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| Journal of the New Zealand Medical Association,
13-August-2010, Vol 123 No 1320
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If nobody smoked tobacco in New Zealand from 2020
onwards, what effect would this have on ethnic inequalities in life
expectancy?
Tony Blakely, Kristie Carter, Nick Wilson, Richard Edwards,
Alistair Woodward, George Thomson, Diana Sarfati
The public health case for concern and action on tobacco use
in Aotearoa-New Zealand is overwhelming; 4500 to 5000 deaths per year in New
Zealand can be attributed to tobacco use.1
The long-run trends in life expectancy show continual
improvement in non-Māori life expectancy and a substantial increase in
Māori life expectancy since the turn of the
19th
Century.2-4 Over the last century, average
annual reductions in mortality have been approximately 3.5% per annum for
Māori and 2.0% per annum for non-Māori (Woodward and Blakely, work in
progress). Such reductions do not occur by chance, but reflect concerted policy
and public health efforts, in addition to general improvements in health
services and standard of living. Furthermore, closing of ethnic inequalities in
life expectancy are far from guaranteed, as evidenced by a widening of
Māori:non-Māori life expectancy gaps in the 1980s and 1990s associated
with structural changes in New Zealand
society.3,5–7
The gap in life expectancy between Māori and
non-Māori c.2006 remains large at 7 to 8 years, but has narrowed from the 9
to 10 year gap c.1996.3,4,7 Such a pattern
suggests the possibility of a return to long-run trends of closing ethnic gaps
in mortality in New Zealand.
One of the greatest obstacles to extending the long-run
improvements in life expectancy into the future is tobacco use. We have
previously quantified the impact of smoking on ethnic and socioeconomic
inequalities in New Zealand during the
1990s.8–11 A Tupeka Kore Vision has been
developed which seeks the end of tobacco use in New Zealand by
2020.12
This paper asks the question: if New Zealand did end tobacco
smoking by 2020, what would the effect be on life expectancy by 2040, and in
particular the gap between Māori and non-Māori?
To attempt to answer this question, we present estimates of
life expectancy for Māori and non-Māori, and current- and
never-smokers, in 1996–99 and then project these life expectancy estimates
out to 2040. Assuming a substantive upgrade in tobacco control such that smoking
prevalence is negligible by 2020, and allowing a 20 year wash-out period for the
majority of tobacco’s effect on excess mortality, we assume that life
expectancy in 2040 will be that projected for never-smokers.
MethodsIn an accompanying paper in this issue of the
Journal,7 we present life-tables and
life expectancies for multiple combinations of time, ethnic group, income
tertiles and smoking status, using mortality rates from linked census-mortality
data.7 Here we use life-tables and life
expectancy by sex/smoking/ethnicity, estimates of future mortality decline among
never-smokers, and estimates of future rate differences for current- versus
never-smokers (and ex- compared to never-smokers in one analysis), to estimate
life expectancy in 2040.
Life-tables and life expectancyBriefly, the method used to create the life-tables
brings together three pieces of information:
These three
inputs were combined to produce mortality rates by single year of age for each
subpopulation, and complete life-tables including central death rates
(mx) and probabilities of death
(qx), calculated for each age (x:
0-100), which were then used to derive other life-table functions
such as life expectancy for each subpopulation. The life-tables used in this
paper were generated for males and females by ethnicity (Māori and
non-Māori), and smoking status (never-, current- and ex-smoker), for the
1996-99 census-mortality cohort. For smoking life-tables, mortality rates up to
age 14 were assumed to be those of the sex by ethnic group (i.e. not stratified
by smoking status). (The 2006 Census, which also includes a smoking variable, is
not yet linked to mortality data.)
ProjectionsWe focus first on projections for never- and current-
smokers. The method of estimation to 2040 involved three steps:
These steps are outlined in more
detail below.
Step 1—We set an initial
estimate of the annual percentage reduction in never-smoker mortality rates
mx of 2.5% for Māori and 1.5% for
non-Māori. These figures are consistent with Statistics New Zealand
projections for low, medium and high mortality scenarios of 2.1%, 1.6% and 1.0%
percent per year reductions in mortality rates for males (ethnic groups
combined), and 2.4%, 1.8% and 1.3% percent per year reductions for females (http://www.stats.govt.nz/methods_and_services/TableBuilder/population-projections-tables.aspx).
