Findings of the present study indicated that the risk of developing an excessive fat accumulation in adipose tissue might be a consequence of exposure to several occupational or work-related factors and it is profoundly different for male and female workers. Previous studies observed that gender differences, regarding BMI levels and obesity prevalence, could be detected within the same occupational group or with reference to specific occupational variables (19, 29, 30). Although these data have been explained by calling into question in turn demographic, socio-economic, and cultural or lifestyle factors, the common conclusion in these studies was to deepen the research on this topic. In this context, we cannot obviously exclude the possibility that our results related to gender differences may be due to the contribution of determinants other than those considered in this study. However, the observation that in the adjusted analysis male and female workers showed a different susceptibility to obesity, even after having taken into account some key variables (i.e. age, educational level, sedentariness of work, psychosocial stressors and chronic diseases) suggests that, at least for some occupational factors, the role played by sex-specific differences is significant.
Therefore, assuming that this hypothesis is valid and considering workplaces as optimal and privileged adult settings where it is possible to plan, apply, and implement appropriate interventions to prevent and treat obesity, in our opinion these measures should certainly include, but at the same time not be limited to, healthy lifestyle behaviours promotion. Indeed, doing a regular physical activity and/or having a healthy and balanced diet are general recommendations that are always valid for all people (or workers) regardless of sex, demographic and socio-cultural variables and type or characteristics of the work being performed. Therefore, if we really want to take advantage of the workplaces to have available more strategies that are effective to win the battle against obesity, we have to begin to consider that this condition is not just a consequence of a personal choice, but rather it is caused by a complex interplay between an individual and the environment in which he lives (14). In this regard, to properly address this issue we need more qualitative and quantitative data to try answering some unsolved questions. For example, in this regard, what are the occupational groups or workers’ categories that are at increased risk of obesity? Furthermore, are there other occupational risk factors besides sedentary work and diet that can be associated with obesity? Are they potentially modifiable factors? Moreover, considering the increase of women in the labour force and their increasingly involvement in roles and activities that were traditionally male focused, is it possible that some gender differences in work-related factors does exit potentially associated with obesity? Findings of our study provide helpful indications to address some aspects of the aforementioned questions. First of all, evaluating the main socio-demographic characteristics of the sample (sex, age and educational level) higher BMI values and overweight or obesity prevalence were observed in male workers, at increasing age and in subjects with a lower education (Table 1). These results are in accordance to the previous evidence, thus confirming that these variables are correlated with obesity (19-21, 29, 30, 37). Therefore, these socio-demographic determinants should be taken into account when trying to establish correlations between BMI and occupational groups or work-related factors, since they may be responsible for some variance in BMI levels (30).
The analysis of BMI according to different occupational sectors, revealed that male workers involved in healthcare and social assistance had the highest prevalence of overweight and obesity, whereas their female counterpart showed higher prevalence values in agriculture, fishing and hunting (overweight) and in construction, healthcare and social assistance (obesity) (Table 2). Overall, these data are consistent with the findings of previous studies further confirming that occupations that required sedentary behaviours or implied low levels of physical activity are characterized by increased levels of overweight and obesity prevalence (although this association is weaker in female workers) (20, 29, 30, 37). Nevertheless, some important differences should be pointed out since, differently by our results, several research groups observed higher prevalence rates in transportation and warehousing workers (19, 29-31, 37) and lower levels in the healthcare sector (31, 37). In our study, using the ATECO classification, transportation and warehousing workers are included in the same group of information and communication as well as workers included in the healthcare and social assistance sector carry out different job activities (i.e. healthcare practitioners and technical, healthcare support and protective services), whereas were considered individually in other studies (31, 37). Therefore, it is quite likely that these conflicting results are due to differences in classification of several occupational sectors although it is not possible to rule out an influence of socio-demographic and cultural factors (30).
With regard to these socio-demographic characteristics, we have also conducted an adjusted analysis in order to explore to what extent the BMI values (and the related overweight/obesity prevalence) observed in the several occupational groups were affected by differences both in the distribution of these variables and other work-related factors (Table 2). Findings confirmed that, for female workers, these determinants could have a significant impact in changing the OR in specific occupational groups. On the other hand, few occupational categories (i.e. agriculture, fishing and hunting and other public and personal services) were associated in a statistically significant manner with increased OR even after adjustment, thus suggesting that other work-related factors, specific for these occupational groups and not captured or assessed in the present study, can contribute to overweight and obesity. Moreover, the differences of occupational effect by gender point out that sex-specific factors other than socio-demographic and work-related determinants may influence the likelihood of overweight and obesity. Therefore, additional research on this topic investigating the reasons of weight disparity between male and female workers in different job categories is desirable and suggested (19, 30).
Besides knowing the obesity prevalence rates in the different workers’ categories, however, it is also important to understand the reasons that determine them, and that is, in other words to identify the work-related factors (in addition to sedentary work, low physical job demand, worksite nutrition) that could possibly be associated with obesity. In this regard, a high risk of developing an overweight/obesity condition was observed in subjects who worked long hours (34, 39), similarly a working time ≥ 35 and > 40 or > 50 hours per week was significantly associated with increased BMI values in men (40) and with obesity in workers of both sexes (21, 37), whereas Kim et al., (35) found an association between this condition and long working hours only in female workers. In our study, no statistically significant association has been found between long working hours and overweight or obesity, even if female workers who worked > 40 and ≥ 55 hours/week showed the highest overweight and obesity prevalence, respectively. On the contrary, surprisingly in male workers the highest level of obesity was observed in the group that had the lowest working hours.
