Urinary sodium excretion and blood pressure in children: absence of a reproducible association

Salt restriction for treatment of hypertension - current state and future directions

PURPOSE OF REVIEW

Given the adverse effects of excess dietary sodium chloride (also known as table salt) on blood pressure (BP) and cardiovascular disease (CVD), restriction of dietary sodium is recommended by numerous guidelines. The strictest of these recommend no more than 1.5 g/day of dietary sodium among hypertensive persons. However, average dietary sodium intake in the population is closer to 5 g/day and there is debate about whether too much sodium restriction may be associated with increased CVD risk. Herein, we aim to provide a balanced update on this topic.

RECENT FINDINGS

In 2021, the Salt Substitute and Stroke Study (SSaSS) demonstrated a significant reduction in BP, CVD, and death among Chinese adults randomized to a low sodium salt-substitute supplemented with potassium. This trial largely puts to rest any remaining debate about the benefits of dietary sodium restriction among persons with excess baseline intake (dietary sodium intake fell from approximately 5 down to 4 g/day in the active arm of SSaSS). However, whether achieving and maintaining a dietary sodium of less than1.5 g/day is feasible in real-world settings and whether this low an intake is harmful remain open questions.

SUMMARY

Aiming for sodium intakes of 2--3 g/day in the general population and as low as 2 g/day in persons with hypertension or CVD seems most reasonable, but there is some uncertainty around lower targets.

Impact of growth, gonadal hormones, adiposity and the sodium-to-potassium ratio on longitudinal adolescent measures of blood pressure at puberty

Blood pressure (BP) rises rapidly at puberty. While this is partly due to normal development, factors like excess adiposity and a high intake of dietary sodium relative to potassium may contribute to a true increase in hypertension risk. This study aimed to assess the relative impact of growth, gonadal hormones, adiposity and the sodium-to-potassium ratio (Na:K) on longitudinal BP measures at puberty. This study analysed data from a three-year longitudinal cohort study of pubertal adolescents. Anthropometry, body composition (bio-electrical impedance), serum testosterone and oestradiol (mass spectrometry) were measured annually. Na:K was measured from three-monthly urine samples. These variables were used to predict annual BP measures using mixed modelling and ordinal regression. Data from 325 adolescents (11.7 ± 1.0 y; 55% male) were analysed, showing typical growth patterns at puberty. Systolic BP increased over time in both sexes (p < 0.01), with boys exhibiting a significantly steeper rise compared to girls. Adiposity variables (BMI z-score, percent body fat, fat mass, waist-to-height ratio) strongly and consistently predicted systolic and diastolic BP in both sexes (all p < 0.05). Systolic BP was also significantly and positively related to height (p < 0.05). No associations with BP were identified in either sex for gonadal hormones or Na:K. Similar results were obtained when BP was classified into hypertension categories. Relative to other developmental and diet-related variables tested, adiposity was found to be the strongest most consistent predictor of BP in pubertal adolescents. Findings highlight the importance of dedicated youth obesity management interventions and policy measures for reducing long-term hypertension and cardiovascular disease risks.Australian New Zealand Clinical Trials Registry ACTRN12617000964314.

Assessing the Association of Sodium, Potassium Intake and Sodium/Potassium Ratio on Blood Pressure and Central Adiposity Measurements amongst Ellisras Undernourished, Rural Children Aged 5–13 Years: South Africa

Background: Numerous studies have shown how diet, such as sodium (Na) and potassium (K) intake, is an important risk factor for non-communicable diseases (NCDs). This study aimed to assess the relationship between sodium intake, potassium intake; and sodium/potassium ratio with blood pressure (BP) and abdominal obesity amongst Ellisras rural children. Method: In this cross-sectional study, data on dietary intake of sodium and potassium were collected using a 24-h recall questionnaire from a total of 765 participants, aged 5–13 years. Blood pressure and anthropometric measurements were also collected. Generalised linear models and Pearson correlation were conducted to assess the association of sodium intake, potassium intake; and their ratio with BP, waist circumference (WC), and waist-to-height ratio (WHtR). Results: In both age groups, less than 14.9% of males and 19.8% of females consumed above the recommended adequate intake (AI) of sodium. In addition, both age groups had more than 90% of males and females who consumed below the recommended AI of potassium. Moreover, the sodium/potassium ratio was above the WHO recommended level in more than 30% of males and females. The study found a significant, weak positive correlation of sodium intake with systolic BP (SBP), diastolic BP (DBP), and with WHtR. A significant, weak positive correlation was also found between sodium/potassium ratio and WHtR. In addition, a significant association was found between potassium intake and systolic BP. Conclusion: Although our study found a notable low average intake of sodium and potassium as compared to the recommended values. There was positive correlation found between sodium intake and BP. Furthermore, a positive correlation of sodium intake and sodium/potassium ratio with WHtR was also found.

