Introduction

Cardiovascular disease (CVD) is not only prevalent in adults and the elderly. Recent evidence highlighted the increasing trends of childhood and adolescent hypertension as well as related CVDs as future health challenges on a global scale with major economic implications [1,2,3]. Global evidence indicates that adult non-communicable diseases (NCDs), including CVD and type 2 diabetes, originate from early life or biological programming due to the interactions of environmental and genetic factors during a critical period of development, namely the first thousand days of life [4,5,6]. More importantly, even earlier changes in the biomechanical makeup of blood vessels may be compromised during fetal (intrauterine) development due to maternal nutrition [7], maternal smoking [8], maternal health (i.e., eclampsia, gestational diabetes) [9], access to health care (low socioeconomic status, lack of medical insurance) [10], and prematurity/low birthweight [11]. These early life determinants of CVD may predispose children and adolescents to accelerated biological aging, termed early vascular aging (EVA).

Aside from predispositions to genetic and environmental risk factors of certain phenotypes, there are also socioeconomic, sociocultural, and metabolic determinants to define an individual’s health status. Alongside these determining risk factors for NCDs and especially CVD is the complexity of ethnic or racial differences that are regularly reported in CVD morbidity and mortality, with an increased burden among especially black (African and African-American) and Hispanic populations [12, 13] compared with white or Asian populations. Until now, genetics studies have not succeeded in explaining genetic predispositions to CVD among various racial or ethnic groups [14, 15]. In addition, clear biological definitions of ethnicity and race are still lacking. In an analysis from the 1998 South Africa Demographic Health Survey, authors highlighted unambiguous racial and income disparities among black African and white (European descent) South Africans. Black South Africans had less access to healthcare services and mostly fell in the lower socioeconomic classes compared with white South Africans [16]. Yet, 20 years later, this disproportion is still markedly unchanged in especially the sub-Saharan Africa context. Racial inequalities should remain a global social concern, since marked differences among race groups have been reported in health-related studies with no clear pathophysiological explanations. Evidence in this regard is lacking even more in pediatric and adolescent populations.

This review will focus on the evidence of EVA in children and adolescents, its characteristics, and multifactorial determinants with specific reference to race.

Definition and diagnosis of early vascular aging

The concept of premature vascular aging was described by Nilsson (1996) as the result of adverse psychosocial and environmental factors hindering the health-preserving mechanisms of human physiology [17]. Since then, the concept of EVA has been well demonstrated, but with limited focus in children, adolescents and young adults.

Definitions

With “normal” or chronological aging, biological changes manifest and may develop to disease states when an individual reaches the end stages of life. Chronological age is the number of years, months, or days lived since the day of birth and an obvious risk factor for CVD morbidity and mortality in the presence of established risk factors [18]. Biological aging is different from chronological aging as it reflects a number of factors contributing to a gradual decline in physiological and biochemical functionality of individuals across the lifespan. Some of these factors include genetics, lifestyle behaviors, and disease states such as hypertension, atherosclerosis, and diabetes mellitus. However, the aging process can be accelerated at a biological level, rendering a mismatch between the chronological and biological age. This dissociation between chronologic and biologic aging is termed EVA. EVA is therefore a state of accelerated adverse changes in the biochemical and cellular components of the vascular tree contributing to augmented forward pulse wave reflections at younger ages [19]. These early changes have particular detrimental effects on target organs such as the heart, brain, and kidneys.

Diagnosis

EVA can be diagnosed by the presence of abnormally high arterial stiffness (arteriosclerosis) for a specific age and sex [20]. Arterial stiffness is central to the development of EVA, whereby individuals with reduced arterial elasticity can be identified by non-invasive measurement of pulse wave velocity (PWV) [21]. Carotid-femoral PWV or aortic PWV is perhaps the most commonly used measure of arterial stiffness and is defined as the velocity of the arterial pulse wave travelling between two sites (distance × 0.8) along the arterial wall (transit time) [22]. In general, mostly in adult populations, higher (> 10 m/s) PWV indicates arterial stiffness and an increased risk for future cardiovascular events [23].

