Passive Smoking - Evidence

Evidence

Epidemiological studies show that non-smokers exposed to second-hand smoke are at risk for many of the health problems associated with direct smoking.

In 1992, the Journal of the American Medical Association published a review of available evidence on the relationship between second-hand smoke and heart disease, and estimated that second-hand smoke exposure was responsible for 35,000 to 40,000 deaths per year in the United States in the early 1980s. The absolute risk increase of heart disease due to ETS was 2.2%, while the attributable risk percent was 23%.

Research using more exact measures of second-hand smoke exposure suggests that risks to non-smokers may be even greater than this estimate. A British study reported that exposure to second-hand smoke increases the risk of heart disease among non-smokers by as much as 60%, similar to light smoking. Evidence also shows that inhaled sidestream smoke, the main component of second-hand smoke, is about four times more toxic than mainstream smoke. This fact has been known to the tobacco industry since the 1980s, though it kept its findings secret. Some scientists believe that the risk of passive smoking, in particular the risk of developing coronary heart diseases, may have been substantially underestimated.

A minority of epidemiologists have found it hard to understand how second-hand smoke, which is more diluted than actively inhaled smoke, could have an effect that is such a large fraction of the added risk of coronary heart disease among active smokers. One proposed explanation is that second-hand smoke is not simply a diluted version of "mainstream" smoke, but has a different composition with more toxic substances per gram of total particulate matter. Passive smoking appears to be capable of precipitating the acute manifestations of cardio-vascular diseases (atherothrombosis) and may also have a negative impact on the outcome of patients who suffer acute coronary syndromes.

In 2004, the International Agency for Research on Cancer (IARC) of the World Health Organization (WHO) reviewed all significant published evidence related to tobacco smoking and cancer. It concluded:

These meta-analyses show that there is a statistically significant and consistent association between lung cancer risk in spouses of smokers and exposure to second-hand tobacco smoke from the spouse who smokes. The excess risk is of the order of 20% for women and 30% for men and remains after controlling for some potential sources of bias and confounding.

Subsequent meta-analyses have confirmed these findings, and additional studies have found that high overall exposure to passive smoke even among people with non-smoking partners is associated with greater risks than partner smoking and is widespread in non-smokers.

The National Asthma Council of Australia cites studies showing that second-hand smoke is probably the most important indoor pollutant, especially around young children:

• Smoking by either parent, particularly by the mother, increases the risk of asthma in children.
• The outlook for early childhood asthma is less favourable in smoking households.
• Children with asthma who are exposed to smoking in the home generally have more severe disease.
• Many adults with asthma identify ETS as a trigger for their symptoms.
• Doctor-diagnosed asthma is more common among non-smoking adults exposed to ETS than those not exposed. Among people with asthma, higher ETS exposure is associated with a greater risk of severe attacks.

In France, exposure to second-hand smoke has been estimated to cause between 3,000 and 5,000 premature deaths per year, with the larger figure cited by Prime minister Dominique de Villepin during his announcement of a nationwide smoke-free law: "That makes more than 13 deaths a day. It is an unacceptable reality in our country in terms of public health."

There is good observational evidence that smoke-free legislation reduces the number of hospital admissions for heart disease. In 2009 two studies in the United States confirmed the effectiveness of public smoking bans in preventing heart attacks. The first study, carried out at the University of California, San Francisco and funded by the National Cancer Institute, found a 15 percent decline in heart-attack hospitalisations in the first year after smoke-free legislation was passed, and 36 percent after three years. The second study, carried out at the University of Kansas School of Medicine, showed similar results. Overall, women, non-smokers, and people under age 60 had the most heart attack risk reduction. Many of those benefiting were hospitality and entertainment industry workers.