Commentary: Epidemiological transition and socioeconomic inequalities in blood pressure in Jamaica

Martin Gulliford

Public Health Sciences, King’s College London. E-mail: martin.gulliford{at}kcl.ac.uk

Mortality in low-income countries is predominantly caused by infectious diseases in association with under-nutrition, but economic development is associated with an epidemiological transition to a state more characteristic of high-income countries in which most deaths are caused by chronic non-communicable diseases. Recent declines in cardiovascular mortality in the more affluent countries have led to the suggestion that there will be a further transition in which ‘degenerative’ conditions associated with ageing will increase in importance.1

From the perspective of epidemiological transition, inequalities in health arise because different groups in a population progress through these transitions at different rates. Typically, more affluent groups make these transitions more rapidly than poor or ethnic minority groups. This is evident in low-income countries where under-nutrition and infectious diseases continue to affect the poor, while non-communicable disorders emerge among the more affluent.2 In high-income countries most interest has focused on socioeconomic inequalities in cardiovascular mortality which disadvantage the poor. These inequalities have widened as mortality has declined more rapidly in groups with higher socioeconomic status. Thus cardiovascular diseases appear to be associated with affluence during the phase of increasing mortality but with poverty during the phase of decreasing mortality.3 Risk factors such as obesity are considered to be associated with affluence in low-income countries but with lower socioeconomic status in high-income countries.4 However, there is a lack of evidence to support these generalizations, and the situation in countries at intermediate levels of economic development is unclear.

The International Collaborative Study for Hypertension in Blacks (ICSHIB) has provided important evidence for populations of West African descent.5 The study reported data for population samples in Nigeria and Cameroon; for populations of West African descent living in Jamaica, Saint Lucia, and Barbados; and for people living in Maywood, Illinois, USA. The age-adjusted prevalence of hypertension ranged from 12% in men and 14% in women in rural Africa, to 30% in men and 35% in women in Maywood, USA. The Caribbean countries showed an intermediate prevalence of hypertension. In the Caribbean and the USA, the higher prevalence of hypertension was associated with an increased prevalence of obesity, especially in women, and with greater intake of dietary sodium.5,6 The authors estimated that the mean body mass index and the urinary sodium to potassium ratio accounted for 70% of the observed geographical variation in hypertension prevalence.5

In Africa, hypertension has been associated with urbanization. In a study from Nigeria derived from ICSHIB, rural farmers had lower blood pressure and less hypertension than urban groups.7 Within an urban environment workers engaged in higher status paid, or pensioned, work had higher blood pressures than poorer unwaged workers.7 In contrast to the positive association between blood pressure and socioeconomic status observed in Nigeria,7 a recent systematic review of studies from high-income countries found that 42 out of 50 eligible reports showed a negative association between blood pressure and socioeconomic status.8 This pattern of association was more consistent in women than men.

This paper by Mendez et al.9 explores these issues in a ‘peri-urban’, middle-income country setting using data from a Jamaican sample based on the ICSHIB study. The authors analysed blood pressure, hypertension, and hypertension management in relation to individual income and educational attainment in men and women. There were important gender differences, women showing more frequent obesity and hypertension. There was no simple linear trend in blood pressure or hypertension with increasing levels of income or education in either sex. Instead, there was evidence that women with intermediate levels of income had the lowest diastolic blood pressures, and were less likely to have hypertension than those with the highest incomes. Women with the lowest incomes had intermediate levels of diastolic blood pressure and hypertension which were not significantly different from the highest income group used for reference. In men, there was evidence that the association of income with blood pressure varied according to educational level. Less educated men with low incomes had higher blood pressures than better educated men at the same income level, or men with similar education but higher incomes. In better educated men, blood pressure increased with income level.

Colhoun et al.8 suggested that the negative gradient in blood pressure with increasing socioeconomic status observed in high-income countries might be explained by variations in body mass index and alcohol consumption. The present observations were independent of adjustment for body mass index category. Nevertheless, the findings raise a question concerning the socioeconomic distribution of body mass index in Jamaica. Alcohol use did not appear to be an important confounder in the present analyses. Mendez et al. allude to the possible role of more recently identified risk factors for high blood pressure. Forrester et al. found that in Jamaican school children under 10 years of age, blood pressure was negatively associated with birthweight.10 Other data suggest that the association between birthweight and blood pressure may be less consistent in African origin populations than in other groups.11

Mendez’s results suggest that the socioeconomic distribution of blood pressure and hypertension in Jamaica is complex, combining aspects of the inequalities found in both higher- and lower-income countries. In this transitional stage, the findings appear paradoxical because the results for lower-income subjects are more consistent with the pattern of inequality found in high-income countries, while the results for higher-income women and better-educated men are more consistent with the pattern of inequality reported from lower-income countries. This paper adds to the evidence showing that there is variation in the association of measures of socioeconomic status with risk factors12 and disease outcomes3 in middle-income countries.

