It's more evidence that precisely pins down this somewhat difficult-to-determine health risk, writes Paul Brennan, PhD, with the International Agency for Research on Cancer in Lyon, France.
His study appears in the current International Journal of Cancer.
More than 50 studies have looked at this link between nonsmokers who develop lung cancer and the role that secondhand smoke played. However, it's never been clear just how much the risk increases with increased exposure from multiple sources, such as a spouse's smoking, childhood exposure to smoke, as well as exposure in the workplace and social settings.
In this newest study, Brennan and colleagues pool together data from the two largest studies thus far on secondhand smoke and lung cancer.
The 1,263 men and women in the studies had never smoked, but had developed lung cancer. They represented five metropolitan areas in the U.S. (Atlanta, New Orleans, Houston, Los Angeles, and San Francisco) and 11 areas in Germany, Italy, Sweden, Spain, Portugal, and the United Kingdom. All provided information on secondhand smoke exposure during their lives.
The odds of lung cancer were calculated in individuals who were ever exposed to smoke. They also looked at the duration of secondhand smoke exposure to the risk of developing lung cancer. Secondhand smoke exposure:
- From a spouse carried an 18% increased risk; if that exposure occurred for 30 years, the risk went up to 23%.
- In the workplace brought a 16% higher risk; 21 years of exposure increased risk to 25%.
- In social settings increased risk by 17%; 20 years or more pushed risk up to 26%.
Those who got secondhand smoke from all three sources had a 32% higher risk of lung cancer, depending on length of exposure.
Even after occupation, diet, and other possibly skewing factors were taken into account, the risks still held, he writes.
In fact, his estimates may be conservative, since a similar previous study found a 24% increased risk for spousal exposure and a 39% risk for workplace exposure, writes Brennan.
His study provides clear evidence that continuous exposure to secondhand smoke indeed increases a nonsmoker's risk of developing lung cancer, Brennan concludes.
SOURCE: Brennan, P. International Journal of Cancer, Dec. 10, 2003: vol 109.