Gender differences in the association of individual and contextual socioeconomic status with hypertension in 230 Latin American cities from the SALURBAL study: a multilevel analysis | BMC Public Health

We investigated associations of individual-level and area-level education with hypertension in adults from 230 Latin American cities. We found a clear gradient across individual-level education, but in opposite direction between genders. In women, higher education levels were associated with a lower proportion of hypertension. In men, higher education levels were associated with a higher proportion of hypertension. Although interaction terms between individual-level and area-level education were not always statistically significant, descriptive analyses suggested that an inverse association of individual-level education with hypertension became stronger or emerged as city or sub-city education increased.

Our results also demonstrated that higher sub-city-level education was associated with higher odds of hypertension in both genders. Moreover, the association of city-level education with hypertension varied across countries. In Peru, there was an inverse association (higher city education was associated with lower proportion of hypertension), 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 self-reported 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, 28, 29]. Explanations for gender disparities may include more physically demanding jobs for less educated men [30] or differential patterning of other risk factors by SES in women and men [31]. 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 [32, 33].

Furthermore, women’s appearance is heavily emphasized in patriarchal societies [34], with heteronormative gender norms often shaping more educated women’s behaviors [35] (e.g. they are more likely to face pressure to adjust their bodies to social expectations) [35]. 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] and this could be especially pronounced in lower SES men which could explain the strong positive association of individual-level education with self-reported hypertension that we observed.

Our sensitivity analysis based on objective measures of blood pressure showed a different pattern for individual level education in men: the highest education category had significantly lower odds than the lowest category. This is consistent with the argument that differences in access and utilization of health care by SES in men could explain the positive association of individual-level SES with hypertension that we observed. Of note the gender differences in associations of education with hypertension that we report here as similar to those reported by Braverman et al. [24] for diabetes and Mazariego et al. [25] for obesity in SALURBAL in previous work.

Our study also showed sub-city and city contextual effects. After accounting for individual education, we found a positive association between sub-city-level education and hypertension for both genders. Lower access to health care (and consequent diagnosis of hypertension) in areas of lower education could at least partly explain this finding [16,17,18]. However, 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 a positive association of sub-city education with hypertension may include other factors associated with area-level SES including the nature of work [36], access to and consumption of processed foods [37], sedentary behaviors [38, 39], 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 [40].

Significant associations between city-level education and hypertension were limited to individuals residing in Peru; higher educational attainment of the population at the city level was associated with a lower proportion of hypertension in women and men. While the highest global prevalence of hypertension was observed in some Latin American and Caribbean countries, the lowest global prevalence of hypertension was found in Peru [2, 19] and the stages of the hypertension of the epidemic could be linked to social patterning and differences across cities. Country differences in access to care and the patterning of access to care by city SES could also play a role when self-reported hypertension is used as a hypertension indicator. The positive association between city-level education and hypertension in Peru is a question that deserves additional research.

Our results also suggest possible interactions between contextual- and individual-level education. In women, the inverse association of individual-level education with hypertension became stronger as sub-city and city education increased. In men, the positive association of individual-level education with hypertension was lost, and an inverse gradient emerged (higher education, lower hypertension prevalence) as sub-city education increased. This is consistent with findings from prior works showing that inverse social gradients in cardiovascular risks emerge as contextual education increases [24, 25]. 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 inverse education gradients if lower SES groups have lower access to care. Third, gestational hypertension was not excluded in Argentina and Guatemala. Gestational hypertension data will be limited to some women who were pregnant at the time of the survey. In countries where we have information on current pregnancy (Brazil, Chile, Mexico, Peru and El Salvador), the presence of this condition was reported by approximately 4% of women aged 18 to 49 years, with only 19 (1.8%) of these were considered hypertensive. Therefore, we do not believe this is likely to have had a significant impact on our results. Fourth, we did not adjust for hypertension risk factors such as physical activity, diet, smoking, obesity, and diabetes because we view them as likely mediators of the associations we are investigating [15, 41]. In addition, it is not possible to rule out residual confounding due to unmeasured or unknown factors. Fifth, survey years are not always aligned with the census years from which area-level education 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. To our knowledge, this is the first transnational study to examine the association between individual- 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 education and hypertension, with higher individual-level education associated with lower odds of hypertension among women and higher odds among men. Second, we identified that higher sub-city-level education was positively associated with hypertension in both women and men. Third, we identified that higher city-level education 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.