Sodium excretion and racial differences in ambulatory blood pressure patterns

Influence of Age, Heart Failure and ACE Inhibitor Treatment on Plasma Renin Activity in Children: Insights from a Systematic Review and the European LENA Project

BACKGROUND

Plasma renin activity (PRA) has gained relevance as prognostic marker in adults with heart failure. The use of PRA as a clinically meaningful parameter in children and children with heart failure requires a thorough knowledge of the factors that influence PRA to correctly assess PRA levels. We aim to evaluate the influence of age, heart failure and angiotensin-converting enzyme inhibitor (ACEi) on PRA levels in children.

METHODS

We conducted a systematic literature search to identify studies on PRA levels in healthy children and in children with heart failure. In addition, we analysed PRA data measured before (n = 35, aged 25 days-2.1 years), 4 hours after (n = 34) and within the first 8 days of enalapril treatment (n = 29) in children with heart failure from the European project Labeling of Enalapril from Neonates up to Adolescents (LENA).

RESULTS

Age has a profound effect on PRA levels in healthy children, as PRA levels in the literature are up to about 7 times higher in neonates than in older children. Children with heart failure younger than 6 months showed 3-4 times higher PRA levels than healthy peers in both the literature and the LENA studies. In the LENA studies, the ACEi enalapril significantly increased median predose PRA by a factor of 4.5 in children with heart failure after 4.7 ± 1.6 days of treatment (n = 29, p < 0.01). Prior to treatment with enalapril, LENA subjects with symptomatic heart failure (Ross score ≥3) had a significantly higher PRA than LENA subjects with asymptomatic heart failure of comparable age (Ross score ≤2, p < 0.05).

CONCLUSIONS

Age, heart failure and ACEi treatment have a notable influence on PRA and must be considered when assessing PRA as a clinically meaningful parameter.

CLINICAL TRIAL REGISTRATION

The trials are registered on the EU Clinical Trials Register (https://www.clinicaltrialsregister.eu).

TRIAL REGISTRATION NUMBERS

EudraCT 2015-002335-17, EudraCT 2015-002396-18.

Salt sensitivity of blood pressure in childhood and adolescence

Although moderation of sodium intake is recommended population-wide, it remains uncertain who benefits from salt restriction. Salt sensitivity refers to changes in blood pressure in response to sodium intake and may occur with or without hypertension. Unfortunately, there is no practical way to assess salt sensitivity in daily practice. Assessment of salt sensitivity even in research studies is challenging with varying protocols utilized which may contribute to differing results. Building on studies in animals and adults, risk factors and conditions associated with salt sensitivity have been identified in the pediatric and young adult populations. This review presents the limited evidence linking obesity, low birth weight, diabetes, chronic kidney disease, and race/ethnicity with salt sensitivity in children, adolescents, and young adults. The impact of stress on sodium handling is also reviewed. The influence of age on the timing of introduction of dietary salt restriction and the long-term influence of salt sensitivity on risk for hypertension are considered. Lastly, interventions other than salt restriction that may improve salt sensitivity and may inform recommendations to families are reviewed.

Sodium intake and blood pressure in children and adolescents: a systematic review and meta-analysis of experimental and observational studies

Background

High sodium intake is a cause of elevated blood pressure in adults. In children and adolescents, less evidence is available and findings are equivocal. We systematically reviewed the evidence from experimental and observational studies on the association between sodium intake and blood pressure in children and adolescents.

Methods

A systematic search of the Medline, Embase, CINAHL and CENTRAL databases up to March 2017 was conducted and supplemented by a manual search of bibliographies and unpublished studies. Experimental and observational studies involving children or adolescents between 0 and 18 years of age were included. Random-effects meta-analyses were performed by pooling data across all studies, separately for experimental and observational studies, and restricting to studies with sodium intake and blood pressure measurement methods of high quality. Subgroup meta-analyses, sensitivity analyses and meta-regressions were conducted to investigate sources of heterogeneity and confounding. The dose-response relationship was also investigated.

Results

Of the 6572 publications identified, 85 studies (14 experimental; 71 observational, including 60 cross-sectional, 6 cohort and 5 case-control studies) with 58 531 participants were included. In experimental studies, sodium reduction interventions decreased systolic blood pressure by 0.6 mm Hg [95% confidence interval (CI): 0.5, 0.8] and diastolic blood pressure by 1.2 mm Hg (95% CI: 0.4, 1.9). The meta-analysis of 18 experimental and observational studies (including 3406 participants) with sodium intake and blood pressure measurement methods of high quality showed that, for every additional gram of sodium intake per day, systolic blood pressure increased by 0.8 mm Hg (95% CI: 0.4, 1.3) and diastolic blood pressure by 0.7 mm Hg (95% CI: 0.0, 1.4). The association was stronger among children with overweight and with low potassium intake. A quasi-linear relationship was found between sodium intake and blood pressure.

Conclusions

Sodium intake is positively associated with blood pressure in children and adolescents, with consistent findings in experimental and observational studies. Since blood pressure tracks across the life course, our findings support the reduction of sodium intake during childhood and adolescence to lower blood pressure and prevent the development of hypertension.

Race and sex differences in asleep blood pressure: The Coronary Artery Risk Development in Young Adults (CARDIA) study

Nocturnal hypertension and non-dipping blood pressure are each associated with increased risk of cardiovascular disease. We determined differences in nocturnal hypertension and non-dipping systolic/diastolic blood pressure among black and white men and women who underwent 24-hour ambulatory blood pressure monitoring at the Coronary Artery Risk Development in Young Adults study Year 30 Exam in 2015-2016. Asleep and awake periods were determined from actigraphy complemented by sleep diaries. Nocturnal hypertension was defined as mean asleep systolic/diastolic blood pressure ≥ 120/70 mm Hg. Non-dipping systolic and diastolic blood pressure, separately, were defined as a decline in awake-to-asleep blood pressure < 10%. Among 767 participants, the prevalence of nocturnal hypertension was 18.4% and 44.4% in white and black women, respectively, and 36.4% and 59.9% in white and black men, respectively. After multivariable adjustment and compared with white women, the prevalence ratio (95% confidence interval) for nocturnal hypertension was 1.65 (1.18-2.32) for black women, 1.63 (1.14-2.33) for white men, and 2.01 (1.43-2.82) for black men. The prevalence of non-dipping systolic blood pressure was 21.5% and 41.0% in white and black women, respectively, and 20.2% and 37.9% in white and black men, respectively. Compared with white women, the multivariable-adjusted prevalence ratio (95% confidence interval) for non-dipping systolic blood pressure was 1.66 (1.18-2.32), 0.91 (0.58-1.42) and 1.66 (1.15-2.39) among black women, white men, and black men, respectively. Non-dipping diastolic blood pressure did not differ by race-sex groups following multivariable adjustment. In conclusion, black women and men have a high prevalence of nocturnal hypertension and non-dipping systolic blood pressure.

