Morbidity-Mortality Paradox Among South Asians Living in Britain
Matthew Wallace, Ined
Frances Darlington-Pollock, University of Liverpool
Morbidity-mortality paradox amongSouth Asians in Britain
University of Liverpool
Migration from SouthAsia (India, Pakistan, and Bangladesh) played a pivotal role in the rebuilding ofBritain after WWII, with individuals encouraged to move to fill severe laborshortages across Britains industries1. While the nature of these streams has changed (from labor, to familyreunification, to education), South Asians have continued moving to Britain. In2011, India became the largest non-UK country of birth in Britain, with Pakistan4th, and Bangladesh 8th. The morbidity-mortality literatureon South Asians is fascinating: they are found to report higher limitinglong-term illness (LLTI) rates2-4 while experiencing lower mortality than the UK-born5-7. Such an inconsistency may be down to study design i.e. differingdefinitions, time periods, and age-ranges. For example, some define migrants bycountry of birth5,6, ethnicity (which includes the G2+)3 or a combination thereof7. Regardless, LLTI is an effective proxy for mortality so such an inconsistencyremains striking. We question whether the paradox is real i.e. are South Asiansliving longer, but in worse health, than the UK-born (which would impact demandfor health services, requiring culture-specific policies) or, whether it isgenerated by either an overestimation of LLTI or an underestimation ofmortality. Initially, we aim to calculate LLTI and mortality ratios for SouthAsians, using a consistent definition (country of birth), age group (20-85+)and period (2010-2012), to determine whether we observe a morbidity-mortalityparadox. If so, we want to see if it differs according to the two most fundamentaldemographic characteristics: sex and age.
We calculateage-adjusted and age-specific LLTI and mortality incidence rate ratios (IRR) viaPoisson regression by sex, using the age range 20-24 up to 85+. Death andpopulation counts are taken from the 2011 Census and Office for NationalStatistics Mortality tables; LLTI and population counts are taken from a 5% sampleof the 2011 Census. The age-adjusted results are displayed in Figure 1 whichfor the first time presents comparable LLTI and mortality estimates among SouthAsians. The age-specific results are displayed in Figure 2, illustrating at whatages the paradox (when it is observed) emerges.
In Fig.1, wefind the paradox in all groups except Indian males who have an LLTI IRRconsistent with their mortality IRR. We observe a difference by sex in thescale of LLTI IRR, but not mortality, which is consistent.
Figure1. Age-adjusted mortality and LLTI ratios relativeto UK-born.
In Fig.2,mortality differences are pronounced at young adult ages but approximate fullytowards the reference line, usually around age 50. Interestingly, in four ofthe six groups, mortality decreases post-retirement (65+). For LLTI, a commonshape is shared in Pakistanis and Bangladeshis, in which LLTI is not differentfrom the reference at young ages, rises above the reference line at age 40,peaks at age 60 and declines thereafter. For Indians, the shape is different,with both males and females reporting lower levels of LLTI before age 40 (withmales attenuating to the reference, but females rising above). Thus the paradoxtaken in its definition of high illness-low mortality emerges from age 40.
Figure2. Age-specific mortality and LLTI ratios relativeto UK-born.
We will use anindividual-level, longitudinal dataset which allows us to track South Asiansand UK-born by their linked LLTI-mortality status. In doing this, we will beable to investigate differences in mortality (rates, time-to-death, and causeof) among South Asians relative to the England and Wales-born by LLTI status.Additionally, we will also calculate emigration rates by country of birth andLLTI status.
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6 Wallace,M. & Kulu, H. Mortality among immigrants in England and Wales by majorcauses of death, 1971-2012: A longitudinal analysis of register-based data. SocSci Med 147, 209-221, doi:10.1016/j.socscimed.2015.10.060 (2015).
7 Scott,A. P. & Timaeus, I. M. Mortality differentials 1991-2005 by self-reportedethnicity: findings from the ONS Longitudinal Study. Journal of epidemiologyand community health 67, 743-750, doi:10.1136/jech-2012-202265(2013).