If nobody smoked tobacco in New Zealand from 2020 onwards, what effect would this have on ethnic inequalities in life expectancy?

Background: Smoking contributes to the 7 to 8 year gap between Maori and non-Maori life expectancy (2006 Census). To inform current discussions by policy-makers on tobacco control, we estimate life-expectancy in 2040 for Maori and non-Maori, never-smokers and current-smokers. If nobody smoked tobacco from 2020 onwards, then life expectancy in 2040 will be approximated by projected never-smoker life expectancy.
Method: Life-tables by sex/ethnicity/smoking status for 1996-99 were estimated by merging official Statistics New Zealand life-tables, census data and linked census-mortality rate estimates. We specified six modelling scenarios, formed by combining two options for future per annum declines in mortality rates among never-smokers (1.5%/2.5% and 2.0%/3.5% for non-Maori/Maori; i.e. assuming a return to long-run trends of closing ethnic gaps as in pre-1980s decades), and three options for future per annum reductions in the mortality rate difference comparing current to never-smokers (0%, 1% and 2%).
Results: In 1996-1999, current smokers had an estimated 3.9 to 7.4 years less of life expectancy relative to never-smokers. This smoking difference in life expectancy was less among Maori than among non-Maori. If the 2006 census smoking prevalence remains unchanged into the future, we estimate the difference in 2040 between Maori and non-Maori life expectancy will range from 1.8 to 6.1 years across the six scenarios and two sexes (average 3.8). If nobody smokes tobacco from 2020 onwards, we estimate additional gains in life expectancy for Maori ranging from 2.5 to 7.9 years (average 4.7) and for non-Maori ranging from 1.2 to 5.4 years (average 2.9). Going smokefree as a nation by 2020, compared to no change from the 2006 Census population smoking prevalence, will close ethnic inequalities in life expectancy by 0.3 to 4.6 years (average 1.8 years; consistently greater for females).
Discussion: If smoking persists at current rates it will become an even greater constraint on life expectancy improvements for New Zealanders in the future. Continued increases in life expectancy, and closing of the Maori:non-Maori gaps in life expectancy, would be greatly assisted by the end of tobacco smoking in Aotearoa-New Zealand by 2020.