Clinical importance of early vascular aging

With increasing age, pulse pressure widens and systolic hypertension develops as long-term manifestations of arterial stiffening [24]. PWV is a sensitive technique to measure arterial stiffness and can detect early adverse changes in pulse wave reflections. By measuring PWV, EVA can be assessed to identify individuals (at younger ages) with accelerated aging or adverse medial layer morphological changes due to inherent features as well as interactions with environmental exposures [25]. The impact of these vascular changes and subsequent increased arterial (aortic) stiffness on cardiac remodeling is inevitable. Aortic stiffening increases left ventricular load as well as myocardial perfusion pressure, but limits the delivery of blood to the capillary beds during diastole. Evidently, increased arterial stiffness may contribute to myocardial ischemia [26] and cardiac failure [27]. Aside from the direct relationship between aortic stiffness and cardiac dysfunction and hypertrophy is also the downstream effects of arterial stiffening on the microvasculature within vital organs including the brain [28, 29] and kidneys [30, 31]. Therefore, the non-invasive measurement of PWV in a clinical setting may assist in the risk stratification of individuals (even in young asymptomatic individuals) and the possibility for primordial prevention. Carotid-femoral PWV by applanation tonometry has been established as a highly sensitive biomarker in identifying individuals with various phenotypes and can aid in therapeutic guidance [32, 33].

Not only does PWV assess arterial stiffness, but it also provides valuable predictive information for cardiovascular outcomes as an intermediate end-point and an independent predictor of cardiovascular events and all-cause mortality [34, 35]. The predictive power of PWV for CVD was first described in high-risk groups with chronic kidney disease (CKD), hypertension, or diabetes [36,37,38]. Later, in the general population [39], one standard deviation increase of PWV predicted a 30% increased risk for future cardiovascular events [34]. However, standardization of PWV measurements with various devices and across different populations still requires attention.

Etiology and prevalence of early vascular aging over the life course

In recent consortia and research, evidence led to the appreciation of the way in which early life (including pre-conception and intrauterine development) exposures to risk factors determine the origin and trajectories of disease across the life course [16]. The life course in this context refers to the reciprocal influences of especially environmental exposures on the biological determinants of health during the different stages of life including pre-pregnancy, gestation, infancy, adolescence, and adulthood [40].

In a statement by the Lancet Commission on hypertension, the concept of EVA was used to develop a life course strategy of CVD prevention and treatment, aiming to reduce cardiovascular risk factors, target organ damage and cardiovascular events throughout the different stages of life including childhood [6]. The authors highlighted that genetic susceptibility and epigenetic imprinting during fetal life can alter the life course trajectories and underlined the importance thereof in the management of raised blood pressure (BP) [6]. In an effort to further elucidate this concept, we adapted the life course trajectory approach (Fig. 1) to indicate that the presence of intrauterine risk factors (early life programming) already predisposes the fetus to increased future cardiovascular risk and the early onset of cardiovascular abnormalities in early childhood.

Fig. 1
figure 1

An adapted life course model in the setting of early vascular aging and the consequences of early-life programming prior to birth. SES socioeconomic status, *Amended from Olsen et al., with permission from The Lancet [6]. Copyright ©2016, Elsevier

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In Fig. 1, points A, B, and C indicate the relative risk of an individual on the health disease continuum based on the determinants and phenotype of fetal programming. The ideal life course is illustrated with a green line, and at point A, the risk of accelerated biological aging or EVA is much lower compared with an individual at points B and C. Such individuals (at point A) are theoretically defined as healthy or undergo supernormal vascular aging [20], with the least adverse cardiovascular disease manifestations throughout the life course. The majority of individuals intercepts the health disease continuum at point B, following an average life course in which hypertension and arterial stiffness manifests in late adulthood and middle age, with subsequent cardiovascular morbidity and mortality in advanced age. However, some individuals intercept the health-disease continuum at point C with accelerated biological aging and vascular compromise at very young ages, even in infancy, childhood, and adolescence. These individuals are believed to be subjected to maternal risk factors involved in the early life programming mismatch contributing to the increased relative risk of EVA, as discussed below.

Etiology

Evidence from BP tracking studies suggests that the development of blood vessel structure and function could be influenced by early somatic growth [41,42,43,44]. This may be the reason increased arterial wall stiffness (arteriosclerosis) and thickness (atherosclerosis) of large arteries are proposed to be present in children and adolescents in the early phases of elevated BP [45]. As with atherosclerosis, arterial stiffness is believed to start in early life on the basis of fetal programming of the medial elastin content of the arteries, as well as of other vasculature and capillaries [46, 47]. Therefore, EVA may start in utero as a result of adverse intrauterine environmental exposures for survival, which may contribute to an increased risk of vascular deterioration in early postnatal life [19].

