Established pairs

Thirty-nine established pairs of occupational risk factors and health outcomes, considered to have a sufficient evidence base, were selected for inclusion (table 1). The burden of disease attributable to established occupational risk factors was estimated using the Comparative Risk Assessment (CRA) framework, a systematic evaluation of the changes in population health that result from modifying the population distribution of exposure to a risk factor or a group of risk factors (22, 23). Recent burden of disease estimates from the Global Burden of Disease Study (26), openly available at http://ghdx.healthdata.org, were used to derive population attributable fractions (PAF). PAF quantify the proportion of deaths or disability-adjusted life years (DALY) lost from a particular health outcome that is attributable to a specific risk factor.

Estimation methods

For each pair, the total number of deaths and DALY for each health outcome in the WHO Global Health Estimates total disease envelopes for 2000, 2010 and 2016 (27) were multiplied by the pair’s PAF. This resulted in the estimates of the numbers of deaths and DALY from the health outcome that are attributable to its respective occupational risk factor. For pairs for which there are larger PAF, a larger fraction of the total burden of disease from the health outcome will be estimated.

Recently added pairs

Following scoping reviews, 16 additional pairs of occupational risk factors and health outcomes were selected, which may contribute substantially to the work-related burden of disease. Systematic reviews and meta-analyses were conducted for these pairs to gather evidence for the WHO/ILO Joint Estimates on the prevalence of exposure to occupational risk factors and on the effect of exposure to these risk factors on health outcomes (2–19). The new methods used (28) have been published in an international academic journal (29). WHO and ILO determined that there were two pairs for which there was sufficient quality and strength of evidence to proceed to burden of disease estimation: exposure to long working hours (defined as working ≥55 hours per week) and the health outcomes of ischemic heart disease and stroke. It should be noted that evaluation of the evidence for some of these pairs is ongoing.

To provide exposure data for these two new pairs, new WHO/ILO databases on exposure to long working hours were developed from data shared by Member States with one or more of WHO, ILO and Eurostat. The databases provided data on the number of workers exposed to long working hours. They used results from 2324 surveys (mostly labor force surveys) from 154 countries, as well as 1742 quarterly datasets of labor force surveys conducted in 46 countries (25).

Estimation methods

Prevalence of exposure. We used an established multilevel model and data from direct exposure measurements provided by the two new WHO/ILO databases to predict the geographical and temporal prevalence of exposure to long working hours (30). As is essential in modelling studies, several modelling assumptions needed to be made. Based on advice from a WHO/ILO technical advisory group and available evidence, an exposure window of ten years, evenly spaced around a lag time of ten years, was agreed upon (ie, to estimate burden of disease in 2016 for example, exposure was modelled for the time window of 2001–2010). The annual prevalence of exposure to long working hours for each year within this window was used in exposure modelling (25). Sensitivity analyses (eg, altering the lag time and the length of the time window) were conducted to test our assumptions.

Burden of disease. As for the established risk factors, the burden of disease attributable to exposure to long working hours was estimated within the CRA framework (22, 23). From the systematic reviews, a pooled risk ratio (RR) of 1.17 [95% confidence interval (CI) 1.05–1.31] was found for risk of ischemic heart disease following exposure to long working hours (≥55 hours/week) (9); for stroke, a pooled RR of 1.35 (95% CI 1.13–1.61) was found (3). These pooled RR, along with the prevalence estimates produced by WHO and ILO, were used to calculate the PAF for these two new pairs. These PAF were then applied to the health outcomes’ total disease burden envelopes from the WHO Global Health Estimates for the years 2000, 2010 and 2016 (27), as described above for the established pairs, yielding the number of deaths and DALY from each health outcome attributable to exposure to long working hours (25).

Inequalities. To improve workers’ health equity between and within countries, health inequalities in the work-related burden of disease must be monitored. For describing inequalities between regions, sexes and age groups, we used the global number of deaths or DALY per 100 000 working-age (≥15 years) population as the reference. For specific regions, sexes or age groups, we calculated (i) the rate difference: the rate for the specific group minus the reference rate (an absolute inequality measure); and (ii) the rate ratio: the rate for the specific group divided by the reference rate (a relative inequality measure) (31).

