Social Determinants of Health

Health is shaped far more by the conditions in which people are born, grow, live, work, and age than by individual health behaviours or health care alone. The Dahlgren-Whitehead model (1991) conceptualises these influences as layers surrounding the individual: genetic and biological factors at the core, surrounded by individual lifestyle factors, social and community networks, living and working conditions, and finally broad socioeconomic, cultural, and environmental conditions at the outermost layer. All layers interact; upstream determinants (macro-level) constrain what is possible at downstream levels.

Poverty is central. Absolute poverty means lacking the resources to meet basic human needs (food, shelter, warmth). Relative poverty is defined in relation to the median income in a given society — typically below 60% of median household disposable income. Relative poverty drives health inequalities through material deprivation, psychosocial stress, and restricted access to education, transport, and services. In New Zealand, both Māori and Pacific peoples have significantly higher rates of relative poverty than European/Pākehā populations.

New Zealand has two deprivation indices. NZiDep is an individual-level measure based on self-reported material deprivation across eight domains (e.g., going without food, not being able to meet essential costs). NZDep (now in its 2018 version) is an area-based small-area deprivation index calculated from Census variables including income, employment, transport, living space, owned home, qualifications, and access to communication. NZDep deciles (1 = least deprived, 10 = most deprived) are widely used in health services research and funding formulae.

Health literacy — the ability to obtain, understand, and act on health information — mediates the relationship between education and health. Low health literacy is associated with poorer chronic disease management, higher hospitalisation rates, and lower uptake of preventive services. It is prevalent in New Zealand, particularly among older adults and some Pacific communities.

Education directly shapes health through knowledge, health literacy, employment prospects, and income. Higher educational attainment is associated with lower all-cause mortality in every country studied. Employment provides income, social identity, structure, and purpose; precarious or hazardous employment increases risks of mental health problems, injury, and cardiovascular disease. Housing quality profoundly affects health: in New Zealand, cold, damp housing — often due to poor insulation, single-glazing, and inadequate heating — is strongly associated with group A streptococcal pharyngitis, rheumatic fever (rates in Māori and Pacific children are among the highest in the developed world), and respiratory infections including bronchiectasis. Mould in housing contributes to asthma and respiratory disease.

The social gradient in health means that each step up the socioeconomic ladder is associated with better health outcomes — this is not just a threshold effect between poor and non-poor. Marmot's Whitehall studies demonstrated this gradient in British civil servants. In New Zealand, this gradient is clearly evident in all-cause mortality, hospitalisation, and disease prevalence data stratified by NZDep decile and ethnicity.