Associations of urinary sodium levels with overweight and central obesity in a population with a sodium intake

Background

Previous studies have reported an association between dietary sodium intake and overweight/central obesity. However, dietary survey methods were prone to underestimate sodium intake. Therefore, this study investigated the associations of calculated 24-h urinary sodium excretion, an index of dietary sodium intake, with various obesity parameters including body mass index (BMI) and waist circumference (WC) in a population with a relatively high sodium intake.

Methods

A total of 16,250 adults (aged ≥19 years) and 1476 adolescents (aged 10-18 years), with available information on spot urine sodium levels and anthropometric measurements from the Korea National Health and Nutrition Examination Survey (KNHANES) were included in this study. We calculated 24-h urine sodium excretion levels from spot urine sodium levels using the Tanaka formula.

Results

In adults, those with high sodium excretion levels (≥ 3200 mg) showed increased odds of overweight and central obesity compared to those with low urinary sodium excretion level (< 2200 mg) (odds ratio [OR] = 2.17, 95% confidence interval [CI] = 1.90-2.49 for overweight; OR = 2.50, 95% CI = 2.13-2.94 for central obesity). These associations were also observed in adolescents (OR = 5.80, 95% CI = 3.17-10.60 for overweight; OR = 4.19, 95% CI = 1.78-9.89 for central obesity).

Conclusions

The present study suggests that reducing salt intake might be important for preventing overweight and central obesity, especially in adolescents. However, because the present study was conducted with cross-sectional study design, further longitudinal studies are warranted to confirm the causal relationship between urinary sodium excretion and overweight/central obesity.

Angiotensin II and the Natriuretic and Blood Pressure Response to Mental Stress in African Americans

Objective

To test the hypothesis that Angiotensin II (Ang II) is a contributing factor to the response pattern in African Americans (AAs) who retain rather than excrete sodium during mental stress.

Design/Study Participants

Double-blind, randomized, cross-over trial of 87 healthy AAs aged 18 to 50 years.

Interventions

The study participants received either a placebo or irbesartan, (150 mg PO), an Ang II receptor antagonist, for seven days prior to stress testing. Urinary sodium excretion (UNaV) and systolic blood pressure (SBP) were collected prior to and throughout a mental stress protocol (rest and stress period).

Setting

A southeastern university.

Main Outcome Measures

Ang II, SBP, and sodium retention.

Results

During the placebo condition, 62 participants showed the expected increase in UNaV (excreters) while 25 participants reduced UNaV during stress (retainers). Irbesartan retainers demonstrated a reversal in the direction of their natriuretic response, now increasing UNaV in response to stress (∆ UNaV of -.094 mmol/min with placebo vs .052 mmol/min on irbesartan; P<.001). In excreters, irbesartan reduced SBP levels during both rest (-2.36 mm Hg; P=.03) and stress (-4.59;P<.0001), and an even more pronounced reduction in SBP was demonstrated by retainers on treatment during both rest (-4.29 mm Hg; P=.03) and stress (-6.12; P<.001).

Conclusions

Ang II contributes to sodium retention in retainers. Furthermore, our findings indicate that suppression of Ang II has a beneficial effect on SBP during rest and stress in this population.

The Reproducibility of Racial Differences in Ambulatory Blood Pressure Phenotypes and Measurements

BACKGROUND

We examined the reproducibility of differences in ambulatory blood pressure (BP) monitoring (ABPM) phenotypes and other parameters (sustained hypertension, masked hypertension, nocturnal hypertension, and nondipping) between African Americans and Whites.

METHODS

A total of 420 participants untreated for hypertension attended 2 research visits 1 week apart during which traditional office BP averages and ABPM session averages were determined. We computed percent agreement in ABPM phenotypes across the 2 visits stratified by race and associated kappa statistics with 95% confidence intervals.

RESULTS

Whites on average were older, more likely to be male, and had a higher body mass index. There was no significant difference in sleep quality as defined by sleep diary between the 2 races. There were also no significant differences between races in the proportions of participants with sustained hypertension, sustained normotension, or masked hypertension at either testing session. The prevalence of nocturnal hypertension was 59% vs. 75% (P = 0.012) at session 1 and 59% vs. 73% (P = 0.024) at session 2 for Whites and African Americans, respectively, with moderate reproducibility for both (kappas 0.45 and 0.44). Nocturnal BP nondipping had a prevalence 29% vs. 53% (P < 0.001) at session 1 and 29% vs. 47% (P = 0.004) at session 2 for Whites and African Americans, respectively, with fair reproducibility (kappas 0.28 and 0.29).

CONCLUSIONS

Our findings support that African Americans indeed exhibit a greater preponderance of abnormal nocturnal BP patterns than Whites. Our work is some of the first to demonstrate that these abnormal patterns are modestly reproducible.

