Evidence linking air pollution to health inequalities

In document New Horizons (Page 192-198)

As outlined earlier, the relationship between pollution and health inequalities is not just that pollution exposure is distributed unevenly between population groups. The second mechanism that can act independently or concurrently is that of differential susceptibility, in which for the same level of pollution, more socially disadvantaged groups – and others in the population – can be more vulnerable to exposure than high ones. Factors such as poor health status (for example COPD, asthma and existing CVD), adverse health behaviours (for example smoking and diet), multiple environmental exposures (for example occupational) and psychosocial stress are more prevalent in lower socioeconomic status groups and may act in addition or synergy (that is, as effect modifiers) with pollution exposure.

The ‘triple jeopardy’ for disadvantaged groups of first, higher exposure to air

pollution, and second a greater burden of poor health, may then be further added to by a third effect arising from greater susceptibility to the impact of pollution.43 These processes have been most investigated in relation to air pollution, and are the focus of this section. Existing evidence is reviewed, being careful to exclude studies that do not formally test differences in susceptibility between socioeconomic groups. Studies in many countries have considered the role of short- and long-term pollution exposure in explaining socioeconomic gradients in health outcomes with a plausible aetiological pollution link. Health outcomes considered include all-cause and cause- specific mortality, respiratory health (for example asthma), birth weight, and hospital admissions due to a respiratory condition.

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International evidence

Recent global and European studies reviewing the evidence that socioeconomic status (SES) modifies the effect of air pollution on health, broadly suggest that irrespective of differences in exposure, lower SES populations experience the greater effects of air pollution. The evidence base is particularly strong (number of studies and quality of study design) in the United States with a handful of studies in other, mostly European, countries.

A systematic review of the international literature found lower SES groups were at higher risk of death due to short-term exposure to particulate matter (PM10 and PM2.5).44 Similarly a review of the literature on differential effects of ozone-health relations by SES noted evidence of associations between ozone exposure and mortality for some (for example unemployment and lower occupational status) but not all (for example low education and poverty) lower SES groups.45 Other studies review the evidence relating to particular ‘vulnerable’ groups. For example, an international review found lower socioeconomic status pregnant women are more vulnerable to air pollution with an increased risk of having a child with low birth weight at term.46 On the other hand, another review found limited evidence that the association between air pollution and children's asthma exacerbations varied between SES groups.47

UK evidence

Whilst, as already summarised, there is a significant body of work in the UK

documenting socioeconomic inequalities in air pollution exposure, few studies have examined whether there is a synergistic relationship between SES and air pollution that acts to affect health. To date there have been six UK studies explicitly

addressing this question, another using a composite environmental index as the exposure metric (including measures of air pollution), and a further Europe-wide study that includes UK data (Table 6.2).

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Table 6.2 Socioeconomic inequalities in air pollution exposure - Europe-wide studies including UK data

Authors and year of publication

Pollutant(s) SES indicators Geographical unit Location Population Findings

Wheeler & Ben-

Shloma (2005)48 NOPM2, SO2, benzene, 10

Household social class

1991 census wards England Participants aged 16–79 in the Health Survey for England 1995, 1996, 1997

Differential effect of air pollution on lung function for males only; effect in social classes III to V double that in social classes I & II. Briggs et al

(2008)43

Road traffic, industry, electro-magnetic frequency radiation, disinfection by- products in

drinking water & radon

Index of Multiple Deprivation (& constituent domains)

3 levels of analysis: super output areas, census wards & districts

England Full population Some evidence of greater risk of poorer general health for those living in more socially disadvantaged areas Pearce et al (2010)42 Composite ‘Multiple Environmental Deprivation Index’ including of PM10,

NO2, SO2, and CO, plus

greenspace Area-level income deprivation 10,654 Census Area Statistics Wards

UK-wide Full population Influence of multiple environmental deprivation on health greater in the least

income-deprived areas Jephcote & Chen

(2012)49 PM10 road-transport emissions Area-level measure of social deprivation (Carstairs Index), ethnicity 187 Lower Level Super Output Areas

Leicester Children aged 0–15 Double-burden of road transport emissions and social deprivation related to children's respiratory health.

