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Smoky homes: a review of the exposure and effects of
secondhand smoke in New Zealand homes
George Thomson, Nick Wilson, Philippa Howden-Chapman
This article reviews the evidence of the exposure to
secondhand smoke (SHS) in New Zealand homes, and the evidence of the effects of
that exposure. Work on this topic is part of research by the Housing and Health
Research Programme/He Kainga Oranga of the University of Otago, on the health
risks in the domestic indoor environment. SHS exposure in New Zealand workplaces
has previously been reviewed.1
Secondhand smoke is a major public health problem in New
Zealand,2 with no known safe level of exposure.
SHS is associated with cardiovascular disease, cancers, respiratory and
reproductive problems, and the damage of genetic material, potentially affecting
the health of future generations. It has been described as the most dangerous
common environmental air pollutant in developed
countries.3,4
The health impact from SHS can be immediate, with reductions
in arterial elasticity in healthy young adult non-smokers after 30 minutes
exposure.5
Infants and children have characteristics that make them
even more likely to be affected by SHS. They have smaller airways, higher
respiratory rates, and immature immune systems. Infants inhale double the
quantity of household dust compared to adults, and so inhale more dust
containing SHS particulates (perhaps 40 more times more per body weight than
adults). Infants also have greater hand/object/mouth contact, and so absorb
proportionately more SHS through ingestion, as well as through
inhalation.6
SHS exposure for children increases the risk of: asthma
exacerbations, lower respiratory illness, lung damage, middle ear disease,
behavioural and learning problems, and Sudden Infant Death Syndrome
(SIDS).7 In addition to the direct effect of
SHS exposure on infants, the exposure of pregnant women to SHS adversely affects
the health of their children.8
MethodsA search was made for
literature on SHS in the home setting during April–May 2004, through
Medline, EBSCO, and Proquest electronic databases, using combinations of the
search terms: Zealand, Maori, environmental, tobacco, secondhand, smok*, home*,
infant*, child*, and parent*. The references within the material found enabled
further publications to be accessed. In addition, reports were obtained by
inquiries to official and other agencies. Data on the types of households with
smoking members were obtained by an analysis of the 1996 Census
results.9 Additional trend analyses were
conducted on some of the survey data using the software package Epi Info
2000.
ResultsThe
prevalence of exposure to SHS—A 2003 survey of those aged 15 years
and over indicates that 18% of the general population are exposed to SHS in
their own home, with 20% also reporting exposure to SHS in
other people’s
homes.10 Twenty-two percent of children were
potentially exposed.11 These findings are
compatible with the high proportion of respondents who reported smoking bans in
their homes (75% of Maori, 80% overall).10
However, a survey of Year 10 students (aged 14–15 years) reported 30%
exposed to SHS at home,12 and a 2002 survey of
Year 10 and 12 students reported 44% of their homes as
smoky.13
There are little data on the amount of
time per day that people are exposed to
SHS in New Zealand homes. In 1996, survey respondents, who were exposed to SHS
‘away from work’ (not necessarily at home), reported an average of
3.4 hours exposure on weekdays (4.4 hours for Maori). At weekends, those exposed
to SHS reported an average of 4.4 hours exposure ‘in their homes’
per day (5.1 hours for Maori).14
The average reported time spent smoking in the 1999
New Zealand Time Use Survey was 1.6
hours per day for those who smoked,
with women aged 12–29 years reporting smoking an average 1.9
hours/day.15 No data were found on the time
spent smoking in homes.
In the 1996 Census, 38% of households with children (aged 17
and under), included smokers. Because over 7% of the adults living with children
did not specify their smoking status, and non-reporting of smoking by those aged
under 15 is probable, the proportion of households with smokers and children
could have been significantly larger. Overall, households with children were
more likely to contain a reported smoker than all households (38% compared to
33% respectively).9
The existence of smokers living in a household does not
necessarily lead to direct SHS exposure
inside the home, nor does the absence of smokers living in a household prevent
direct exposure in the home. Non-reported smokers under 15 may not smoke inside
their homes. A 1996 survey reported that 30% of all smokers, and 37% of Maori
smokers, restricted their smoking to outside their
houses.14 The overall proportion was even
higher (40%) among smokers in houses with children under 5 years.
On the other hand, in a 2001 survey of Year 10 students,
where neither parent smoked, 11% of
students still reported that they were exposed to SHS in the
home.16 Thus some children appear to be still
exposed to SHS from visitors or non-parent household members.