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.

Urine Spot Samples Can Be Used to Estimate 24-Hour Urinary Sodium Excretion in Children

Background

The gold standard to assess salt intake is 24-h urine collections. Use of a urine spot sample can be a simpler alternative, especially when the goal is to assess sodium intake at the population level. Several equations to estimate 24-h urinary sodium excretion from urine spot samples have been tested in adults, but not in children.

Objective

The objective of this study was to assess the ability of several equations and urine spot samples to estimate 24-h urinary sodium excretion in children.

Methods

A cross-sectional study of children between 6 and 16 y of age was conducted. Each child collected one 24-h urine sample and 3 timed urine spot samples, i.e., evening (last void before going to bed), overnight (first void in the morning), and morning (second void in the morning). Eight equations (i.e., Kawasaki, Tanaka, Remer, Mage, Brown with and without potassium, Toft, and Meng) were used to estimate 24-h urinary sodium excretion. The estimates from the different spot samples and equations were compared with the measured excretion through the use of several statistics.

Results

Among the 101 children recruited, 86 had a complete 24-h urine collection and were included in the analysis (mean age: 10.5 y). The mean measured 24-h urinary sodium excretion was 2.5 g (range: 0.8-6.4 g). The different spot samples and equations provided highly heterogeneous estimates of the 24-h urinary sodium excretion. The overnight spot samples with the Tanaka and Brown equations provided the most accurate estimates (mean bias: -0.20 to -0.12 g; correlation: 0.48-0.53; precision: 69.7-76.5%; sensitivity: 76.9-81.6%; specificity: 66.7%; and misclassification: 23.0-27.7%). The other equations, irrespective of the timing of the spot, provided less accurate estimates.

Conclusions

Urine spot samples, with selected equations, might provide accurate estimates of the 24-h sodium excretion in children at a population level. At an individual level, they could be used to identify children with high sodium excretion. This study was registered at clinicaltrials.gov as NCT02900261.

Estimation of salt intake and excretion in children in one region of Switzerland: a cross-sectional study

PURPOSE

Salt intake among children in Switzerland is unknown. The objectives of this study were to determine salt excretion and to identify the main dietary sources of salt intake among children in one region of Switzerland.

METHODS

We conducted a cross-sectional study using a convenient sample of children 6-16 years of age in Valais, Switzerland, between 2016 and 2018. All children visiting several regional health care providers and without any clinical condition that could affect sodium intake or excretion were eligible. Each child completed a 24-h urine collection to assess salt excretion and two dietary questionnaires to assess dietary sources of salt intake. Weight and height were measured.

RESULTS

Data were available on 94 children (55 boys and 39 girls; mean age 10.5 years; age range 6-16 years). The mean 24-h salt urinary excretion was 5.9 g [SD 2.8; range 0.8-16.0; 95% confidence interval (CI) 5.3-6.5]. Two-thirds (62%) of the children had salt excretions above recommendations of maximum intake (i.e., ≥ 2 g per day for children up to 6 years of age and ≥ 5 g per day for children 7-16 years of age). The salt excretion tended to be higher during the week-end (6.0 g, 95% CI 5.4-6.6) than during the week (5.4 g, 95% CI 4.3-6.7). The main sources of salt intake were pastas, potatoes, and rice (23% of total salt intake), pastries (16%), bread (16%), and cured meats (10%). One child out of three (34%) added salt to their plate at the table.

CONCLUSIONS

Salt intake in children in one region of Switzerland was high. Our findings suggest that salt intake in children could be reduced by lowering salt content in commonly eaten foods.

TRIAL REGISTRATION NUMBER

NCT02900261.

Sodium intake and blood pressure in children and adolescents: protocol for a systematic review and meta-analysis

INTRODUCTION

Hypertension is a major risk factor for cardiovascular diseases. In adults, high sodium intake is associated with elevated blood pressure. In children, experimental studies have shown that reducing sodium intake can reduce blood pressure. However, their external validity is limited, notably because the sodium reduction was substantial and not applicable in a real-life setting. Observational studies, on the other hand, allow assess the association between blood pressure and sodium intake across usual levels of consumption. There is also evidence that the association differs between subgroups of children according to age and body weight. Our objective is to conduct a systematic review and meta-analysis of experimental and observational studies on the association between sodium intake and blood pressure in children and adolescents and to assess whether the association differs according to age and body weight.