Genetic-environmental interactions and ethnocultural influences may increase individual susceptibility to early-life programming of the vasculature [48,49,50,51]. For instance, fetal undernutrition is accompanied by suboptimal vascular growth and development with reduced elasticity, arterial compliance, and overall high peripheral resistance in the offspring [52]. Maternal nutrition and/or underlying disease states such as obesity and gestational diabetes can affect fetal nutrition and contribute to potential genetic changes during fetal development [53]. A population-based analysis indicated a 29% increased overall rate of early onset of CVD in offspring, if the mothers had diabetes during pregnancy [9]. In addition, reports have indicated higher risk of gestational diabetes among women from race groups other that non-Hispanic white race [54, 55].

Although the etiology of racial differences in early life programming is scant and perhaps only studied as biological fragments to understand the complexity of early life exposures on cardiovascular health and its future implications, evidence suggest that black children with lower birth weight compared with their white counterparts are at higher risk of having impaired vascular structure and function [56]. However, this may also be true for other race groups, as studies indicated that not only African-American babies (born at term) but also Indian, Pakistani, Bangladeshi, and black Caribbean offspring have lower birth weights than those from European ancestry [57, 58]. A study on prematurity also indicated that children born extremely preterm (compared with controls) have an increased future cardiovascular risk due to altered arterial hemodynamics of especially the smaller resistance blood vessels [59]. Systolic hypertension, elevated glucose levels, and hypercholesterolemia were also more prominent (compared with controls) as measured almost 6 years later in a group of preterm infants [60]. It appears that altered maternal lipid metabolism (higher triglycerides and total cholesterol) contributes to adverse prenatal programming of the hypothalamic-pituitary-adrenal axis by increasing a child’s stress response as evidenced by greater cortisol reactivity [61]. This could be in part the mechanism to explain the link between the early life origin of CVD and the emotional functioning or psychological stress of a child [62]. In addition, researches have shown a clear association between multiple adverse childhood experiences and increased arterial stiffness as measured by PWV [63].

Prevalence of early vascular aging

The prevalence of arterial stiffness or rather EVA remains to be clearly defined, since evidence regarding the prevalence of EVA is limited in both adult and pediatric populations. Studies have indicated higher PWV values in low cardiovascular risk populations (under 30 years of age) and estimated the prevalence of EVA at 12.5% in Portugal (n = 2542; age 18–96 years) [64] and 37.3% in Austria (n = 10 973; age 20–94 years) [65]. It is also believed that the prevalence of EVA is proportional to the prevalence of hypertension and related co-morbidities such as obesity and type 2 diabetes mellitus, due to the latter being late manifestations of increased arterial stiffness [24]. From the USA, approximately 11% of children and adolescents have high BP [1], whereas in South Africa, the prevalence of childhood hypertension ranges between 7.5% and 22.3%, dependent on location, region, and culture [2]. Whether the prevalence of EVA relates to the prevalence of hypertension remains to be determined.

Although cardiovascular morbidity and mortality are traditionally attributed to numerous modifiable risk factors including unhealthy dietary and sedentary behaviors, low physical activity, psychosocial stress, hypertension, tobacco use, abnormal lipids, glucose intolerance, and obesity [66], there are other adverse risk factors often overlooked. Among these are low socioeconomic class, psychosocial stress, infectious diseases, lack of healthcare, and poor lifestyle choices as observed in low to middle-income countries have cumulative harmful effects on cardiovascular health, especially in populations with an exceptional proportion of ethnic and/or race variation [67, 68].

Race or ethnic differences in early vascular aging among children and adolescents

The etiology of racial differences in EVA is complex, but there is an appreciation of biological and socioeconomic factors that are at least partly involved [69]. Although many determinants of EVA could explain potential racial differences, there is limited evidence to unravel the origin of such differences in the early onset of CVD. In this section, we provide a brief overview of studies comparing components of EVA (BP, PWV, carotid intima media thickness, and left ventricular mass) from studies that included two or more race/ethnic groups in children and/or adolescents.