Time trends in SHS
exposure—Reported exposure to SHS in homes appears to have been
decreasing over the last 15 years (Table 1). Between 1996 and 2003, the
reduction for Maori and the total population was highly statistically
significant (p<0.001 for trend for both). The ASH surveys of Year 10 students
also indicate a steady reduction over time (p<0.00001 for trend) (Figure 1).
Table 1: The proportion of New Zealanders aged over 14
years reporting regular SHS exposure at home (National surveys)
† Only non-smokers
asked.17,18; ‡ Smokers and non-smokers
aged 15 plus14; *Aged 15 plus, exposed to SHS
in their home in one of the last seven
days.10
Figure 1: SHS exposure at home for Year 10 students,
1992–2003*
![]() * Year 10 students, asked if
people smoked in their home. In 2003, the question changed to one asking
students if people smoked in their home in one of the last 7
days.12,16,19
The unequal SHS exposure by
ethnicity, income, socioeconomic status, and location—Different
population groups are exposed to very different levels of SHS. Maori are almost
twice as likely to report SHS exposure compared to the whole population (Table
1). In 2001, 59% of 14–15 year old students in Year 10 attending schools
classified by the Ministry of Education as being of socioeconomic decile 1 and 2
(i.e. the most deprived) had a parent who smoked. This compared with 27% of
students in decile nine and ten schools.16 In
2003, the rate of SHS exposure reported by adults was 37% in households with an
income under $10,000, compared to 7% for households with incomes between
$70,000–$100,000.9
Two local studies give further insights on the likelihood of
differential SHS exposure in populations. A 1993–94 survey of rural or
small-town Bay of Plenty children found smokers in homes of 57% of the children
(41% of Pakeha [New Zealand European], 71% of
Maori).20 A 1993 survey of Christchurch
children compared a random group of 6–7 year olds from across
Christchurch, with all 5–8 year olds in an industrial suburb of
Christchurch (Hornby). Twenty-nine percent of the Christchurch-wide children
were reported to have a smoker in their home, compared to 44% in
Hornby.21 In comparison, national Census data
from 1996 showed that 38% of households with children reported smokers in the
household.
The health effects from
home-related SHS exposure—There have been two recent New Zealand
studies that estimate the effect of SHS exposure at home on mortality. The first
conservatively estimated over 250 deaths in New Zealand per year resulting from
current home SHS exposure; over double the mortality from workplace
exposure.22 This estimate did not include the
effects of SHS on current smokers.
The second study of two large cohorts utilised 1981 and 1996
Census data for never-smoking adults aged 45–74 and linked mortality data.
It found an increased risk of death of 15% (per person/year), for those who
lived in a household with smokers, compared to those that did
not.23 This may be an underestimate, as the
increased risk of death from home
exposure may be even greater if the confounding effect of SHS exposure outside
homes on New Zealanders could be allowed for. These two studies have been
compared, and found to be broadly consistent in their
findings.24
Data from the Dunedin longitudinal study indicated that
parental smoking significantly impaired the lung function of children as they
developed between ages 9 to 15.25 A study of
children aged 3–27 months, who were hospitalised with lower respiratory
illness, showed that the more severely ill children had higher hair nicotine
levels, indicating greater exposure to SHS.26
In a study of Canterbury infants born during 1992, there was
a statistically significant (52%) increased risk of hospitalisation within 10
months for infants of smoking mothers (allowing for ethnicity and educational
level). The study estimated that 14% of all infant hospitalisations for children
aged 6–10 months were attributable to maternal smoking (before and after
birth).27 Furthermore, the number of
respiratory illness hospitalisations
(attributable to SHS) of New Zealand children aged 2 years has been estimated as
over 500 per annum.28
Based on 1991–1993 data, the risk of SIDS was
increased by maternal smoking and a combination of maternal smoking and bed
sharing. The latter combination increased the risk by five times, compared to
children with non-smoking mothers.29 The total
New Zealand deaths from SIDS that were attributable to SHS have been estimated
at about 50 per year.2 In addition, two New
Zealand studies have found a significantly increased risk of carriage of
Neisseria meningitidis among those
exposed to SHS.30,31
Other likely consequences of SHS exposure in the home
include an estimated 15,000 episodes of childhood asthma annually, more than
27,000 medical consultations for child respiratory problems, and 1500 operations
in hospital to treat glue ear.28 In addition,
surveys in 2001 and 2002 of Year 10 and 12 students indicate that smoking inside
the home increases the normalcy of smoking for children, and thus the likelihood
of children becoming smokers.13,16
DiscussionThe
exposure of children—This review suggests that while SHS exposure
in New Zealand homes appears to have been reduced over time, older children
are consistently more likely to report being exposed than adults. This finding
contrasts with research from Ontario, Australia, and California, which indicates
that households with children are more
likely to be reported as smokefree, compared to all
households.32–35 However, these overseas
surveys questioned adults. The New Zealand high school students may have
been more candid than adults, or they may have been more or less accurate in
their perceptions and memory of exposure.
