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PASSIVE SMOKING

(January 2002)

How dangerous is second hand smoke? You would think, from all the media reports, that the question has been answered to every one's satisfaction. That is not the case.

Two older reveiw articles remain pertinent today. The March 25, 1999 issue of The New England Journal of Medicine includes a summary article titled, "Passive Smoking and the Risk of Coronary Heart Disease-A Meta-analysis of Epidemiologic Studies".

The authors reviewed a total of 18 studies and concluded that, when they are taken together, there is an increased risk of 25 percent among those exposed to second hand smoke - a little less for those exposed to the smoke of 1 to 19 cigarettes a day, a little more for those exposed to the smoke of 20 or more cigarettes per day.

The authors conclusion is "passive smoking is associated with a small increase in the risk of coronary heart disease".

An editorial by Dr. John C. Bailar III, in the same issue of the Journal, questions the conclusions. He points out that active smoking increases the risk of coronary heart disease by about 75 percent. He finds it hard to believe that second hand smoke could increase the risk by 25 percent; that is just too large a fraction of the risk from active smoking.

Bailer finishes the editorial with this : "I regretfully conclude that we still do not know with accuracy how much or even whether exposure to environmental tobacco smoke increases the risk of coronary heart disease."

An article about the same time in the journal Epidemiologic Reviews reviews the effects of second-hand smoke on lung cancer among non-smokers. There are some thirty-five studies on lung cancer and second-hand smoke. Studies conducted in the United States and Europe show only a very small increase in risk (17 to 22 percent). The authors then give several reasons for being skeptical about the results. A major problem is that lung cancer occurs quite infrequently among non-smokers. The alleged very small increase that is claimed is not impressive. The Environmental Protection Agency conclusion that 3,000 cases of lung cancer each year (of the total number of 164,000 annually) are due to the effects of second-hand smoke on the lungs of non-smokers is just a guess, and probably an exaggeration at that .

Smoking is harmful. It would be much better if nobody smoked. That is unequivocally true. Second-hand smoke is potentially dangerous for adults with bronchitis or asthma, and can induce angina (heart pain) in those with coronary heart disease; and, it is irritating to a lot of non-smokers. But, does second-hand smoke cause lung cancer or heart attacks? The answer is that we still don't know for sure. A lot of the public fear of second-hand smoke is based on assumptions that are still controversial and unsettled. Understandably, that conclusion will offend a lot of people, but we should be careful not to exaggerate the risks due to passive smoking (second-hand smoke). That does not change the fact that active cigarette smoking is responsible for at least 85 percent of lung cancer, is a major risk factor for heart attacks, and is a risk factor for stroke, and for many other diseases. Furthermore, the evidence for passive smoking increasing the risk of asthma, ear infections, and upper respiratory infections in young children is quite good.

for the ability of passive smoke to cause heart attacks and cancer.

He, J., et al. Passive smoking and the risk of coronary heart disease. The New England Journal of Medicine. Vol 340. (March 25) Pgs 920-926. 1999.

Brownson, R.C., et al. Epidemiology and prevention of lung cancer in nonsmokers. Epidemiologic Reviews. Vol 20. (No. 2) Pgs 218-236. 1998.