We found striking differences between common occupational groups in Sweden, both in terms of prevalence of type 2 diabetes, which ranged from 2.5% to 8.8% in men and from 1.2% to 6.4% in women, and incidence, which ranged from 3.44 to 9.41 per 1000 person-years in men and from 2.20 to 7.20 per 1000 person-years in women. The highest prevalence and incidence were seen among manufacturing workers, motor vehicle drivers and cleaners, whereas civil engineers, architects, teachers, physiotherapists, writers, managers and computer scientists had the lowest incidence as well as prevalence.
The association between occupation and type 2 diabetes coincided with vast differences in the prevalence of lifestyle risk factors. With the register data, we could show that individuals in high-risk occupations were more likely to be overweight, smoke and have lower physical fitness than those in low-risk occupations, and this most likely contributes to a high prevalence and incidence of type 2 diabetes. Interestingly, these differences were already seen at young ages, at the time of first pregnancy in women, and in men at the time of military conscription, which was at the age of entering the labour market. These findings indicate that job title is a risk indicator rather than a causal factor in relation to type 2 diabetes. In line with this, previous studies have shown that the excess risk of type 2 diabetes in individuals with low SES is mainly attributable to adverse lifestyle factors, primarily obesity [
19,
20]. Of note, the lifestyle information was based on historical data, and the differences in prevalence of lifestyle factors may be even larger at older ages. It should also be noted that this information was only available for about half of the study population. Still, this finding fits with previous observations showing that individuals who develop type 2 diabetes differ metabolically from those who do not, up to 25 years prior to diagnosis [
21]. On top of the strong lifestyle selection into different occupations, it is possible that working life adds more risk factors in the form of long sitting times, irregular working hours and stress. This is certainly true for motor vehicle drivers, which includes bus, taxi and lorry drivers. However, engineers and computing professionals are also likely to be sedentary, yet they are at very low risk of type 2 diabetes. Manufacturing work on the other hand may be associated with less sitting than white collar work, but may be stressful and include shift work. The role of working conditions in the promotion of type 2 diabetes is an important area to explore further. In addition, individuals with low SES may be exposed to poorer living conditions, relating to social support, housing and material conditions, which may make them more vulnerable to developing type 2 diabetes [
22]. In this context, it is also important to note that we observed that individuals without an occupation, e.g. those who are unemployed or on disability pension, had very high incidence and prevalence of type 2 diabetes.