Analyses from the Study of High Blood Pressure in Pediatrics: Adult Hypertension Onset in Youth (SHIP-AHOY) [70] has emphasized the importance of BP measurement in children, along with the most recent sets of guidelines for BP in pediatric populations [71, 72]. Moreover, target organ damage has already been observed in adolescents with BP levels below the current clinical definition for hypertension [73]. Differences in BP based on race/ethnicity are regularly reported in adults, yet limited, evidence of these differences exists in childhood and adolescents. These race/ethnic differences in BP have been described by potential differences in intrauterine growth, based on birth weight, followed by the effects of early weight gain and growth in body height and current stature [74]. We summarized key studies that reported on BP differences by race (Table 1). The majority of studies comparing BP between different race groups are from the USA. These studies have reported mostly higher BP in black (African-American or African Caribbean) compared with children or adolescents from white or other (Asian, South Asian, Indian, Pakistan, Bangladesh) race groups. Many cross-sectional and longitudinal studies from the USA [56, 74,75,76, 78, 79, 81, 83, 84] and South Africa [82, 85] showed consistently higher BP (although inconsistent on whether the highest is systolic BP or diastolic BP) in the black compared with white population groups. The majority of these studies only compared BP without correcting for age, adiposity, stature, or other important confounders. In addition, a study from England [86] included large numbers of black, white, Asian, and other race groups and reported that black (African-Caribbean) children had similar mean systolic BP to white Europeans, but higher mean diastolic BP after correcting for age and sex. The same study also indicated that mean systolic BP tended to be slightly higher among black Caribbean, but lower among black Africans (p = 0.004); however, there was no heterogeneity for diastolic BP. Longitudinal studies mostly provide descriptive comparisons of the baseline BP profiles, and although these studies reported similar trends of higher BP in especially black children and adolescents, there are also inconsistencies. A multicenter study [77] performed an adjusted comparison between the black and white children that were born preterm and reported no race/ethnic differences, but after adjusting for neighborhood socioeconomic status, racial differences emerged over time. Similarly, studies from the USA [84, 87] and another from Brazil [88] indicated no differences in BP between black and white/non-black children and adolescents.

Table 1 Studies comparing blood pressure in children and adolescents by race
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In a recent brief review, it became clear that studies investigating racial differences of arterial stiffness were mostly from the USA and some from Brazil and South Africa [89]. These studies reported that PWV was highest in especially black (African American, Brazilian, and South African) compared with the white groups. However, many of these studies were (i) inconsistent in reporting adjusted means of PWV, (ii) were mostly of cross-sectional design, or (iii) some studies only included one racial group. Additionally (Table 2), we provide an overview of comparative studies that measured PWV in children from different race/ethnicity.

Table 2 Studies comparing pulse wave velocity in children and adolescents by race
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Since there are no universal cutoffs for PWV in children and adolescents, comparative studies have proven useful in determining racial/ethnic differences in arterial stiffness and potentially EVA. Socioeconomic and psychosocial factors are becoming essential contributors to consider when investigating early manifestations of adverse vascular alterations in black populations. In a longitudinal study [87], Thurston et al. investigated association between race and socioeconomic (SES) with arterial stiffness in adolescents (age 14–16 years). The study found that PWV was higher in the black (African American) group as compared with the white group. A larger proportion in the black participants were from families with low household income, low levels of parental education, and had lower scores on the neighborhood SES assessment. Lower or medium family income and lower neighborhood SES were positively associated with PWV, even after adjustments for covariates. Despite a small sample size (n = 107, divided into black and white groups) (age 9–12 years), Lefferts et al. observed high PWV in black (African American) children as compared with white children after adjustments for covariates including age, sex, BMI, mean arterial pressure, and SES [81]. The study also noted a lower SES in the black children as compared their white counterparts.

Certain disease states may serve as facilitators for accelerated vascular aging in certain race/ethnic groups. In a population (age 11–26 years) with type 1 diabetes, a higher PWV was associated with non-Hispanic white race/ethnicity and higher in type 1 diabetes patients as compared with the controls; however, no comparative data was shown [90]. The regression analyses were adjusted for modifiable and non-modifiable risk factors. Furthermore, black (African American) adolescents with type 2 diabetes presented with a higher PWV compared with whites [91]. In the same study, multiple regression analyses further demonstrated that age, lipids, BP, and duration of diabetes were differently associated with arterial stiffness in individual race/ethnicity groups. A study in Brazil including both black and non-black children and adolescents (age 6–18 years) showed that in puberty and post-pubertal stages, black individuals had higher PWV as compared with the non-black group, even after adjustments for multiple confounders [88]. In black South African boys (age 6–8 years), there was a consistently higher PWV when measured across various segments of the vascular tree (Fig. 2) as compared with the white boys [82].

Fig. 2
figure 2

Ethnic differences in pulse wave velocity between black and white boys (ages 6–8 years) from South Africa. Adapted from Mokwatsi et al. [82]

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The contribution of heritability on racial/ethnic differences in arterial stiffness remains questionable. A twin study (age 11.9–30.0) reported that heritability traits did not display any differences between blacks and whites, despite black participants presenting with a higher PWV as compared with their white counterparts [78]. It is therefore clear that exposure to unfavorable environmental factors play a significant role in the prominence of higher PWV in black children and adolescents as compared with their white peers.

