as a measure of immune damage, but this may be too simplistic of a measure, and thus it lacks reliability and validity. This study has further implications in that mice were used instead of human beings, so other factors such as personality, culture and self-perception would be either very difficult to measure, or simply do not exist within a species lacking in the social intelligence of humans, and is therefore not representative of human’s response to stress and how it effects immune function.
To summarise the research that links the body’s response to stress and immune suppression is correlational: we can say that there is a relationship between the two variables, but not stress does not directly cause a suppression of the immune system.
Here's what a teacher thought of this essay
This is a great essay. It is not too long and doesn't try to pack in too many studies or too much procedural detail, but it is packed with analysis and evaluation of research and commentary on the conclusions that can and can't be drawn. One of its strengths is the way that studies have been counterposed to draw out points of comparison and contrast. Excellent