The potential impact of income redistribution on obesity prevalence in New Zealand

Abstract

To quantify the association between absolute individual income and relative individual income and obesity prevalence in Aotearoa, New Zealand in 2016. Then to model the potential effect of the Families Package (an income redistribution policy) implemented in 2021 on obesity prevalence. Methods: Treasury modelled estimates of the change in income experienced by individuals due to the Families Package. Logistic regressions using New Zealand Health Survey 2016/17 data generated an association between absolute income and obesity. Linear regressions determined the effect of income inequality (measured by Gini) on national obesity prevalence (from the NCD-RisC) in OECD countries. Potential impact fractions were used to apply the change in income distribution to each of these associations. Findings: The Families Package had a modest effect on New Zealand's income distribution, changing Gini from 0.577 to 0.572. Absolute individual disposable income was associated with obesity in a shallow, inverted J-shaped fashion in females living with other adults. The inverted J-shape indicated that additional income provided to low-income females might increase their prevalence of obesity. In males, the association was curvilinear and modified by age and ethnicity. Income inequality was significantly linearly associated with female obesity prevalence, while there was no clear association in males. Female obesity prevalence was modelled to decrease by 0.12% due to the changes to absolute income, and 0.98% due to changes to income inequality. Conclusions: Despite being the most substantial change to income distribution in New Zealand in decades, this policy is a modest intervention to change a known determinant of obesity. There was some evidence that income redistribution could exacerbate the socioeconomic gradient of obesity. While uncertainty is innate to modelling at this level, it remains a vital tool to understand the effect of interventions that target systemic determinants of health. Health economic analyses should be employed to determine the cost-effectiveness of these interventions. Understanding the effects of redistributive policies allows researchers to inform policy development to improve public health. Further studies should model the effect of this and other income interventions on a broad range of health outcomes to comprehensively capture the potential effects of income redistribution.