Hypertension in sub-Saharan Africa: cross-sectional surveys in four rural and urban communities

Abstract

Background: Cardiovascular disease (CVD) is the leading cause of adult mortality in low-income countries but data on the prevalence of cardiovascular risk factors such as hypertension are scarce, especially in sub-Saharan Africa (SSA). This study aims to assess the prevalence of hypertension and determinants of blood pressure in four SSA populations in rural Nigeria and Kenya, and urban Namibia and Tanzania.

Methods and findings: We performed four cross-sectional household surveys in Kwara State, Nigeria; Nandi district, Kenya; Dar es Salaam, Tanzania and Greater Windhoek, Namibia, between 2009-2011. Representative population-based samples were drawn in Nigeria and Namibia. The Kenya and Tanzania study populations consisted of specific target groups. Within a final sample size of 5,500 households, 9,857 non-pregnant adults were eligible for analysis on hypertension. Of those, 7,568 respondents ≥ 18 years were included. The primary outcome measure was the prevalence of hypertension in each of the populations under study. The age-standardized prevalence of hypertension was 19.3% (95%CI:17.3-21.3) in rural Nigeria, 21.4% (19.8-23.0) in rural Kenya, 23.7% (21.3-26.2) in urban Tanzania, and 38.0% (35.9-40.1) in urban Namibia. In individuals with hypertension, the proportion of grade 2 (≥ 160/100 mmHg) or grade 3 hypertension (≥ 180/110 mmHg) ranged from 29.2% (Namibia) to 43.3% (Nigeria). Control of hypertension ranged from 2.6% in Kenya to 17.8% in Namibia. Obesity prevalence (BMI ≥ 30) ranged from 6.1% (Nigeria) to 17.4% (Tanzania) and together with age and gender, BMI independently predicted blood pressure level in all study populations. Diabetes prevalence ranged from 2.1% (Namibia) to 3.7% (Tanzania).

Conclusion: Hypertension was the most frequently observed risk factor for CVD in both urban and rural communities in SSA and will contribute to the growing burden of CVD in SSA. Low levels of control of hypertension are alarming. Strengthening of health care systems in SSA to contain the emerging epidemic of CVD is urgently needed.

Figure 1. Participation in the 4 surveys (household and individual level).

*HH  =  households, **Repeating sampling done because household were difficult to locate due to poor registries used for sampling, ^†BP =  blood pressure.

Figure 2. Hypertension prevalence and distribution of blood pressure.

2A: Age-standardized and age stratified hypertension prevalence. 2B: Distribution of blood pressure in patients with hypertension (treated and untreated cases). Optimal  =  systolic blood pressure (SBP) <120 and diastolic blood pressure (DBP) <80; Normal  =  SBP 120–129 and/or DBP 80–84; Pre-HT (hypertension)  =  SBP 130–139 and/or DBP 85–89; Grade 1 =  SBP 140–159 and/or DBP 90–99; Grade 2 =  SBP 160–179 and/or DBP 100–109; Grade 3 =  SBP> = 180 and/or DBP> = 110.

Figure 3. Awareness, treatment and blood pressure control in patients with hypertension.

Definitions: Aware  =  respondents who self report to have hypertension, Treated  =  respondents who self report to have hypertension, and who indicate to take drug treatment for hypertension, Controlled  =  respondents who self report to have hypertension, and who have a blood pressure below 140/90 (patients who use drug treatment or for whom treatment status is unknown).