Uncertainty. All estimates of exposure to occupational risk factors and of burden of disease were produced with their 95% UR (25), using bootstrapping (32). Consistent with previous global health estimates (33–36), the 2.5% and 97.5% quantiles of the random deviates of the exposures were calculated and assigned as the lower and upper limits of the UR, respectively. Here, we present 95% UR for key estimates in the text; however, they are available for all estimates in the online estimates repository (www.who.int/teams/environment-climate-change-and-health/monitoring/who-ilo-joint-estimates).

Main findings

Globally in 2016, exposure to the 19 selected occupational risk factors was attributable for an estimated 1 879 890 (95% UR 1 835 140–1 924 640) deaths and 89.72 (95% UR 88.61–90.83) million DALY due to the respective health outcomes.

Table 1 shows the numbers of deaths and DALY corresponding to each occupational risk factor – health outcome pair, with rates per 100 000 working-age population [rates per 100 000 total population are available in the Global Monitoring Report (20)]. The pair with the highest number of deaths was chronic obstructive pulmonary disease attributable to occupational exposure to particulate matter, gases and fumes (450 381 deaths, 95% UR 430 248–470 514). The pair with the highest number of DALY was stroke attributable to exposure to long working hours (12.60 million DALY, 95% CI 11.82–13.39 million). Figure 1 displays deaths and DALY by occupational risk factor and figure 2 displays deaths and DALY by health outcome. Figures 3 and 4 show the rates of deaths and DALY per 100 000 of working-age population by country (numbers provided in the supplementary material, www.sjweh.fi/article/4001, table S1).

Figure 1

Total number of work-related deaths and DALYs, by occupational risk factor, 183 countries, for the year 2016. Source: WHO and ILO (20).

Figure 2

Total number of work-related deaths and DALYs, by health outcome, 183 countries, for the year 2016. Source: WHO and ILO (20).

Figure 3

Death rates (per 100 000 working-age population, ie, age ≥15 years) in 2016 from the 41 pairs of occupational risk factors and health outcomes. Source: WHO and ILO (20).

Figure 4

DALY rates (per 100 000 working-age population, ie, age ≥15 years) in 2016 from the 41 pairs of occupational risk factors and health outcomes. Source: WHO and ILO (20).

The two new pairs of risk factor and health outcome contributed substantially to the burden of work-related disease. Exposure to long working hours and ischemic heart disease, and exposure to long working hours and stroke combined were responsible for 39.6% of deaths (744 924, 95% UR 744 924–784 328) and 25.9% of DALY (23.26 million, 95% UR 22.15–24.37 million), making this previously unquantified occupational risk factor the one with the largest attributable burden of disease. Detailed breakdowns and interpretations of these findings can be found elsewhere (20, 25). Additionally, the WHO/ILO Joint Estimates are available for each pair, disaggregated by sex and age group, and at global, region and country levels, from dedicated websites hosted by WHO (www.who.int/teams/environment-climate-change-and-health/monitoring/who-ilo-joint-estimates) and the ILO (www.ilo.org/global/topics/safety-and-health-at-work/programmes-projects/WCMS_674797/lang--en/index.htm).

Trends over time

In absolute terms, the global number of occupational risk factor-related deaths from 2000 to 2016 increased by 177 914 between 2000 and 2016. Global work-related DALY increased by 9.67 million from 2000 to 2016.

In terms of rates, globally between 2000 and 2016 rates of total deaths attributable to exposure to occupational risk factors decreased from 39.9 to 34.3 deaths per 100 000 working-age population; this corresponds to a 14.2% decrease in the rate. Similarly, global DALY rates decreased from 1878.4 to 1635.9 DALY per 100 000 working-age population.

