We investigated associations of individual-level and area-level SES with hypertension in adults from 230 Latin American cities. We found a clear gradient across individual-level SES, but in opposite direction between genders. In women, higher SES levels were associated with a lower proportion of hypertension. In men, higher individual-level SES was associated with a higher proportion of hypertension. Although interaction terms between individual-level and area-level SES were not always statistically significant, descriptive analyses suggested that an inverse association of individual-level SES with hypertension became stringer or emerged as city or sub-city SES increased.
Our results also demonstrated that higher sub-city-level SES was associated with lower odds of hypertension in both genders. Moreover, the association of city-level SES with hypertension varied across countries. In Peru, there was an inverse association (lower proportion of hypertension with a better education at the city level), while in other countries there was no association in women or men.
A recent meta-analysis of 51 studies found that educational attainment was a stronger predictor of hypertension prevalence than income or occupation [6]. However, to our knowledge, transnational studies investigating associations of individual-level and area-level SES with hypertension using the same indicator at different levels and in different countries have not been conducted.
We found that hypertension was inversely associated with education among women, but positively associated with education among men. Evidence limited from LMICs generally shows a higher prevalence of hypertension in women with lower education levels compared with higher education, while for men, evidence is mixed [3, 11, 25, 26]. Explanations for gender disparities may include more physically demanding jobs for less educated men [27] or differential patterning of other risk factors by SES in women and men [28]. Moreover, being a woman and having low education may be linked to higher exposure to chronic stress conditions, such as informal employment, single parenthood and role overload, violence, and stress at home [29, 30].
Furthermore, women's behaviors are heavily influenced by heteronormative gender rules in patriarchal societies, especially the more educated women. For instance, these women are more likely to face pressure to change their bodies to align with social expectations [31]. Surveillance bias may also explain part of the association observed between education and hypertension in men. Men often search less for health systems and medical advice [18]. Nonetheless, men with the highest SES are less likely to remain undiagnosed and report more chronic diseases [16, 17]. Consistent with this argument, our sensitivity analysis based on objective measures of blood pressure revealed that men with higher SES had lower odds of hypertension.
Our study also showed sub-city and city contextual effects. After accounting for individual SES, we found a positive association between sub-city-level SES and hypertension for both genders. Lower access to health care (and consequent diagnosis of hypertension) in areas of lower SES could explain this finding [16–18]. On the other hand, we observed a similar pattern when objective measures of hypertension were used. In consonance with our findings, a positive association between area-level SES and hypertension was also previously reported in Brazil using objective hypertension measures [4].
The mechanisms underlying this association may be related to contextual factors associated with area-level SES including the nature of work [32], access to and consumption of processed foods, sedentary behaviors [33, 34] promoted by work and urban environments (e.g., car dependence), or even factors such as levels of pollution, heat, and noise, all of which have been linked to hypertension [35] and the risk of cardiovascular disease [36].
Significant associations between city-level SES and hypertension were limited to individuals residing in Peru; better educational performance of the population at the municipal level was associated with a lower proportion of hypertension in women and men. While the highest prevalence of hypertension was observed in some Latin American and Caribbean countries, the lowest global prevalence of hypertension was found in Peru [2]. It is possible that the hypertension epidemic is not yet very deep in this country, reflecting a pattern different from others. Thus, the positive association between city-level SES and hypertension in Peru is a question that deserves additional research.
Our results also suggest possible interactions between contextual- and individual-level SES. In women, the inverse association of individual-level SES with hypertension became stronger as sub-city and city SES increased. In men, the positive association of individual-level SES with hypertension was lost, and an inverse gradient emerged (higher SES, lower hypertension prevalence) as sub-city SES increased. This is consistent with findings from prior works showing that inverse social gradients in cardiovascular risks emerge as contextual SES increases [37, 38]. It may be related to the social patterning of risk factors for hypertension that emerges as socioeconomic development increases.
This study has some limitations. First, we use a cross-sectional design, which does not allow us to draw causal inferences; however, descriptive information is also important to public policy. Second, the ascertainment of hypertension status was through self-report, which may have led to differential information bias, with groups with less access to healthcare under-represented, and consequently, resulting in underestimates of education gradients. Third, it is not possible to rule out residual confounding due to unmeasured or unknown confounding factors. Fourth, survey years are not always aligned with the census years from which area-level SES information was drawn. Finally, despite efforts to harmonize surveys across countries, some heterogeneity may still exist and affect our results. Nonetheless, to attenuate these potential remaining differences we used the country as fixed effects for the main analyses.
On the other hand, this study has several strengths. As far as we know, this study is the first to examine the association between individual-level and area-level SES with hypertension using the same indicator at different levels. Second, our study included a large sample of individuals (109,184) and cities (230) representing a significant proportion of the urban population of Latin America and used a large harmonized dataset. Third, our multilevel approach allowed us to analyze individual and macro-level contextual factors. In addition, the associations were adjusted for country-fixed effects removing the effect for unmeasured country factors such as differences in healthcare and education systems across countries.
In conclusion, our results demonstrate gender and social inequalities in hypertension in Latin American cities. First, we identified gender differences in the relationship between individual SES and hypertension, with higher individual-level SES associated with lower odds of hypertension among women and higher odds among men. Second, we identified that higher sub-city-level SES was positively associated with hypertension in both women and men. Third, we identified that higher city-level SES was associated with lower odds of hypertension in both sexes in Peru. Thus, our results suggest that strategies to deal with the burden of hypertension in LIMCs should adopt equity-based and context-sensitive efforts.