Race/ethnicity determines the relationships between oxidative stress markers and blood pressure in individuals with high cardiovascular disease risk

Oxidative stress (OS) and cardiovascular (CV) reactivity are related to CV morbidity and mortality. However, little is known about the relationships between these CV risk factors and their confounders. We hypothesize that higher OS is linked to higher blood pressure (BP) reactivity to acute laboratory stressors and in the natural setting. We studied 137 subjects with a family history of hypertension and early myocardial infarction. There were 63 European Americans (EAs) (38 males) and 74 African Americans (AAs) (35 males), aged 19-36 (27.6±3.1). The protocol included a competitive video game, cold stressor and ambulatory BP recording. Blood samples were drawn six times for OS markers (8-hydroxydeoxyguanosine (8-OHdG) and 8-Isoprostane) assay. Repeated measures analyses of covariance were used to test for mean differences and Pearson correlations were used to test OS and BP associations. There were no significant race/ethnicity differences in BP reactivity to either stressor (both P's>0.48). 8-OHdG levels were significantly lower across all time points for AAs than for EAs (P<0.05), while levels of 8-isoprostane did not differ significantly (P>0.10). Averaged 8-OHdG levels significantly correlated with systolic blood pressure (SBP) reactivity (r=0.45, <0.01) and 24-h, daytime and nighttime SBP (r range=0.37-0.42, all P's<0.02) for EAs but not for AAs, whereas 8-isoprostane levels were significantly correlated with reactive SBP and nighttime diastolic blood pressure (DBP) (both r's=0.38, P<0.01) for AAs but not for EAs. These findings suggest a link between OS and BP changes in subjects at high risk for CV disease (CVD). Further, race/ethnicity determines which OS marker will impact BP variation implying race/ethnicity differences in OS-related mechanisms of CVD.

Caffeine intake antagonizes salt sensitive hypertension through improvement of renal sodium handling

High salt intake is a major risk factor for hypertension. Although acute caffeine intake produces moderate diuresis and natriuresis, caffeine increases the blood pressure (BP) through activating sympathetic activity. However, the long-term effects of caffeine on urinary sodium excretion and blood pressure are rarely investigated. Here, we investigated whether chronic caffeine administration antagonizes salt sensitive hypertension by promoting urinary sodium excretion. Dahl salt-sensitive (Dahl-S) rats were fed with high salt diet with or without 0.1% caffeine in drinking water for 15 days. The BP, heart rate and locomotor activity of rats was analyzed and urinary sodium excretion was determined. The renal epithelial Na⁺ channel (ENaC) expression and function were measured by in vivo and in vitro experiments. Chronic consumption of caffeine attenuates hypertension induced by high salt without affecting sympathetic nerve activity in Dahl-S rats. The renal α-ENaC expression and ENaC activity of rats decreased after chronic caffeine administration. Caffeine increased phosphorylation of AMPK and decrease α-ENaC expression in cortical collecting duct cells. Inhibiting AMPK abolished the effect of caffeine on α-ENaC. Chronic caffeine intake prevented the development of salt-sensitive hypertension through promoting urinary sodium excretion, which was associated with activation of renal AMPK and inhibition of renal tubular ENaC.

Nocturnal Blood Pressure in Young Adults and Cognitive Function in Midlife: The Coronary Artery Risk Development in Young Adults (CARDIA) Study

BACKGROUND

Nocturnal blood pressure (BP) is associated with risk for cardiovascular events. However, the relationship between nocturnal BP in young adults and cognitive function in midlife remains unclear.

METHODS

We used data from the ambulatory BP monitoring substudy of the Coronary Artery Risk Development in Young Adults Study, including 224 participants (mean age 30 years, 45% men, 63% African Americans). At the 20-year follow-up, the Stroop test (executive function), Digit Symbol Substitution Test (psychomotor speed), and Rey Auditory Verbal Learning Test (verbal memory) were assessed.

RESULTS

Baseline mean office, daytime, and nocturnal BP were 109/73, 120/74, and 107/59 mm Hg, respectively. Nocturnal BP dipping, calculated as (nocturnal systolic BP [SBP]--daytime SBP) × 100/daytime SBP, was divided into quartiles (Q1: -39.3% to -16.9%; Q2: -16.8% to -13.2%, Q3 [reference]: -13.1% to -7.8%, and Q4: -7.7% to +56.4%). In multiple regression analyses, the least nocturnal SBP dipping (Q4 vs. reference) and higher nocturnal diastolic BP level were associated with worse Stroop scores, with adjustments for demographic and clinical characteristics, and cumulative exposure to office BP during follow-up (β [standard error]: 0.37 [0.18] and 0.19 [0.07], respectively; all P < 0.05). Digit Symbol Substitution Test and Rey Auditory Verbal Learning Test were not significantly associated with nocturnal SBP dipping or nocturnal SBP/diastolic BP levels.

CONCLUSIONS

Among healthy young adults, less nocturnal SBP dipping and higher nocturnal diastolic BP levels were associated with lower executive function in midlife, independent of multiple measures of office BP during long-term follow-up.

Racial differences in abnormal ambulatory blood pressure monitoring measures: Results from the Coronary Artery Risk Development in Young Adults (CARDIA) study

BACKGROUND

Several ambulatory blood pressure monitoring (ABPM) measures have been associated with increased cardiovascular disease risk independent of clinic blood pressure (BP). African Americans have higher clinic BP compared with Whites but few data are available on racial differences in ABPM measures.

METHODS

We compared ABPM measures between African American (n = 178) and White (n = 103) participants at the Year 5 Coronary Artery Risk Development in Young Adults study visit. BP was measured during a study visit and the second and third measurements were averaged. ABPM was conducted over the following 24 hours.

RESULTS

Mean ± SD age of participants was 29.8 ± 3.8 years and 30.8 ± 3.5 years for African Americans and Whites, respectively. Mean daytime systolic BP (SBP) was 3.90 (SD 1.18) mm Hg higher among African Americans compared with Whites (P < 0.001) after age-gender adjustment and 1.71 (SD 1.03) mm Hg higher after multivariable adjustment including mean clinic SBP (P = 0.10). After multivariable adjustment including mean clinic SBP, nighttime SBP was 4.83 (SD 1.11) mm Hg higher among African Americans compared with Whites (P < 0.001). After multivariable adjustment, the African Americans were more likely than Whites to have nocturnal hypertension (prevalence ratio: 2.44, 95% CI: 0.99-6.05) and nondipping (prevalence ratio: 2.50, 95% CI: 1.39-4.48). The prevalence of masked hypertension among African Americans and Whites was 4.4% and 2.1%, respectively, (P = 0.49) and white coat hypertension was 3.3% and 3.9%, respectively (P = 0.99). Twenty-four hour BP variability on ABPM was higher among African Americans compared with Whites.

