Shy guys 'risk heart disease'

The risk of dying from heart disease and stroke is increased by 50% in men who avoid social contact, compared with men who are more sociable, The Times and other newspapers reported on 11 July 2007. The Times suggested that shy men "have heightened physiological responses to unfamiliar situations" and that these stress responses "can have a profound effect on men’s health". It said that the researchers did not investigate why shy men have an increased risk of cardiovascular disease.

The study does not assess why social avoidance may be linked to cardiovascular disease, so it is not clear whether trying to change behaviour would alter the risk of death from that disease.

Where did the story come from?

The story was based on a study by Jarett Berry and colleagues from Northwestern University in Chicago. The participants were men who had worked for Western Electric Company’s Hawthorne Works in Chicago and who had been there for at least two years by 1957. The study received funding from the American Heart Association, the National Heart, Lung, and Blood Institute, and Chicago Health Research Foundation. It was published in the peer-reviewed journal Annals of Epidemiology .

What kind of scientific study was this?

This was a cohort study investigating whether different levels of social avoidance in men affected their rate of death from cardiovascular disease (CVD), coronary heart disease (CHD) and other causes. A random sample of 1,945 men aged 40–55 took part. The assessment covered their medical history, a physical examination and tests for cardiovascular disease, and a questionnaire on marital status and occupation classification.

All participants also completed the Cook-Medley hostility scale, which includes a section on social avoidance. This section has four questions relating to tendency to avoid social contact. Each participant was given a score for social avoidance, and placed in one of four groups depending on their level of social avoidance.  The men were followed-up by post, telephone, employer contact and social security records until 1979. In the 11 years to 1990, follow-up was done using death certificates.  

What were the results of the study?

The study found that the risk of CVD and CHD death was, on average, 1.4 times higher for the men with the highest level of social avoidance, compared with the most sociable men. After adjustment for other factors, the risk was an average of 1.5 times higher. There was no difference between any of the groups for non-CVD death.

What interpretations did the researchers draw from these results?

The researchers conclude that social avoidance – shyness – is associated with CVD and CHD death, but not with non-CVD death. They present a hypothesis that social avoidance might promote development of CVD through non-behavioural, physiological mechanisms.

What does the NHS Knowledge Service make of this study?

This study provides preliminary results on risk of death from heart disease, stroke and other causes, in men with different levels of social avoidance. However, there are some limitations to interpretation of the study results and the authors acknowledge these.

• It was not possible to assess non-fatal events because data was only available on people who died. 
• Results were not adjusted for other psychosocial factors that may also occur in shy people (low social support, stress), so it is possible that these variables could be responsible for the differences in death from heart disease and stroke. 
• It is a secondary analysis of data collected as part of a larger observational study. This limited the type of data available, and the study authors were not able to verify individual cases.  
• The participants in the study were all from a particular geographic area, and the study did not include black people, so it may not apply to everyone.  

While this study adjusted the results for several known cardiovascular risk factors, there may be other unknown factors, internal or external, present in the group of socially avoidant men that are linked to risk of CVD death.
 
The study does not assess why social avoidance may be linked to cardiovascular disease, so it is not clear whether trying to change behaviour would alter risk of CVD death.

This study highlights the differences between linking and causation. Biological variables are often identified in studies but it is the relationship of the variable which needs to be investigated. Variables can be shown to be causal factors or risk markers. Additional research would then be needed to show that changing the causal factor can reduce the probability of disease.