We modified these estimates to allow for ethnic
variation in mortality rate reductions (the long-run trends suggest mortality
rates are falling faster for Māori), and assumed that mortality reductions
in the future will be the same for males and females. Extrapolating to 2040, we
multiplied the non-Māori mx in
1996, for every single year of age, by
0.98544 = 0.514,
where 0.985 is one minus the annual percentage reduction of 1.5% and 44 is 2040
minus 1996. The Māori mx was
multiplied by 0.97544 = 0.328.
We also projected more optimistic annual reductions in
mortality rates of 3.5% per annum for Māori and 2.0% per annum for
non-Māori using the long-run trends of improving life expectancy over the
last 100 years.
Step 2—We have previously found
that the mortality rate difference (not the rate ratio) comparing smokers to
never-smokers, is consistent across time and ethnic
group.11 Therefore, we set one option for the
smoking:non-smoking mortality rate differences in 2040 as being the same as that
observed in 1996-99. However, constant rate differences over time mean
increasing rate ratios if the mortality rate among never-smokers is reducing.
For example, the rate ratio comparing current- to
never-smokers within Māori is roughly 1.5 in 1996-99. Under the
assumption of 2.5% per annum reduction in Māori never-smoker mortality
rates to 2040, a constant rate difference would see the rate ratio increase to
1+ (1.5-1)/0.328 = 2.5. We also explored the effects of alternative assumptions
of 1% and 2% per annum reductions in the rate difference, applied similarly
within sex by ethnic groups. Under the 2% per annum reduction in the rate
difference (and the 2.5% reduction in Māori never-smoker mortality rates),
the rate ratio of 1.5 in 1996 would be about 1.6 in 2040.
Step 3—With mortality rates by
single year of age for all sex/ethnicity/smoking status groups, life-tables were
easily calculated for 2040. Because of the relatively simple nature of our
projections and the differential mortality rate declines by ethnic group, it was
possible for estimated Māori never-smoker mortality rates to be less than
non-Māori never-smoker mortality rates in 2040 for some single years of
age, and likewise for estimates of Māori current-smoker mortality rates to
be less than non-Māori current- smoker rates in 2040. It is possible that
Māori mortality will fall below that of non-Māori at some time in the
future, if the long-run trend since 1900 continues. However, for the purposes of
this analysis, we assumed no more than convergence and therefore, where
necessary, forced the Māori rate to equal the projected non-Māori rate
in 2040.
Ex-smokers—The ex-smoker
compared to never-smoker mortality rate differences and rate ratios obtained
from the NZCMS should be treated with caution. This is because we do not have
data on the time since quitting, which makes ex-smoker mortality experience in
1996-99 difficult to interpret and potentially unreliable as the basis for
future projections. Nevertheless, to provide a point of comparison, we also
calculated life expectancy in 2040 for sex by ethnic groups assuming the 2006
census distribution of smoking behaviour (never-, current-, and ex-smoker). A
parallel method to that described above for current-smoker mortality rate
projections was used for ex-smokers.
Sensitivity analysesIn addition to varying the percentage annual decline in
never-smoker mortality rates, and percentage decline in the smoking:non-smokiing
mortality rate difference, we tested two other assumptions. First, life
expectancy in the future will be influenced by mortality over the age of 100, as
the proportion of centenarians in the population increases.
Thus, we extended the life-tables out to age 120 by
simply assuming that the mortality rate increased by 6% per year of age for
every year of age over 100, where 6% is approximately the change in mortality by
year of age from 90 to 100. (The methods and life-tables in the accompanying
paper in this Journal7 apply to age
100, the top end of current ‘official’ Statistics New Zealand
life-tables.) Altering this 6% percent increase down to 4% and up to 10% had
only a negligible influence of the results presented in this paper, and is
therefore not discussed further here.