METHODS AND ANALYSIS

A systematic search of the MEDLINE, EMBASE, CINAHL and CENTRAL databases will be 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 will be included. The exposure will be dietary sodium intake, estimated using different methods including urinary sodium excretion. The outcomes will be systolic and diastolic blood pressure, elevated blood pressure and hypertension. If appropriate, meta-analyses will be performed by pooling data across all studies together and separately for experimental and observational studies. Subgroup meta-analyses by age and body weight will be also conducted. Moreover, separate meta-analyses for different sodium intake levels will be conducted to investigate the dose-response relationship.

ETHICS AND DISSEMINATION

This systematic review and meta-analysis will be published in a peer-reviewed journal. A report will be prepared for national authorities and other stakeholders in the domains of nutrition, public health, and child health in Switzerland.

TRIAL REGISTRATION NUMBER

CRD42016038245.

High sodium and low potassium intake among Italian children: relationship with age, body mass and blood pressure

BACKGROUND

Hypertension is the leading cause of death in developed countries and reduction of salt intake is recommended as a key preventive measure.

OBJECTIVE

To assess the dietary sodium and potassium intakes in a national sample of Italian children and adolescents and to examine their relationships with BMI and blood pressure (BP) in the framework of the MINISAL survey, a program supported by the Italian Ministry of Health.

POPULATION AND METHODS

The study population included 1424 healthy subjects (766 boys, 658 girls) aged 6-18 years (mean age: 10.1±2.9) who were consecutively recruited in participating National Health Service centers in 10 Italian regions. Electrolyte intake was estimated from 24 hour urine collections tested for completeness by the concomitant measurement of creatinine content. Anthropometric indices and BP were measured with standardized procedures.

RESULTS

The average estimated sodium intake was 129 mmol (7.4 g of salt) per day among boys and 117 mmol (6.7 g of salt) among girls. Ninety-three percent of the boys and 89% of the girls had a consumption higher than the recommended age-specific standard dietary target. The estimated average daily potassium intakes were 39 mmol (1.53 g) and 36 mmol (1.40 g), respectively, over 96% of the boys and 98% of the girls having a potassium intake lower than the recommended adequate intake. The mean sodium/potassium ratio was similar among boys and girls (3.5 and 3.4, respectively) and over 3-fold greater than the desirable level. Sodium intake was directly related to age, body mass and BP in the whole population.

CONCLUSIONS

The Italian pediatric population is characterized by excessive sodium and deficient potassium intake. These data suggest that future campaigns should focus on children and adolescents as a major target in the framework of a population strategy of cardiovascular prevention.

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.

Early life determinants of adult blood pressure

PURPOSE OF REVIEW

While treating high blood pressure in middle age is beneficial in terms of reducing the occurrence of cardiovascular disease, treated and well controlled hypertensive adults still have a substantial excess mortality and reduced survival compared with normotensives. Therefore, identification of the means of preventing hypertension in earlier life is an important objective. There is increasing evidence that adult blood pressure is determined by a range of characteristics from the intrauterine period, through infancy and childhood. The purpose of this review is to provide a summary of the current evidence concerning the early life determinants of adult blood pressure.

RECENT FINDINGS

Children from poorer socioeconomic positions, those whose mothers experience pregnancy-induced hypertension, those whose mothers smoke throughout pregnancy, those with low birthweight, who are not breast-fed, who have high sodium diets in infancy and who are obese in childhood or adolescence tend to have higher blood pressure in adulthood. However, the mechanisms linking these early life factors to later blood pressure and the most appropriate means of preventing adult hypertension by intervening in early life are unclear.

SUMMARY

There is clear evidence that early life factors are important determinants of adult blood pressure. However, there is a need for randomized trials with sufficient resources for long-term follow-up to assess the effects that interventions such as preventing pregnancy-induced hypertension, reducing maternal smoking, increasing breast-feeding, reducing salt consumption in infancy and preventing childhood obesity have on adult blood pressure and cardiovascular disease.

