Night-time work and all-cause mortality in the general working population of Denmark

Abstract

PurposeA recent study among female nurses in Denmark found an increased mortality among night-time workers, which has raised concerns about the sufficiency of the EU Working Time Directive. The aim of the present study was to examine the relationship between night-time work and all-cause mortality among full-time employees in the general workforce of Denmark.MethodsInterview data from the Danish Labour Force Surveys, 1999–2013, were linked to national registers with individual-level data on occupation, industry, socioeconomic status (SES), emigrations and deaths. The participants (N = 159,933) were followed from the end of the calendar year of the interview until the end of 2014. Poisson regression was used to estimate rate ratios for all-cause mortality, with and without stratification by sex and socioeconomic status. A likelihood ratio test was used to test the overall null-hypothesis, which stated that the mortality rates were independent of night-time work, SES × night-time work and sex × night-time work.ResultsThe likelihood ratio test did not reject the null hypothesis (p = 0.14). The rate ratio for all-cause mortality among employees with vs. without night-time work was estimated at 1.07 (95% CI 0.97–1.19) after adjustment for age, sex, SES, calendar time, weekly working hours and time passed since the start of follow-up.ConclusionsThe present study did not find any statistically significant associations between night-time work and all-cause mortality among employees in the general workforce of Denmark.

Night work, mortality, and the link to occupational group and sex

“…A recent meta-analysis did not find any significant effects of night work ( 17 ). Neither did a recent study of a representative sample of 150 000 individuals ( 18 ). However, the (non-significant) risk ratio in that study was 1.07, equal to the HR of 1.07 in the present study.…”

“…However, a recent meta-analysis including three of the studies listed above did not find a significant effect of night shifts on mortality ( 17 ). Furthermore, a study of a representative sample of 159 000 individuals in Denmark did not find a significant association between shift work and mortality ( 18 ), but that study did not adjust for lifestyle variables.…”

“…All cited studies above defined exposure at baseline and did not consider years of exposure, which should be an important factor. Only the studies by Akerstedt et al ( 15 ), Nätti et al ( 16 ), and Hannerz et al ( 18 ) used representative samples of the population, and there is a risk that data from particular occupational groups may not be representative of the population. In addition, most studies, thus far, have been quite small.…”

Prospective Associations Between Working Time Arrangements and Psychiatric Treatment in Denmark: Protocol for a Cohort Study

“…The statistical analyses are thereby blinded in the sense that all hypotheses, inclusion criteria, significance levels, and statistical models will be completely defined before we look at any relation between working time arrangements and psychotropic drugs or psychiatric hospital treatment in the datasets at hand. It should, however, be noted that the exposure data of the project have previously been analyzed in relation to circulatory disease [ 38 , 40 , 48 , 49 ], injuries [ 50 ], and all-cause mortality [ 41 , 42 ].…”

“…We expect that 84% of the included participants are working 32-40 hours a week, that 10% are working 41-48 hours a week, and that the remaining 6% are working more than 48 hours a week [ 41 ]. We expect that 12.6% of the participants will be categorized as exposed to night shift work [ 42 ].…”