CONCLUSIONS

These data suggest racial differences in several ABPM measures exist.

Associations of ambulatory blood pressure with urinary caffeine and caffeine metabolite excretions

Intake of caffeinated beverages might be associated with reduced cardiovascular mortality possibly via the lowering of blood pressure. We estimated the association of ambulatory blood pressure with urinary caffeine and caffeine metabolites in a population-based sample. Families were randomly selected from the general population of Swiss cities. Ambulatory blood pressure monitoring was conducted using validated devices. Urinary caffeine, paraxanthine, theophylline, and theobromine excretions were measured in 24 hours urine using ultrahigh performance liquid chromatography tandem mass spectrometry. We used mixed models to explore the associations of urinary excretions with blood pressure although adjusting for major confounders. The 836 participants (48.9% men) included in this analysis had mean age of 47.8 and mean 24-hour systolic and diastolic blood pressure of 120.1 and 78.0 mm Hg. For each doubling of caffeine excretion, 24-hour and night-time systolic blood pressure decreased by 0.642 and 1.107 mm Hg (both P values <0.040). Similar inverse associations were observed for paraxanthine and theophylline. Adjusted night-time systolic blood pressure in the first (lowest), second, third, and fourth (highest) quartile of paraxanthine urinary excretions were 110.3, 107.3, 107.3, and 105.1 mm Hg, respectively (P trend <0.05). No associations of urinary excretions with diastolic blood pressure were generally found, and theobromine excretion was not associated with blood pressure. Anti-hypertensive therapy, diabetes mellitus, and alcohol consumption modify the association of caffeine urinary excretion with systolic blood pressure. Ambulatory systolic blood pressure was inversely associated with urinary excretions of caffeine and other caffeine metabolites. Our results are compatible with a potential protective effect of caffeine on blood pressure.

Salt, fruit and vegetable consumption and blood pressure development: a longitudinal investigation in healthy children

Low salt intake and high fruit and vegetable intake (FVI) have been shown to reduce blood pressure (BP) in adults. Longitudinal data on the independent effect of both FVI and salt intake on BP in healthy normotensive children are not available yet. In the present study, we aimed to characterise the concomitant influence of salt intake and FVI on BP development throughout childhood and adolescence. We examined 435 healthy subjects, for whom at least three repeated measurements of BP had been taken and who had provided 24 h urine samples and 3 d weighed dietary records between 4 and 18 years of age. BP was measured using a mercury sphygmomanometer (Mercuro 300, WelchAllyn) and salt intake was determined based on 24 h Na excretion. The intra-individual change in salt intake was almost significantly associated with the change in systolic BP (SBP, P= 0·06) and marginally (P= 0·09) with that in diastolic BP (DBP) in puberty, but not in pre-puberty. A 1 g/d increase in salt intake was associated with a 0·2 mmHg increase in SBP. In pre-puberty, but not in puberty, differences in FVI between children predicted between-person variations in SBP and DBP (P= 0·03). Corresponding findings were obtained for 24 h K excretion (a urinary indicator for FVI). A 100 g/d lower FVI was related to a 0·4 mmHg higher BP value. In conclusion, in healthy children and adolescents with BP in the low-normal range, both salt intake and FVI may already start to influence BP, although at a small magnitude. The potential importance of establishing healthy eating habits in childhood for later BP development emphasises the role of higher FVI and lower salt intake in the prevention of hypertension in the long run.

Physiology of endothelin and the kidney

Since its discovery in 1988 as an endothelial cell-derived peptide that exerts the most potent vasoconstriction of any known endogenous compound, endothelin (ET) has emerged as an important regulator of renal physiology and pathophysiology. This review focuses on how the ET system impacts renal function in health; it is apparent that ET regulates multiple aspects of kidney function. These include modulation of glomerular filtration rate and renal blood flow, control of renin release, and regulation of transport of sodium, water, protons, and bicarbonate. These effects are exerted through ET interactions with almost every cell type in the kidney, including mesangial cells, podocytes, endothelium, vascular smooth muscle, every section of the nephron, and renal nerves. In addition, while not the subject of the current review, ET can also indirectly affect renal function through modulation of extrarenal systems, including the vasculature, nervous system, adrenal gland, circulating hormones, and the heart. As will become apparent, these pleiotropic effects of ET are of fundamental physiologic importance in the control of renal function in health. In addition, to help put these effects into perspective, we will also discuss, albeit to a relatively limited extent, how alterations in the ET system can contribute to hypertension and kidney disease.

Regulation of blood pressure and salt homeostasis by endothelin

Endothelin (ET) peptides and their receptors are intimately involved in the physiological control of systemic blood pressure and body Na homeostasis, exerting these effects through alterations in a host of circulating and local factors. Hormonal systems affected by ET include natriuretic peptides, aldosterone, catecholamines, and angiotensin. ET also directly regulates cardiac output, central and peripheral nervous system activity, renal Na and water excretion, systemic vascular resistance, and venous capacitance. ET regulation of these systems is often complex, sometimes involving opposing actions depending on which receptor isoform is activated, which cells are affected, and what other prevailing factors exist. A detailed understanding of this system is important; disordered regulation of the ET system is strongly associated with hypertension and dysregulated extracellular fluid volume homeostasis. In addition, ET receptor antagonists are being increasingly used for the treatment of a variety of diseases; while demonstrating benefit, these agents also have adverse effects on fluid retention that may substantially limit their clinical utility. This review provides a detailed analysis of how the ET system is involved in the control of blood pressure and Na homeostasis, focusing primarily on physiological regulation with some discussion of the role of the ET system in hypertension.

