Friday, May 9, 2008

Canadian study on SHS

Lung cancer has been identified by public health officials as the leading cause of cancer mortality for both sexes in Canada.

Most of the smoking bans implemented across Canada have been predicated on the alleged hazards of secondhand smoke (SHS), also called Environmental Tobacco Smoke or ETS, primarily as it relates to lung cancer and heart disease.

The anti-smoker brigade would have us believe that SHS is such a significant health hazard to non-smokers that it requires draconian measures, in the form of bans, to control it. Some openly encourage discrimination against smokers in the areas of housing, employment and medical care based on the alleged risks of exposure to SHS.

They base their campaign of fear and intolerance on epidemiological studies which they claim show an increased risk of lung cancer and heart disease from exposure to SHS. The evidence they claim is conclusive; but is it? One organization, Freedom2Choose, based in the UK, estimates that for every study showing that SHS is harmful; there are six which find the opposite.

One such study, “Risk factors for lung cancer among Canadian women who have never smoked”, was conducted by The Canadian Cancer Registries Epidemiology Research Group in 2002. A copy of the study is available Here .

The authors note in the results of their study: “For the reported never-smoker women, 71 cases and 293 controls, who reported their residential passive smoking history for at least 90% of their lifetimes, were chosen in the analysis. An increased risk was observed with increasing total of residential plus occupational years, but this was not statistically significant. Compared with those never exposed to either passive or active smoking, the adjusted ORs were: 0.7 (95% CI = 0.2 – 2.3), 1.2 (95% CI = 0.4 – 3.2), 1.5 (95% CI = 0.5 – 4.0), 1.5 (95% CI = 0.6 – 4.1), for 1 to 16, 17 to 30, 31 to 47, and 48 or more years of combined residential and/or occupational ETS exposure, respectively (test for trend, P = 0.16)".

Among their conclusions, the authors suggested that “passive exposure to ETS at home (or at work) may be associated with lung cancer risk”.

The key word here is “may”. Exposure to SHS may or may not be associated with lung cancer. And, please remember that association is not the same as cause. Nowhere does the study suggest that SHS is the cause of lung cancer.

It should also be pointed out that the press regularly reports the findings of these studies as a percentage, which provides an inaccurate representation of the facts.

For example, the OR (Odds Ratio) or relative risk for non-smokers exposed to SHS for 17 to 30 years, is given as 1.2 (95% CI = 0.4 – 3.2). Since studies assign an OR of 1.0 as a control reference, and the OR for 17 to 30 years of exposure is 1.2, the press would say there is a twenty per cent increase in the risk of lung cancer.

But that’s not entirely honest. The more accurate interpretation of the OR is that the relative risk for that amount of exposure would fall, 95 % of the time, between 0.4 and 3.2 (the confidence interval, or CI). Since the lower of the numbers (0.4) in the confidence interval is less than 1.0 (the reference), it suggests that for some of the controls in the study, exposure to SHS acted as a deterrent to the development of lung cancer.

When this happens, the association in not considered to be statistically significant. As noted in the study, “An increased risk was observed with increasing total of residential plus occupational years, but this was not statistically significant”.

But, this information is never provided by the press or those organizations who want the public to believe exposure to ETS is deadly. The majority of epidemiological studies show otherwise.

Why did I choose this study to make my point? Because Health Canada “estimates” that SHS kills 1000 Canadians a year. And, four of the five authors involved in the study were associated with Health Canada.

I wonder if they're making it up?

Recommended Reading: Freedom2Choose

1 comment:

Bob Feal-martinez said...

This is just one of many studies, that actually disproves rather than proves what the authors claim.

Robert Feal-Martinez