Guilford Harbor

The ultimate cause of social disparity in preventative health behavior may be rooted in environmental harm

Wednesday, October 13th, 2010

In a fascinating new article in PLOS One (open access), Daniel Nettle asks why we see social gradients in preventative health behaviors:

People of lower socioeconomic position have been found to smoke more, exercise less, have poorer diets, comply less well with therapy, use medical services less, adopt fewer safety measures, ignore health advice more, and be less health-conscious overall, than their more affluent peers. Some of these behaviors can simply be put down to financial constraints, as healthy diets, for example, cost more than unhealthy ones, but socioeconomic gradients are found even where the health behaviors in question would cost nothing, ruling out income differences as the explanation.

As we often assume with environmental or nutritional issues, maybe simply helping to better educate people is all that’s needed? Probably not, as Nettle points out, and with an interesting twist:

Socioeconomic gradients in health behavior are not easily abolished by providing more information. Informational health campaigns tend to lead to greater voluntary behavior change in people of higher socio-economic position, and thus can actually increase socioeconomic inequalities in health, even whilst improving health overall. Thus, we are struck with what we might call the exacerbatory dynamic of poverty: the people in society who face the greatest structural adversity, far from mitigating this by their lifestyles, behave in such ways as to make it worse, even when they are provided with the opportunity to do otherwise.

What are some of the possible explanations for this pattern, and are they sufficient?

Underlying socioeconomic differences in health behavior are differences in attitudinal and psychological variables. People of lower socioeconomic position have been found to be more pessimistic, have stronger beliefs in the influence of chance on health, and give a greater weighting to present over future outcomes, than people of higher socioeconomic position. These explanations seem clear.

However, they immediately raise the deeper question: why should pessimism, belief in chance, and short time perspective be found more in people of low socioeconomic position than those of high socioeconomic position? These deeper questions are at the level which behavioral ecologists call ultimate, as opposed to proximate causation

To develop more of an ultimate explanation, Nettle hypothesized that lower socioeconomic groups are subject to greater hazard or environmental harm or even simply the perception of living a more hazardous life.  This, in turn, discourages healthy behavior.

To test this hypothesis, he developed a mathematical/statistical model predicting the probability of dying in a given year, which is a combination of extrinsic risks that people cannot control as well as intrinsic risks that they can control through modified health behavior.   Thus, people choosing to take the time to engage healthier opportunities reduce their mortality risk.  Now there’s a tradeoff, however, because the more time people choose to undertake healthy behavior, the less time is left over for leisure activities and other life events.

Overall survival is therefore a combination of all of these factors, which can easily be modeled by assuming a range of values for time spent on health vs. other activities to see what kinds of mortality outcomes arise.

Here are the interesting results he found…

If it is the case that lower socioeconomic position is associated with a greater rate of extrinsic hazards (an assumption which needs justifying, see below), then we should expect people to respond to lower socioeconomic position with reduced preventative health behavior, because the benefits of that behavior to them are indeed lessened. This would in turn make their health outcomes worse, and so the gradient in health outcomes should in general be steeper than the underlying gradient in extrinsic risk exposures. Thus, the observed pattern of substantial socioeconomic gradients in health, which are to a  significant extent mediated by differences in health behavior, is exactly what we would predict if people are behaving adaptively given the environment in which they live.

Previous research on social inequalities in health behavior has found that people faced with socioeconomic deprivation endorse a greater belief in the influence of chance on life outcomes, particularly in the domain of health, are more pessimistic, and devalue future outcomes relative to present ones more sharply, than people of higher socioeconomic position. The model presented here is not in any sense an alternative to these accounts. On the contrary, the model here suggests an ultimate reason why these proximal psychological patterns might persist, and the proximal psychological accounts suggest how the adaptive behavior might actually be delivered. Clearly, people do not perform exact actuarial calculations in deciding whether to adopt a particular health behavior. Instead, they presumably employ some simple evolved heuristics. In this case, these might include something like ‘to the extent you see bad and unpredictable health outcomes besetting your peers, worry about today rather than tomorrow’.

