Night shift work is associated with an increased risk of asthma

Abstract

Introduction: Shift work causes misalignment between internal circadian time and the external light/dark cycle and is associated with metabolic disorders and cancer. Approximately 20% of the working population in industrialised countries work permanent or rotating night shifts, exposing this large population to the risk of circadian misalignment-driven disease. Analysis of the impact of shift work on chronic inflammatory diseases is lacking. We investigated the association between shift work and asthma.

Methods: We describe the cross-sectional relationship between shift work and prevalent asthma in >280000 UK Biobank participants, making adjustments for major confounding factors (smoking history, ethnicity, socioeconomic status, physical activity, body mass index). We also investigated chronotype.

Results: Compared with day workers, 'permanent' night shift workers had a higher likelihood of moderate-severe asthma (OR 1.36 (95% CI 1.03 to 1.8)) and all asthma (OR 1.23 (95% CI 1.03 to 1.46)). Individuals doing any type of shift work had higher adjusted odds of wheeze/whistling in the chest. Shift workers who never or rarely worked on nights and people working permanent nights had a higher adjusted likelihood of having reduced lung function (FEV₁ <80% predicted). We found an increase in the risk of moderate-severe asthma in morning chronotypes working irregular shifts, including nights (OR 1.55 (95% CI 1.06 to 2.27)).

Conclusions: The public health implications of these findings are far-reaching due to the high prevalence and co-occurrence of both asthma and shift work. Future longitudinal follow-up studies are needed to determine if modifying shift work schedules to take into account chronotype might present a public health measure to reduce the risk of developing inflammatory diseases such as asthma.

Keywords: asthma; asthma epidemiology.

Figure 1

Adjusted odds of moderate-severe asthma by current shift work exposure (n=257 219). Forest plot of adjusted ORs with corresponding 95% asymptotic CIs for moderate-severe asthma stratified by current work pattern. Three multivariate logistic regression models were fitted to the data: Model 1 (green circle): age- and sex-adjusted. Model 2 (blue square) covariates: age, sex, smoking status, smoking pack-years, alcohol status, daily alcohol intake, ethnicity, Townsend Deprivation Index, days exercised (walked, moderate and vigorous), body mass index, chronotype, length of working week, job asthma risk and job medical required. Model 3 (yellow triangle): model 2 covariates plus sleep duration.

Figure 2

Adjusted odds of experiencing wheeze or whistling in the chest in the last year by current shift work exposure (n=280 998). Forest plot of adjusted ORs with corresponding 95% asymptotic CIs for experiencing wheeze or whistling in the chest in the last year stratified by current work pattern. Three multivariate logistic regression models were fitted to the data: Model 1 (green circle): age- and sex-adjusted. Model 2 (blue square) covariates: age, sex, smoking status, smoking pack-years, alcohol status, daily alcohol intake, ethnicity, Townsend Deprivation Index, days exercised (walked, moderate and vigorous), body mass index, chronotype, length of working week, job asthma risk and job medical required. Model 3 (yellow triangle): Model 2 covariates plus sleep duration.

Figure 3

Adjusted odds of moderate-severe asthma by lifetime duration of shift work including nights (A) and by average monthly frequency of shifts that included night shifts (B) (n=107 930). Forest plot of adjusted ORs with corresponding 95% asymptotic CIs for moderate-severe asthma stratified by lifetime duration of shift work including nights (A) and by average monthly frequency of shifts that included nights (B). Three multivariate logistic regression models were fitted to the data: Model 1 (green circle): age- and sex-adjusted. Model 2 (blue square) covariates: age, sex, smoking status, smoking pack-years, alcohol status, daily alcohol intake, ethnicity, Townsend Deprivation Index, days exercised (walked, moderate and vigorous), body mass index, chronotype, length of working week, job asthma risk and job medical required. Model 3 (yellow triangle): model 2 covariates plus sleep duration.