Second, we had to estimate mortality rate ratios for
smokers compared to never-smokers beyond the age of 80 in the accompanying
paper,7 because the 1996-99 census-mortality
cohort only included deaths up to age 77. Our assumption was that the predicted
mortality rate ratio for current-smokers compared to never-smokers at age 80
reduced linearly to 1.0 by age 100. For the estimates to 2040 in this paper, we
investigated setting a minimum rate ratio (and hence rate difference) at all
ages – essentially ages above 80 years. Setting such a minimum at 1.2, or
even 1.5, had negligible impact on the estimations in this paper, so is not
presented further.
A copy of the Microsoft Excel spreadsheet used to
generate all estimates in this current paper is provided at the NZCMS website
(www.uow.otago.ac.nz/nzcms-info.html), and allows interested users to
alter any of the input assumptions specified above.
ResultsLife epectancy 1996–9Figure 1 shows estimates of life expectancy in
1996–99, the most recent cohort for which we have smoking data. The
estimates are reproduced in Table 1, with the addition of gaps in years of life
expectancy between Māori and non-Māori within smoking status groups,
and conversely gaps in life expectancy between smoking status groups within
Māori and non-Māori populations.
 Two patterns are evident. First, current-smokers have lower
life expectancy among males and females for Māori and non-Māori
strata. However, the gap between current- and never-smokers is less among
Māori than among non-Māori (4.3 and 3.9 years among Māori males
and females respectively, compared to 7.4 and 6.2 years among non-Māori).
Second, Māori have lower life expectancy in all smoking
strata. However, the gap between Māori and non-Māori is greater among
never-smokers than among current-smokers (10.2 and 8.8 years for male and female
never-smokers respectively, compared to 7.2 and 6.5 years for
current-smokers).
Projections to 2040Table 2 shows our projected 2040
life expectancy estimates for never- and current-smokers for the six scenarios.
Assuming New Zealand is smokefree by 2020, and allowing for a wash-out period of
20 years for past smoking-related mortality risk, then we might assume that 2040
life expectancies are approximated by the never-smokers.
For all scenarios, and all strata of ethnicity by smoking,
there are substantial improvements in life expectancy compared to 1996-99.
Regardless of the scenario, ethnic gaps within strata of smoking are also
reduced. Gaps in life expectancy between current- and never-smokers (column iv,
Table 2) range from 5 to 6 years in Scenario C (2.5/1.5% annual reduction in
Māori/non-Māori never-smoker mortality; 2% per annum reduction in
mortality rate difference between current- and never-smokers) up to 11 to 13
years in Scenario D (3.5/2.5% annual reduction in Māori/non-Māori
never-smoker mortality; 0% per annum reduction in mortality rate difference
between current- and never-smokers). Regardless of the scenario, the impact of
smoking on life expectancy is more similar for Māori and non-Māori
than that observed in 1996-99. ‘
If the 2006 census smoking prevalence remains unchanged into
the future (i.e. ‘total’ in Table 2), we estimate the difference in
2040 between Māori and non-Māori life expectancy to range from 1.8 to
6.1 years across the six scenarios and two sexes (average 3.8 years;
‘ethnic gap’ estimates in column (iii)).
By comparing the life expectancy of
‘never-smokers’ and ‘total’ across scenarios A to F, we
have estimates of the additional gains in projected life expectancy in 2040 if
nobody smoked tobacco from 2020 compared to the 2006 smoking distribution
continuing indefinitely (i.e. column (v) in Table 2). Accordingly, we estimate
additional gains in life expectancy for Māori ranging from 2.5 to 7.9 years
(average 4.7) and for non-Māori ranging from 1.2 to 5.4 years (average
2.9). That is, going smokefree as a nation will (we estimate) result in larger
improvements in Māori life expectancy, compared to non-Māori, and
therefore result in a closing in ethnic inequalities in life expectancy ranging
from 0.3 to 4.6 years (average 1.8 years).
The estimated closing of ethnic gaps in life expectancy was
consistently greater for females, reflecting the particularly high 2006 smoking
prevalence among Māori females.
