Socio-economic factors and cancer

Health and life expectancy are known to be intimately linked with the country’s socio-economic conditions. The classification of individuals in social strata is often based on various personal characteristics, mostly due to the lack of one complementary, measureable and valid index. Lower socio-economic groups, defined by educational attainment, occupational class, income, material possessions or a combination of the above, experience higher rates of premature death than upper socio-economic groups [6].Social determinants of health reportedly include unemployment or job insecurity; early environment exposures including inadequate parental support; addiction to tobacco, alcohol or euphoric drugs; stress at work or in everyday life; dietary intake; type of transport available; poverty; discrimination; social exclusion, and lack of social support networks [8].

Socio-economic differentials in cardiovascular mortality are mostly cited as the driving force behind socio-economic differences in overall mortality [6]. Studies further report that mortality rates from cancer are also higher among individuals of a lower socio-economic class than those of a higher class [1]. In particular, men in lower social strata experience higher risks of cancers of the lung, oral cavity, larynx, pharynx, esophagus, stomach, and, in some populations, liver. Among women, low social class was consistently associated with an increased risk of cancer of the esophagus, stomach, uteri and, primarily, cervix. Irrespective of their gender, individuals in higher social strata experienced a higher risk of colon cancer and skin melanoma and in most populations the risk of breast and ovary cancers was higher among women of high social class [3]. In Greece, socio-economic inequalities in health were first reported in the early 1980s and, in relation to cancer,an inverse relationship was observed between mortality rates and the per capita domestic product [4].

In a recent analysis undertaken in the context of the European Prospective Investigation into Cancer and nutrition (the EPIC study),Gallo and colleagues (2012) analyzed data of15,972deaths from 22 research centers in nine European countries. In their analysis, Gallo and colleagues studiedthe association between the overall or cause-specific mortality and socio-economic characteristics of the study participants, assessed through their educational attainment. The highest level of educational attainment is considered an objective, valid and comparable between-studies index and it is the most commonly used indicator of socio-economic status [5]. In this study, overall mortality among men with the highest educational level was reduced by 43% compared to men with the lowest (hazard ratio (HR) 0.57, 95% confidence intervals (C.I.) 0.52–0.61). Among women, overall mortality was reduced by 29% (HR 0.71, 95% C.I. 0.64–0.78). Correspondingly, cancer mortality was reduced by 32% among men of high education (HR 0.68, 95% C.I. 0.59–0.78) and 7% among women with the highest educational level compared to those with the lowest, without, however, reaching statistical significance among women (HR 0.93, 95% C.I. 0.80–1.07).

The underlying mechanisms are not fully understood. According to several researchers, the observed differences in mortality rates could reflect socio-economic differences in the frequency of disease risk factors, such as smoking, increased alcohol intake, poor diet and obesity [2].

In a recent analysis of 23,697 participants of the Greek part of the EPIC study, the authors assessed socio-economic differentials in the prevalence of established or likely risk factors of premature death, separately for men and women [7]. Obesity, low adherence to the traditional Mediterranean diet, hypertension and the lack of physical activity were substantially more prevalent among the least educated men and women. With respect to smoking, the socio-economic differential among men was limited, whereas among women it was strikingly inverse. The prevalence of smoking among women of low educational attainment was substantially lower than among women withthe highest education. The prevalence of increased alcohol consumption was higher among the less educated men and the more educated women. In the same study, and after controlling for participants’ age, there was essentially no socio-economic differential among either men or women with respect to cancer mortality.

The latter finding in a large sample of the general Greek population may reflect the fact that smoking, the overwhelming known cause of cancer, showed a weak socio-economic differential among men and a reverse one among women (increased prevalence of smoking among women of higher educational attainment). In addition, excessive alcohol consumption, which was evident among the less educated men, is mostly related to cancers of the upper aerodigestive tract (oral cavity, larynx and pharynx), which are relatively rare in the Greek population; whereas among women, excessive alcohol consumption is mostly related to breast cancer, which is a common type of cancer among women in the upper socio-economic group. Lastly, an interpretation of socio-economic differentials in the mortality rates of the Greek population should also take into account data on the differences in availability and utilization of health care and services by population sub-groups.

 

References
  1. Galea S, Tracy M, Hoggatt KJ, Dimaggio C,Karpati A. 2011.Estimated deaths attributable to social factors in the United States.Am J Public Health 101(8):1456–1465.
  2. Gallo V, Mackenbach JP, Ezzati M, Menvielle G, Kunst AE, Rohrmann S, Kaaks R, Teucher B, Boeing H, Bergmann MM, Tjønneland A, Dalton SO, Overvad K, Redondo ML, Agudo A, Daponte A, Arriola L, Navarro C, Gurrea AB, Khaw KT, Wareham N, Key T, Naska A, Trichopoulou A, Trichopoulos D, Masala G, Panico S, Contiero P, Tumino R, Bueno-de-Mesquita HB, Siersema PD, Peeters PP, Zackrisson S, Almquist M, Eriksson S, Hallmans G, Skeie G, Braaten T, Lund E, Illner AK, Mouw T, Riboli E,Vineis P. 2012. Social inequalities and mortality in Europe –results from a large multi-national cohort.PLoS One. 7(7):e39013. Epub 2012 Jul. 25.
  3. Kogevinas M, Pearce N, Susser M, Boffeta P. eds. 1997.Social inequalities and cancer.IARC scientific publications No. 138. Lyon: International Agency for Research on Cancer.
  4. Kyriopoulos J, Kalantidi A, Trichopoulos D. 1983.Associations between social and economic factors and cause-specific mortality in Greece. Mat Med Gr 1983;11:192–196 (in Greek).
  5. Liberatos P, Link BG,Kelsey JL. 1988. The measurement of social class in epidemiology.Epidemiol Rev;10:87–121.
  6. Mackenbach JP, Stirbu I, Roskam AJ, Schaap MM, Menvielle G, Leinsalu M, Kunst AE. European Union Working Group on Socioeconomic Inequalities in Health, 2008.Socioeconomic inequalities in health in 22 European countries. N Engl J Med 358(23):2468–81.
  7. Naska A, Katsoulis M, Trichopoulos D, Trichopoulou A. 2012.The root causes of socioeconomic differentials in cancer and cardiovascular mortality in Greece.Eur J Cancer Prev.21(5):490–496.
  8. World Health Organization, 2008.Closing the gap in a generation: Health equity through action on the social determinants of health: final report of the commission on social determinants of health. Geneva: World Health Organization.

 

Androniki Naska, Assistant Professor of Hygiene and Epidemiology
Dept. of Hygiene, Epidemiology and Medical Statistics, School of Medicine, National and Kapodistrian University of Athens