Secondhand Smoke is Also Lethal

Summarized by Robert W. Griffith, MD
September 3, 2004

Introduction

There has been controversy surrounding the possible ill effects of secondhand smoking. A number of reports find it harmful, others say "it has no effects". Some of the differences in findings may have been due to the relatively small size of these studies. Now, however, there's a report from New Zealand that should be large enough to convince the most skeptical. It's published in the British Medical Journal, and summarized here.

What was done

Information obtained from two New Zealand censuses was used. New Zealanders between 45 and 74 who provided 1981 and 1996 census replies to questions if they had never smoked, and whether they lived with a smoker. All the 'never smokers' were divided into two groups: those who lived with smokers and those who did not. Death rates over the 3 years following the censuses were compared for each group.

What was found

Mortality (expressed as number of deaths per 100,000 persons) is shown in the table below, along with the ratio of 'exposure' to 'no exposure', after adjustment for age, ethnicity, marital status, education, household income, etc:

	Men		Women
	Mortality	Rate Ratio	Mortality	Rate Ratio
1981-1984
No Exposure	1530		1010
Exposure	1684	1.17*	1050	1.06
1996-1999
No Exposure	1025		672
Exposure	1198	1.16*	855	1.28*

* statistically significant (i.e. not considered a chance finding)

It can be seen that living with a smoker in the household increases the 3-year mortality risk by about 15%.

Further evidence

The New Zealand report shows the increased risk of dying for non-smokers living with smokers, but it doesn't detail the causes of the increased deaths. Another study published in the same issue of the British Medical Journal provides some information on this.¹

Helena, Montana, is an isolated US community that imposed a smoking ban for 6 months, from June 2002 to December 2002. (The ban was suspended by a court order after six months.) The investigators analyzed hospital admissions for heart attack (myocardial infarction, or MI) between December 1997 and November 2003. This allowed them to determine if the smoking ban influenced the heart attack rates.

The six month periods June-December were analyzed for the years 1998 through 2003. In 1998 through 2001 and in 2003 the average number of heart attack admissions for the 6 months was 40, whereas it was only 24 during the 6 months when the smoking ban was in force. In other words, the rate of heart attacks admitted to hospital was nearly cut in half during the period when smoking was banned in the workplace and in public places.

Of course, the smoking ban affected both smokers and those non-smokers frequently exposed to secondhand smoke. Unfortunately, the analysis didn't include the proportion of non-smokers among the MI cases. Nevertheless, this study shows that removal of smoking - active and/or passive - is associated with a dramatic reduction in the frequency of heart attacks.

What these studies mean

These studies show that: 1) passive smoking is linked to an increased mortality over a three-year period, and 2) lack of smoking (active and/or passive) is linked to a decrease in heart attacks over a 6-month period. They reinforce the notion that both active and passive smoking cause heart attacks in the short term, and that passive smoking increases death rates.

While further studies are needed to define the relative roles of cardiovascular and respiratory diseases in smoking-linked deaths, the message to smokers is obvious. Your habit is dangerous not only to yourself, but also to your non-smoking spouse and family members, your colleagues at work, and other people around you. Get help and break the habit, now.

Source

• Mortality among "never smokers" living with smokers: two cohort studies, 1981-4 and 1996-9. SE. Hill, TA. Blakely, I. Kawachi, A. Woodward, BMJ, 2004, vol. 328, pp. 988--989

Footnotes
1. Reduced incidence of admissions for myocardial infarction associated with public smoking ban; before and after study. RP. Sargent, RM. Shepard, SA. Glantz, BMJ, 2004, vol. 328, pp. 977--983

Related Links
Smoking Causes Mental Deterioration in Later Life
When You Stop Smoking
3-Cigarettes-a-Day Double a Woman's Risk
The Negative Effects of Smoking on Bones, Joints and Healing

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