IJE Advance Access originally published online on November 8, 2005
International Journal of Epidemiology 2006 35(1):112-113; doi:10.1093/ije/dyi227
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Commentary |
Commentary: Varying relation of socioeconomic status with obesity between countries at different stages of development
Department of Family Medicine, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, South Korea. E-mail: ymsong{at}smc.samsung.co.kr
The stage of social and economic development of a society seems to contribute to the varying relation of socioeconomic status (SES) and obesity between countries. Fezeu et al.1 reported a positive SES/obesity relation, a different finding from that observed in developed countries. In this commentary, I would like to discuss how we might interpret their findings paying attention to the increasing obesity problem.
Fezeu et al.1 examined the relation between SES and adiposity in a population-based cross-sectional study conducted in urban Cameroon.
In a study of SES and obesity, one important methodological issue is whether adjustment should be made for factors such as related energy intake and expenditure. These factors might be better considered to be mediating factors that should not be adjusted to examine the association between SES and obesity. In the study, Fezeu et al. have considered leisure time physical activity as one of the confounders in the relation between SES and adiposity while having included ownership of motorized transport and a television that could have a negative influence on the level of non-leisure time or leisure time physical activity into the items of household amenities, an indicator of SES in the study. Dietary factors were not taken into account in the study. Physical activity is closely related to the level of energy expenditure, and both leisure time and non-leisure time activity (e.g. transportation, occupational work, and house chores) are important contributors. In terms of the relation with SES, leisure time physical activity is known to have a positive relation whereas non-leisure time physical activity has been in the opposite direction historically.2 Therefore, meticulous consideration of leisure time as well as non-leisure time activity seems necessary to avoid a biased result in a study of SES and adiposity.
In developed Western countries, SES has been inversely associated with obesity with only a few exceptions regardless of the measures of SES: education, income, or occupation. However, the association was consistently positive in most countries at an earlier stage of development.3 Fezeu et al.1 demonstrated a positive association between SES and adiposity in the Cameroon population. The finding was consistent with that of previous studies from developing countries and it raises some issues about the SES/obesity relationship.
Why is the relation so different between countries according to the stage of socioeconomic development? Should we expect the inverse relation between SES and obesity to appear with the socioeconomic development even in those countries where currently a positive relation is observed? Exploring these issues would provide a better understanding of the mechanism of how SES is associated with obesity.
The studies in Western countries that have already gone through social and economic development early in 20th century cannot give much insight into this issue. However, studies from the countries in Asia, Latin America, and Africa currently experiencing markedly rapid socioeconomic transition and increasing burden of obesity could provide useful information.
A positive association between SES and obesity in the cross-sectional study by Fezeu et al.1 does not seem to provide any support for previously suggested causal models that obesity may tend to reduce the SES or that obesity and low SES may share some causes that promote both obesity development and SES reduction.4 Instead, the positive association between SES, measured by household amenity, and adiposity seems to support the assumption that changes in lifestyle (dietary pattern and physical activity) accompanying socioeconomic transition of a society would explain the varying association between SES and obesity.2,5–7 Household amenities measured in the study included a range of facilities related to food preparation, food storing, and leisure time and non-leisure time activities.
Some studies performed in China, an Asian country currently experiencing both rapid economic and social development, have demonstrated rapid changes in dietary pattern, physical activity, and prevalence of obesity in the country.5,6,8 According to these studies, the poor were more vulnerable to the effect of income change. Nutritional transition seemed to occur faster among the poor than the rich because food demand was more price-sensitive and income-sensitive among the poor. Meanwhile, mechanization of labour and motorized transportation introduced by socioeconomic development resulted in marked reduction of physical activities. Although research evidence is inadequate, the effects of reduced non-leisure time physical activities are thought to be greater among the poor because historically they have been more likely to do hard physical work. Another problem is that poor people can hardly afford the direct and indirect costs of leisure time physical activities while high SES people can afford more leisure time activities and have greater opportunity for recreational exercise.
These transitions in dietary and physical activity would cause a transient higher prevalence of obesity among affluent people during the early stage of development, but the obesity problem would then shift to poor people with ongoing socioeconomic change.
Recent studies reported that the burden of obesity seemed to shift towards the poor rapidly at an earlier stage of the economic and social development of each country particularly in the developing world.9,10 Several reasons were raised to explain the positive relation between SES and obesity commonly seen at an early stage of socioeconomic development: food scarcity and high energy expenditure among the poor, greater capacity of the high SES to get adequate food supply, and cultural values favouring plump body shapes as a symbol of privilege and wealth have been evoked. However, with socioeconomic development, these factors having protected poor people against obesity tend to dissipate.
Therefore, a positive association between SES and obesity currently being observed in developing countries should not be interpreted as an indication of better health among underprivileged in terms of obesity related health. Even before the rates of obesity among poor people in developing countries increase, public action should be implemented to prevent against obesity and related burdens among them, while taking account of the social and economic status of each society.
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1 Fezeu L, Minkoulou E, Balkau B et al. Association between socio-economic status and adiposity in urban Cameroon. Int J Epidemiol, 2006;35:105–11.
2 Droomers M, Schrijvers CTM, van de Mheen H, Mackenbach JP. Educational differences in leisure-time physical inactivity: a descriptive and explanatory study. Soc Sci Med 1998;47:1665–76.
3 Sobal J, Stunkard AJ. Socioeconomic status and obesity: A review of the literature. Psychol Bull 1989;105:260–75.[CrossRef][ISI][Medline]
4 Sorensen TIA. Socio-economic aspects of obesity: causes or effects? Int J Obes 1995;19:S6–8.
5 Popkin BM. The nutrition transition and obesity in the developing world. J Nutr 2001;131:S871–73.
6 Popkin BM, Gordon-Larsen P. The nutrition transition: worldwide obesity dynamics and their determinants. Int J Obesity 2004;28:S2–9.[CrossRef]
7 Bell AC, Ge K, Popkin BM. The road to obesity or the path to prevention: motorized transportation and obesity in China. Obes Res 2002;10:277–83.[ISI][Medline]
8 Du S, Mroz TA, Zhai F, Popkin BM. Rapid income growth adversely affects diet quality in China-particularly for the poor! Soc Sci Med 2004;59:1505–15.
9 Popkin BM. The shift in stages of the nutrition transition in the developing world differes from past experiences! Public Health Nutr 2002;5:205–14.[CrossRef][ISI][Medline]
10 Monteiro CA, Moura EC, Conde WL, Popkin BM. Socioeconomic status and obesity in adult populations of developing countries: a review. Bull World Health Organ 2004;82:940–46.[ISI][Medline]
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