How to treat hypertension in blacks: review of the evidence

Presentation, response to therapy, and clinical outcome differ according to race for patients with hypertension. Black patients have a higher prevalence and earlier onset of hypertension than other ethnic groups, with poorer prognosis than white patients. Blacks are more likely to be salt-sensitive, and to have a low plasma renin activity than are whites. They are at much greater risk of developing cardiovascular and renal complications. Despite many advances in the understanding and treatment of cardiovascular diseases, black patients continue to have increased morbidity and mortality from the end-organ complications of hypertension. The explanations for these observations remain incompletely understood, but genetic differences, added to socio-economic and environmental factors, have been proposed to explain this disparity. The first therapeutic approach is to decrease salt and increase potassium intakes. Diuretics (thiazides and potassium-sparing agents) and calcium channel blockers constitute the first antihypertensive drug choices. The angiotensin-converting-enzyme inhibitors, the angiotensin II receptor blockers and beta-blockers appear to be less effective in blacks with regard to uncomplicated hypertension, especially in older people, but addition of a small dose of diuretic improves their efficacy. These combinations are preferred among patients with chronic kidney disease or heart failure. The goal for blood pressure target is the same in blacks as it is in whites, being a blood pressure of less than 140/90 mmHg in uncomplicated hypertension and less than 130/80 mmHg in patients with diabetes mellitus or chronic kidney disease.

Salt intakes around the world: implications for public health

BACKGROUND

High levels of dietary sodium (consumed as common salt, sodium chloride) are associated with raised blood pressure and adverse cardiovascular health. Despite this, public health efforts to reduce sodium consumption remain limited to a few countries. Comprehensive, contemporaneous sodium intake data from around the world are needed to inform national/international public health initiatives to reduce sodium consumption.

METHODS

Use of standardized 24-h sodium excretion estimates for adults from the international INTERSALT (1985-87) and INTERMAP (1996-99) studies, and recent dietary and urinary sodium data from observational or interventional studies--identified by a comprehensive search of peer-reviewed and 'grey' literature--presented separately for adults and children. Review of methods for the estimation of sodium intake/excretion. Main food sources of sodium are presented for several Asian, European and Northern American countries, including previously unpublished INTERMAP data.

RESULTS

Sodium intakes around the world are well in excess of physiological need (i.e. 10-20 mmol/day). Most adult populations have mean sodium intakes >100 mmol/day, and for many (particularly the Asian countries) mean intakes are >200 mmol/day. Possible exceptions include estimates from Cameroon, Ghana, Samoa, Spain, Taiwan, Tanzania, Uganda and Venezuela, though methodologies were sub-optimal and samples were not nationally representative. Sodium intakes were commonly >100 mmol/day in children over 5 years old, and increased with age. In European and Northern American countries, sodium intake is dominated by sodium added in manufactured foods ( approximately 75% of intake). Cereals and baked goods were the single largest contributor to dietary sodium intake in UK and US adults. In Japan and China, salt added at home (in cooking and at the table) and soy sauce were the largest sources.

CONCLUSIONS

Unfavourably high sodium intakes remain prevalent around the world. Sources of dietary sodium vary largely worldwide. If policies for salt reduction at the population level are to be effective, policy development and implementation needs to target the main source of dietary sodium in the various populations.

Ethnic Differences in Urine Concentration: Possible Relationship to Blood Pressure

The mechanisms that account for the susceptibility of black individuals to hypertension and their reduced ability to excrete sodium are poorly understood. Vasopressin administration has been shown in healthy humans to delay sodium excretion along with its antidiuretic action. Black individuals have been reported to have higher vasopressin levels than white individuals. Therefore, this study investigated retrospectively 24-h urine volume (V) and urine concentration index (urine-to-plasma ratio of creatinine concentration), as well as their possible relationships with BP, in a cohort of 141 healthy young black and white individuals (18 to 40 y). Black individuals were found to have a significantly lower V and higher urine concentration than white individuals, especially during daytime. In addition, they exhibited a blunted nocturnal fall in fluid and electrolyte excretion and a higher pulse pressure than white individuals. Higher urine concentration and lower V were associated significantly with higher PP (but not with systolic or diastolic BP) in men. These relations remained significant after adjustment for age, body mass index, and sodium and potassium excretion. These results suggest that an enhanced tendency to concentrate urine may delay the excretion of the daily ingested fluid and sodium and may increase pulse pressure in young normotensive individuals. The higher urine concentration that is observed in black individuals (which could represent an adaptation to better water conservation) may participate in their enhanced susceptibility to hypertension. If these results are confirmed in further studies, then vasopressin V2 receptor antagonists might offer a novel antihypertensive strategy, especially in the black population.

A comparison of awake???sleep blood pressure variation between normotensive Japanese???American and Caucasian Women in Hawaii

OBJECTIVE

To compare awake-sleep ambulatory blood pressure variation between Japanese-American and Caucasian women in Hawaii, specifically determining whether Japanese-Americans have reduced dipping of blood pressure during sleep, as is found in comparisons of Japanese and US samples.

METHODS

Normotensive school teachers from East Hawaii who were either of Japanese-American (n = 70) or Caucasian (n = 48) ethnicity were recruited. They wore an ambulatory blood pressure monitor (Spacelabs 90207) that took measurements every 15 min during waking hours and every 30 min during sleep for a 24-h period on a normal workday. All subjects provided demographic information and underwent a series of anthropometric measurements the day before monitoring. Japanese-American subjects also answered questionnaires relating to cultural identity and migration history.

RESULTS

The Japanese-American women had significantly higher mean diastolic (P < 0.01) blood pressure during sleep. These ethnic differences in sleep blood pressure persisted when analyses controlled for age, body mass index, and the waist-hip circumference ratio. There were also significant differences in the proportion by which blood pressure dipped from waking to sleeping, with the Japanese-American women dipping significantly less than the Caucasian women (P < 0.05 systolic, P < 0.001 diastolic).

CONCLUSIONS

Normotensive Japanese-American women have higher sleep pressure, and a smaller awake-sleep dip, in pressure than Caucasian women. The relative elevation of blood pressure in Japanese-American women during sleep, but not at other times of the day, is similar to the pattern seen among Japanese women in Japan.

