Abstract
The study aimed to assess the proportion mediated by the duration of exposure to ergonomic factors at work on the relationship between socioeconomic position (SEP) and low walking speed. This cross-sectional study was performed on data collected at baseline on 19,704 men and 20,273 women 45–70 years old, currently or previously employed, enrolled in the Constances cohort. SEP was assigned through current or last occupation, categorized in three classes, based on the European Socioeconomic Classification. Walking speed was assessed through one measurement of normal walking for 3 m and dichotomized at the lowest quintile of the sex- and age- (5-year) specific distribution. Self-reported workplace exposure throughout working life to repetitive work, intense physical work, and lifting/carrying heavy loads was used to assess the duration of exposure to each factor, categorized in four classes. Through Poisson regression models, adjusted for BMI, smoking, alcohol intake, hypertension, physical activity, diabetes, cardiovascular diseases, and a cognitive score, the attenuation in the prevalence ratio (PR) of low walking speed by SEP produced by the inclusion of duration of exposure to each factor was evaluated. The mediating effect of work ergonomic exposures on the relationship between SEP and low walking speed was assessed using the weighted method by Vanderweele. In the fully adjusted model without ergonomic exposures, both men and women in the middle and the lowest SEP had a significantly increased risk of low walking speed compared with those in the highest SEP (men: PR = 1.30 and PR = 1.46, respectively; women: PR = 1.24 and PR = 1.45, respectively). The inclusion in separate regression models of exposure duration to repetitive work, intense physical work, and handling of heavy loads produced modest risk attenuations in both men and women, all smaller or around 10%. Mediation analysis revealed in both sexes significant mediation effects for most ergonomic exposures considered, although also with low mediation effects. Significant differences in walking speed by SEP were observed in this large sample, but the proportion of such differences explained by the duration of exposure to ergonomic factors at work was low using either the risk attenuation or the mediation analysis methods.
Highlights
Walking speed has often been used as a marker of physical performance because it is an objective indicator assessed through a simple test, which has been shown to predict disability, dementia, and mortality in older populations [5,6,7,8], as well as incidence of cardiovascular disorders [9, 10]
The frequency distribution of the characteristics of the study population by sex revealed among men a higher proportion of subjects belonging to higher socioeconomic position (SEP), of current smokers, and of overweight people, or affected by hypertension, diabetes, or cardiovascular diseases, compared with women, whereas the distribution of the other covariates was quite comparable across sex (Table 1)
In a population of subjects in early old age, we found a significant SEP gradient in walking speed in both sexes, with an increased risk of ∼45% for subjects in the lowest SEP, compared with the highest
Summary
Physical functioning is an important asset of older subjects, which influences their autonomy and their performance in daily life, such as participation in social activities and independent living [1].Several studies have observed differences in physical functioning between socioeconomic groups among older subjects, with lower functioning among more disadvantaged people [2,3,4].Walking speed has often been used as a marker of physical performance because it is an objective indicator assessed through a simple test, which has been shown to predict disability, dementia, and mortality in older populations [5,6,7,8], as well as incidence of cardiovascular disorders [9, 10]. Several studies have observed differences in physical functioning between socioeconomic groups among older subjects, with lower functioning among more disadvantaged people [2,3,4]. Low walking speed has been associated consistently with low socioeconomic position (SEP) in epidemiological studies [15,16,17,18], especially with adult SEP [19]. Besides low SEP, several risk factors have been reported to increase the risk of reduced walking speed, including behavioral risk factors, such as smoking, physical inactivity, obesity [20], other cardiovascular risk factors [21], hypertension and cerebral small vessels disease [22], high C-reactive protein levels [23], genetic factors [24], and osteoarticular diseases, especially knee osteoarthritis [25]
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