Carotid intima media thickness (CIMT), as a surrogate for the detection of atherosclerosis and early development of endothelial dysfunction [92], has also been reported as a determinant of EVA [93]. Only a few studies (mostly cross-sectional) have reported differences in CIMT among children and adolescents of different race/ethnicity (Table 3). The majority among these studies included comparisons between black (American, African, Caribbean) and white or Hispanic populations, with little comparative studies that included other racial or ethnic populations. Importantly, many of these studies reported on the unadjusted means of CIMT and did not necessarily consider any adjustment for BP, body composition, age, or sex. All studies from the USA reported significantly higher CIMT in black children [81, 95, 96] and/or adolescents [94], whereas one study reported borderline higher CIMT in the black compared with white group [87]. A UK study population, with multiple race/ethnic groups, reported higher CIMT in the black (African and Caribbean) compared with white, South Asian, Asian, and other (Indian, Pakistani, or Bangladeshi) race/ethnic groups, after adjustments for multiple covariates including age and sex [97]. From South Africa, one study reported higher CIMT in black compared with white boys, after adjustment for mean arterial pressure [82]. From the community of Bogalusa, USA, children (age 4–17 years) were cross-sectionally surveyed between 1973 and 2002 (not in Table 3) and were examined with CIMT as an additional measurement (not performed at baseline). The comparative analysis showed higher CIMT in black men (0.880 mm vs. 0.839 mm) and women (0.790 mm vs. 0.762 mm) compared with their white counterparts (p < 0.00) [98].

Table 3 Studies comparing carotid intima media thickness in children and adolescents by race
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A recent systematic review reported on studies that investigated echocardiography in children and adolescents from various parts of the world and different race groups [99]. However, most of those studies did not perform any racial comparisons, making the current literature on the racial differences in these measurements highly limited, especially from countries other than the USA. Studies claim that children with left ventricular hypertrophy (LVH) are more likely to be of non-white race and have a higher BMI z score [100]. In Table 4, we listed studies in children and adolescents that compared left ventricular mass (LVM) between two or more race groups. Multiple studies from the USA reported higher unadjusted LVM in black compared with white children and adolescents [76, 79, 102, 108]. The higher LVM was more evident in black girls compared with boys for baseline and follow-up [105]. LVM adjusted for body surface area, stature, or body height to the power 2.7, yielded similar differences with higher LVM in black than white groups [79], along with the higher LVM in black girls and boys compared with their white counterparts [76, 105, 107]. Comparative studies have also reported no differences in LVM between black and white children or adolescents [106]. A longitudinal study with a very small sample size (black: n = 25 and white: n = 36), reported higher LVM (unadjusted and adjusted for body surface area) in white girls and black boys and after an approximate 6-year follow-up. LVM was higher in white boys and girls (unadjusted) and in white boys after considering indexing for body surface area compared with the black groups [101]. A retrospective study performed a racial/ethnic comparison of data from three different sites in the USA, and reported the highest LVM (indexed by body surface area) in the Hispanic group (n = 20) compared with the black and white groups [104]. Detail on age per race/ethnic group as well as secondary causes of hypertension per race/ethnic group were not reported in this analysis. One study from an Italian group also confirmed higher LVM in black (n = 30) compared with white (n = 60) adolescents, although this study was performed in athletes visiting Italy from Central or West Africa [103]. Based on the limited and inconsistent evidence, it remains uncertain whether LVM is universally higher in certain race/ethnic populations, especially in the context of EVA in children and adolescents.

Table 4 Studies comparing left ventricular mass in children and adolescents by race
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Pathological determinants of early vascular aging

Similar to the multifactorial etiology of hypertension, EVA develops in the presence of cumulative risk factors in vulnerable populations such as children and adolescents, especially those with significant differences noted by race or ethnicity. It is becoming increasingly evident that early stages of CVD, such as hypertension and LVH, start to manifest in childhood and adolescence, with black children manifesting these risk factors earlier than white children [13, 82]. Therefore, race or ethnicity is considered risk factors of EVA and subsequent CVD. In low and middle-income countries, obesity and other NCDs are consequences of a combination of poverty, living environments, the availability of fast foods, and especially the consumption of energy-dense, but micronutrient-poor diets. However, there is substantial evidence to suggest that early life nutrition and intrauterine risk factors play a pivotal role in the progression towards adult NCDs [109].

