Night work can be divided into numerous categories of occupation that involve working outside standard hours, often switching from day to night.
In Europe and in the United States, night work has increased in recent decades and represents 19–25% of all workers. In France, night work was limited to specific sectors for women until 2001. Since then, in accordance with the European law based on the principle of gender equality in the workplace, it is no longer subject to such restrictions.
Several jobs in different sectors or services involve duties that must be performed 24/7. The main sectors with such constraints are health and security, along with certain industrial activities that require continuous production.
The impact of night work on health is well documented. Disruptions in the circadian rhythm (the biological clock regulating the day-night cycle) can affect well-being and health. Effects on alcohol consumption, diet, sleep, reproduction, mental health, diabetes, several cancers etc. have been described for specific professions. Because of its singular nature, night work is subject to enhanced individual medical surveillance. In 2019, night shift work was classified as ‘probably carcinogenic to humans’ (group 2A) by the International Agency for Research on Cancer (IARC).
Based on census data and job-exposure matrices, this article published in the journal BMC [1]- Public Health estimates for the first time the number and proportion of night workers in France, by occupation and sector of activity. It also analyses the evolution of night work over a 34-year period, from 1982 to 2015.
3 questions for : Marie-Tülin Houot, Data Support, Processing and Analysis Department (DATA), Santé publique France and Corinne Pilorget, Environmental and Occupational Health Department (DSET), Santé publique France
In occupational risk epidemiology, it is important to take into account the risk factors of specific exposures (chemical, biological or physical exposures, postural or organisational constraints, psychosocial risks), that vary according to the type/place of work . The job-exposure matrices make it possible to evaluate exposure to these different risk factors on the basis of occupation alone (role and sector of activity), without questioning workers about the specific risks of their jobs, of which they are not always aware.
Information about whether an individual is engaged in night work is not always collected for studies, or only for a given period, and it may not be known for the entire professional career. The job-exposure matrix for night work provides, per job and per 5-year period between 1993 and 2012, the probability of having worked between midnight and 5 a.m., either regularly or occasionally. The evaluation was differentiated according to sex due to the regulations that considerably limited night work for women before 2001. For this reason, two “sex-specific” job-exposure matrices are available to document night work among men and women separately.
This matrix was constructed a posteriori using data from the annual employment surveys conducted by the National Institute of Statistics and Economic Studies (INSEE). In these surveys, which include around 150,000 people, a question night work within the respondent’s main job was repeatedly asked between 1993 and 2012. These individual data were combined by 5-year period and the proportions for usual and occasional night workers among men and women were estimated for each job and each period. The job-exposure matrices are available on the Exp-pro portal.
Night work, in its globality, considering usual and occasional night work, increased slightly in proportion between 1982 and 2015 (15.8% vs. 16.4%), which represented 3,670,000 night workers in 1982 and 4,370,000 in 2015 in France.
The most significant evolution in night work over the 34 years studied concerns the change in ratio between occasional and usual night work. In 1982, regular night work accounted for 24% of overall night work, whereas by 2015 its share had almost doubled to 42%.
The second notable shift concerns the difference in night work between men and women. The evolution of night work over the period studied is not very significant among men, around 22% of whom perform night work, whereas a clear increase from 7% to 10% among women was observed over the same period. The difference is even more significant for regular night work. Thus, among women, the proportion of regular night work rose sharply between 1982 and 2015 (+150%), due to the increase from 173,000 regular night workers in 1982 to 581,000 in 2015 following the change in regulations. In particular, between 1999 and 2007 there was a 69% increase in the proportion of female regular night workers, while the proportion of female active workers increased by only 4.5% over the same period. Among men, the number of regular night workers rose from 712,000 to 1.20 million over the period (+74% in proportion).
The sectors showing a marked increase in night work are related to service industries (1.97 million night workers in 1982 vs 3.3 million in 2015), including the transport and health sectors.
The study presented in this article was carried out in collaboration with the Exposome and Heredity team of the Centre for Research in Epidemiology and Population Health at the National Institute of Health and Medical Research (INSERM) (1), which will use the night work matrices to assess exposure when conducting studies on breast cancer, both in women and in men. Other research teams can also use these matrices, like all of the job-exposure matrices developed in the Matgéné programme of Santé publique France (see box: Matgéné programme – Job-exposure matrices).
Since 2019, the IARC has classified night work as a probable human carcinogen (group 2A). Crossing the matrices on night work with population data from a sample of employment histories collected in parallel with the 2020 and 2021 Health Barometers of Santé publique France will allow the production of indicators for exposure over the whole career. These estimates for the proportion of exposed workers considering all jobs held during their career will then be used to calculate the share of exposure to night work in the occurrence of several pathologies including breast cancer, i.e. the fraction of the risk attributable to this occupational exposure. These data will add to the information already available on the burden of disease.