Both student surveys reported a much higher level of SHS
exposure at home (30% or more) than the level reported by the 2003 survey of
those aged 15 and over (18%). As well as possible differences in accuracy and
honesty, New Zealand households with teenage children may be more likely to have
smoking inside, compared to all New Zealand households. While households
without children are less likely to contain smokers, this does not appear to
explain the differences between the exposures reported by the surveys. The
validation of self-reporting surveys by objective monitoring is an ongoing need,
if only because of possible changes in the accuracy of self-reports over time.
Biomarkers and other objective monitors for SHS exposure
include levels of cotinine, and hair
nicotine.36–38 The cotinine levels
measured in non-smokers is a substance produced by the metabolism of nicotine,
and thus serves as a proxy for all the many elements of SHS. Cotinine levels can
be found in blood, saliva, or urine. Other monitors include fixed gauges such as
monitor badges that can be placed inside houses or on
clothes,39 and air sampling (nicotine
concentration and particulate levels as a proxy for SHS). The contamination by
SHS of interior surfaces could also be measured, and the nature of that
contamination analysed.
Using the same survey question to establish the SHS exposure
status of homes, the 2002 survey of Year 10 and 12 students reported 44% of
homes as smoky,13 compared to the 30% reported
by the 2003 survey of Year 10 students.12 While
both were national surveys, there is some difference in their samples. The
survey conducted in 2002 generally used two classes of Year 10 students and one
class of Year 12 students, randomly selected in each participating school,
resulting in a total of 914 Year 12 students and 2,520 Year 10 students, with a
mean age 15.0 years (Personal communication, H Darling,
2004).13
The 2003 survey of Year 10 students was limited to those
aged 14 or 15 years, with a sample of around
30,000.12,16 Such sample differences may
therefore explain some part of the discrepancy in these results, along with a
downward trend in SHS exposure. Nevertheless, the reason for such a large
difference is still not readily explainable.
Differing trends for
smoking prevalence, tobacco consumption and home SHS exposure—The
reported fall (by over one-third) in home SHS exposure during 1996–2003,
for both Maori and the whole population, contrasts with the static rate of adult
smoking prevalence during the period (from 26% to
25%).40 Apart from a movement to smoking
outside, other possible reasons for this contrast are that a constant proportion
of smokers were tending to concentrate in a smaller proportion of households,
and/or that the size of households with smokers was decreasing relative to other
households. This pattern, of SHS exposure declining faster than smoking
prevalence, is repeated in data from
California,35,41 the
USA,42,43 and
Australia.44,45
Tobacco consumption
in New Zealand fell from 1511 cigarette equivalents per smoker in 1996,
to 1187 per smoker in 2002.40 This 21%
reduction suggests that the duration and intensity of home SHS exposure will
have declined on average. However, as the dose response effect of SHS does not
appear to be linear,46,47 a decrease in
duration and intensity may not result in an equivalent reduction in harm to
health among those exposed to SHS.
The exposure of particular
populations and possible trends—The New Zealand pattern of greater
SHS exposure at home for those in low-income households is consistent with
American evidence.48,49 It is also consistent
with the New Zealand evidence for total SHS exposure at work and
home.50 The higher SHS exposure means that the
existing financial disadvantage of low-income households is compounded by the
likelihood of increased illness and premature death. Therefore, improved control
of the SHS problem has potential to reduce health inequalities in the New
Zealand setting.
The proportion of the New Zealand population that is Maori,
Pacific, and Asian (particularly those under 18 years) is growing. By 2016, just
over half of all children are projected to be in these three ethnic
groups.51 Thus, if current differentials in SHS
exposure levels persist, the population effect of higher SHS exposure on Maori
children may become relatively more important.
