Occupational exposure to high levels of noise, greater than 90 dBA, and night shift work appear to be associated with an increased risk of ischaemic heart disease (IHD), a population-based study from New Zealand has found. However, no such association was seen for long working hours and sedentary work.

The investigators carried out a longitudinal data linkage study using Statistics New Zealand’s (Stats NZ) Integrated Data Infrastructure, a longitudinal meta-dataset of routine datasets administered by government agencies, Stats NZ surveys (including the 2013 census) and non-government organisations.

The study population consisted of all New Zealand residents aged 20-64 years who were employed at the time of the 2013 census. The authors gathered data on incident IHD between 2013 and 2018 based on hospital discharge, prescription and death records.

Information on occupation and number of working hours was obtained from the census. Exposure to sedentary work, loud noise and night shift work was assessed using New Zealand job exposure matrices.

Hazard ratios (HR) were adjusted for age, socioeconomic status, smoking and ethnicity.

Of the 8 11,470 men and 783, 207 women in employment at the time of the census, 15,012 men (1.9%) and 5,595 women (0.7%) were identified with incident IHD during a median follow-up of 5.8 years. The majority of cases, 81% of men and 75% of women with IHD, were identified through hospital discharge records.

For men, there was a higher risk of IHD for the highest category of noise exposure (> 90 dBA):

•  HR 1.19 (95% CI: 1.07-1.33)

Night shift work was associated with a raised risk of IHD for both men and women:

• Men HR 1.10 (95% CI: 1.05-1.14)

• Women HR 1.25 (95% CI: 1.17-1.34)

The population attributable fractions for night shift work were 1.8% for men and 4.6% for women.

No clear association with working long hours and sedentary work and IHD were observed.

As well as the traditional risk factors for cardiovascular disease environmental and psychological factors are also implicated and these factors can be linked to occupation.

The study authors state: ‘In conclusion, this study showed an association between night shift work, high levels of noise and higher IHD risk. The impact of night shift work on IHD in New Zealand may be significant, as suggested by the population attributable fractions of 1.8% for males and 4.6% for females.’

They add: ‘The study does not support a role for sedentary work or long working hours, although results need to be interpreted with caution due to exposure assessment limitations, in particular the absence of information on exposure duration.’

These findings may aid in risk stratification of patients and inform employers regarding health risks associated with working conditions and patterns.

Dr Peter Savill