Poor cardiovascular health is associated with subclinical atherosclerosis in apparently healthy sub-Saharan African populations: an H3Africa AWI-Gen study

Cardiovascular disease (CVD) is a leading cause of global deaths [1, 2] raising huge public health concerns. Sub-Saharan Africa (SSA) is experiencing a rising burden of non-communicable diseases including CVD [2], alongside a reduction in the prevalence of infectious diseases [3]. Increasing urbanization, changing lifestyles, and population aging are probably accounting for the surge in the prevalence of CVD in SSA [3, 4]. This presents a challenge to the health systems of African countries and requires a pragmatic approach to the prevention of CVD. Where risk equations such as Framingham [5] and Pooled Cohort Equations (PCE) [6] have served as valuable tools in assessing the risk of CVD globally, these have inherent limitations especially when applied to an African population [7]. The American Heart Association and the American Stroke Association (AHA/ASA) developed the Cardiovascular Health Index (CVHI) as a new public health metric for assessing and monitoring cardiovascular health [8‐11]. The components of the CVHI often referred to as life’s simple seven include smoking, dietary intake, physical activity, body mass index (BMI), blood pressure, glucose, and total cholesterol.

Due to the lack of data on incident CVD events, carotid-intima media thickness (CIMT) is often used as an alternate marker of CVD risk. Increased CIMT has been shown to be related to several risk factors for CVD and CVD risk globally [12, 13] including SSA populations [14].

The CVHI metric is proven to be related to CIMT, a marker of subclinical atherosclerosis [15], and coronary artery calcification [16] in both Caucasian and Asian populations [17]. In Africa, the association of CVHI with subclinical atherosclerosis has only been reported in a relatively small study of HIV-positive (n = 105) and non-infected (n = 100) individuals [18] in Uganda and recently in a rural setting in Limpopo, South Africa [19]. Expanding the evidence to a larger pan-African population would help to clarify whether the CVHI can be used as a simple screening tool for cardiovascular health within the existing health systems of resource-constrained SSA countries. Therefore, we set out to assess the association between cardiovascular health, using CVHI, and subclinical atherosclerosis in a large understudied African population living in SSA.

After excluding participants (7.5%) with missing data, 9011 adults from Burkina Faso, Ghana, Kenya, and South Africa were included in these analyses. Basic characteristics are presented in Table 1. Fifty one percent of the study population was women and the average age was 51 ± 7 years. Physical activity levels were high (higher mean moderate-to-vigorous physical activity − minutes/week) in the populations from the two rural sites of West Africa. The average fruit and vegetable intake in the combined AWI-Gen population was 3 ± 2 servings per day. Mean BMI and systolic and diastolic blood pressure were highest in South Africa and Kenya and lowest in Ghana and Burkina Faso (Table 1).

The prevalence of each of the 3 levels of cardiovascular health (poor, intermediate, and ideal) for the total sample, the total sample stratified by sex, and the various countries is presented in Fig. 1. In the combined sample, iCVH was 31.9% with women (38.2%) having a higher prevalence than men (25.6%). Rural sites in Ghana (50.6%) and Burkina Faso (44.3%) had the highest prevalence of iCVH while the more urban sites in Kenya (37.4%) and South Africa (11.3%) had the lowest. The prevalence of the poor, intermediate, and ideal levels of each of the 7 CVHI components, according to sex and country, is presented in Table 2. The majority of participants were in the ideal category for total cholesterol, fasting glucose, physical activity, BMI, and blood pressure with unhealthy diet and smoking placing the majority of participants in the poor category. Burkina Faso and Ghana had more participants in the ideal category for most CVHI components than South Africa and Kenya, except diet and physical activity where Burkina Faso had the least ideal levels compared to other countries.