Inequalities in work-related burden of disease

By geographic region. The absolute differences in death rates by WHO region, compared with the global rate, ranged from 10.7 (in the South-East Asia Region) to -12.0 deaths per 100 000 working-age population (in the Region of the Americas). For DALY, in absolute terms, rate differences by WHO region ranged from 463.3 DALY per 100 000 working-age population in South-East Asia to -564.1 DALY per 100 000 working-age population in the Americas. For both deaths and DALY, the rate ratios varied from 1.3 for South-East Asia to 0.7 for the Americas.

By sex. The death rate per 100 000 working-age males is 51.4, 17.1 per 100 000 higher and 1.5 times the rate for both sexes. The death rate of 17.2 per 100 000 working-age females is lower compared with the rate for both sexes, this is 17.1 per 100 000 lower and 0.5 times this rate. For DALY, a similar pattern was seen.

By age group. Older age groups carried disproportionally greater disease burden, with the age group 85–89 years having the highest rate difference (higher than the global rate by 212.6 deaths per 100 000 working-age population) and highest risk ratio (7.2). Conversely, the rate for the age group 15–19 years was 4.3 deaths per 100 000 working-age population, yielding a rate difference of -30.0 and a rate ratio of 0.1 compared to the global rate. Similarly for DALY, the older age groups were more burdened.

Preventive actions

Actions required vary by occupational risk factor, to reduce the burden related to many of the established risk factors and their health impacts (as here quantified), governments should develop interventions to reduce risk factors with the active involvement of employers and workers or their representatives, as part of a hierarchy of controls (39). Where it is not possible to eliminate risk factors or use less hazardous substitutions, engineering controls can be introduced, followed by administrative controls. As a last and least-preferred option, workers can be protected with personal protective equipment.

The burden of stroke and ischemic heart disease attributable to exposure to long working hours was previously unquantified. The generation of the first estimates for this burden may motivate actors to address this risk factor. ILO Conventions define the maximum limits of working hours in industrial and services sectors (40, 41) as 48 hours per week (with some specific exceptions). Human resources management and work organization management can be used to prevent exposure to long working hours, in particular for some specific working modalities (eg, teleworking, self-employment and freelancing) (42). Additionally, occupational health services can play an important role. All workers should be covered (43), and occupational health risk assessments should consider numbers of working hours and other cardiovascular risk factors (eg, obesity, physical activity, smoking and diet) that exposure to long working hours could influence. The introduction of social protection floors would enable people to stop working unhealthy long hours, by guaranteeing access to essential health care and basic income security. This would particularly benefit disadvantaged workers (eg, those in the informal economy, and vulnerable groups such as pregnant women, older people and migrant workers) (44).

Strengths and limitations

The WHO/ILO Joint Estimates have used established methods to quantify the work-related burden of disease attributable to 19 occupational risk factors (22, 23). A pair was only proceeded for estimation if WHO and ILO judged there to be sufficient quality and strength of evidence for the pair, providing confidence that the burden of disease estimates reported are attributable to the occupational risk factor. As a result, the organizations have estimated that 1.9 million deaths and 89.7 million DALY are attributable to the selected 41 pairs of occupational risk factor and health outcome.

There are some limitations that should be considered when interpreting the estimates. First, these estimates are affected by the source and quality of input data, and the type and complexity of the models of exposure and health estimates. A wide range of approaches have been used to collect and synthesize data. Although estimates have been included only if the underlying body of evidence was judged to be of sufficient quality and strength, some are based on exposure data from limited sources and from areas of limited country and regional coverage. To improve future estimates, more large-scale global official datasets of exposure to occupational risk factors are needed, ideally from direct measurement or through strong proxies such as occupation and industrial sector. Similarly, more primary studies need to be conducted on the effect of exposure to occupational risk factors on health outcomes (29). In particular, more evidence is needed from low- and middle-income countries.

Second, while estimates have been included only if WHO and ILO, supported by a large number of individual experts, judged the underlying body of evidence to be of sufficient quality and strength, this is based on judgement. As this is subjective it may be that other organizations or individuals reach a different judgement. This was demonstrated by a commentary indicating disagreement with the rating of “sufficient evidence for harmfulness” that there is of long working hours with regard to ischemic heart disease (45). The WHO/ILO Working Group, composed of a large number of individual experts, acknowledged and responded to the commentary, elaborating on why the assigned rating is supported by the evidence (46). WHO and the ILO are collaborating on the WHO/ILO Joint Estimates with over 200 individual experts based around the world, to ensure that judgements made represent the views of a diverse and representative expert group.