Prevention of essential hypertension in minority populations

The precursors of essential hypertension (EH) begin in childhood. If the etiology of the evolution of EH were discovered, interventions may be developed to lead to the primary prevention of EH. In particular, one ethnic group, African-Americans (Blacks), are at increased risk of development of EH in adulthood. Hemodynamic changes in response to stressors are termed measures of cardiovascular reactivity (CVR). Ethnic difference in CVR are known to exist; are these markers or mechanisms of EH evolution? Investigations are underway to discover the mechanism(s) of the excessive vasoconstriction which appears to be characteristic of the CVR responses in Blacks. These may lead to the pharmacologic, or non-pharmacologic, interventions which may be initiated in childhood and prevent EH in adults.

Renin inhibition improves pressure natriuresis in essential hypertension

Pressure natriuresis (PN), i.e., a rise in renal sodium excretion in response to a higher BP, is involved in long-term BP regulation. PN is blunted in essential hypertension, but the mechanism is unknown. This study assessed the role of the renin-angiotensin-aldosterone system (RAAS) in PN in eight essential hypertensive men from the individual correlations between spontaneous fluctuations in BP and time corresponding changes in sodium excretion (collected at 2- and 4-h intervals for 48 h), during strict sodium balance, without treatment, and during renin inhibition (remikiren, 600 mg oral compound). Without treatment, daily values for mean arterial pressure were 109.5 +/- 1.9 and 107 +/- 1.9 mmHg, for urinary sodium excretion were 37.2 +/- 2.8 and 42.0 +/- 2.8 mmol/24 h, and for plasma renin activity were 2.34 +/- 0.48 and 2.23 +/- 0.44 nmol/L per h, respectively, for two consecutive days. During remikiren treatment, mean arterial pressure was 101.9 +/- 1.7 and 100.8 +/- 1. 7 mmHg (P: < 0.05, versus baseline). Urinary sodium excretion was 39. 3 +/- 3.7 and 45.2 +/- 5.3 mmol/24 h (not significant versus baseline), and plasma renin activity was 0.79 +/- 0.11 and 0.82 +/- 0.13 nmol/L per h (P: < 0.05 versus baseline). During remikiren treatment, BP correlated positively with sodium excretion in all patients but in only three of eight patients without treatment. The slope of the regression equation was steeper during remikiren treatment in seven of eight patients. Thus, the relationship between BP and natriuresis was more readily apparent during RAAS blockade, suggesting that RAAS activity blunts PN in hypertensive patients. Improved PN may contribute to the hypotensive effect of RAAS blockade and to maintenance of sodium balance at a lower BP level without volume expansion.

The conjoint trait of low high-density lipoprotein cholesterol and high triglycerides in adolescent black and white males

To evaluate the interrelationships among body composition, blood pressure, and lipid phenotypes in adolescent black and white boys, we assessed racial distributions of lipids, blood pressure, and obesity and their joint occurrence in black and white boys aged 10 to 15 years. Subjects were recruited from Cincinnati (OH) schools. Because the differences in high-density lipoprotein cholesterol (HDL-C) and triglycerides (TGs) are the most profound coronary heart disease (CHD) risk factor differences between black and white males, we assigned subjects to one of four low-HDL-C and high-TG categories (normal and increased risk) using the age/race-specific 25th (HDL-C) and 75th (TG) percentiles. We then assessed racial distributions of lipids, blood pressure, and obesity by these phenotypes. Age differences between the black and white participants were significant, with the former about 3 months younger (P=.03), but black boys were more mature and were significantly taller and heavier and had a greater body mass index ([BMI] weight in kilograms divided by height in centimeters squared). Differences in the sum of the triceps, subscapular, and suprailiac skinfolds were not significant. Blacks had significantly higher HDL-C, lower TG, and higher diastolic blood pressure (DBP), but differences in systolic blood pressure (SBP) were not significant. In both racial groups, the body composition measures were significantly correlated with HDL-C, TG, and blood pressure levels; the correlations between HDL-C and both weight and BMI were significantly stronger in white boys. The proportion of boys of each race with low HDL-C and high TG was similar by design. In both racial groups, subjects with the conjoint trait had a significantly greater BMI, triceps skinfold, and sum of skinfolds than subjects in the other phenotypic groups. For white boys, participants with the conjoint trait had the highest SBP and DBP; differences in SBP were significant for comparisons to the normal- and high-TG group alone, and differences in DBP were significant for the comparison between normal and low HDL-C alone. For black boys, subjects with both normal HDL-C and TG had significantly lower SBP than boys with either the conjoint trait or high TG alone; none of the group differences in DBP were significant. Black had significantly less dense LDL (more LDL-C per apolipoprotein [apo] B). In each racial group, boys with the conjoint trait had the most dense LDL, significantly more dense than in any of the other phenotypes in black boys and significantly more dense than in boys with low HDL-C alone and normal boys in the white group. In both racial groups, the occurrence of no risk factors (>75th percentile TG, BMI, SBP, and DBP or <25th percentile HDL-C) and three or more risk factors was greater than expected by chance alone, and the occurrence of exactly one risk factor and two factors was less. When examined by phenotypic groups within race, boys in each racial group with the normal phenotype had a greater than expected percentage with no risk factors, and white boys with the conjoint trait were more likely to have a marked increase in multiple risk factors. Possible mechanisms for this clustering of risk factors and for the racial differences in the patterns are discussed.

Predictors of future ambulatory blood pressure in youth

OBJECTIVE

The objective of this study was to determine the predictors of future ambulatory blood pressure in normotensive youths with family histories of essential hypertension.

STUDY DESIGN

Eighty-eight healthy youths (mean age 10.9 +/- 2.5 years; 52 blacks, 36 whites; 45 boys) were studied. During an initial visit anthropometric variables and hemodynamics were measured at rest and before, during, and after three laboratory stressors: postural change, forehead cold, and video game challenge. The subjects' ambulatory blood pressure was monitored for 24 hours as part of a follow-up evaluation an average of 2.5 years later.

RESULTS

Anthropometric and demographic variables and measures of reactivity to laboratory stressors were related to future daytime and nighttime ambulatory blood pressure.

CONCLUSION

These findings provide important information on the predictors of ambulatory blood pressure and underscore the importance of resting blood pressure and adiposity. These results support the guidelines of the Second Task Force, which recommend the measurement of blood pressure and adiposity in the context of ongoing health care.