Tracking studies have shown that children and adolescents with elevated BP have a higher risk of developing hypertension in early adulthood [45, 72, 110] and this transition to adult hypertension was mostly determined by modifiable cardiovascular risk factors including poor dietary habits (high dietary salt intake, fructose, processed and fast foods), poor sleep patterns, stress, and a lack of sufficient physical activity [45]. Furthermore, childhood nutrition is a major driver of child mortality and morbidity in countries with large ethnic inequities, with a substantial burden of under-and overnutrition, and a rapid growth of obesity, driven by the excessive consumption of sugar containing drinks, ultra-processed foods, and extensive sedentary lifestyle [16]. Underweight trends among children and adolescents are still alarmingly high especially in African and Southeast Asia compared with obesity. With obesity in children and adolescents reaching a plateau in high-income countries, the prevalence is still rising in low-income and middle-income countries. This has important consequences, including the short-term developments of psychiatric, psychological, and psychosocial disorders in childhood and the increased long-term risk of developing NCDs later in life [111].

In light of the abovementioned modifiable and non-modifiable risk factors contributing to EVA, EVA is typically felt to be manifest as the long-term development of endothelial dysfunction, arterial stiffness, LVH, and early kidney damage.

The vasculature

Arterial stiffness is defined as reduced arterial distensibility or compliance (in the tunica media) as a result of continuous adaptations in the molecular and biomechanical makeup of blood vessels [112, 113] and endothelial dysfunction. Endothelial dysfunction is defined as the state of impaired vasodilation due to proinflammation and prothrombic properties of the blood vessel walls [114]. Endothelial dysfunction is also associated with several CVDs in adults, including hypertension, coronary artery disease, chronic heart failure, peripheral artery disease, diabetes mellitus, and CKD [114]. However, several mechanisms involved in reduced vasodilatory responses of the endothelium are also evident in pediatric populations including reduced nitric oxide bioavailability, oxidative stress, and the activation of vasoactive peptides known to promote vasoconstriction. A study in black and white boys (mean age of 7.29 years) reported lower urinary nitrate-to-nitrite molar ratio, as a measure of nitric oxide bioavailability, in black boys compared with the white boys, suggesting a lower reabsorption rate of nitrite or lower nitric oxide generation and underlying sub-clinical endothelial dysfunction [115]. This result may further indicate genetic differences in renal carbonic anhydrase isoforms and anion transporters among children of black African ancestry. Furthermore, markers of oxidative stress (thiobarbituric acid-reactive substances and 8-hydroxy-2-deoxy guanosine) related to increased arterial stiffness and diastolic BP in boys with linked maternal lifestyle and cardiovascular risk factors, suggesting potential family-related early onset of increased cardiovascular risk [116]. Studies in children and adolescents reported higher arterial stiffness in black and Hispanic populations at ages as early as 6 years [80, 82, 84, 87] compared with white, non-Hispanic, and Asian children. Aside from studies that reported the higher BP, PWV, and CIMT in black and Hispanic populations, there are numerous intermediate determinants of EVA that contribute to the premature development of endothelial dysfunction and subsequent arterial stiffness. Increased aortic wall thickness and impaired vasomotor function was described as functions of increased arterial stiffness [117], as observed in preterm infants with systemic hypertension [118]. In addition, low birth weight and other complications such as bronchopulmonary dysplasia also contribute to the early onset of arterial stiffening [118].

Other determinants of endothelial dysfunction and arterial stiffness include metabolic factors (impaired glucose and lipid metabolism and insulin resistance), oxidative stress [119,120,121] and inflammation, as well as the increased deposition of matrix substances, all of which contribute to altered hemodynamics and subsequent hypertension [122,123,124]. In addition, increased carotid artery intima-media thickness and early atherosclerosis, capillary rarefaction and dysfunctional vascular regulation along with microvascular and macrovascular injury have been reported in children [125, 126], but ethnic-specific comparison studies are still limited. Metabolomics analyses also confirmed race/ethnic disparities, where PWV associated adversely with β-alanine, 1-methylhistidine, and L-proline in black South African children, which may suggest potential early compromise in cardioprotective metabolic pathways in children of African ancestry [127].

The heart and the kidneys

The vascular compromise in EVA has a direct impact on the heart and other target organs. Perhaps one of the most dynamic measures of increased cardiovascular risk is LVM. Increased LVM, also defined as LVH, is a prominent independent predictor of cardiovascular morbidity and mortality in adults [128, 129] and a sensitive marker of risk in children [130]. With exposure to various environmental factors (pollution, violence, poverty, availability to drugs, access to alcohol and cigarettes), aging, and lifestyle behaviors (exercise and dietary intake of healthy and unhealthy food), the wall of the left ventricle has the ability to remodel in response. LVM may be one of the earliest markers of hypertension mediated target organ damage or manifestations of EVA. From the Bogalusa Heart Study in Louisiana, adolescence was described as a critical age period for the development of LVH in later life due to the impact of BP trajectories in childhood on adult LVH and geometric patterns [131]. This study included a population of 65% white and 35% black children, adolescents, and adults (ages 4–51 years) and reported higher BP and LVM in the black participants, highlighting the reality of ethnic specific risks in the setting of EVA.