There were inverse linear associations between CIMT and CVHI in our combined population (r = − 0.064; p < 0.001) and for Burkina Faso (r = − 0.126; p < 0.001), Ghana (r = − 0.085; p < 0.001), Kenya (r = − 0.178; p < 0.001), and South Africa (r = − 0.199; p < 0.001), and these are presented as line plots in Additional file 2: Figs. S3 and S4. In the adjusted multilevel mixed-effects generalized linear regression model for the combined population, a unit increase in the CVHI was associated with − 5.54 [− 6.75, − 4.32] μm decrease in common CIMT (Fig. 2). The risk of atherosclerosis (high common CIMT) was progressively lower with increasing CVHI in each country, sex, and household SES category in both the combined sample (Fig. 2) and the sex stratified analyses (Figs. 3 and 4). A similar inverse association was observed in women (− 4.44 [− 6.23, − 2.65]) and in men (− 6.27 [− 7.98, − 4.64]) (Figs. 3 and 4, respectively).

Sequential adjustments of the regression models are presented in Table 3 and demonstrate minimal effects of adjustment on the β-coefficients. All models demonstrated a significant inverse association between the CVHI and common CIMT, except in women from Burkina Faso and men from Ghana, where the associations were again negative but with the upper 95% CI just overlapping zero. In adjusted analyses looking at the contribution of the individual components of CVHI to common CIMT, we observed that blood pressure, BMI, and hyperglycemia were associated with common CIMT in the combined population, while smoking and physical activity were associated with common CIMT in women only (see Table 4).

Results from this large population-based study of middle-aged men and women from four countries in sub-Saharan Africa highlight relatively high levels of ideal cardiovascular health. We have also shown a significant inverse linear association between increasing CVH score and common CIMT independent of age, educational status, household socio-economic status, HIV infection, and ART use and prior history of cardiovascular or chronic kidney diseases. To our knowledge, this study is the largest to demonstrate an association between the CVHI metric and subclinical atherosclerosis in an apparently healthy adult population from multiple countries in SSA.

The prevalence of ideal cardiovascular health (iCVH) was 31.9% in the combined AWI-Gen population, and this was higher than the 6.8% reported in the multi-ethnic study of atherosclerosis (MESA) conducted among Caucasians, Chinese, African Americans, and Hispanics in the USA [25]. Similarly, data from the Behavioral Risk Factor Surveillance System study which used information obtained telephonically from nearly 1.4 million subjects in the USA reported a much lower prevalence of iCVH (5.1%) in 2009 than reported in the current study [28]. The iCVH levels among our participants from Ghana was 50.9% and higher than reported by the Research on Obesity and Diabetes among African Migrants (RODAM) study conducted among Ghanaians residing in rural (25.7%) and urban (7.5%) areas and their counterparts in the diaspora (< 5%) [29]. Further to this, a systematic review by Peng et al. showed that participants from Africa were likely to have higher proportions of ideal CVH compared to North and South Americans, Asians, Europeans, and the Oceania’s [30]. The RODAM study, however, used the comprehensive five dietary components (as described in the original CVHI) to define healthy diet whereas only two components were available for use in the AWI-Gen study. This may therefore result in over classifying AWI-Gen participants into the ideal diet category. This notwithstanding, the broad range of iCVH levels observed in the various settings may be a reflection of the level of ongoing epidemiological transition from communicable to non-communicable diseases. Thus, the iCVH levels were much higher in rural communities in Ghana and Burkina Faso and lower in the more urban settings of Kenya and South Africa and lowest in Europe and the USA.

We observed an inverse association of the iCVH with common CIMT levels independent of age, educational status, socio-economic status, HIV infection, and ART use. Similar to our findings, several other studies conducted in Caucasian, African-American, and Asian populations have observed increasing CVHI score is associated with lower risk of subclinical atherosclerosis [15, 17, 31‐35]. It has been reported that a proportion of residual phenotypic variance is due to the additive effects of genes [36]. Although we did not adjust for the effect of genes in this paper, the Emory Twin Study did report that shared genetic and other familial factors do not confound the association of CVHI with CIMT [15]. Our results did not show any significant disparities in the association between CVHI and CIMT across different levels of socio-economic wealth quintiles as has been previously reported in a multi-ethnic population, including African Americans, in the USA [25]. This may be due to the fact that participants in our population did not show significant difference in wealth distribution.

