I have been interested in the relationship between Mediterranean Diet and Dementia which has led me to the Seven Countries Study – the first study to characterise the diet and the health benefits. One of the papers linked to the study involved US railroad workers and is freely available here. The research team included Dr Ancel Keys (see citation in Appendix B). Although my main question was about Dementia, this study asked about the health effects of sitting behaviour which I have written about previously in several posts.
As a slight aside, when I was reading through this paper which dates back to 1962 I was intrigued to see a reference to the London transport executive who at that time were undertaking a study on the relationship between physical activity and coronary artery disease in bus drivers and conductors. It was also interesting to see the reference to the use of IBM punch cards by the railworkers, a software program written to analyse the data, as well as the use of ICD-6 (International Classification of Diseases) by the researchers.
The researchers looked at three groups of workers – office workers, signal men and section men. Office workers were characterised as having more sedentary jobs. Signal men were considered intermediate in physical activity and included foremen. Section men were responsible for maintenance of the railroad and were characterised as more physically active.
Section men had more violent deaths than office workers. Office workers on the other hand had more deaths from coronary artery disease than section men and in the age group 60-64 this difference was particularly marked.
‘ASHD deaths account for 76 per cent of the difference in nonviolent death rates between clerks and section men‘
where ASHD refers to atherosclerotic heart disease.
Indeed in the age group 60-64 the mortality (non-violent deaths) in the clerks was 19 per 1000 compared to 10 in section men. In other words there was almost a two fold increase in the mortality in the sedentary workers.
The last word about this question can’t be from 1962 but it’s interesting to note that there is more recent work that supports this.
Appendix A – Technical Details
The main hypothesis was that ‘men in sedentary occupations have more coronary heart disease than those in occupations requiring moderate to heavy physical activity’
Age adjusted mortality for ASHD was
(a) Clerks 5.7/1000
(b) Switchmen 3.9/1000
(c) Section men 2.8/1000
In Table 3, the researchers present a 95% confidence interval for the non-violent mortality rates (per 1000). For the 60-64 year age group the values are
(a) Clerks: 19.28 +/- 2.054
(b) Switchmen: 15.59 +/- 1.929
(c) Section men: 9.93 +/- 1.966
The researchers use a Chi-squared test to analyse the difference between the groups and chose a 5% value for significance.
Appendix B – Full Citation
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I come from a family of railroad workers. There is another phenomenon that can be observed in workers who do the heavy lifting when they retire. If they suddenly become sedentary they are at high risk for rapid onset of obesity and coronary artery disease. I think a study of lumberjacks would be an interesting one because in many cases they are expending 8-9,000 calories per day and unless they rapidly compensate in reduced caloric intake when they stop working – would be at very high risk for weight gain.
George Dawson, MD
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Interesting – also didn’t realise about the energy expenditure in lumberjacks.
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