Saturday, February 9, 2013

Non-smoking Wives and Lung Cancer

The effects of second-hand smoke on the development of lung cancer have long been a topic of interest in the health field. A study, Non-smoking wives of heavy smokers have a higher risk of lung cancer: a study from Japan, by Takeshi Hirayama, interviewed and followed over 250, 000 adults in 29 health centers and 6 prefectures across Japan. Of these, 91, 540 wives were followed for 14 years. Throughout this time the wives and their husbands were asked independently about their daily lifestyle habits. In the study they also categorized the participants by age and how many cigarettes they smoked a day. They also tested if the husbands'other habits impacted the wives' health such as alcohol and found that they did not. They also identified other variables that could have an impact on the development of the disease such as urban and agricultural factors. The study found that mortality increased up to twofold and those couples who lived in rural areas were more likely to have lung cancer because they were more likely to be around each other more often.

This study was very interesting because Japan seemed like an ideal place to do the study seeing that only 15% of the women smoke while 73% of the men did.  Accurate results could be expected because the study was conducted over an extended amount of time because the researchers actually followed these people for 14 years. This study proved significant because it proposed a link between non-smokers and lung cancer rather than what might have been expected which is that direct smokers would have lung cancer. It also produced evidence that supported their claim. I think it was interesting that they defined the category of non-smokers by breaking them into groups of rural and urban couples to further analyze. I thought it was important that they also tried to find links between smoking and other diseases that others might propose to counteract their findings.

The advantage of using the type of study design used here is that the data was based on real people’s lifestyles and not simulations. Also, because one is following around the same couples for an extended period of time, the data collected is coherent and consistent. They did not require the participants to alter their behaviors which lessened the likelihood that they would drop out or alter their responses.

The study seemed effective because it made use of a population where the amount of male smokers in Japan greatly overcomes the population of female smokers. The fact that the lung cancer rates in both groups were similar showed that some other factor besides direct smoking could have impacted the women’s chances of developing the disease. Of course, there could be other factors that could have been observed like food and family history and housing and working environments. The study included a large number of participants, one of the ways to ensure a cause and effect relationship. A problem that could be presented is that although this was cohort study, and they did not make people change their lifestyle behaviors, they still could have received false information as a result of recall and report bias. For instance, a husband might not report exactly how many cigarettes they have had in a day because they do not want to seem like too much of a heavy smoker. In addition to this, they had to make sure there was an absence of confounding variables by trying to relate other habits to lung cancer.  I think the study overall was a good study because it was like a foundation for future findings that we know of today that allow us to be more careful of the habits of people we are around and the environments we are in.


  1. I thought that the most important comment you made and the one on which you focused was about the gap between the percentage of men who smoked and the percentage of women who smoked, which I think I forgot to mention in my own post. This seemed to be the whole reason for the study - the mystery of why Japanese women who didn't smoke were repeatedly diagnosed with lung cancer - and you're right about it making Japan an ideal place to do the study.

    Researchers were able to observe populations of non-smokers living with smokers easily, for the simple fact that they were readily available to them. When so few women smoke (compared to the amount of men at the time of the study), couples are an easy source to look at to gauge the affect of smoke on non-smokers because they are already living together. As you said, none of their habits had to be changed and they could simply be observed, which worked very well for this study considering its length and population size.

  2. For decades, public health advocates have attempted to link cigarette smoking and lung cancer. The attempt to make a causative link between smoking and lung cancer has been stymied by the long timespan prior to the development of lung cancer, the relative rarity of the disease and the numerous confounding factors that are concurrent in individuals who smoke. This landmark prospective cohort study sought to show an association between second-hand (aka side-stream) smoke exposure, lung cancer incidence, overall mortality and lung cancer attributable mortality. For more information about criteria of causation please see the Bradford Hill criteria:
    The study designers utilized a cohort design in order to analyze the risk associated with second hand smoke exposure (risk ratio = relative risk). Cohort studies are often difficult to accomplish due to the length of follow-up time, the overall cost of the study and the possibility of a large number of study participants to be lost to follow-up. In contrast, case-control studies identify cases (those with disease) and controls (those similar but without disease) and attempt to distinguish different rates of past exposure. This study sought to prove that smoke exposure was specifically related to an increase in lung cancer incidence, environment of residence is not a confounder of this relationship and that smoke exposure and lung cancer incidence has a dose response relationship (more smoke exposure causes more cancer). The authors further point out that considering their results, future comparisons of the health status between smokers and nonsmokers should control for the secondhand smoke exposure of nonsmokers.
    You accurately pointed out in your blog post that this study was more easily accomplished in Japan due to the difference in smoking behavior in women and men. Considering the Hill criteria linked to above, do you feel the results of this study support second hand smoke as a cause for lung cancer? Which of these criteria do you think are met by this study?