Elsevier

Social Science & Medicine

Volume 63, Issue 5, September 2006, Pages 1267-1275
Social Science & Medicine

What mediates the inverse association between education and occupational disability from back pain?—A prospective cohort study from the Nord-Trøndelag health study in Norway

https://doi.org/10.1016/j.socscimed.2006.03.041Get rights and content

Abstract

Low education is consistently associated with an increased risk of back pain disability, but the underlying mechanisms for this relationship are poorly understood. In a seven-year prospective observational study of 38,426 employed men and women between 25 and 59 years in Norway, we investigated to what extent occupational class, working conditions and individual lifestyle mediated the effect of formal education on disability pensioning from back pain.

Each additional year of formal education was associated with decreased risk for disability pensioning from back pain for both men [age adjusted Hazard Ratio (HR) 0.77; (95% Confidence Interval, 0.72–0.82)] and women [HR 0.76(0.71–0.82)]. Adjustment for occupational class and factors related to working conditions (authority to plan own work, physically demanding work, concentration and attention and job satisfaction) and individual lifestyle (smoking, body mass index, physical exercise and alcohol consumption) reduced the effect of education by 39% [HR 0.86(0.79–0.93)] for men and by 21% [HR 0.81(0.73–0.89)] for women. Working conditions contributed most to the explanation for men, while occupational class, working conditions and life style factors contributed equally for women. Subgroup analyses indicate small differences between full-time and part-time employees, while some differences were found between subcategories of back diseases.

The study indicates that there is a strong and unexplained effect of education on back pain disability pensioning, which is not mediated by occupational class, working conditions or individual lifestyle.

Introduction

In most of the western world there is a growing concern about the proportion and socioeconomic consequences of work incapacity from back pain (BP). Early retirement due to BP is considered to be the extreme endpoint of a disabling process (Krause & Ragland, 1994), which is a great burden to the individual and costly for the society (Waddell & Norlund, 2001a; van Tulder, Koes, & Bouter, 1995).

Low socioeconomic status has consistently been associated with increased mortality and morbidity (Mackenbach, Kunst, Cavelaars, Groenhof, & Geurts, 1997). Education is often considered to be the best indicator of socioeconomic status, because it is easy to observe and unlikely to be affected by diseases that begin in adult life. Dionne and colleagues reviewed the scientific evidence on the relation between educational status and measures of the frequency and the consequences of BP, and concluded that no other single trait is so strongly and consistently related to BP disability as formal education (Dionne et al., 2001).

The underlying mechanisms for the inverse relationship between educational attainment and BP disability are poorly understood. Many studies have used socioeconomic status as a measure of occupational exposure, suggesting that the relationship between BP disability and socioeconomic status could be largely related to manual versus non-manual jobs, but evidence from empirical studies are sparse (CSAG Epidemiology Review, 1994). People with low education are more likely to work in physically and psychosocially demanding jobs, and there is empirical evidence that these factors play an important role in the aetiology and prognosis of BP (Hoogendoorn, van Poppel, Bongers, Koes, & Bouter, 1999; Hoogendoorn, van Poppel, Bongers, Koes, & Bouter, 2000) The association between BP disability and socioeconomic status may, however, have different causes and pathways. For example, well-educated people are more likely to be aware of the negative health effects of life style factors such as smoking, obesity, sedentary lifestyle and alcohol consumption. Some of these factors have also been considered as possible risk factors for BP (Leboeuf-Yde, 1999; Leboeuf-Yde, 2000).

Studying possible factors contributing to the explanation of educational inequalities in BP disability may advance our understanding of BP, and educational inequalities in BP disability can only be reduced when the causal mechanisms are understood and when important intermediate factors are identified. Therefore the aim of this study was to examine to what extent the inverse relationship between formal education and disability retirement from BP is mediated by factors related to the working conditions and to the individual lifestyle.

Section snippets

Methods

Data were available from a seven-year prospective population-based cohort study, by merging computerized files with individual data from the national medical insurance system (National Insurance Administration [NIA]), the Nord-Trøndelag Health Survey 1984–86 (HUNT-1), (Holmen et al., 1990) and population registries from the national bureau of statistics (Statistics Norway) at the individual level. The study was approved by the Regional Ethical Committee and by the Data Inspectorate.

Results

From 1987 to 1993 there were 322 women (2.1%) and 393 men (1.7%) between 25 and 59 years of age who were granted disability pension due to back diseases. The general characteristics of the study population are shown in Table 1. The incidence of BP disability increased from 0.2% for those with >13 years of education to 3.3% for those with<9 years of education. Occupational class, four of the five factors related with working conditions, (“Authority to plan your own work”, “Physically demanding

Discussion

The present study indicates that less than 50% of the educational inequalities in BP disability retirement could be explained by occupational class and factors related to working conditions and life style. Working conditions contributed most to the explanation for men, while the three groups of explanatory variables contributed equally for women. Subgroup analyses indicate small differences between full-time and part-time employees, while some differences were found between subcategories of

Acknowledgement

The Nord-Trøndelag health study (HUNT) is a collaboration between the HUNT Research Centre, Faculty of Medicine, Norwegian University of Science and Technology, Verdal; the Norwegian Institute of Public Health; the National Health Screening Service of Norway; and Nord-Trøndelag county council. This study was funded in part by grants from the Norwegian Research Council and the Norwegian Royal Ministry of Social Affairs. The authors would like to thank Dr. Petter Mowinckel at the Diakonhjemmet

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