Hypertension in South Asians

Elevated blood pressure (BP) is a growing health problem in South Asia, where it is the second largest risk factor for disability-adjusted life years lost, predominantly because of its strong relationship with cardiovascular disease (CVD) development. Within India, it has been estimated that hypertension accounts for 57% of all stroke related deaths and 24% of coronary artery disease related deaths. Thus, a significant proportion of death and disability in the region can be reduced by improving BP control.

In South Asia, there has been a steady rise in both the age- and sex-adjusted mean population BP, and the prevalence of hypertension, over the past two decades. Significant gaps in hypertension management are also present across South Asia, with less than half of individuals with high BP aware of it, and poor control in more than 80% with high BP. If left unaddressed, these trends will substantially increase CVD morbidity and mortality related to elevated BP. This chapter will focus on the epidemiology of hypertension and its management in South Asian populations. First we will examine the prevalence of hypertension, and its variation across South Asia. Next, we will examine the major modifiable and genetic risk factors associated with hypertension incidence in South Asians, and finally, we will summarize current gaps in hypertension management that need to be addressed in the region.

Prevalence of Hypertension in South Asian Populations

Definition of Hypertension in the South Asian Population

It has been recommended that some CVD risk factors in South Asians (e.g., obesity) warrant lower thresholds to define risk when compared with other ethnic groups. This is because of evidence that CVD in South Asians occurs at lower age and risk factor thresholds. Studies also suggest that certain physiologic BP parameters (e.g., pulse pressure, postexercise BP) differ, and that BP may have a stronger association with stroke risk in South Asians compared with white Europeans. However, there is no definitive evidence that, for a given BP, South Asian populations are at a higher CVD risk, and a systolic blood pressure (SBP) greater than 140 mm Hg and/or diastolic blood pressure (DBP) greater than 90 mm Hg remains the currently accepted threshold to diagnose hypertension in South Asian populations.

Prevalence of Hypertension in South Asia

Estimates of hypertension vary substantially across countries in South Asia, which is partly due to demographic differences between the populations studied. For example, in a systematic review of 33 observational studies (of 220,539 participants, with a mean age of 43.7 years) from seven countries in South Asia, the prevalence of hypertension was approximately 27%, ranging from 17.9% in Bangladesh to 33.8% in Nepal. By contrast, in the Prospective Urban Rural Epidemiology (PURE) study, which studied a slightly older population cohort of 33,000 participants (mean age 48.5 years, age range 35 to 70 years) from India, Pakistan, and Bangladesh, hypertension was diagnosed in one-third of individuals, with the highest prevalence in Bangladesh (39.3%), followed by Pakistan (33.3%), and lowest in India (30.7%). Despite these observed differences between studies, the prevalence of hypertension has been consistently shown to be higher in men compared with women, and in urban compared with rural areas.

In fact, transition from the rural to urban environment is a key societal factor driving the increasing prevalence of hypertension. In India, the prevalence of hypertension has increased dramatically over the past several decades with a higher burden reported in urban areas. In a systematic review of 142 studies conducted in India, it was estimated that 29.8% of adults had hypertension; and in urban areas, where extensive changes in health-related behaviors have already occurred, the prevalence of hypertension was higher (33.8%) compared with rural areas (27.6%) ( Fig. 4.1 ). Furthermore, the prevalence of hypertension varied substantially in rural areas (which was not observed in urban areas) likely reflecting the different stages of economic development, urbanization and transitions in health-related behaviors occurring across rural environments in India.

FIG. 4.1, Variations in hypertension prevalence in India by urban-rural area and geographic locations. In this systematic review of epidemiologic studies of hypertension in India, significant variation in the prevalence of hypertension was observed across different geographic region in rural areas, whereas urban areas had a similar hypertension prevalence. Overall, hypertension prevalence was higher in urban areas compared with rural areas. wgt , Weight.

Prevalence of Hypertension in South Asians Who Have Migrated to North America or Europe

Compared with other ethnic groups living in the same macroenvironment, South Asians have a unique cardiovascular risk profile, characterized by a higher risk of diabetes, higher percent body fat, and lower high density lipoprotein concentration compared with other ethnic groups. Some studies suggest that the risk of hypertension is also modestly increased in South Asians compared with Caucasians living in the same country. In a systematic review of 13 hypertension prevalence studies (n ≈ 650,000 individuals) in Canada, the risk of hypertension was slightly higher in South Asians compared with Caucasians (odds ratio [OR] 1.11, 95% confidence interval [CI] 1.02 to 1.22, p = 0.02). However, this association has not been consistently observed among South Asian populations residing in Europe. Also, while the prevalence of some cardiovascular risk factors (e.g., obesity) appear to be steadily increasing in these South Asian populations over time, whether such a trend is also occurring with the prevalence of hypertension is not clearly established.

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