The role of gender and family support on dietary compliance in an African American adolescent hypertension prevention study

Social support experiences vary markedly across gender groups, and little is known about the role of social support in promoting healthy dietary compliance in African American adolescents who are at increased risk for developing hypertension. This study examined the relation between gender, dietary social support, and compliance to a low sodium diet. Casual blood pressures were also examined in relation to dietary compliance and gender One hundred eighty-four healthy African American adolescents (83 boys, 101 girls) participated in an intensive 5-day low sodium diet (50 mEq/24 hr) as part of a hypertension prevention program. Emotional dietary social support from family members and friends was measured at baseline. Compliance was defined as urinary sodium excretion of < or = 50 mEq/24 hr at postsodium restriction. The results indicated a significant Gender x Compliance effect for positive family support (p < .05). Girls who were compliant reported higher levels of dietary support from family members (19.2 +/- 7.8) than boys who were compliant (16.9 +/- 7.0). In contrast, boys who were compliant reported lower levels of dietary support from family members (16.9 +/- 7.0) than boys who were not compliant (20.2 +/- 7.5). Systolic blood pressure showed a trend toward decreasing in compliant participants (104.4 +/- 8.4 vs. 101.7 +/- 8.0, mm Hg, p < .06), but the effect diminished when Quetelet Index (kg/m2) was controlled for in the analyses (p < .12). These results suggest that higher levels of emotional dietary support from family members are associated with better adherence to short-term sodium restriction for African American girls as compared to boys. Further research is needed to determine the long-term impact of social support on sodium restriction in adolescent populations.

Variability in salt sensitivity classifications in black male versus female adolescents

Salt sensitivity (changes in blood pressure in response to alterations in salt intake) may be a risk factor for hypertension. In the present study, we examined the prevalence of salt sensitivity based on two different classifications in healthy black male and female adolescents (aged 13 to 16 years). A total of 135 black adolescents participated in a 50 mmol/24 h low sodium diet for 5 days and a 150 mmol/24 h NaCl supplement for 10 days. Dietary compliance was defined as sodium excretion less than or equal to 50 mmol/24 h for the low sodium diet and greater than or equal to 165 mmol/24h for the high NaCl supplement. Salt sensitivity was defined by two classifications: (1) as a decrease in mean blood pressure greater than or equal to 5 mm Hg from baseline to the low sodium diet, and (2) as an increase in mean blood pressure greater than or equal to 5 mm Hg from the low sodium diet to the high NaCl supplement. With classification 1, 14% of boys were identified as salt sensitive compared with 22% of girls. With classification 2, however, 31% of boys were identified as salt sensitive compared with 18% of girls. Analyses based on changes in systolic pressure demonstrated similar findings across sex, although overall classifications based on systolic pressure yielded a greater percentage of salt-sensitive subjects. These sex differences in classification patterns were not due to differences in other important variables, such as changes in sodium excretion, potassium excretion, or Quetelet index. These results suggest that the prevalence of salt sensitivity differs by sex depending on the type of protocol used for the classification of salt sensitivity in a black pediatric population.

Effect of low sodium diet or potassium supplementation on adolescent blood pressure

The roots of essential hypertension extend back into the first two decades of life, suggesting that effective intervention during those years may lead to a reduction in the incidence of adult hypertension. Decreasing the dietary sodium/potassium ratio offers a potentially effective approach to blood pressure reduction. This study tested the feasibility of 3-year sodium reduction or potassium supplementation in adolescents and the effect of these interventions on the rate of rise of blood pressure during adolescence. After 19,452 5th to 8th grade students were screened, 210 from the upper 15 percentiles of blood pressure distribution (105 boys, 105 girls) were randomly assigned to one of three groups: low sodium diet (70 mmol sodium intake per day), potassium chloride supplementation (normal diet plus 1 mmol/kg potassium chloride per day), or placebo (normal diet plus placebo capsule). Capsules for the potassium chloride and placebo groups were administered in a double blind protocol. Blood pressure was measured every 3 months for 3 years. The effect of the intervention was determined by comparing the rate of rise (slope) of blood pressure among the groups using a random-coefficient growth curve model. The boys groups and the girls placebo group had similar positive blood pressure slopes that were significantly different from zero. The girls low sodium group had a slightly negative slope (significantly lower than the slope of the girls placebo group), and the girls potassium group had a slightly positive slope. Both of these slopes were not significantly different from zero and were significantly lower than the slopes of the respective boys groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Hypertension, coronary artery disease and insulin resistance--linked disorders with an impact on treatment

Coronary artery disease is a very common disorder for which hypertension is a well-recognized risk factor. However many trials of antihypertensive therapy have failed to demonstrate a reduction in the incidence of coronary events. One explanation is that hypertension is a disorder associated with hyperinsulinaemia, obesity and non-insulin dependent diabetes. Furthermore certain antihypertensive drugs, notably thiazide diuretics, increase the hyperinsulinaemia and thereby increase one of the other coronary risk factors. In this review the links between hypertension and hyperinsulinaemia are explored and the mechanisms whereby an increased plasma insulin can lead to the more rapid development of coronary artery disease are explained. These observations may influence the choice of drugs used to treat hypertension.