DiscussionIf the 2006 census smoking prevalence remains unchanged into
the future, and background non-smoking related mortality continues to decrease
more so for Māori than non-Māori, we estimate that the difference in
2040 between Māori and non-Māori life expectancy will be about three
and a half years (averaged across sex). However, if nobody smokes tobacco from
2020 onwards, we estimate about 5 years of additional gain in life
expectancy for Māori (range across six scenarios and sexes 2.5 to 7.9
years) and about 3 years for non-Māori (range 1.2 to 5.4 years),
therefore contributing about 2 years (range 0.3 to 4.6 years) of
closing in ethnic inequalities in life expectancy.
We emphasise that our exact estimates are quantitatively
uncertain. But we do conclude that if nobody smokes tobacco by 2020 in New
Zealand there will be substantive improvements in overall population life
expectancy. And it will be an important, if not necessary, step towards the
ending of Māori:non-Māori inequalities in mortality by 2040—200
years after the signing of the Treaty of Waitangi.
A number of subsidiary findings also arise out of our
projections. Perhaps surprisingly at first glance, we find that the gap between
current- and never-smoker life expectancy in 1996-99 was less among
Māori (4.3 and 3.9 for males and females respectively) than among
non-Māori (7.4 and 6.2). The reason for this is that the absolute
additional mortality burden from smoking (i.e. the rate difference in mortality
between current- smokers and never-smokers) is about the same across ethnic
groups, sexes and time.8
The corollary of this is that the relative risk comparing
the mortality of smokers and never-smokers is less among Māori.
This is due to the much higher background mortality among Māori
never-smokers compared to non-Māori never-smokers, which in turn is due to
all the other non-tobacco determinants of mortality that vary between Māori
and non-Māori.9 11 However, if as we
assumed in this paper, Māori mortality rates fall faster than
non-Māori mortality rates in the next few decades (i.e. if mortality rate
reductions return to their long-run trends of the last century, as opposed to a
reversed pattern in the 1980s and 1990s3 4 13
associated with structural changes in the economy), then the relative impact of
smoking on mortality among Māori will increase faster than among
non-Māori. That is, the Māori life-table will move into a state where
smoking has a larger impact on life expectancy gains than it does now.
Thus, by 2040 we estimate that the gap in life expectancy
between current-smokers (hypothetical if the country is free of tobacco smoking
by then) and never-smokers will be similar for both Māori and
non-Māori (Table 2).
There are a number of limitations in our analyses. First and
foremost, we necessarily make a number of assumptions to project life expectancy
in 2040. Therefore, our projections must be interpreted as indicative only. For
example, if it is assumed that mortality cannot continue to decline at the rates
it has in the last 100 years, and that our 2.0%/3.5% per annum reductions in
non-Māori/Māori never smoker mortality are too optimistic (partly
because some of the rapid fall in mortality rates may be due to smoking
cessation itself), then scenarios A, B and C would be assumed to be more
accurate.
As another example, we think that a 2% per annum decline in
the smoking:non-smoking mortality rate difference into the future is unlikely,
and that 0% or 1% is more likely. Accordingly, we have presented six scenarios
in this paper for readers to peruse, and we have provided a copy of our Excel
spreadsheet at the NZCMS website to allow testing of alternative assumptions
(www.uow.otago.ac.nz/nzcms-info.html). We have also undertaken
sensitivity analyses varying assumptions of the decaying smoking:non-smoking
mortaltiy rate ratio above age 80 and future mortality rate decline among never
smokers above age 100 – neither greatly affected the results presented
here.
Finally, and importantly, the general conclusion remains
unaltered across the Scenarios we specified: smoking will have a bigger impact
on life expectancy in the future; and if Māori life expectancy converges
with non-Māori life expectancy then the impact of smoking will also become
more similar between the two ethnic groups.
Second there are limitations in the underlying NZCMS data,
including likely misclassification biases of smoking status and incomplete
linkage of mortality records. Regarding the former, this has probably led to
some underestimation of difference in mortality by smoking status, therefore
underestimating differences in life expectancy between never- and
current-smokers. Regarding the latter, we used linkage weights that have been
shown elsewhere to correct reasonably well for linkage
bias.14
Third, we have not explicitly allowed for passive smoking.
