Second-hand Smoke and Lung Cancer

In a study conducted from 1966-1979, non-smoking women with heavy smoking husbands were studied over a 14 year time period in 29 districts of Japan. The study was done in order to relate the risk of lung cancer and mortality to second-hand smoke. In a test control of 91,540 women over the age of 40, there was a significant increase in lung cancer and mortality rate compared to women with non-smoking husbands. Also, data was organized by the husband’s occupation, and the results show that women in agricultural families had the highest rate of lung cancer. In summary, the overall results demonstrated that a high exposure to second-hand smoke directly correlates to lung cancer.

I thought that the most interesting part of this study was the separation of variables and classifications of the women that were being studied. By classifying them into groups concerning the husband’s occupation, age group, and location, the validity of this study was intensified. This is also contributed to what I found to be the most important part of this study, the related measures of other types of cancer within the subjects. Such diseases as cervical cancer, stomach cancer, and ischemic heart disease were not found to be related to the exposure to second-hand smoke in the women exposed to cigarette smoke. This type of isolation is important because it allows the results to be more specific and accurate towards lung cancer’s relationship to second-hand smoke.

This study’s design proves three significant factors that assist in the validity of its results. First, the study was conducted over a wide range – nearly all of Japan – and not just in a single district. This is effective because it takes into account a variety of environmental factors that might differentiate the results. For instance, if the data was simply collected over one district, then certain air pollution might contribute to the results. Secondly, the study was done over a long period of time and with many test subjects. 14 years and 91,540 women are a lot of data, more than enough to come up with solid conclusions. And thirdly, a strong control group was established. Lung cancer cases from women who smoked were reliable data to compare to the second-hand smoke population. Also, as previously stated, by classifying the subjects and eliminating other side effects from second-hand smoke, attributable risk was easily identified.

In Schneider Chapter 6, there were 4 criteria highlighted in proving cause and effect. I believe that the results from this study support second-hand smoke as a cause of lung cancer because they follow these criteria. First, there needs to be a large number of subjects being tested, and this study tested 91,540 women. Second, the higher the relative risk or odds ratio there is, the more valid the cause and effect relationship is. The risk ratios of women having lung cancer due to husbands who were occasional smokers, ex-smokers or 1-19 cigarettes a day, and daily smokers of 20 or more cigarettes a day were 1-00, 1-61, and 2-08, respectively. These increased levels of risk ratios support such claims. Thirdly, there should be an effective dose-response relationship. As previously stated, there were several classifications dividing the results of the subjects such to fit this criterion. Fourth, epidemiologic evidence is attributable if there is a known connection between exposure and disease. This study follows this criterion because it also measured other cancers and diseases from the test subjects to find no relatable evidence that second-hand smoke would cause such cancers and diseases. Overall this study presents significant evidence that second-hand smoke contributes to lung cancer.