Current and birth weights exert independent influences on nocturnal pressure-natriuresis relationships in normotensive children

The objective was to study the impact of birth weight on the relationship between ambulatory blood pressure and urinary sodium excretion in children and adolescents. The study included 134 healthy children (61 boys), all Caucasians, who were born at term after a normotensive pregnancy. For each subject, a 24-hour ambulatory blood pressure monitoring and a complete urine collection were simultaneously performed according to the protocols designed. Average ambulatory blood pressure (BP) and the urinary excretion rates for sodium, potassium, and creatinine were calculated separately for 24-hour, awake, and sleep periods defined by a mini-diary. The excretion rate of sodium during sleep time was positively correlated with ambulatory systolic BP; such a positive relationship was not found for waking hours. Consequently, the impact of birth weight on the relationship between blood pressure and the urinary sodium excretion rate was analyzed during sleeping hours. Stepwise multiple regression analysis shows that although current weight was the strongest predictor for the sodium excretion rate during sleep (P<.001), there was also an independent significant direct relationship for birth weight (P<.04) after controlling for age, sex, and the average of systolic BP during sleep. Adjusted for current weight, a significant difference in the regression slopes relating urinary sodium excretion rate and systolic BP during sleep exists between children in the lowest (<3.100 kg) and the highest tertiles (>3.500 kg) of birth weight (P<.02). Differences in sodium excretion rates, adjusted for current weight, between the two extreme tertiles of birth weight became significant at the highest systolic BP (P<.04). The children who had the lowest birth weight tended to excrete less sodium during sleep. The results of the present study show a blunted pressure natriuresis curve in children and adolescents with the lowest birth weight. Whether this abnormal renal sodium handling may be present as an initial or as an intermediate mechanism leading to higher BP values must be assessed in additional studies.

Effects of blood pressure control on progressive renal disease in blacks and whites. Modification of Diet in Renal Disease Study Group

African Americans (blacks) have a disproportionately high incidence of end-stage renal disease due to hypertension. The Modification of Diet in Renal Disease (MDRD) Study found that strict blood pressure control slowed the decline in glomerular filtration rate (GFR) only in the subgroup of patients with proteinuria. The present report compares the effects of blood pressure control in black and white MDRD Study participants. Fifty-three black and 495 white participants with baseline GFRs of 25 to 55 mL/min/1.73 m2 were randomly assigned to a usual or low mean arterial pressure (MAP) goal of < or = 107 or < or = 92 mm Hg, respectively. GFR decline was compared between randomized groups and correlated with the level of achieved blood pressure. The mean (+/-SE) GFR decline over 3 years in the low blood pressure group was 11.8+/-7.3 mL/min slower than in the usual blood pressure group among blacks (P=.11) compared with 0.3+/-1.3 mL/min slower among whites (P=.81) (P=.12 between blacks and whites). In both blacks and whites, higher baseline urine protein excretion was associated with a greater beneficial effect of the low MAP goal on GFR decline (P=.02 for both races). Combining both blood pressure groups and controlling for baseline characteristics, higher follow-up achieved MAP was associated with faster GFR decline in both blacks (P<.001) and whites (P=.002), with a sevenfold stronger relationship in blacks (P<.001). These secondary analyses support the prior recommendation for a lower than usual blood pressure goal (MAP < or = 92 mm Hg) in black and white patients with proteinuria (> 1 g/d). In addition, a lower level of blood pressure control may be even more important in blacks than in whites in slowing the progression of renal disease.

Potassium intake and cardiovascular reactivity in children with risk factors for essential hypertension

OBJECTIVES

Our study objectives were as follows: (1) to determine whether urinary excretion of potassium is lower in black than in white children, (2) to determine whether cardiovascular reactivity (CVR) varies inversely with dietary intake of potassium, and (3) to confirm that CVR is greater in black than in white children, and in children with a family history of hypertension than in those without such a history.

STUDY DESIGN

Baseline measurements included 24-hour urinary sodium, potassium, and creatinine levels and food intake (by questionnaire). Resting and stress blood pressure were measured during blood sampling, cold water foot immersion, and a video game before and after 1 week each of supplementation with potassium citrate, 1.5 mmol/kg per day, and placebo administered in random order.

RESULTS

Thirty-nine children aged 7 to 15 years were studied. White subjects had higher baseline excretion of potassium than black subjects (p < 0.001) and higher vegetable intake (p < 0.01), which were positively correlated (r = 0.53, p < 0.001). At baseline, the 24-hour urinary potassium/creatinine ratio varied inversely with diastolic CVR to the video game stressor in white children (r = -0.55, p = 0.02). Cardiovascular reactivity was not attenuated measurably by potassium supplementation compared with placebo. The CVR was greater in children with a family history of hypertension than in those without, but was not greater in black children than in white children.

CONCLUSIONS

The urinary potassium/creatinine ratio is higher in white than black children because their intake of vegetables is greater; dietary potassium intake may modulate CVR, particularly in white children with a family history of hypertension, but may need to be supplemented for more than 1 week to demonstrate attenuation of CVR; and a family history of hypertension may be a stronger predictor of enhanced CVR than is race.

Pathophysiology and treatment implications of hypertension in the African-American population

Regardless of the etiology, hypertension remains a major public health problem in African-Americans and is associated with significant morbidity and mortality. Additional data on the pathophysiology of this disease in this population are needed, as are data on the best therapies to decrease the high complication rate. Because many of the large studies on hypertension have included few African-Americans, recruitment of this ethnic group into clinical trials should be promoted. Further studies into the genetic factors in the pathophysiology of racial differences in hypertension may shed more light on this complex issue.