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Authors and year of publication

Pollutant(s) SES indicators Geographical unit Location Population Findings

Richardson et al (2013)50

PM10 Mean household

income

268 sub-national regions (NUTS level)

Europe- wide

Full population Lower income regions more susceptible to health effects.

Restricted to circulatory disease mortality in Eastern Europe and male respiratory mortality in Western Europe

Halonen et al (2016)51

Traffic pollution including NOx, NO2, tailpipe emissions, PM2.5 and PM10 Area-level measure of social deprivation (Carstairs Index), ethnicity 27,686 Census Output Areas Greater London

Full population Higher risk of emergency hospital admissions for cardio- respiratory diseases among those living in areas with the highest socioeconomic deprivation Brunt et al

(2016)52 Ambient NOconcentrations 2, PM10, PM2.5 Area-level measure of

income- deprivation

1909 Lower-layer Super Output Areas

Wales Full population Interactions between air pollution and deprivation strengthened

associations with all- cause and respiratory disease

Milojevic et al (2017)53

Ozone and particulate matter (sub-divided into PM10, PM2.5, PM2.5-10,

primary, nitrate and sulphate PM2.5) Area-level income & employment domains of the Index of Multiple Deprivation 1,202,578 residential postcodes in

England Full population PM2.5 pollution made a

modest contribution to socioeconomic gradient attributable life years lost.

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The UK work has covered a variety of different pollutants, sources (ambient, traffic, industrial), measures of SES (both individual and area-level indicators), populations (adults, children) and health outcomes. There has been no relevant UK work on indoor pollution.

Studies of overall and cause-specific mortality, life years lost, and hospital

admissions point to an increased health risk of pollution exposure amongst those living in disadvantageous social circumstances. For example, a study in London of annual concentrations of a range of traffic pollutants, and emergency hospital admissions for cardio-respiratory outcomes found some evidence of increased risk amongst those living in more socially disadvantaged neighbourhoods.51 Similar findings have been noted in Leicester for hospitalisations amongst children49, all- cause and respiratory disease mortality in Wales52, and general health43 and life years lost across England53, although in all cases the evidence was mixed or suggested modest effects.

A UK wide study of ‘multiple environmental deprivation’ (a composite index of

various health-related features of the environment including measures of PM10, NO2, SO2, and CO) found that whilst more socially disadvantaged populations were

exposed to higher levels of multiple environmental deprivation, the influence of multiple environmental deprivation on health was most pronounced in the least

income-deprived areas.42 Therefore contrary to the findings of most other work in the UK, the physical environment did not exert a disproportionately detrimental effect on the health of the most socially disadvantaged groups, although given the small number of areas with high levels of social disadvantage and ‘high quality’ environments this finding should be treated with caution.

Finally, a Europe-wide analysis (including the UK) of 268 subnational regions found that lower income regions had higher average pollution (PM10) concentrations and that populations of these regions were more susceptible to pollution, although any effect seemed to be limited to circulatory disease mortality in Eastern Europe and male respiratory mortality in Western Europe.

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UK evidence: summary and limitations

Tentative evidence exists for the UK of an interactive relationship between air pollution and socioeconomic status in which differential susceptibility affects health outcomes. However, several limitations restrict the conclusions that can be drawn:

• Most obviously, the UK evidence base is small, particularly when compared to

the United States.

• Unlike elsewhere, all UK studies use cross-sectional study designs which limit the

quality of the evidence. There are no studies examining how SES and air pollution exposure accumulate over the life course.

• Many UK studies rely on ecological associations; key variables such as health

and SES are captured at the ecological (rather than individual) level. There is also a poor understanding of scale, with previous international work emphasising that findings can be highly sensitive to the chosen geographical unit of analysis.

• There is little understanding of the temporal resolution of pollution exposure and

the implications for health inequalities. For instance, pollution can vary

significantly by season and time of day. Most geographic studies focus on home locations yet people move between different environments as part of their daily routines.

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In document New Horizons (Page 192-198)