El Dorado's Lost City of Uranium and Good Health?
In epidemiology, whenever lower incidence and lower rates of mortality from cancer occurs in a population commonly assumed to be at risk cognitive dissonance is always lurking. What generally happens is that the good news is shrugged off as "the healthy worker effect" and epidemiologists resolve to re-sift the data in order "to get the right answers". The "right answers" of course are often only those that support our preconceptions.
That means there aren't many people willing to even consider the possibility that working in a chemical plant or going off to war or spending a career mining / processing uranium while being exposed to low levels of gamma radiation might actually confer a health benefit. Nevertheless, the so-called healthy worker effect (which is called the healthy warrior effect for those who served in the armed forces) appears so commonly and across so many trades that you have to wonder if something besides simply screening employees for good health is at work. If you're interested here are three studies worth pondering.
In this month's journal of Occupational Medicine you'll find an excellent discussion in "The Healthy Worker Effect in US Chemical Industry Workers". The study was of thousands of Dow Chemical employees - three million years worth of employment combined. The overall risk of death from any cause was lower than expected as was the risk of dying from nine types of cancer thought to be related to smoking. Nevertheless the authors, an epidemiological team working for the Dow Chemical Company, concluded that the findings were likely due to the healthy worker effect though with a caveat. Some have suggested that the healthy worker effect arises because employers dismiss employees with health problems. However, in this study the health outcomes of those employed for a decade or more were the same as those who didn't last very long with the company. The finding thus suggests that the presumed healthy worker effect was generated as each employee was considered for employment such that workers destined to get cancer decades later somehow were never hired in the first place making it in fact a "healthy hire effect".
For another example see "Psychiatric Diagnoses in Historic and Contemporary Military Cohorts: Combat Deployment and the Healthy Warrior Effect". Despite some claims in the media that might make one assume otherwise those who serve in the military see lower than expected numbers of ailments including psychological ones. Here the suggestion is that those prone to psychological illness are screened out as what risk there was of developing psychological issues after combat was concentrated in those with preexisting mental health issues.
Finally, published last month in the journal Radiation Research, there's "Mortality (1950 - 1999) and Cancer Incidence (1969 - 1999) in the Cohort of Eldorado Uranium Workers". With the exception of lung cancer incidence and mortality which demonstrated a small increase in risk, the Eldorado uranium miners managed to have significantly lower risks of dying from any cause, lower risks of dying from all cancers combined (lung cancer included) and a lower risk of developing any type of cancer cumulatively (lung cancer again included).
Now be honest. If someone had asked you yesterday whether you'd pick (A) uranium workers, or (B) the average Canadian male, as the group likely to have a much larger risk of getting cancer and of dying of cancer which would you have chosen?
So what's at work here? Is it simply that those prone to developing cancer in the distant future are somehow weeded out and never hired in the first place? Or does it perhaps have something to do with the nature of blue collar employment over the last 50 years? To me it all looks a lot like the compliance effect - the phenomenon whereby e.g. those who lead very ordered and structured lives and who thus always take their placebo at the appointed time manage not only to do better than those less disciplined and also on a placebo but oftentimes better even than those less disciplined but at least irregularly taking real medication. So I'll go out on a limb and guess that the claims of toxic tort plaintiffs notwithstanding, large employers engaged in manufacturing not only didn't shorten the lives of their workers they lengthened them by imposing the very order and rigidity about which so many bitterly complain in their depositions.
