Date Published: February 22, 2011
Publisher: Public Library of Science
Author(s): Silvia Stringhini, Aline Dugravot, Martin Shipley, Marcel Goldberg, Marie Zins, Mika Kivimäki, Michael Marmot, Séverine Sabia, Archana Singh-Manoux, Alan D. Lopez
Abstract: Further analysis of data from two prospective cohorts reveals differences in the extent to which health behaviors attenuate associations between socioeconomic position and mortality outcomes.
Partial Text: Differences in morbidity and mortality between socioeconomic groups constitute one of the most consistent findings of epidemiologic research . The first comprehensive investigation of the reasons behind social inequalities, the Black Report, identified four possible explanations: artefactual, natural or social selection, materialist/structural, and cultural/behavioural . Much subsequent research, although recognising the existence of socioeconomic differences, has yet to provide a complete understanding of the mechanisms behind the association between markers of socioeconomic status (SES) and health ,. A better understanding of these mechanisms is essential in order to identify targets for intervention aimed at reducing social inequalities in health.
In the Whitehall II study, a total of 537 participants, corresponding to 5% of the total population (4% men and 8% women), were excluded from the analysis because they had missing data on health behaviours at baseline (ten for smoking, 94 for alcohol consumption, 33 for fruit and vegetables consumption, and 416 for physical activity, categories not mutually exclusive) or had not been followed up for mortality (11 participants). The analysis was based on the remaining 9,771 participants (68% male and 32% female). Those excluded tended to have a lower occupational position at baseline (42% versus 22% in the lowest occupational group, p<0.001) and had a higher mortality rate (4.7 per 1,000 person-years versus 3.6 in the included sample). There were no age differences between the included and excluded men (44.0 versus 44.2 y, p = 0.6); excluded women were older (47.0 versus 45.1 y, p<0.001). Nonincluded participants had in general worse health behaviours than those included in the analysis. In the GAZEL study, a total of 2,865 participants, corresponding to 14% of the total population (13% men and 16% women), were excluded from the analysis because they had missing data on occupational position (25 participants) or on health behaviours at baseline (132 for smoking, 23 for alcohol consumption, 1,861 for fruit and vegetables consumption, and 2,091 for physical activity) or died before the start of the follow-up in 1992 (91 participants), all categories not mutually exclusive. The analysis was based on the remaining 17,760 participants (76% male and 26% female). Those excluded tended to have a lower occupational position (28% versus 16% in the lowest group, p<0.001) at baseline, and had a higher mortality rate (6.6 per 1,000 person-years versus 3.1 in the included sample). There were no age differences between the included and nonincluded sample although the latter had in general worse health behaviours. Our principal objective in these analyses was to examine whether the finding that health behaviours explained a large proportion of the association between SES and mortality in a British cohort was generalisable to other contexts. The comparison cohort in the present analysis was the French GAZEL cohort. Our hypothesis that health behaviours explain most of the social inequalities in mortality was not replicated. These results need to be interpreted in light of the fact that the associations between socioeconomic factors and mortality and that between health behaviours and mortality were similar in both cohorts. Thus, in both cohorts, SES and health behaviours were strong predictors of mortality. However, the causal chain leading from SES to health behaviours to mortality was not played out in a similar manner in the two contexts because of major differences in the social patterning of unhealthy behaviours. Indeed, relative and absolute inequalities across socioeconomic groups in smoking, following an unhealthy diet, and being physically inactive were greater in the British Whitehall II than in the French GAZEL study. As a consequence, health behaviours were less important mediators of the SES-mortality association in the GAZEL study. Source: http://doi.org/10.1371/journal.pmed.1000419