Sunday, May 9, 2010

Health Outcomes: The interaction of class and health behaviors

I have recently discussed (Poverty, Primary Care and the Cost of Medical Care, February 10, 2010) the “Whitehall Studies” conducted by Sir Michael Marmot and colleagues that “demonstrate that there is a more or less linear correlation between health (including longevity) and increasing social class". That piece discussed the report of a panel headed by Marmot, “Fair Society, Healthy Lives”, that shows that these problems have not been resolved. A new paper from the follow-up “Whitehall II” study, conducted by Silvia Stringhini and colleagues from both Britain and France, “Association of socioeconomic position with health behavior and mortality”, (JAMA Mar24/31,2010;303(12):1159-66), examined the role of alcohol, tobacco, diet, and physical activity in accounting for these differences over an extraordinarily long 24-year follow-up period.

Stringhini, et. al., found that in fact adverse health behaviors accounted for about 42% of the increase in mortality in lower socioeconomic groups (which was about 1.6 times as high in lowest than in the highest socioeconomic group). Smoking was the most powerful negative factor, with the others contributing a smaller amount. “There was a marked social gradient in health behaviors at baseline. Participants in the lower socioeconomic positions were more likely to smoke, abstain from alcohol consumption, follow an unhealthy diet, and be physically inactive and less likely to consume heavy amounts of alcohol.” Most of this is consistent with the observations of physicians and epidemiologists in the US, with the surprising exception of alcohol use being lower in lower income groups. This may be a difference between the US and Britain; in Britain, in the 20th century, cirrhosis was a disease largely of the upper class who could afford the highly taxed, and high alcohol content, distilled spirits. Another possibility (and this is my speculation, not data) is that the lower socioeconomic group studied by Whitehall II in England may have a large component of Muslims, who do not drink. In any case, the impact of smoking, poor diet, and physical inactivity accounted for a significant part of the class difference in mortality, although it did not account for even the majority of that difference.

Thus, this study supports two well-established assumptions: 1) that adverse health behaviors are a significant contributor to ill health and higher age-adjusted mortality rate, and 2) that people in lower socioeconomic groups have worse health and higher mortality rates, much, but not all, of which can be associated with their higher rates of adverse health behaviors. Previous work on the results of Whitehall have suggested, and demonstrated evidentiary support for, the hypothesis that stress in daily life (of worrying about how you will pay the rent and feed your family, whether you are going to lose your job, or, particularly in the case of ethnic and racial minorities, not only whether you will be arrested or harassed by the authorities but the indignities of ongoing discrimination), mediated through only partially understood neurochemical pathways, account for much of this effect. However, to the extent that people can divest themselves of risky health behaviors, they can decrease, if not eliminate, their higher risk for adverse health outcomes.

In the same issue of JAMA, James R. Dunn of McMaster University in Canada, has a very insightful editorial commenting on the Stringhini article, “Health behavior vs the stress of low socioeconomic status and health outcomes” (JAMA, Mar24/31, 2010;303(12):1199-1200). He repeats the caution of the Whitehall authors that the population studied in the Whitehall cohort may not be representative of the British population overall (and, by extension, of the US or Canadian population). Indeed, the cohort was originally selected by Marmot and colleagues to reduce the confounding that might come from general studies of people in different classes because of occupational risks. Dunn points to the association of the stress of low socioeconomic status and the prevalence of adverse health behaviors: “…it is possible to consider both factors [stress and behavior] as part of the same pathway between relatively low socioeconomic status and health. Unhealthy behaviors are more common among individuals with low socioeconomic status because of the stress of low socioeconomic status. Accordingly, there is a direct causal pathway between low socioeconomic status and poor health as well as an indirect causal pathway through health behavior, which reinforce one another over the lifecourse.” That is, the stress of being poor makes you more likely to do unhealthful things that we know about (smoking, poor diet, low physical activity) that make you less healthy, and also makes you less healthy through a pathway that we don’t completely understand.

Dunn notes that while changing health behaviors in lower socioeconomic populations would be a good thing, “The problem is that traditional individually oriented health behavior education interventions are not very effective, and individuals with low socioeconomic status have been notoriously difficult to reach with such programs”. He discusses a variety of early childhood developmental characteristics, especially “executive function” and “self regulation” which might increase the probability of not adopting or stopping adverse health behaviors, which are on average less well developed in those growing up in lower socioeconomic groups, presumably also as a result of the stress impacting them as young children.

The relatively good news from the Stringhini study is that the prevalence of many adverse health behaviors did decrease over the time period studied. For smoking, the prevalence decrease from 10.1% to 4.8% in the highest, and from 29.7% to 16.5% in the lowest socioeconomic groups and unhealthy diet from 5.8% to 1.0% and 14.9% to 5.2% respectively diet; on the other hand, sedentary behavior increased from 6.6% to 21.4% in the highest and from 35.4% to 41.6% in the lowest socioeconomic groups. Again, extending this to the whole British population is uncertain, and in the US the prevalence of obesity (a combination of both poor diet and physical inactivity) is growing at a staggering rate in all age groups, and especially in low socioeconomic groups.

The take-home message is that all people should be encouraged and supported to adopt healthful and eschew unhealthful behaviors, particularly related to smoking, diet and exercise, and the degree to which any programs can be demonstrated to be successful for large numbers of individuals or, better yet, groups, they should be promulgated and replicated. However, to have greater success, programs will have to strike closer at the etiologies of these behaviors. A lower level, achievable (and achieved in some jurisdictions) by legislation, exemplified by indoor smoking bans, calorie and fat content labeling of foods, especially fast foods, and banning the use of toys as gifts in fast-food meals (as recently done in Santa Clara County, CA), can have much more significant impact (see “Promoting health through tobacco taxation” by Ali and Koplan from JAMA, and “Cardiovascular effect of bans on smoking in public places: a systematic review and meta-analysis” by Meyer, et. al., in JACC, cited in The Public’s Health: Smoking and Salt, February 6, 2010).

The greatest changes, however, involve even more significant societal changes: the elimination of the wide disparity in income and opportunity, thus socioeconomic status, and of racism. Health-focused, as well as social justice focused, policies should try to achieve this end, but in the US it will be a long time coming. In the meantime, it remains a good idea to choose your parents wisely; being born white and rich still significantly enhances your health status.

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