Effects of cynical hostility, anger out, anxiety, and defensiveness on ambulatory blood pressure in black and white college students

This study asked whether individual differences in four personality traits (cynical hostility, anger out, anxiety, and defensiveness) would predict waking and sleeping ambulatory blood pressure and heart rate and whether information about these traits would provide a source of racial and gender differences in these measures. Ambulatory blood pressure and heart rate were recorded over a 24-hour period in 58 black and 86 white college students equally divided by gender. Waking and sleeping values were examined as a function of gender, race, and personality factors. Independent of personality factors, women had lower ambulatory blood pressure and higher heart rate than men, and black subjects had higher blood pressure levels and less of a decrease in heart rate from waking to sleeping than white subjects. The above differences were associated with personality factors. Black subjects scoring high on cynical hostility had elevated daytime and nighttime systolic pressure. Black subjects scoring high on both anxiety and defensiveness had higher waking diastolic blood pressure. Additional effects were shown for heart rate as a function of anger out, anxiety, and defensiveness. Given the special significance of ambulatory blood pressure for cardiovascular disease, these findings underscore the importance of personality factors for cardiovascular risk and their relevance for race and gender differences in this risk.

Racial differences in the pathogenesis of hypertension

Hypertension occurs at an earlier age, is more prevalent, and is more often complicated by target organ damage in African-Americans than whites. Reasons for this increased severity of hypertension in African-Americans remain obscure. Based on studies recently completed in their laboratory, the authors propose that greater sympathetic reactivity to stress and a greater prevalence of NaCl sensitivity contribute to the earlier development of hypertension in African-Americans. Using microneurography to record muscle sympathetic nervous system activity, it was found that normotensive blacks manifest greater increases in sympathetic activity to cold stress than normotensive whites. If true of other types of stressors, greater sympathetic reactivity would predispose blacks to the development of hypertension. Using a telemetry-based monitoring system, the authors recently reported that both spontaneously hypertensive rats and normotensive Wistar-Kyoto rats manifest acute sensitivity to high dietary NaCl ingestion, but that the Wistar-Kyoto rats are able to compensate, thereby avoiding sustained increases in blood pressure. Based on these animal studies, it is proposed that elevated nocturnal pressures observed in blacks by other investigators may reflect the greater prevalence of NaCl sensitivity in the black population. As in animal models of NaCl-sensitive hypertension, blacks may retain ingested NaCl, resulting in sustained increases in blood pressure.

Racial differences in the age-related increase in left ventricular mass in youths

We determined the factors related to left ventricular mass adjusted for body size in 60 black (mean age, 13 +/- 2 years) and 40 white (mean age, 14 +/- 2 years) normotensive youths. The factors examined included age, sex, systolic blood pressure, diastolic blood pressure, plasma renin activity, plasma aldosterone concentration, and sodium and potassium intake as determined by 24-hour excretion. Sex (beta = 13.3, P < .003), age (beta = 2.88, P < .001), and systolic blood pressure (beta = 0.41, P < .02) were independent predictors in the sample as a whole, accounting for 37% of the variance of left ventricular mass adjusted for height. Separate analyses were performed for black and white subjects. In the black subjects, age (beta = 4.4, P < .004) followed by sex (beta = 11.85, P < .02) were independent factors, accounting for 43% of the variance of left ventricular mass adjusted for height. In contrast, in white subjects systolic blood pressure (beta = 0.4, P < .003) followed by sodium excretion (beta = 0.13, P < .05) were independent factors, with gender (beta = 8.89, P < .07) tending to account for 36% of the variance. Similar results were observed for left ventricular mass adjusted for body surface area. In conclusion, the age-related increase in adjusted left ventricular mass in black but not white youths may in part account for the early development of cardiovascular disease among the black population.

Pressor reactivity, ethnicity, and 24-hour ambulatory monitoring in children from hypertensive families

We assessed blood pressure responses of a multiethnic (Black and White) sample of 120 children of hypertensive families to orthostasis, video game, forehead cold, and dynamic exercise, and monitored the children's ambulatory pressure 24 hours later. Thirteen children were studied twice (1-year stability). The Black children exhibited higher 24-hour ambulatory systolic and diastolic pressures than the White children. Regardless of ethnicity, peak and mean systolic pressures during each task were generally positively correlated with mean systolic pressure while the children were awake and asleep. Associations between diastolic pressor responses and ambulatory measurements were somewhat dependent upon ethnicity and task. Relatively few reactivity-ambulatory correlations were significant, using pressor reactivity change scores. The children who participated twice exhibited significant 1-year stability for most ambulatory and pressor measurements. Children's pressor responses to laboratory tasks may generalize to the natural environment.

Altered blood pressure during sleep in normotensive subjects with type I diabetes

This study was designed to examine the circadian pattern of blood pressure in children and young adults with type I diabetes who were completely normotensive by standard criteria. Forty-five patients and the same number of age- and sex-matched control subjects were studied. In diabetic children of 10-14 years of age, the nocturnal fall in systolic and diastolic blood pressures was intact. In diabetics of 15-20 years of age, the fall in systolic blood pressure was blunted; in diabetics of 21-37 years of age, the fall in both systolic and diastolic blood pressures during sleep was blunted. When data from all diabetic subjects were pooled and analyzed in a multiple linear regression model, mean blood pressure during sleep correlated best with urinary albumin excretion (r = 0.60). On the basis of this finding, we subdivided our patients into two groups: a microalbuminuric group (urinary albumin excretion > 30 mg per 24 hours; mean, 160.3 +/- 29.7; n = 11) and a normoalbuminuric group (urinary albumin excretion < 30 mg per 24 hours; mean, 6.6 +/- 6.5; n = 34). Both systolic and diastolic blood pressures during sleep were higher in microalbuminuric (121.1 +/- 3.3 and 69.3 +/- 2.5 mm Hg, respectively) than in normoalbuminuric diabetics (114.2 +/- 1.8 and 60.1 +/- 1.2 mm Hg, p < 0.05) or control subjects (113.3 +/- 1.2 and 60.1 +/- 1.2 mm Hg, p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Racial aspects of blood pressure in children and adolescents

The incidence, prevalence, and severity of essential hypertension are higher in minority adult populations, especially black Americans. Studies have not uniformly shown that black children and adolescents have higher blood pressure values than whites of the same age. The goal of this article is to review data available comparing minority and white populations. A section discussing studies addressing racial differences in related topics is included to demonstrate the existing fields of research that may not be familiar to the general pediatrician.