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

Long working hours and health in Denmark: a post hoc analysis of three cohort studies

BACKGROUND

To protect the safety and health of workers, national legislations often stipulate an upper limit to weekly working time. The purpose of the present study was to provide information that may facilitate the obtainment of evidence-based limits to weekly working time.

OBJECTIVE

To estimate incidence rate ratios (RRs) of (i) hospital treatment or death due to accidental injuries, (ii) redeemed prescriptions for psychotropic drugs and (iii) redeemed prescriptions for antihypertensive drugs, respectively, as continuous functions of weekly working hours among employees in the general population of Denmark.

METHODS

Baseline data on working time arrangements were obtained from the Danish Labor Force Surveys of 1999-2013. Follow-ups with a mean duration of 1.8, 4.0 and 6.6 years for accidental injuries, psychotropic drugs and antihypertensive drugs, respectively, were accomplished through national registers. Adjusted RRs were obtained through Poisson regression in the interval 32-80 weekly working hours (wwh). The reference (standard working hours) was set at 37 wwh. RR estimates were interpreted in accordance with a modified version of Monson's guide to strength of associations, in which a RR in the open interval 0.83 to 1.2 is classified as 'no association' (too weak to be detected by observational studies).

RESULTS

The estimated RRs as well as the upper and lower limits of their 95% confidence intervals lied within the no-association zone throughout the intervals 32-76, 32-64 and 32-69 wwh, for accidental injury, psychotropic drug use and antihypertensive drug use, respectively. The estimated RRs for psychotropic drug use decreased from 1.08 (95% CI: 1.03-1.13) at 32 wwh to 0.96 (0.93-0.99) at 45 wwh. They thereafter increased to 1.00 (0.95-1.06) at 55 wwh and 1.31 (1.08-1.63) at 80 wwh. The estimated RRs for accidental injury and antihypertensive drug use increased slowly from 1.00 at 37 wwh to 1.04 (0.88-1.24) and 1.11 (0.94-1.31), respectively, at 80 wwh.

CONCLUSION

These results suggest that, from a societal perspective, the effect of wwh on the rates of these types of morbidity is negligible throughout the interval 32-64 wwh.

Prospective Associations Between Fixed-Term Contract Positions and Mental Illness Rates in Denmark's General Workforce: Protocol for a Cohort Study

BACKGROUND

In 2018, 14% of employees in the European Union had fixed-term contracts. Fixed-term contract positions are often less secure than permanent contract positions. Perceived job insecurity has been associated with increased rates of mental ill health. However, the association between fixed-term contract positions and mental ill health is uncertain. A recent review concluded that the quality of most existing studies is low and that the results of the few studies with high quality are contradictory.

OBJECTIVE

This study aims to estimate the incidence rate ratios (RRs) of psychotropic drug use and psychiatric hospital treatment. These ratios will be considered, first, in relation to the contrast fixed-term versus permanent contract and, second, to fixed-term contract versus unemployment.

METHODS

Interview data with baseline information on employment status from the Danish Labor Force Surveys in the years 2001-2013 will be linked to data from national registers. Participants will be followed up for up to 5 years after the interview. Poisson regression will be used to estimate incidence RRs for psychiatric hospital treatment for mood, anxiety, or stress-related disorders and redeemed prescriptions for psychotropic drugs, as a function of employment status at baseline. The following contrasts will be considered: full-time temporary employment versus full-time permanent employment and temporary employment (regardless of weekly working hours) versus unemployment. The analyses will be controlled for a series of possible confounders. People who have received sickness benefits, have received social security cash benefits, have redeemed a prescription for psychotropic drugs, or have received psychiatric hospital treatment for a mental disorder sometime during a 1-year period preceding baseline will be excluded from the study. The study will include approximately 134,000 participants (13,000 unemployed, 106,000 with permanent contracts, and 15,000 with fixed-term contracts). We expect to find approximately 16,400 incident cases of redeemed prescriptions of psychotropic drugs and 2150 incident cases of psychiatric hospital treatment for mood, anxiety, or stress-related disorders.

RESULTS

We expect the analyses to be completed by the end of 2021 and the results to be published in mid-2022.

CONCLUSIONS

The statistical power of the study will be large enough to test the hypothesis of a prospective association between fixed-term contract positions and mental illness in the general workforce of Denmark.

INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID)

DERR1-10.2196/24392.

Long working hours and psychiatric treatment: A Danish follow-up study

Objective:

This study aimed to estimate prospective associations between long working hours and (i) redeemed prescriptions for psychotropic drugs and (ii) psychiatric hospital treatment due to mood, anxiety or stress-related disease, among full-time employees in Denmark.

Methods:

Full-time employees who participated in the Danish Labor Force Survey sometime in the period 2000–2013 (N=131 321] were followed for up to five years in national registers for redeemed prescriptions for psychotropic drugs and psychiatric hospital treatment due to mood, anxiety or stress-related disease. Rate ratios (RR) were estimated for 41–48 versus 32–40 and >48 versus 32–40 working hours a week. The analyses were controlled for sex, age, night shift work, calendar time of the interview and socioeconomic status (SES). Prevalent cases were excluded in primary analyses.

Results:

The RR for psychotropic drugs were estimated at 0.94 [99% confidence interval (CI) 0.88–1.01] for 41–48 versus 32–40 working hours a week and 1.08 (99% CI 0.99–1.18) for >48 versus 32–40 working hours a week. The corresponding RR for psychiatric hospital treatments were estimated at 0.90 (95% CI 0.75–1.08) and 0.96 (95% CI 0.76–1.21). We did not find any statistically significant interaction between weekly working hours and age, sex, SES or night shift work.

Conclusion:

Long working hours as they occur in in the general working population of Denmark are not an important predictor of mental ill health.