A new epidemiology study from the American Cancer Society indicates that women who spend more than six hours per day of leisure time sitting are at an increased risk of developing multiple myeloma. This was a large study of 77,642 women and 69,260 men followed between 1992 and 2009.

What in the world does this mean? Sitting is bad for women, but not for men? Or, perhaps, women who sit a lot are doing something really dangerous which causes myeloma—what the authors call “unhealthy behaviors.” But women are always complaining that it is the men who are sitting on the sofa watching sports and eating snacks and drinking beer. So what is going on here?

This article is helpful in highlighting the problems with epidemiology, a discipline which is searching for meaningful associations. When famed epidemiologists Doll and Hill were investigating the link between smoking and lung cancer in the UK, they observed that the strongest link was between the rising incidence of lung cancer and the introduction of automatic washing machines into the UK. Was this important? No – because it had no meaning. Washing machines do not leak fumes that cause lung cancer. To establish a link you need to show, for example, that cigarettes contain chemicals which cause cancer. They showed a clear link between the number of packs/years smoking and lung cancer.

One also needs a good dose of common sense! If you park your car in the driveway and a storm comes along then a tree falls and crushes your car, should you always be afraid of trees? No, you should be afraid of storms, clean out the garage and park your car in the garage.

The problem arises, such as in the case of “sitting,” when something is sort of plausible. We know exercise is good and too much sitting could be bad. But how does that relate to myeloma in women? In this study they looked for cross associations with being overweight, diet and diabetes. These are tangible things which might have impact. No clear linkages were found. Other activities of both women and men were considered. Were they still working? Where they sitting at home or in a car, etc. Ultimately, there was no theory as to what was going on.

Bottom line: Sitting too much is certainly not healthy, but how this links to causing myeloma is unknown. Unless a plausible causal link is shown, this information becomes “interesting, but not yet important.” In contrast, we do have real concern about toxic fumes from the 9/11 event because cancer-causing chemicals were involved. This is a plausible link which we must always look for. So stay tuned! Any plausible linkages will certainly be reviewed and discussed.

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You mention a link between rising incidence of automatic washing machines and lung cancer in an English study. Perhaps, it does make sense. Automatic washing machines free up more time which, if idle, could increase the amount of cigarettes smoked in a given time period. A link between myeloma in women and sitting is much more puzzling and I won't even attempt to comment!

Dear Allen,

You raise a very good point, which was actually discussed at the time. There was a significant increase in the number of women in the UK who took up smoking in the 1950s and 1960s – maybe because they had more free time. Now, we just need to figure out what sitting women are doing today that is so dangerous!

Thank you,
Brian Durie

correlation does not equal causation.

Agreed ! --- Thank you

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