The rising burden of CVD morbidity and mortality in SSA has been reported to occur in younger age groups [1, 37]. This, coupled with high levels of unawareness of risk factors and challenges with secondary prevention, calls for the evaluation of simple tools that can be used in routine screening for subjects with poor CVH in primary prevention efforts. The significant independent association of CIMT with the CVHI demonstrated in this study makes a strong case for the utility of the CVHI metric in the routine screening of CVD risk in the broader SSA population irrespective of SES status.

We observed in the combined sample that BMI, blood pressure, and hyperglycemia were the CVHI metrics most strongly associated with common CIMT. The former 2 components were also associated with common CIMT in both women and men while physical activity and smoking related with common CIMT in women but not men. This could be due to the fact that women were less likely to smoke compared to men and equally had healthier physical activity levels than men. These findings have implications for prioritizing particular CVHI components for the primary prevention of atherosclerotic cardiovascular diseases in SSA. Although total cholesterol did not correlate with CVHI, cholesterol levels in Africans remain lower than in the Western World. However, with urbanization, cholesterol levels are increasing and thus may well contribute in the near future, to atherosclerotic cardiovascular disease in SSA [38].

Our study does have some limitations. Reliance on self-reported smoking, physical activity, HIV infection status, and ART use may result in recall and social desirability biases. Diet was ascertained as self-reported servings of fruits and vegetables per day instead of derived from five components (fruits and vegetables per day; portions of fish a week; servings of fiber-rich whole grains per day; sodium per day and sugar-sweetened beverages per week) as recommended by AHA, which could have resulted in misclassification of certain participants in terms of their dietary intake. In addition, the cut points used for classifying each of the components of the CVHI metric were largely based on those used in populations of European ancestry. This brings into question whether these cut points are appropriate for use in African populations. However, the cut points used in the CVHI for defining cholesterol, blood pressure, glucose, and BMI levels are used globally for the categorization of these disease markers and are recognized cut points in the clinical guidelines of many African nations; their use within these countries has not been widely questioned. Other cut points have been challenged for their use within African populations and include those for HDL and triglycerides [39], HbA1c [40], and waist circumference [41], but none of these factors are used within the CVHI metric.

Another possible shortcoming of the use of the CVHI in African populations is the high prevalence of underweight which is classified in the ideal category for BMI but is associated with increased cardiovascular risk. However, a large meta-analysis has shown that low BMI is more strongly associated with respiratory disease than CVD mortality, but it must be noted that this review included few studies from Africa [42]. Future studies confirming the applicability of the CVHI criteria to African populations, especially those for BMI, would be important. In the current study, it was essential to use the existing CVHI criteria so that we were able to compare our data to those from studies conducted in both African and non-African populations.

Despite these limitations, the greatest strength of this work is that it used a large cohort of African individuals from 4 different SSA countries and a standardized data collection protocol, with laboratory assays performed at a single laboratory. In addition, a large number of possible confounding or modulatory variables were measured for use in the multiple regression models. Furthermore, this is the largest African study to use the CVHI to assess cardiovascular health and its association with common CIMT and provides important information on the utility of this metric for screening for individuals at high risk for CVD in resource-poor environments.

The CVHI score has a significant inverse, independent association with common CIMT in older adults across four sub-Saharan African countries. This makes a case for its use as a simple tool to monitor cardiovascular health at a population and clinical level in SSA. The current study demonstrates that primary prevention of atherosclerotic CVDs in SSA should focus on reducing smoking and obesity, improved control of hypertension and hyperglycemia, and higher levels of physical activity.