Interestingly, we found that shift workers have higher prevalence rates for overweight and obesity and this difference was statistically significant for female workers. In this regard, Luckhaupt et al., (37) and Di Milia and Mummery (34) obtained similar results showing an increasing prevalence of obesity and BMI levels in shift workers performing night or rotating shifts compared to day or evening shift workers. The increased odd of being overweight/obese in female workers persisted after adjustment for socio-demographic characteristics, variables related to health and safety protection and chronic diseases (Table 4) and a similar trend was observed also taking into account the exposure to night shifts (1 or 2 times per week) (Table 5). However, male shift workers were associated with an increased OR only when considering age, educational level or health surveillance and no statistically significant association was detected with regard to night shift work (Tables 4 and 5). Overall, these findings seem to suggest that the association among shift, night work and obesity is influenced by gender-specific variables. It has been suggested that inadequate or difficult working conditions can trigger a stress response that in turn may enhance the risk of obesity (41). Indeed, when a person experiences a stress condition the production of hormonal factors (especially of adipokine that are strongly linked to appetite and fat storage) changes substantially (42-44). Considering that, key sex differences in fat storage in men and women include differential insulin sensitivity and adipokine production it is plausible to hypothesize that the gender-specific differences observed in our study are due to this sex asymmetry (13, 17, 18).
Then, assuming the possibility that stressors can play a role in promoting weight gain, few studies have investigated the possible association between several psychosocial working conditions and obesity (20, 37). In this regard, a correlation was observed between hostile work environment and, to a lesser extent, job insecurity (37), whereas in the study carried out by Choi et al., (20) job demand, supervisor and/or co-worker support were not associated with increased obesity prevalence and only low job control in female workers showed a statistically significant difference. Our data are similar to those provided by Choi et al., (20) as no association has been established between male and female workers’ exposure to work-related stress and prevalence rates for overweight and obesity. Furthermore, we studied also the type of contract (permanent or temporary) as a possible work-related stress factor since, having a temporary contract, is for workers a major source of concern about becoming unemployed. This variable was taken into consideration also by Luckhaupt et al, (37) who, while observing a greater prevalence of obesity in temporary workers compared to permanent ones, failed to identify a statistically significant association between work arrangement and obesity. Similarly, in the current study, no overall differences were found as regard to the type of contract. However, it should be noted that the analysis with the logistic regression models provided interesting findings highlighting, important differences between male and female workers (Table 3). Indeed, among females it seems that having a permanent contract is a protective factor against the risk of developing an obesity condition whereas this variable is instead associated with greater OR in men. Providing an explanation for these conflicting results is quite challenging since, several other factors of social, cultural and work-related nature (that have not been evaluated in our work) could be responsible for the differences obtained. Nevertheless, once again, the observation of a divergence of results by gender would suggest the need to focus attention primarily on the role played by biological/physiological gender differences in favouring or combating obesity in workplaces. That is, further research should verify whether exposure to specific occupational risk factors (i.e. long working hours, shift and night work, psychosocial stressors) is able to influence (and how) the expression of the aforementioned biological and physiological characteristics or of the functioning of some organ systems (e.g. the endocrine system) that could therefore determine a different propensity to obesity in male and female workers due to its significant impact on metabolism and adipose tissue storage.
Finally, our data showed a statistically significant association between overweight and obesity prevalence and several chronic conditions such as musculoskeletal, respiratory and cardiovascular diseases both in male and female workers (Table 1). These results further underline the importance of preventing and adequately treating obesity as excess weight gain is an important risk factor for several non- communicable diseases.
Strengths, limitations and future perspectives
Some strengths of this manuscript might be found. First, this addresses a large sample of Italian workers representative of the Italian working population, filling the gap of the lacking of studies on occupational factors and risk of obesity in the Italian context. Having studies on national representative samples represents a value add when investigating on aspects related to overweight and obesity, since there is huge evidence of external socio-cultural factors, such as diet culture, acceptable lifestyles, behavioural patterns affecting a person’s weight. Secondly, we included several occupational factors in the risk of obesity by adjusting for main confounders. Even if there are studies considering occupational aspects, they mostly refer to specific occupational populations and sectors. Moreover, we consider a large set of occupational variables including the ones generally less investigated (e.g. work shift, night work, type of contract) in relation to the obesity, and relevant under the perspective of gender differences. Finally, this study does not limit to control for gender, but takes into consideration gender-specific differences in studying occupational factors associated to the risk of obesity in order to characterize better the risk of obesity categories and contribute in the identification of workplace-targeted intervention strategies.
Some limitations may be addressed too in the view of future improvements. First, the cross-sectional design that allows us to describe associations but not causation. In other words, we are not able to draw causal inferences about the effect of the different variables on overweight and obesity since we cannot define the directionality of the associations observed. Nevertheless, data were collected as part of a national project, a well-established worker-population survey named INSuLa, on a representative sample including reliable information on several socio-demographic variables and working conditions. This survey is becoming a monitoring system allowing to appreciate changes over time. Moreover, thanks to this study, we collected by data some suggestions to integrate measures in the next waves. To this regard, aspects related to the attitudes and behaviours related to meal during the work time and physical activity will be considered in the future and linked to the BMI.
As second limitation is related to the self- report nature of the body weight and height measure. Consequently, BMI calculations are subject to error and our findings might be potentially vulnerable of reporting bias. As it is noting people have a tendency to overestimate their height and, at the same time, to underestimate their weight and this self-report bias is higher among overweight and obese individuals (45, 46). However, in this regard, it has been observed that in adult subjects measured and perceived BMI values are strongly correlated (47) and a limited number of studies, evaluating the differences between self-reported and measured anthropometrics in selected working categories, provided evidence that self-reported weight and height information is a reliable tool to assess BMI in large population worker samples (48-50). Future studies might provide investigation on validity of self-report vs measured BMI in specific Italian occupational groups and considering some sociodemographic differences (as gender, age, educational level).