Exposure from re-emission
from deposited SHS particulates—The reported exposure to SHS does
not take into account the re-emission of material from the tobacco smoke
deposited on household surfaces, clothes, and skin. There may also be SHS
exposure due to direct hand or mouth contact with household surfaces, clothes,
and skin.6 A 1996 study of child inpatients
(aged 3 months to 10 years) in Wellington found that reported smoking outside by
others in the household did not reduce hair nicotine in the
children.52 This may have been due to
misreporting, to the child’s exposure outside their own house, to smoke
brought inside on clothes or other objects, and to
previous smoking in the house (due to
the long life of smoke residues).
Improving surveillance and
research—No national data have been published on the SHS exposure
of Pacific Peoples or Asian groups, or of pregnant women and infants. Therefore,
information from the routine national Health Surveys of the Ministry of Health
is needed to fill this gap. Furthermore, regional data from national surveys of
SHS exposure need to be analysed, to help focus District Health Board
policymakers on areas and groups at particular risk.
As shown above, some local rates of SHS exposure may be
double the national rates. National and local data are also needed on the
duration of exposure, and some of the
direct and indirect effects of SHS exposure at home—including primary care
visits, school and work absenteeism, and unintentional injury rates. Evidence on
some of these outcomes will be available in the future from the
Housing, Insulation and Health Study of
the Housing and Health Research
Programme.53
Research on the financial costs of SHS in homes is desirable
to determine the resulting health care spending, lost pay, lost and lower
production, and the costs of work and other injuries. Other related spending
that could be isolated are those of higher cleaning and maintenance costs, lower
home resale prices, and higher insurance
costs.54 Apart from the direct health care
costs, other indirect and intangible costs from childrens’ sickness
(resulting from SHS) that could potentially be measured include: time off work
for parents to care for sick children, healthcare-related transport, and the
downstream financial and other costs of the psychological stress on
parents.55
At present, there is a lack of a standardised classification
system of SHS exposure levels that can be recognised by New Zealand
policymakers, health professionals, and others as requiring action to protect
the general population or particular vulnerable groups (e.g. those with
established respiratory conditions). This lack is echoed in other
jurisdictions.56 In contrast to the official
national target developed for smokefree workplaces in New
Zealand,57 there is no such target for
increasing the prevalence of smokefree homes.
Policy implications for SHS
control—The recent decrease in home SHS exposure is a public health
success, but the evidence still indicates a significant danger to health within
homes for at least a fifth of the New Zealand population. The consequent
mortality is likely to be at least double that from workplace SHS exposure
before 2004, and is likely to become relatively greater as workplace SHS
exposure is sharply reduced.
An investment and policy focus by Government and other
agencies is needed to reduce SHS exposure for all New Zealanders, with the
priority on improving the protection of those groups most at
risk—children, Maori, and those in low-income households. Child exposure
is a particular concern, as children may have no one to negotiate smokefree
homes on their behalf.
The recent increase in smokefree workplaces, due to the
Smoke-free Environments Amendment Act
2003, is likely to support the trend towards smokefree homes. This is
because the existence of smokefree workplaces changes social
norms,58 with some resulting association
between working in smokefree places and living in smokefree
homes.59,60
Apart from improving health and reducing a range of costs,
smokefree homes have a protective effect for the risk of child smoking uptake,
and also help smokers reduce and quit
smoking.33 There is evidence that comprehensive
tobacco control programs are associated with increased smokefree
homes.61,62 Possible options for central
Government include strengthening tobacco control programmes, especially for
groups most at need, and strengthening mass media campaigns that specifically
promote smokefree homes. Indeed, a Government target for the verifiable
reduction of home SHS exposure is essential.
Author information:
George W Thomson, Research Fellow; Nick A Wilson, Senior Lecturer;
Philippa Howden-Chapman, Associate Professor, Department of Public Health,
Wellington School of Medicine and Health Sciences, University of Otago,
Wellington
Acknowledgements:
Comments from Dr Murray Laugesen and an anonymous reviewer on drafts were
much appreciated. In addition, we thank all the agencies and individuals who
helped us access data, particularly the Health Sponsorship Council and Helen
Darling. (The Health Research Council of New Zealand funds the Housing and
Health Research Programme.)
Correspondence: Dr
George Thomson, Department of Public Health, Wellington School of Medicine and
Health Sciences, University of Otago, PO Box 7343, Wellington South. Fax: (04)
389 5319; email: gthomson@wnmeds.ac.nz
References:
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