Occupational groups and ischaemic heart disease in New Zealand – a longitudinal linkage study
Authors: Barnes L.A , Eng A , Corbin M , Denison H.J , t'Mannetje A , McLean D , Ellison-Loschmann L , Jackson R , Douwes J 
Published: November 2020

Abstract

Background/Introduction
Occupation is a poorly characterised risk factor for cardiovascular disease (CVD), with females and minority populations particularly under-represented in research. There is also a lack of longitudinal studies using detailed health data that does not rely on self-reports.

Purpose
This study aimed to address these gaps by assessing the association between a range of occupational groups and ischaemic heart disease (IHD) in New Zealand (NZ), through linkage of population-based occupational surveys to routinely collected health data. Half of the study population were females and 40% were indigenous Māori (who comprise 15% of the total 4.8 million NZ population), which enabled sex and ethnicity-specific aspects of the relationship between occupation and IHD to be assessed.

Methods
Two probability-based sample surveys of the NZ adult population (New Zealand Workforce Survey (NZWS); 2004–2006; n=3003) and of the Māori population (NZWS Māori; 2009–2010; n=2107), for which detailed occupational histories and lifestyle factors were collected, were linked with routinely collected health data available through Statistics NZ. Cox regression was used to calculate hazard ratios (HR) for “ever-worked” in any one of nine major occupational groups, with “never worked” in that occupational group defined as the reference group. Analyses were controlled for age, deprivation and smoking, and stratified by sex and ethnicity.

Results
The strongest associations were found for “plant/machine operators and assemblers” and “elementary workers”, particularly among female Māori (HR 2.19, 95% CI 1.16–4.13 and HR 2.03, 1.07–3.82 respectively). In contrast, inverse associations with IHD across all groups were observed for “technicians and associate professionals”, which was significant for NZWS males (HR 0.52, 0.32–0.84). There were some sex and ethnic differences, particularly for “clerks”, where a positive association was found for NZWS males (HR 1.81, 1.19–2.74), whilst an inverse association was observed for Māori females (HR 0.42, 0.22–0.82). Duration analyses (≤2 years, 2–10 years and 10+ years) showed significant dose-response trends for “clerks” in NZWS males, and “plant/machine operators and assemblers” and “elementary workers” in Māori females. Further adjustments for other potential confounders such diabetes mellitus, hypertension and high cholesterol did not affect the results.

Conclusion
Associations between occupation and IHD differed significantly across occupational groups and between sexes and ethnicities, even within the same occupational groups. This suggests that results may not be generalised across these groups and occupational interventions to reduce IHD risk may therefore need different approaches depending on the population and specific groups of interest.

Funding Acknowledgement
Type of funding source: Other. Main funding source(s): Health Research Council (HRC) of New Zealand