**4. Hypertension in African cities**

Hypertension is a leading risk factor for mortality, and is the prime risk factor for the CVD epidemic in Africa [34]. Hypertension is defined as an average systolic blood pressure ≥140 mmHg and/or average diastolic blood pressure ≥90 mmHg among adults aged at least 18 years. Data available on hypertension prevalence are from a wide range of studies [35, 36], majority of which are not age-standardized, and this limits the opportunity for reliable comparison between different African countries and cities. Nevertheless, several WHO STEPwise surveys reported a hypertension prevalence of 19.3–39.6% in Africa [35, 37]. Additional data from epidemiological modeling project suggest that 216.8 million people will have hypertension by 2030. Urban settings consistently have a higher prevalence of hypertension compared to rural areas [38, 39] (**Figure 4**)**.**

Of great concern, is the proportion of individuals with hypertension who remain underdiagnosed, lack access to treatment and are prone to severe complications and increased risk of premature deaths [40]. Evidence from a review of hypertension in 23 African countries, shows that less than half of those with hypertension are aware of their diseases and only one third of those who are aware start treatment, and less than 10% of those on treatment have their blood pressure controlled [41]. It is thus crucial to understand the risk factors driving the rise of hypertension in urban areas to inform preventive interventions. Several factors have been cited as responsible for the rise of hypertension among urban populations in Africa.

Early studies by Donnison et al. (1929) in an African rural community established the role of civilization and urbanization on the development of hypertension [42]. Later, Poulter et al. (1990) established social-behavioral origins with sedentary lifestyles and increased consumption of unhealthy diets among rural– urban migrants in Kenya as major factors driving elevated blood pressure [43]. Researchers also observed that mean diastolic blood pressure of migrants (aged 15–34 years) who moved to the cities increased markedly over time, compared to

#### **Figure 4.**

*Prevalence of hypertension by rural–urban residence in selected African countries. Source of data: World Health Survey (2003).*

their controls in the rural areas. In addition, migrants' mean urinary sodium: potassium ratio, weight and pulse rate were higher than for controls [43]. Cooper et al., also hypothesized that environmental and behavioral changes that occur when individuals move from rural to urban settings all coalesce to increase predisposition to hypertension [44].

Urban poverty which is common in African cities, is also known to mediate deleterious risks factors for hypertension among urban residents [45]. In LMICs, poverty exposes people to behavioral risk factors for NCDs and in turn, resulting NCDs become an important driver for poverty. The urban poor experience increased vulnerability to unhealthy diets and physical inactivity. Evans et al., (2010) found that informal settlements within cities in South Africa had unhealthy diets and inadequate physical activity because they lacked access to organized markets for healthy foods, and had inadequate resources for physical activity [46].

Urban living in South Africa, Tanzania and Cameroon was also reported to be associated with increased exposure to tobacco use, excessive alcohol intake, unhealthy diets (high in salt, and sugar and less in fiber) and also physical inactivity [47, 48]. In the next section, we review how urban environment modifies NCD risk factors.
