The relationship between objectively-measured attributes of the built environment and selected cardiovascular risk factors in a South African urban setting

Non-communicable diseases, such as cardiovascular disease (CVD), are the leading cause of death in high income and many low- and middle income countries (LMICs) [1], including South Africa [2]. Rises in CVDs diagnoses are attributable to obesity, high blood pressure and physical inactivity [3] compounded by a change in lifestyle behaviors [4]. These rising figures of CVDs are of concern in South Africa and other countries in the region [5].

Rapid epidemiological shifts in population health and disease burden have been linked to changes in the built environment that may promote or adversely affect active transport, such as walking to and from places, because this has been associated with reduced risk of obesity, and non-communicable diseases (NCDs) [6‐8]. A recent research indicates that high levels of physical activity may attenuate the negative health burden such as obesity [9]. However, the majority of studies concerning objective and subjective measures of the built environment, including attributes of walkability such as land use mix and proximity to home, street or network connectivity, population density, pedestrian infrastructure, aesthetics, and safety, have been undertaken in developed or high-income countries [10‐12], where the context, culture and perceptions regarding access may be specific [13]. At least one study in a middle-income country has linked aspects of the neighborhood and built environment such as: water supply, garbage collection and street lighting to health status in older adults, [14]. Nevertheless, both objective and subjective studies incorporating measures of the built environment are sparse [15] and those studies that have used them have shown mixed results in both low-income [16] and high-income countries [17]. Thus, it is unknown whether one measurement method is more effective than the other for assessing the neighborhood environment and its association with obesity, body mass index (BMI), hypertension and physical activity especially among South African adults.

Built environments that support utilitarian walking, with destinations in close proximity, have been linked to lower body mass index (BMI) [18], blood pressures (BP) [19] and more walking for transport [20]. Access to a mix of recreational and non-recreational destinations such as schools, coffee shops, supermarkets, other retail shops and services within the residential neighborhood, has been reported to be positively related with walking for transportation and leisure [21, 22]. However, it has been suggested that lack of facilities for pedestrians, perceived neighborhood safety, less accessible destinations, and poorly-connected street patterns, were all associated with reduced physical activity and obesity risk. A study in the USA found that the absence of nearby nonresidential destinations, lack of footpaths or poor quality when available, disagreeable community, inexistent interesting sites, presence of waste and physical disorders were significantly associated with obesity [23]. Other studies have associated a walkable environment with walking, bicycling, using public transit, and a decreased likelihood for driving or owning a car [24]. Studies have also linked a high availability of fast-food outlets relative to conventional restaurants in a neighborhood environment, with higher and lower BMI, respectively [25]. In addition, a recent systematic review found most built environment attributes to be related with cardiovascular disease risk factors such as BMI, PA, hypertension, and type 2 diabetes [26].

Given that cardiovascular disease in South Africa and Africa at large is increasing [5], developing and implementing built environment strategies that promote physical activity and thus reduce CVD risk, requires input from context-specific studies. Yet, there is little empirical evidence that has used objectively-measured attributes of the built environment with CVD risk factors in an urban African context. Therefore, the aim of this study was to evaluate the relationship between objectively-measured built environmental attributes with BMI, systolic BP (SBP), diastolic BP (DBP) and physical activity in adult South Africans.

In the current study, participants, in general, met the WHO recommendations of 150 min/week for MPA and MVPA, but with very low levels of VPA. In univariate regression analysis, we observed statistically significant positive relationships between objectively measured distances to the shopping center and body mass index. While, distance to a community center was positively associated with diastolic blood pressure, proximity to a shopping center was inversely associated with diastolic blood pressure. After adjusting for age and gender, the distance to a community center (1000) remained associated with BMI, DBP and MVPA. The distance to shopping center (1600 m and 1000 m) were positively associated with BMI and SBP, respectively (Table 3). In a further adjustment for history of hypertension, distance to a community center (1000 m) and shopping center (1000 m) remained positively associated with DBP.

This study supports the growing evidence that a walkable neighborhood environment is associated with fewer CVD risk factors [23, 33, 34]. For example, in a subjective assessment of neighborhood environment, attributes such as proximity to local stores, transit stops, four-way intersections, sidewalks, shade from trees, pleasant scenery, high traffic volume, crosswalks and well-lit streets were significantly associated with physical activity [35]. In a similar study, land use mix-diversity and safety from traffic was associated with hypertension [36]. Another study consistently found that built environment attributes were associated with obesity [37].

A number of potential advantages have been suggested that explain the beneficial effects of living near community services, including increased physical activity, and lowering obesity and hypertension [38]. However, the mechanism by which the interaction between built environment attributes and CVD risk factors occurs has yet to be fully elucidated. Nevertheless, one possible interpretation could be that the short distance from the respondents’ home to the community center, for example, increases physical activity through walking, thereby lowering the risk of developing obesity and hypertension. Considering the low wages of our participants and the low prevalence of car ownership, it is likely that most participants were relying on walking and public transport essentially, when they perceive proximal rather than distant destinations. Because individuals participate in regular physical activity, availability of facilities within walking distance can positively impact on energy expenditure which may assist in weight control [37].

Another potential mechanism for the relationship between proximity to a community center, and health outcomes may be found in a study from the Netherlands, where high quality, open public space was associated with a lower systolic blood pressure [38]. Another study showed that individuals living in sprawling areas are likely to walk less in their leisure time, overweight, and have greater prevalence of hypertension than those living in more compact places [39]. This implies public open space may affect health, not only through providing physical activity space, but also through its contribution to environmental improvement, such as air quality. In addition, it is possible that individuals living close to the community center (health facility) may be more aware of their hypertension status and able to access anti-hypertensive drugs. For example, in Ethiopia individuals from long distant areas were less likely to be adherent to hypertension treatment as compared to those who resided closer to health centers [40].

In this study setting, the shopping center was located near to the rail station, meaning that poor residents staying far away will usually need to take public transport to access the shopping center, thus resulting in less frequent walking trips. In addition, a proportion of our participants, who were employed, had to cover long distance to and from jobs. As a consequence, they may have had less time to shop and prepare healthy food for their households or may have had to depend on street food and ‘spaza’ shops for meals clustered near rail or bus stations, which were less unhealthy [41]. All these factors aggravate participants’ risk for health inequalities through unhealthy food choices and decreased physical activity, and subsequently favoring the development of cardio-metabolic risk factors such as obesity and hypertension.

The current study has provided for the first time, evidence to support an association between access to community resources and amenities, proximity to community and shopping centers, as well as transit stops, and objectively measured physical activity, along with CVD risk factors, BMI, SBP and DBP among South African adults. The current study indicates that public health approach such as increasing proximity and access of community services in neighborhoods would potentially assist in reducing population’s cardio-metabolic disease risk, by creating opportunities for physical activity and healthy food choices. However, similar studies should be replicated in other African countries before any firm conclusions can be ascertained.