This paper reflects the research and thoughts of a student at the time the paper was written for a course at Bryn Mawr College. Like other materials on Serendip, it is not intended to be "authoritative" but rather to help others further develop their own explorations. Web links were active as of the time the paper was posted but are not updated.
2002 Second Paper
Pain has been an under-researched area of medicine, but today physicians are increasingly interested in the workings and treatment of various types of pain. In particular, a growing body of research exists on the different ways in which men and women may experience pain and the implications of these differences for medical treatment. Does the sex of an individual make a difference in their pain experience? Numerous researchers believe that women are more sensitive to pain than men, while others believe that the differences between the pain experiences of men and women are not significant. Over the course of my research I found that part of the problem in trying to answer the question lies in how scientists measure the pain experience of men and women.
The difference in the pain experience of men and women is an understudied area because most previous studies of pain and its potential treatments have only used men or male animals. For scientists, using only males was simpler since women have reproductive hormone cycles that could complicate the studies. The implication of this, of course, is that sex differences in the experience of pain (and in many other aspects of health) has remained an understudied area. However, in 1993 President Clinton signed the NIH Revitalization Act, which requires the inclusion of women in NIH research. In 1996 the NIH formed a Pain Research Consortium, and in 1998 the NIH held a conference entitled "Gender and Pain" (1).
At the NIH conference, some researchers argued that sex differences in pain are substantial and argued specifically that women are more sensitive to pain. For example, women report pain more often and also report it at higher levels than men. Additionally, when men and women are exposed to the same pain stimulus, women will say that they are in pain more quickly than men (1).
However, others believe that sex differences in the experience of pain may not be so significant. The higher reported pain levels of women may be due more to gender socialization than to biological differences between men and women. For example, in most laboratory pain studies women report about twenty percent more pain than men (2). However, researchers at the University of Florida examined pain reporting of chronic pain patients in a clinical setting and found that women reported only three to ten percent more pain than men, a significantly smaller difference. The researchers believed that women may not always experience more pain, but rather are socialized to acknowledge pain and thus are more likely to report it in both laboratory and clinical settings. Men are taught to not acknowledge pain, so in a short-term lab experiment they are less likely than women to admit that they are in pain. However, men experiencing chronic pain want relief for their long-term suffering, so gender socialization in less of a barrier to acknowledging pain in a clinical setting (2).
A recent University of Washington study, presented at the NIH "Gender and Pain" conference, also suggests that men and women with chronic pain experience similar levels of pain. The study had two rounds, the first examining 202 men and 226 women with chronic non-cancer related pain. The researchers examined "prior treatment for pain, pain severity, emotional distress, interference of pain with life, and impact of pain on functional activities." Researchers did not find women reporting more severe pain, or "interference of pain with life" or "functional activities." The only area of significant difference between men and women was emotional distress, since women reported higher levels of depression. Since depression is generally thought to be higher among women, the researchers did not believe that the depression was necessarily pain related (3).
The second round of the study examined 91 men and 52 women with cancer-related chronic pain. In this sample, the researchers found no differences between the sexes in the various measures of pain. Unlike the first study, there was no difference in depression levels between men and women, perhaps because in the second sample all of the patients were suffering from a potentially deadly illness (cancer) and therefore more generally prone to depression. The University of Washington researchers concluded that in treating chronic pain, the sex of the patient is less important than their psychosocial characteristics such as coping ability, marital satisfaction, and the impact of outside life activities (3).
Additionally, research on a genetic basis for pain differences between men and women is inconclusive. Researchers on pain differences in animals such as mice have found that generally the female animals appear more sensitive to pain and do not respond as much to pain relievers as males. However, the differences between males and females do not tend to be large (4). Furthermore, researchers believe that "even within gender, there are individual differences in feeling pain that are linked to still undiscovered genes" large (4). Researchers at Johns Hopkins University and the National Institute on Drug Abuse have located a gene that may be responsible for individual variations in pain sensitivity. The gene codes for the mu opiate receptor, which binds with endogenous painkillers such as endorphins as well as exogenous painkillers such as morphine and heroin. These receptors are found primarily in the thalamus, the cerebral cortex, the visual cortex, and the basal ganglia, but with a great deal of individual variation in their number large (5). Researchers examined eight mouse strains with variations in the mu opiate gene, and found that the mice with more active form of the gene had a greater number of mu opiate receptors in the brain and a higher pain tolerance. While still a new area of research in humans, studies on human mu opiate genes have found individual variations in the regulatory portion of the gene that may account for individual variations in pain experience large (5).
How, then, do we know whether men and women experience pain differently? The genetic evidence for a gender basis of pain is not conclusive and points to individual variations as more significant than sex variations. Another challenge is that we cannot "see" pain, only a subject's reaction to a painful stimulus. In the case of humans, we also can use their description of their physical discomfort. However, women are socialized to more freely acknowledge their pain and men to minimize theirs, how can we know if the actual pain experience of men and women is different? I found it difficult to reach a conclusion, in part since this is a relatively new area of research. Additionally, while I used research focusing on chronic pain, there is a huge range of types of pain that humans can experience. Therefore, examining pain solely through the person's sex gives an incomplete picture. The differences may lie more at the level of the individual and the intersection of their current pain experience with their psychological and social background.
1) NIH website, Overview page for the April 1998 NIH Gender and Pain Conference.
2) American Psychological Association Monitor Online, article on sex differences in pain.
3)NIH website, abstract of a chronic pain study presented at the NIH Gender and Pain conference.
4) Intel Health article,"Gender, Genes Are Linked to Pain Response."
5) Scientific American article entitled "Personal Pain", on the role of the mu opiate gene in pain sensitivity.
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