Second-Hand Smoking Increases Risk Of Adult Death By 15 %
New Zealand researchers publish world’s largest study on second-hand smoking and mortality
Adults who have never smoked and who live with smokers have a 15 per cent higher risk of death than those living in a
smoke-free household, says Dr Sarah Hill, lead author of a study conducted by the University of Otago’s Wellington
School of Medicine and Health Sciences and to be published Monday by the prestigious British Medical Journal.
The research uses New Zealand Census-Mortality Study data for all adult census respondents who had never smoked and were
aged 45-74 years at the time of either the 1981 or 1996 population censuses.
Smoking status data was available for all household members aged 15 and over, and death rates were monitored for three
years after the two censuses.
Those who had never smoked but who were living in households with one or more current smokers were regarded as being
exposed to secondhand smoke in the home. Those living in households with no current smokers were regarded as not
exposed.
The findings were conclusive: adults who had never smoked and who lived with smokers had about a 15 per cent higher risk
of death than those living in a smoke-free household, even after taking into account differences in age, ethnicity,
marital status, and socioeconomic position.
“This result was consistent with previous studies in this area, but what makes it truly significant is that it is more
precisely measured than ever before due to its being based on a large study,” Dr Hill says.
“The findings also add to the weight of evidence of harm caused by second-hand smoking, and emphasise the importance of
hard-hitting television commercials that are being launched at Parliament on Wednesday,” says Dr Tony Blakely, co-author
and principal investigator of the New Zealand Census-Mortality Study.
The television commercials urge parents to protect their children from second-hand smoke by either quitting or smoking
outside. The commercials are funded by the Ministry of Health and developed by the Health Sponsorship Council and The
Quit Group.
BACKGROUND AND OTHER QUESTIONS
What data did the researchers use to arrive at their conclusions? The study authors used information from the 1981 and
1996 New Zealand censuses, anonymously linking this with routinely collected death records from 1981-1984 and 1996-1999.
This information forms part of the New Zealand Census-Mortality Study (NZCMS) that is conducted in collaboration with
Statistics New Zealand. The NZCMS was funded by the Health Research Council of New Zealand, and is now funded by the
Ministry of Health and the University of Otago. More information on the NZCMS can be found at:
www.wnmeds.ac.nz/nzcms-info.html
So how many New Zealanders die each year from second-hand smoking? This study looked at mortality only among adult
non-smokers aged 44 to 77 years. Second-hand smoking has adverse health effects on other age groups, including children.
Other researchers have estimated the total number of deaths caused by second-hand smoking in New Zealand: this is
thought to be around 347 per year. The NZCMS research findings published on Monday are consistent with this previous
estimate.
What does this study add to what we already know? This is the largest study to examine the risk of mortality in
second-hand smokers. Its findings are consistent with previous smaller studies, but because of its larger size the
results have a higher degree of statistical accuracy. This adds considerable weight to the existing evidence of harm
caused by exposure to second-hand smoke.
Where can I find the actual study? The study will be electronically published at www.bmj.com late on Monday 7 April. The
actual hardcopy publication will appear in late April.
Hill, S., Blakely, T., Woodward, A., & Kawachi, I. British Medical Journal. Increased mortality amongst never-smokers living with smokers: evidence from two
New Zealand cohorts 1981-84 and 1996-99.
Who else could speak knowledgeably about these results to the media? Professor Alistair Woodward University of Auckland
Tel: 64 9 373-7599, extn: 86361 Mobile: 027 490-5954 Email: a.woodward@auckland .ac.nz (Professor
Woodward is a co-author of the study, and has an extensive track record of tobacco-related research and policy-advice.
He is also a past-member of the National Health Committee.)
Iain Potter, Director, Health Sponsorship Council Tel: 64 4 472-5777 Mobile: 027 446-4103 (Mr
Potter is co-ordinating the second-hand smoke campaign that is being launched on Wednesday 7 April.)
What do the results actually look like?
Fig: Death rates per 100,000 for never-smoking adults by household second-hand smoking exposure, adjusted for age and
ethnicity
The Figure shows that for both sexes, and in both 1981-84 and 1996-99, never smokers living in households with one or
more smokers have higher death rates than never smokers living in smoke free households.
Put another way, the death rate among adult never smokers exposed to second-hand smoking compared to never smokers
living in smoke-free homes was: 10 per cent for males in 1981-84 4 per cent for females in 1981-84
17 per cent for males in 1996-99 27 per cent for females in 1996-99
These results for 1981-84 were of borderline statistical significance in 1981-84, but were clearly statistically
significant in 1996-99.