Third, it must be noted that not all occupational risk factors and attributable burdens of disease have yet been quantified. The production of estimates for some pairs was not possible in this estimation cycle, such as: occupational exposure to biological risk factors and infectious diseases; occupational exposure to psycho-social risk factors and mental health outcomes; and occupational exposure to ambient air pollution and its various health outcomes. Further, while there are established methods for estimating the burdens of silicosis, asbestosis, coal worker’s pneumoconiosis and unspecified pneumoconiosis attributable to occupational exposure to dusts and fibers, WHO and the ILO are currently reviewing these methods and the available bodies of evidence (10); these pairs were therefore not included in this estimation cycle. While this means that the work-related burden of disease is almost certainly higher than the current estimate of selected pairs, the addition of such pairs in future will broaden the scope of these estimates and capture the work-related burden of disease more comprehensively.

Fourth, estimates by their nature are modelled based on certain assumptions (like the appropriate time window of exposure). While the assumptions made draw from the latest evidence base and are transparently reported, as evidence develops, it is possible that new evidence may emerge in the future which could lead us to alter these assumptions. Sensitivity analyses were performed and reported to assess the impact of alternative assumptions related to exposure to long working hours (25).

Concluding remarks

The WHO/ILO Joint Estimates report that globally in 2016 1.88 million deaths and 89.72 million DALY from health outcomes were estimated to be attributable to the 19 occupational risk factors covered. A disproportionately large work-related burden of disease is observed in the WHO African Region (for DALY), South-East Asia Region and the Western Pacific Region (for deaths), males and older age groups. Future steps should include estimation of disease burden for more occupational risk factor and health outcome pairs, as more high-quality data and evidence become available, to ensure more of the work-related burden of disease is captured.

The WHO/ILO Joint Estimates have widened the scope of the global CRA and strengthened the global capacity for modelling disease burden in occupational health. They allow the global monitoring of exposure to occupational risk factors and the work-related burden of disease, to detect inequalities and trends over time. This will enable policy-makers and institutions to plan, cost, implement and evaluate actions to prevent exposure to occupational risk factors and their attributable burden of disease.

Disclaimers

The authors alone are responsible for the views expressed in this article and they do not necessarily represent the views, decisions or policies of the institutions with which they are affiliated.

The designations employed and the presentation of the material in this publication do not imply the expression of any opinion whatsoever on the part of WHO concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries. Dotted and dashed lines on maps represent approximate border lines for which there may not yet be full agreement.

Terminology used to refer to countries, territories, and areas as well as representation of countries, territories, and areas, including delimitation of frontiers or boundaries, and any direct or indirect attribution of status in this publication follow exclusively the institutional style and practice of WHO. All reasonable precautions have been taken by WHO to verify the information contained in this publication.

However, the published material is being distributed without warranty of any kind, either expressed or implied. The responsibility for the interpretation and use of the material lies with the reader. In no event shall WHO be liable for damages arising from its use.

Funding sources

Financial support for the preparation of this publication was provided by the United States Centers for Disease Control and Prevention National Institute for Occupational Safety and Health through its cooperative agreement with WHO (grant nos 1E11 OH0010676-02, 6NE11OH010461-02-01 and 5NE11OH010461-03-00); the German Federal Ministry of Health (BMG Germany) under the BMG–WHO Collaborative Programme 2020–2023 (WHO specified award reference 70672); and the Spanish Agency for International Cooperation (AECID) (WHO specified award reference 71208). The European Union also provided financial support to the ILO through the Vision Zero Fund (VZF) project on filling data and knowledge gaps on occupational safety and health in global supply chains, implemented within the framework of the ILO Flagship Programme “Safety + Health for All”. The study sponsors had no role in the study design, collection, analysis and interpretation of the data, writing of the report, or the decision to submit the paper for publication.