And here’s where the environmental link comes in:

Several lines of evidence suggest that the assumption that lower socioeconomic position is associated with a greater degree of extrinsic hazard may not be unreasonable. First, studies of health inequalities generally find that controlling for behavioral factors (smoking, diet, etc.) attenuates socioeconomic gradients in health outcomes, but does not abolish them entirely. Of course, this could simply mean that not enough controls have been included, but it could also suggest that there is a residuum of health hazard which is extrinsic and thus not responsive to individuals’ behavioral decisions. Second, there are some health risk factors whose spatial distribution is socioeconomically patterned, and which people living in more deprived areas can do very little to avoid save for not living there. The clearest examples are noise, lead, and air pollution in the form of fine particles and nitrogen oxides. The levels of these hazards are higher in poor neighbourhoods, and their effects on morbidity and mortality well established. Third, many studies have found effects of living in poor neighbourhoods on health outcomes, above and beyond the effects of individual level socioeconomic characteristics. For example, poorer neighbourhoods are associated with substantially increased chances of accidental death or homicide, and heart disease, even once individual characteristics are adjusted for. This suggests that there are hazards fundamentally associated with living in these areas, which affect whoever it is that lives there.

In general, the model presented here draws the focus of health policy away from merely providing information or exhorting behavioral change, and onto extrinsic mortality. As with other neo-material approaches to health inequalities, it reminds us of the need to address the fundamental economic inequities which mean that some neighbourhoods contain higher risks of pollution, toxicity, and accident than others. More specifically, it suggests that reducing these structural inequities will reap a double dividend. It will have a primary effect on mortality inequality, and also a secondary effect as people respond to the primary effect by increasing their health-promoting behavior. Indeed, the secular trend in health behavior amongst middle-class people could be interpreted in this way. As economic development has eliminated many of the uncontrollable sources of danger, individuals have increased their investment in behaviors that mitigate those risks which do respond to individual choice. We need to create a similar dynamic in the most disadvantaged areas.

However, whilst changing structural conditions is the most important priority, the model also suggests that it is worth paying attention to people’s perceptions of extrinsic mortality. That is, in poor communities, individuals may perceive the local environment to be extrinsically dangerous to a greater extent than is in fact true (for example, because they are affected by social stereotypes or media portrayals). The model suggests that the psychological mechanisms which underlie behavioral decisions should be responsive to perceived levels of extrinsic mortality. If these perceptions are unrealistic, then they may lead to excessive fatalism and consequent disinvestment in health behavior. Thus, researchers and practitioners could usefully examine the genesis and malleability of people’s perceptions of the extrinsic dangers of their environments, and the relationships of these to their health attitudes and health behaviors.

What I love about this article is how it situates problems of sociology, psychology, public health, and justice squarely in the context of the environment—both actual and perceived.  And it encourages those of us interested in public health and well being to borrow a page from people engaged in environmental justice and just sustainability initiatives.

I also like how this result dismantles traditional notions of environmentalism and public health and forces us to consider new ways of studying pervasive problems in our world, where environmental studies scholars collaborate more with sociologists, psychologists, and historians to understand the ultimate causes of linked social-environmental challenges.

Nettle, D. (2010). Why Are There Social Gradients in Preventative Health Behavior? A Perspective from Behavioral Ecology PLoS ONE, 5 (10) DOI: 10.1371/journal.pone.0013371


Photo credit: postopp1

4 Responses to “The ultimate cause of social disparity in preventative health behavior may be rooted in environmental harm”

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  3. Alan says:

    Fascinating. In a superficial way, it speaks to the need to inform patients in deprived areas of the mechanisms and purposes of their therapy – as in the MSF/TAC model of HIV/AIDS treatment in which patients are given extensive education to understand their anti-retroviral therapy. I’m thinking that it maybe enhances the realisation that their well-being in relation to their HIV is not a matter of chance, but something that they can take responsibility for should they wish.

    It also speaks to the poor response to preventive messages in HIV in sub-Saharan Africa. We know the messages have got out there, but we also know that they haven’t dramatically affected peoples’ behaviour – despite the dramatic consequences of HIV infection. Many here in South Africa have already talked about the short-term outlook brought about by the huge uncertainties that the poor face.

    I love the conclusion that dealing with these wider problems could have knock-on effects. But the problem as always, is ameliorating those extrinsic factors in the context of a massive skills-shortage and a lack of government commitment.

  4. Kim Smith says:

    I agree that this is a fascinating and provocative study. Thanks for posting it!


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