Underweight or overweight/obesity during childhood is an additional risk factor for the development of LVH as these markers of suboptimal nutrition are associated with accelerated CV deterioration and early vascular compromise. This has been confirmed by reports indicating LVH and left ventricular diastolic dysfunction in 9–19-year olds with obesity, prior to the development of sustained hypertension [132]. LVH is also a sensitive marker of target organ damage in children with high BP and CKD [130]. In children with CKD, LVH develops early and becomes more prevalent as renal function decreases; however, this may be dependent on BP as a study reported that a reduction in BP might predict a decline in LVH in children with CKD [133].

The degree of renal function is important—children with end-stage renal disease (ESRD) on dialysis had worse measures of arterial stiffness than those with a functional kidney transplant and healthy age-sex-matched controls [134, 135]. Litwin et al. even suggested partial reversal in CKD-associated arterial wall remodeling as patients displayed attenuation of arterial pathology after kidney transplantation than patients on dialysis irrespective of exposure to similar dialysis vintage [134]. In another study, PWV was not significantly different between children with mild CKD and healthy children, while in children with mild-to-moderate CKD, PWV was independently associated with increasing age, mean arterial pressure and black ethnicity [136].

Chronic kidney disease can also promote tissue growth and adversely impact left ventricular function via non-hemodynamic pathways such as chronic inflammation, vitamin D deficiency, and higher levels of parathyroid hormone [137, 138]. Vitamin D and its interactions with the renin-angiotensin-aldosterone system (RAAS) have been implicated in arterial stiffness. Vitamin D supplementation was shown to alleviate local arterial stiffness and improved flow-mediated dilatation in children with CKD [106]. Fibroblast growth hormone-23 (FGF23), a hormone that is released from bone and works on the kidney has been positively associated with LVH in children aged 1–21 years [139, 140]. FGF23 increases activity of the RAAS by decreasing active vitamin D [141]. On the other hand, FGF23 may promote sodium retention and subsequently volume expansion independent of RAAS [142]. In the Framingham Heart Study (including the Offspring cohort and the Omni cohort), FGF23 was positively associated with African-American and Asian ethnicity [143]. However, in the CARDIA study, FGF23 was associated with an increase in BP over time and an increased incident of hypertension, with no racial/ethnic differences in hypertension [144].

Ethnic differences regarding the activity of RAAS are also well established with populations of African ancestry presenting with a suppressed RAAS across all ages [145,146,147]. The suppressed RAAS phenotype is not unique to individuals of African descent, but it is also common in Asians and elderly populations of other ethnicities [148, 149]. The low RAAS activity is due to, among others, retention of sodium and water, which increases the load against which the heart must work [146, 150]. In black boys with a mean age of 16 years, an increase in aldosterone was associated with decreased sodium excretion and increased BP and LVM [107]. Another study showed a stronger association between aldosterone and BP with aging from adolescence (mean age 10.6 years) to adulthood in black participants [147]. Early kidney damage and dysregulation in the RAAS may also stem from fetal conditions. Young adults born preterm present with smaller kidneys and higher angiotensin I, BP, and albumin-to-creatinine ratio compared with full-term controls [151], predisposing preterm babies to early vascular alterations and CVD development at young ages. A recent study developed a nomogram to predict aldosterone in children, which may improve assessment of RAAS dysfunction and treatment of pediatric hypertension to delay EVA [152]. Further studies in children and young adults from different ethnicities are needed to confirm if race-specific normal ranges are essential.

An increase is arterial stiffness was also observed in cases of children with acute post-streptococcal glomerulonephritis that progressed into CKD. Post-infectious glomerulonephritis (PIGN) is usually a result of group A streptococcal infections, and it is characterized by acute kidney injury, increased BP, glomerular hematuria, mild proteinuria, and edema [153]. Yu et al. demonstrated an association between arterial stiffness and PIGN in children [153]. The mechanisms are not yet clear, but may be due to the renal inflammatory response in PIGN [154, 155], and also suggest that glomerular changes may reflect vascular changes outside the kidney in response to infection. Rural and overcrowded communities are particularly vulnerable to epidemic clusters and outbreaks of PIGN [153]. PIGN used to be the most prevalent kidney disease in black South African children; however, focal glomerulosclerosis and rapidly progressive glomerulonephritis (mostly due to streptococcal infection) later became the first and second causes of renal failure requiring kidney transplantation [156].