Economic changes do not always proceed in a single direction and living conditions sometimes deteriorate rather than improving. When socioeconomic and health conditions are changing the impact on different segments of society will vary, and there may be inconsistent patterns of exposure at different stages of life. Associations of blood pressure with measures of socioeconomic status including education, income, and occupation may then vary in different groups. The paper provides evidence of variation according to gender and educational attainment. There might also be different patterns of association in different age groups. In the Jamaican centre of the WHO study of cardiovascular disease and steroid hormone contraception,3 which included young women aged 15–49 years, the highest risk of stroke was in women with low rather than high educational attainment. Variation between localities, especially between rural and urban areas, or areas where tourism has developed, may also be important.7 Surveillance at a national level is required to monitor these changes as they affect different population groups.

Mendez’s findings bring to mind the motto inscribed on Jamaica’s coat of arms—‘out of many, one people’. It is clear that the problems of hypertension and associated disorders need to be addressed for all groups in society. Intervention studies have identified the kind of changes that can reduce blood pressure13 but there remain important gaps in our knowledge concerning how public policies and community-based interventions may be used to bring about such changes,14 and in the commitment to implementation.


    References
 Top
 References
 
1 Mackenbach JP. The epidemiologic transition theory. J Epidemiol Community Health 1994;48:329–31.[ISI][Medline]

2 Gwatkin DR. Distributional implications of alternative strategic responses to the demographic epidemiological transition. An initial inquiry. In: Gribble JN, Preston SH (eds). The Epidemiological Transition. Policy and Planning Implications for Developing Countries. Washington DC: National Academy Press, 1993, pp. 197–228.

3 Chang C, Marmot MG, Farley TMM, Poulter NR. The influence of economic development on the association between education and the risk of acute myocardial infarction and stroke. J Clin Epidemiol 2002; 55:741–47.[CrossRef][ISI][Medline]

4 Sobal J, Stunkard AJ. Socioeconomic status and obesity: a review of the literature. Psychol Bull 1989;105:260–75.[CrossRef][ISI][Medline]

5 Cooper R, Rotimi C, Ataman S et al. The prevalence of hypertension in seven populations of West African origin. Am J Public Health 1997; 87:160–68.[Abstract]

6 Kaufman JS, Durazo-Arvizu RA, Rotimi CN, McGee DL, Cooper RS. Obesity and Hypertension Prevalence in Populations of African Origin. Epidemiology 1996;7:398–405.[ISI][Medline]

7 Kaufman JS, Owoaje EE, James SA, Rotimi CN, Cooper RS. Determinants of hypertension in West Africa: Contribution of anthropometric and dietary factors to urban-rural and socioeconomic gradients. Am J Epidemiol 1996;143:1203–18.[Abstract]

8 Colhoun H, Hemingway H, Poulter NR. Socio-economic status and blood pressure: an overview analysis. J Hum Hypertens 1998;12:91–110.[CrossRef][ISI][Medline]

9 Mendez MA, Cooper R, Wilks R, Luke A, Forrester T. Income, education, and blood pressure in adults in Jamaica, a middle-income developing country. Int J Epidemiol 2003,32:399–407.

10 Forrester TE, Wilks RJ, Bennett FI et al. Fetal growth and cardiovascular risk factors in Jamaican schoolchildren. BMJ 1996;312:156–60.[Abstract/Free Full Text]

11 Law CM, Egger P, Dada O et al. Body size at birth and blood pressure among children in developing countries. Int J Epidemiol 2001;30:52–57.[Abstract/Free Full Text]

12 Monteiro CA, Conde WL, Popkin BM. Independent effects of income and education on the risk of obesity in the Brazilian adult population. J Nutr 2001;131:881S–86S.[Abstract/Free Full Text]

13 Vollmer WM, Sacks FM, Ard J et al. Effects of diet and sodium intake on blood pressure: subgroup analysis of the DASH-sodium trial. Ann Intern Med 2001;135:1019–28.[Abstract/Free Full Text]

14 Ebrahim S, Davey Smith G. Exporting failure? Coronary heart disease and stroke in developing countries. Int J Epidemiol 2001;30:201–05.[Free Full Text]





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