Socioeconomic Status and Health Behaviours: Chicken, Egg, or Both

A study by Silvia Stinghini and colleagues from Villejuif, France, published in this week’s edition of JAMA re-examines the relationship between socioeconomic status and mortality in the famous British Whitehall study.

This longitudinal cohort study includes around 10,000 English civil servants, aged 35 to 55 years, 654 of whom have died since the study began 24 years ago.

When adjusted for sex and year of birth, civil servants in the lowest civil service employment grade (as a surrogate for socioeconomic status) had a 1.60 times higher risk of death from all causes than those with the highest employment grade. The risk for cardiovascular mortality was in fact 3 times higher for the lowest socioeconomic group.

However, this apparently strong impact of socioeconomic position declined remarkably when data was adjusted for repeated measures of health behaviours like smoking, alcohol consumption, diet, and physical activity.

Thus, when these behaviours were entered as time-dependent covariates the increased risk was reduced by 45% for cardiovascular mortality and 94% for noncancer and noncardiovascular mortality.

Thus clearly, a large part of the association between socioeconomic status and mortality is not due to the difference in socioeconomic status per se, but rather due to the poorer health behaviours associated with this status.

There are three possible inferences from these findings:

1) Poor people tend to make poor health “choices” because they are poor. (direct causality)

2) Poor people tend to be poor because they make poor health “choices”. (reverse causality)

3) Certain people tend to be both poor and make poor health “choices”. (no causality)

Reasoning 1) would imply that if people were less poor they would perhaps make better health “choices”.

Reasoning 2) would imply that if people made healthier “choices” they would perhaps be less poor.

Reasoning 3) would imply that that there is something else happening that makes people both poorer and (independently) more likely to make poorer health “choices”.

As pointed out in an accompanying editorial by James Dunn, McMaster University, Hamilton, Canada, most people tend to simplify the debate by explaining the poorer health “choices” of lower socioeconomic status with the greater “stress” of lower socioeconomic status.

But an emerging view could be that both health behaviours and lower socioeconomic status may well be independent expression of factors such as early childhood development, which are well known to affect self-regulation (the ability to guide goal-directed activities over time and across changing circumstances) or higher executive functions (like the skills involved in organisation, planning, self-monitoring, or self-control).

Deficits in these abilities or functions would not only make someone less likely to achieve a higher socioeconomic status but would also influence their ability to adopt and sustain healthy behaviours.

Obviously with obesity these lines of reasoning become far more complex. For e.g. in developing countries, it is often the people in the higher socioeconomic strata that gain weight. Even in Canada, middle class men rather than men in the lower economic group appear to be at higher risk for obesity.

Certainly interesting stuff to ponder on over the long weekend.

AMS
Edmonton, Alberta