Wednesday January 19 2011
The study cannot tell us much about the existence of man flu
“The male of the species is a wimp over colds,” according to the Daily Mail. The newspaper says that working men are far more likely to succumb to “man flu” when under stress but that woman will carry on regardless.
The story is based on a small study of South Korean workers that suggests that men who reported stress at work were more likely to experience cold symptoms than men under low stress. Women showed no association between work stress and cold symptoms.
This small study had several limitations, including a low number of participants and a high drop-out rate. Other problems that may make the results less reliable include participants assessing their own cold symptoms and job stresses, and researchers not looking at the participants’ risk of exposure to cold viruses. Korean social structure also means that men tend to provide most of a family’s income, which may give them different working patterns from their female counterparts. Stress and the cold are both common causes of work-related sickness in the UK, and assessments of how stress interacts with infection would be valuable. However, this study has too many limitations to inform us about their relationship or the potential existence of “man flu”.
Although the Daily Mail reported that “scientists say that men are really wimps”, this finding does not feature in the research paper.
Where did the story come from?
The study was carried out by South Korean researchers from Inha University, Seoul National University, Keimyung University School of Medicine and Ajou University School of Medicine. It was funded by an Inha University research grant.
The study was published in the peer-reviewed journal, Occupational Medicine.
Both the Daily Mail and The Daily Telegraph went beyond the study’s findings by linking the research to “man flu”, although these suggestions do appear to be based on the researchers’ own comments that men may “overrate symptoms” while women may be “more stoical” when dealing with colds.
It should be noted that the study itself looked at symptoms of cold, not flu.
What kind of research was this?
This prospective cohort study used surveys to look at the experiences of over 1,200 Korean workers to find out if work-related stress made workers more susceptible to the common cold. Cohort studies, which examine occurrences in groups of people over time, are often used to look at possible associations between certain events (in this case, job stress) and health outcomes (in this case, cold symptoms). Prospective studies follow people over time rather than examining their histories, and are therefore considered to be more reliable. In this instance, using a prospective study design means the researchers knew which participants were stressed prior to becoming ill, helping to rule out the possibility that being ill was the source of their stress.
The researchers say that psychological stress is a risk factor for infectious diseases. While stress at work is a problem for many workers, there has so far been little research on the effect of work-related stress on the incidence of infection.
What did the research involve?
Researchers recruited study participants from 40 manufacturing companies in a region of South Korea. They conducted their initial survey in September 2006, collecting information on factors such as sex, age, marital status, education and smoking and drinking habits, and on work characteristics such as job type, tenure and working hours. They measured stress at work using a standard self-reported questionnaire used in South Korea for estimating occupational “stressors” (factors that cause stress). They divided people into “high” and “low” work stress, based on average values.
Six months later they circulated out a second questionnaire on whether participants had experienced common cold symptoms in the previous four months. They analysed their results to assess any possible association between cold symptoms and work stress, using standard statistical methods. They stratified their results according to gender and other characteristics, and adjusted findings for smoking habits and other factors thought to affect the risk of cold symptoms.
What were the basic results?
Out of a total workforce of 3,408 people invited to participate, some 2,174 workers (64%) completed the initial survey. Of these, only 1,241 participated in the second survey (36% of invited workface, 57% of participants). Fifty-two percent of men and 58% of women reported cold symptoms in the four months before the second survey.
Men who reported being in the “high” group for three of the work stressors in the questionnaire were more likely to report having had a cold than those who were in the “low” group for these stress factors. For women, there was no significant association between any work stressors and cold symptoms.
More detailed findings:
- Men who reported having high job demands were 74% more likely to report cold symptoms on follow-up than men who reported low job demands (OR: high job demand group 1.74 95% confidence interval [CI] 1.28 to 2.36).
- Men who reported “insufficient job control” were 42% more likely to report cold symptoms than men who did not (OR 1.42 CI 1.05 to 1.93).
- Men who reported “inadequate social support” were 40% more likely to report cold symptoms than men who did not (OR 1.40 CI 1.03 to 1.91).
- There was no association between other workplace stressors – such as job insecurity and insufficient reward – and cold symptoms.
How did the researchers interpret the results?
Overall, the researchers conclude that work-related stress may increase the risk of getting a cold. They point out that past studies have suggested that stress may trigger changes in the immune system as well as leading to unhealthy lifestyle habits. The researchers also say that the absence of any association between job stress and cold symptoms in women may partly be explained by the study’s small female sample size [Note: this cannot be verified as the research paper does not report the number or proportion of male and female participants in the study.]
However, they also say that gender differences in reporting cold symptoms and also in exposure to stress may have contributed to the result. They suggest that men tending to “overrate” symptoms and women being more “stoical” may affect the association between colds and stress.
Also, men – generally the primary wage earners in Korean families – may experience specific work stresses that may have contributed to the association with cold symptoms.
This small study found that among men, certain measurements of workplace stress, such as high job demands and lack of control, were associated with a higher risk of reporting a cold. However, as the authors note the study has several limitations, including its small size, low response rate, reliance on self-reporting and the risk of confounding factors affecting results. Importantly:
- The study did not take account of participants’ risk of exposure to cold viruses, whether at work, at home or in public places. This means that they were unable to adjust for differences in the types of work that men or women do, which could be part of the explanation for the different rates of infection.
- The researchers do not report the numbers of women or men or the proportion of each in their sample. If very few of the 1,241 recruits were women (which is likely), then the small sample size involved may diminish the significance of the study’s gender-specific finding.
The suggestion that men may over-report cold symptoms, while women may be more stoical, has not been proven. It’s also of note that in its assessment of stress the study does not take account of other stressors such as family life (which could affect women more, particularly new mothers).
Work-related stress and its possible impact on sickness rates is a well-recognised and serious issue. Determining whether stress at work can result in increased susceptibility to illnesses, including colds and flu, requires good quality research.