Matgéné Programme – Job-exposure matrices
Developing tools to assess occupational exposure is necessary to improve knowledge and surveillance of occupational risks. Santé publique France coordinates the Matgéné programme, which aims to produce job-exposure matrices adapted to the general French population in order to produce occupational exposure indicators. A job-exposure matrix can be briefly described as a table giving the correspondence between jobs (occupation and sector of activity) and exposure indices (probability, level) to one or more risks. When these matrices are crossed with individual occupational data, exposures are automatically attributed to individuals according to the jobs they hold. The potential applications of these matrices in the field of occupational health surveillance or research are numerous. For example, they can be used to :
- estimate the proportion and prevalence of occupationally exposed people in the general population and to describe the occupations and sectors of activity most concerned at a given time or over the entire professional career
- contribute to the estimation of the share of risk attributable to occupational exposure (burden of disease)
- assess the occupational exposure of subjects in epidemiological studies
- help identify exposures in order to propose adapted prevention measures or medical/social care for workers.
The Matgéné programme’s job-exposure matrices are specifically adapted to the French working population. They provide an assessment for past and current exposure periods, thus making it possible to document past exposures whose impact on current pathologies is proven or suspected. Finally, they document exposure for all workers, employees or self-employed, whether in the public or private sector.
The Matgéné matrices available or under development concern exposure to mineral dusts (silica, cement), organic dusts (leather, flour, cereals, wood), solvents (families of petroleum solvents and fuels, chlorinated solvents, oxygenated solvents), fibres (asbestos, mineral wool, refractory ceramic fibres), formaldehyde, pesticides, noise and night work.
The matrices can be consulted on the Exp-pro portal occupational exposure indicators are available on the Géodes portal.
The matrices and indicators are available upon request to dset-matgene@santepubliquefrance.fr.
For more information: https://exppro.santepubliquefrance.fr/matgene
[1] Houot, MT., Tvardik, N., Cordina-Duverger, E. et al. A 34-year overview of night work by occupation and industry in France based on census data and a sex-specific job-exposure matrix. BMC Public Health, 22, 1441 (2022).
(1) Emilie Cordina-Duverger, Pascal Guénel, Nastassia Tvardik.
For more information :
Occupational exposures and job-exposure matrices :
- Fels A, Houot M, Garras L, Delabre L, Pilorget C. Salaried and self-employed workers in France between 2007 and 2015: Population description and differences in occupational exposure. Bulletin Epidémiologique Hebdomadaire. 2021;(2):22-31.
- Garras L, Delabre L, Houot M, Pilorget C. Panorama des professions et secteurs exposés au formaldéhyde en 2017 [Overview of occupations and sectors exposed to formaldehyde in 2017]. Hygiène et sécurité du travail. 2021(264):70-83.
- Lagarrigue R, Houot M, El Yamani M, Pilorget C, Groupe M. Occupational exposure to oxygenated, petroleum-based and chlorinated solvents of women of childbearing age in France in 2013. Results from the Matgéné programme. Bulletin Epidémiologique Hebdomadaire. 2019(7):137-43.
- Pilorget C, Lagarrigue R, Houot M, Matgéné G. Trends of occupational exposure to oxygenated, petroleum and chlorinated solvents in France between 1999 and 2013. Results from the Matgéné Programme. Bulletin Epidémiologique Hebdomadaire. 2018(12-13):234-40.
- El Yamani M, Fréry N, Pilorget C. Occupational exposures assessment of workers in France: Tools and methods. Bulletin Epidémiologique Hebdomadaire. 2018(12-13):216-20.
Job-exposure matrices and the burden of disease :
- Gilg Soit Ilg A, Houot M, Pilorget C. Estimation de parts de cancers attribuables à certaines expositions professionnelles en France. Utilisation des matrices emplois-expositions développées dans le cadre du programme Matgéné. Saint-Maurice: Santé publique France; 2016. 40 p.
- Marant Micallef C, Charvat H, Houot MT, Vignat J, Straif K, Paul A, et al. Estimated number of cancers attributable to occupational exposures in France in 2017: an update using a new method for improved estimates. Journal of Exposure Science and Environmental Epidemiology. 2021.
Indicators of exposure to night work in France are freely available on :
- Prevalence rate of occupational exposure to night work in the working population
- Prevalence rate of occupational exposure to occasional night work in the employed population
- Prevalence rate of occupational exposure to usual night work in the employed population