Abstract
Background
The behavioural and socio-cultural processes underlying the association between socio-economic position (SEP) and body mass index (BMI) remain unclear. Occupational physical activity (OPA) is one plausible explanatory variable that has not been previously considered.
Objectives
1) To examine the association between OPA and BMI, and 2) to examine whether OPA mediates the SEP-BMI association, in a Canadian population-based sample.
Methods
This cross-sectional study was based on secondary analysis of the 2008 Canadian Community Health Survey data, focusing on adults (age 25–64) working at a job or business (men, n=1,036; women, n=936). BMI was based on measured height and weight and we derived a novel indicator of OPA from the National Occupational Classification Career Handbook. Our analytic technique was ordinary least squares regression, adjusting for a range of socio-demographic, health and behavioural covariates.
Results
OPA was marginally associated with BMI in women, such that women with medium levels of OPA tended to be lighter than women with low levels of OPA, in adjusted models. No associations between OPA and BMI were detected for males. Baron and Kenny’s (1986) three conditions for testing mediation were not satisfied, and thus we were unable to proceed with testing OPA as a mediator.
Conclusions
Notwithstanding the small effects observed in women, overall the associations between OPA and BMI were neither clear nor strong, which could reflect conceptual and/or methodological reasons. Future research on this topic might incorporate other plausible explanatory variables (e.g., job-related psychosocial stress) and adopt a prospective design.
Key words: Body mass index, occupation, physical activity, Canada
Résumé
Contexte
Les processus comportementaux et socioculturels qui sous-tendent l’association entre le statut socioéconomique (SSE) et l’indice de masse corporelle (IMC) sont encore obscurs. L’activité physique au travail (APT) est une variable explicative plausible qui n’a pas encore été envisagée.
Objectifs
1) Examiner l’association entre l’APT et l’IMC, et 2) déterminer si l’APT a un effet modérateur sur l’association SSE-IMC, dans un échantillon représentatif de la population canadienne.
Méthode
Cette étude transversale est fondée sur une analyse secondaire des données de l’Enquête sur la santé dans les collectivités canadiennes de 2008. Elle s’intéresse aux adultes (25 à 64 ans) ayant un emploi ou une entreprise (1 036 hommes et 936 femmes). L’IMC a été calculé selon la taille et le poids mesurés, et nous avons dérivé un nouvel indicateur de l’APT à partir du Guide sur les carrières de la Classification nationale des professions. Nous avons procédé à une régression ordinaire par la méthode des moindres carrés en tenant compte d’une gamme de covariables sociodémographiques, sanitaires et comportementales.
Résultats
L’APT était marginalement associée à l’IMC chez les femmes du fait que, dans les modèles rajustés, les femmes ayant des niveaux moyens d’APT avaient tendance à peser moins que les femmes ayant de faibles niveaux d’APT. Aucune association entre l’APT et l’IMC n’a été décelée chez les hommes. Les trois conditions de Baron et Kenny (1986) pour tester l’effet modérateur n’ont pas été remplies; nous n’avons donc pas pu déterminer si l’APT était une variable modératrice.
Conclusion
Sauf pour de légers effets observés chez les femmes, dans l’ensemble, les associations entre l’APT et l’IMC n’étaient ni claires, ni fortes, mais cela pourrait s’expliquer par des raisons conceptuelles ou méthodologiques. Les recherches futures sur ce sujet pourraient incorporer d’autres variables explicatives plausibles (p. ex., le stress psychosocial lié à l’emploi) et adopter un plan d’étude prospectif.
Mots clés: indice de masse corporelle, professions, exercice physique, Canada
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