Of importance, other factors contributing to the burden of kidney diseases in black South African children emanate from the quadruple burden of disease, which may not be unique to the South African context. Tuberculosis has been linked to focal glomerulosclerosis and Takayasu arteritis (inflammatory vasculitis of the aorta and its main branches), while HIV and its associated opportunistic infections, as well toxicity from antiretroviral drugs, have been implicated in kidney injury in children living with HIV [156,157,158]. Aboriginal children from Australia and New Zealand diagnosed with severe PIGN showed an increased risk to progress to advanced stages of renal damage and even ESRD as compared with the non-Aboriginal population [159,160,161]. It is not yet established if the ethnic-specific manifestations of acute kidney disease may accelerate vascular aging in children and young adults of certain race groups.

Future directions of early vascular aging and race/ethnicity in children and adolescents

While genetic studies have failed to distinguish ethnic or race-specific determinants of CVD risk [162], race/ethnicity remains one of the risk factors regularly reported in multiethnic population studies in relation to hypertension and cardiovascular disease states. Whether race/ethnicity by itself is a risk factor for EVA, or whether it is the convergence of multiple risk factors on the backdrop of race/ethnicity, remains to be confirmed.

In countries such as the USA, race/ethnic variations in health have been regularly reported, with differences in socioeconomic status as a major contributor to racial disparities in health [163]. However, in the recent 2018 World Bank report, South Africa was identified as the most unequal country in the world, with black South Africans reported to have the highest level of poverty, with less access to proper education, are most unemployed, have more female headed households, and have large families and many children per household [164]. With multiple discrepancies in environmental and sociocultural determinants that may adversely influence biological aging, research should be directed to larger, prospective, and standardized protocols to address racial differences in EVA, especially in low to middle-income countries with large ethnic diversity.

Finally, alongside the clinical treatment of the consequences of biological aging, focus should be shifted to the development of primordial prevention and educational programs to promote health from the beginning of life (starting with pregnant mothers, parents, pre-primary school children and teachers). The overall health and economic burden of treating NCDs can be improved—especially in countries with large educational and sociocultural disparities and racial variation.

Conclusion

Although this is not an exhaustive review, the main features of EVA point to important racial differences in risk factors when evaluating the early life determinants of accelerated biological aging. The manifestations of EVA are of particular global and economic interest and should be targeted for primary prevention to curb the current escalating burden of cardiovascular disease, especially in children and adolescents at increased risk by race.

Key summary points

  • Early life programming is an essential determinant of EVA in children and adolescents

  • Children of black or Hispanic race are especially vulnerable to develop EVA due to predisposed risk in hemodynamic and end organ damage

  • Ethnicity by itself can be considered a risk factor for EVA, but may be dependent on converging risk factors in early life

Multiple-choice questions

  1. 1.

    Early vascular aging can be defined as:

  1. a)

    Premature CVD manifestation

  2. b)

    Age-related biological deterioration

  3. c)

    Age-related increases in cardiac function

  4. d)

    Vascular degeneration

  5. e)

    Premature deterioration of the vasculature

  1. 2.

    Which one of the following is the gold standard measure of EVA?

  1. a)

    Carotid intima thickness

  2. b)

    Blood pressure

  3. c)

    Pulse wave velocity

  4. d)

    Nitric oxide

  5. e)

    Oxidative stress

  1. 3.

    The following are key characteristics of EVA except:

  1. a)

    Increased pulse wave velocity

  2. b)

    Oxidative stress

  3. c)

    Increased elasticity of the arterial walls

  4. d)

    Microvascular rarefaction

  5. e)

    Increased vasoconstriction

  1. 4.

    Ethnic differences in intrauterine programming of early vascular aging may be linked to

  1. a)

    Oxidative stress

  2. b)

    Endothelial dysfunction

  3. c)

    Epigenetic modifications

  4. d)

    A and B only

  5. e)

    All of the above

  1. 5.

    EVA and its associated cardiovascular risk can be mitigated by ______.

  1. a)

    Intensifying treatment of hypertension, diabetes and renal diseases in resource poor settings

  2. b)

    Timeous diagnosis and treatment of infectious diseases

  3. c)

    Improving maternal and child health and nutrition

  4. d)

    Both A and B

  5. e)

    Options A, B, C