When a woman falls ill, her pain may be more intense than a man's, a new study suggests.
Across a number of different diseases, including diabetes, arthritis and certain respiratory infections, women in the study reported feeling more pain than men, the researchers said.
The study is one of the largest to examine sex differences in human pain perception. The results are in line with earlier findings, and reveal that sex differences in pain sensitivity may be present in many more diseases than previously thought.
Because pain is subjective, the researchers can't know for sure whether women, in fact, experience more pain than men. A number of factors, including a person's mood and whether they take pain medication, likely influence how much pain they say they're in.
"Whatever the reason, I think it's important to be aware of this pain discrepancy between men and women and look into it further," said study researcher Linda Liu, a doctoral student in Stanford University Biomedical Informatics program.
Future studies, in both people and animals, should analyze their results to see whether sex differences in pain may be present, Liu said. Many studies in animals do not include females, or fail to report the sex of animals used, Liu said.
The study was published online Jan. 12 in the Journal of Pain.
Most human studies examining gender differences in reported pain have compared the number of women with the number of men with a given condition who say they are in pain. But most haven't looked at how intense the pain is, and many have not included enough people to be able to detect differences between the sexes in pain perception, the researchers said.
The new study included information from more than 11,000 patients whose pain scores were recorded in electronic medical records at Stanford Hospital and Clinics between 2007 and 2010. Patients were asked to rate their pain on a scale of zero (no pain) to 10 (worst pain imaginable).
In all, the researchers assessed sex differences in reported pain for more than 250 diseases and conditions.
For almost every diagnosis, women reported higher average pain scores than men. Women's scores were, on average, 20 percent higher than men's scores, according to the study.
Women with lower back pain, and knee and leg strain consistently reported higher scores than men. Women also reported feeling more pain in the neck (for conditions such as torticollis, in which the neck muscles twist or spasm) and sinuses (during sinus infections) than did men, a result not found by previous research.
It could be that women assign different numbers to the level of pain they perceive compared with men, said Roger B. Fillingim, a pain researcher at the University of Florida College of Dentistry, who was not involved with the new study.
But the study was large, and the findings are backed up by previous work, Fillingim said.
"I think the most [simple] explanation is that women are indeed experiencing higher levels of pain than men," Fillingim said.
The reason for this is not known, Fillingim said. Past research suggests a number of factors contribute to perceptions of pain level, including hormones, genetics and psychological factors, which may vary between men and women, Fillingim said. It's also possible the pain systems work differently in men and women, or women experience more severe forms of disease than men, he said.
Future research is needed to find out the exact causes of pain perception differences, and which ones would be best to target for more effective pain control, Fillingim said.
Finding biological markers for pain, such as genes or proteins, would also help take some of the subjectivity out of assessing the experience of pain, Liu said, but the identification of such markers is likely a long way off.
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