This currently affects more Māori than non-Māori. As a result, we have
probably further underestimated the full impact of smoking on ethnic gaps in
mortality in 2040 if current smoking prevalence continues, and will have
underestimated the overall gains in life expectancy and the impact on reducing
ethnic gaps in life expectancy of ending smoking by 2020 .
Fourth, our estimates of the association of smoking with
mortality will be prone to residual confounding. That is, smoking is associated
with other risk factors that positively confound the smoking-mortality
association. Indeed, we have shown this previously using NZCMS data for
socioeconomic position as the potential
confounder.15 There is likely to be some
off-setting between such residual confounding and the misclassification of
smoking and non-inclusion of passive smoking, however it is difficult to know
the net effect.
Policy implicationsWhat does this mean for policy making around tobacco control
and reducing health inequalities? Simply, if tobacco is consumed in the future
as it is currently, this will act as an increasingly important
“handbrake” on overall improvements in life expectancy, and will
also impede the closing of ethnic gaps in life expectancy. Ending tobacco
smoking by 2020 will not only release greater life expectancy gains for the
total New Zealand population, but also accelerate the closure of
Māori:non-Māori gaps in life expectancy.
Is ending tobacco smoking in New Zealand by 2020 feasible?
We argue “yes”, given the availability of a range of existing and
plausible interventions. In addition to intensifying established tobacco control
interventions (e.g. tax rises as just announced in New Zealand, plain packaging
as just announced in Australia, removing residual marketing such as
point-of-sale displays, and enhanced cessation services), new
‘endgame’ solutions are available. For example, a reducing quota
mechanism, or sinking lid 16, of 10 percentage
points per annum reduction in tobacco imports from 2010 to 2020 would ensure
that no tobacco is available for direct retail to the public by 2020.
Alternatively, large recurrent tax rises of about 20% per
annum (accompanied by boosted and strong cessation services) may be able to
drive prevalence down to less than 2% by 2020. Such end-game solutions have been
voiced by both non-governmental organisations in New
Zealand12 and political
leaders17, and are receiving serious scrutiny
by the current Māori Affairs Select Committee Inquiry (due to report in the
next few weeks). Such solutions may even be favoured by New Zealand smokers
since a majority of them regret smoking 18, and
support stronger regulation of tobacco.19
20
ConclusionsAs mortality rates decrease in the future, the relative
impact of smoking on mortality will increase. If nobody smoked tobacco in New
Zealand from 2020 life expectancy will be substantially improved for all, and
our average estimate is that ethnic inequalities in life expectancy will be
about two years less (compared to a scenario of 2006 smoking prevalence
continuing into the future). Making New Zealand smokefree by 2020 is achievable
– but strong political will is needed, along with improved recognition of
the desire of smokers to be free of their addiction.
Competing interests: Although we do
not consider it a competing interest, for the sake of full transparency we note
that some of the authors have undertaken work for health sector agencies working
in tobacco control.
Author information: Tony Blakely, Research
Professor1; Kristie Carter,
Senior Research Fellow1; Nick Wilson, Associate
Professor1; Richard Edwards,
Professor1; Alistair Woodward,
Professor2; George Thomson,
Senior Research Fellow1; Diana
Sarfati, Senior Research Fellow1
Acknowledgements: We
thank June Atkinson for providing smoking prevalence data from the 2006 census,
by sex, age and ethnic group; and Matt Soeberg for assisting with the
construction of life-tables. The life-table work upon which this paper is based
was funded by the Ministry of Health. The New Zealand Census-Mortality Study
(NZCMS) was initially funded by the Health Research Council of New Zealand
(HRC), and is part of the currently HRC-funded Health Inequalities Research
Programme. We thank Robert Beaglehole (Emeritus Professor, University of
Auckland; Chair, Smokefree Coalition), Prudence Stone (Director, Smokefree
Coalition), and Martin Tobias (Senior Adviser, Epidemiology, Ministry of Health)
for comments on a draft of this paper.
Correspondence: Tony Blakely, University of
Otago, Wellington, PO Box 7343, Wellington, New Zealand. Fax: +64 (0)4 3895319;
email: tony.blakely@otago.ac.nz
References:
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