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
In The News
April 2nd, 2010 at 8:55 am
It seems like a person’s educational background would have an impact both on income and health choices. Did they look at that data?
Peace,
Shannon
April 4th, 2010 at 7:42 am
I think it is likely to be a complex set of factors, but mostly in the direction of low income leading to the habits, not the other way around, at least not as frequently.
I think it would be possible to look at people (not civil servants though, who probably aren’t, on the whole, going from rags to riches) who were in poverty before they were 30, but not afterwards, and compare them to people who stayed in poverty and those who were never “exposed” to poverty, and see what the differences are. My hypothesis would be that those who “escaped poverty” would be somewhere in the middle when it came to health habits.
Considering we wouldn’t want to do an experimental design where we took middle-class people and threw them into poverty (although there can be “natural experiments” like this) it would be hard to determine how it worked the other way.
I think calling all of the differences in health habits “stress” is a cop-out. Culture also plays a role — in some cultures that have had to deal with times of plenty but not times of extreme food insecurity, there does appear to be a “built-in” way of thinking about food and movement that is a “middle way” — working to balance pleasure and health. Other cultures value fatness because it provided protection against times when food was lacking — having fatter royalty was a way of preserving the royal line — most people don’t die of fatness before they are able to reproduce, and being fatter at a time before modern medicine meant in many cases that the body could outlast the short-term effects of many acute illnesses.
If we can shift our lense from thinking of fatness, or even those behaviors we lable as “unhealthy,” as bad, but rather serving a purpose, we can have a broader interpretation and more potential solutions. I think that the exposure to stress-relieving activities at earlier developmental stages (birth through early adulthood, in particular) can be a huge factor. If a young person sees everyone around them smoking, and finds smoking relieves their stress, that’s a very bad set-up. But if a young person sees everyone around them using yoga or swimming or other physical activity to relieve stress, that’s something else altogether.
April 6th, 2010 at 10:58 am
Low s-e status ~~ high bad health habits (alcohol, smoking, poor diet, poor exercise)
Is this because low s-e status means less money?
Poor diet and poor exercise may be because of lack of money.
Smoking and alcohol consumption are expensive habits.
Money which could be spent on healthier diet or exercise activities is spent on smoking and drinking.
If the study showed poor diet, low exercise, and LOW alcohol consumption and LOW smoking, then it could be concluded that lack of money could be causing the poor diet and low exercise.
As it is, everybody in the study is employed. The problem seems to be one of an unhealthy culture, not lack of money, somehow associated with low s-e status.