Aldosterone metabolism in the isolated perfused liver of R and S hypertension-prone Dahl rats

The effect of a chronic oral salt load on hepatic metabolism of aldosterone was examined in isolated livers of salt-resistant (R) and salt-sensitive (S) hypertension-prone male Dahl rats perfused with d-[4-14C]aldosterone (10(-9) M). Aldosterone was analyzed by radioimmunoassay and [4-14C]aldosterone radiometabolites by high-performance liquid chromatography. In salt-loaded S rats, systolic blood pressure was 30 mmHg higher than in the other three groups (P less than 0.01). In S rats, on standard and high-salt diets, plasma renin activity was 64% (P less than 0.001) and 50% (P less than 0.01) lower, and, on the standard diet, plasma aldosterone was 50% (P less than 0.01) lower than in R rats. Salt loading suppressed plasma renin activity by 42% (P less than 0.05) in R rats and plasma aldosterone by 66 and 33% (P less than 0.01) in R and S rats, respectively. In isolated perfused liver, hepatic function did not differ between various groups. Hepatic clearance of aldosterone in R rats given water and saline and in S rats given water did not differ, whereas hepatic clearance of aldosterone was 28 and 35% higher in salt-loaded S rats when compared with S rats on water (P less than 0.01) and with salt-loaded R rats (P less than 0.001), respectively. Polar and reduced metabolites of [4-14C]aldosterone were released into the circulation in livers of R and S rats on both diets, but highest relative levels of polar metabolites of aldosterone were found in salt-loaded S rats. In all groups, only polar metabolites of aldosterone were excreted in bile.(ABSTRACT TRUNCATED AT 250 WORDS)

Population based data on urinary excretion of calcium, magnesium, oxalate, phosphate and uric acid in children from Cimitile (southern Italy)

Population based data on 24-h urinary excretion of calcium, oxalate, magnesium, phosphate, uric acid and creatinine were collected from 220 children (aged 3-16 years) living in Cimitile, Campania, southern Italy. Mean excretion rates for 7 days were correlated with age, body weight, body mass index and height. The prevalence of hypercalciuria (greater than 4 mg/kg body weight) and of hyperoxaluria (greater than 60 mg/day) were 9.1% and 1.8%, respectively. The same 20 children were also identified as hypercalciuric when a calcium/creatinine ratio of greater than 0.15 was considered. No significant differences between boys and girls were found in the urinary excretion of the five constituents implicated in urolithiasis. The study data provide additional childhood reference values for urinary excretion of compounds related to stone formation.

Sodium and potassium intake and blood pressure change in childhood

OBJECTIVE

To assess the association between sodium and potassium intake and the rise in blood pressure in childhood.

DESIGN

Longitudinal study of a cohort of children with annual measurements during an average follow up period of seven years.

SETTING

Epidemiological survey of the population of a suburban town in western Netherlands.

SUBJECTS

Cohort of 233 children aged 5-17 drawn at random from participants in the population survey.

MAIN OUTCOME MEASURES

At least six annual timed overnight urine samples were obtained. The mean 24 hour sodium and potassium excretion during the follow up period was estimated for each participant and the sodium to potassium ratio calculated. Individual slopes of blood pressure over time were calculated by linear regression analysis.

RESULTS

No significant association was observed between sodium excretion and the change in blood pressure over time. The mean systolic blood pressure slopes, however, were lower when potassium intake was higher (coefficient of linear regression -0.045 mm Hg/year/mmol; 95% confidence interval -0.069 to -0.020), and the change in systolic pressure was greater when the urinary sodium to potassium ratio was higher (0.356 mm Hg/year/unit; 95% confidence interval 0.069 to 0.642). In relation to potassium this was interpreted as a rise in blood pressure that was on average 1.0 mm Hg (95% confidence interval -1.65 to -0.35) lower in children in the upper part of the distribution of intake compared with those in the lower part. The mean yearly rise in systolic blood pressure for the group as a whole was 1.95 mm Hg. Urinary electrolyte excretion was not associated with diastolic blood pressure.

CONCLUSION

Dietary potassium and the dietary sodium to potassium ratio are related to the rise in blood pressure in childhood and may be important in the early pathogenesis of primary hypertension.

INTERSALT study findings. Public health and medical care implications

INTERSALT found a significant association between 24-hour urine sodium excretion and systolic blood pressure in individuals. There was also a significant association between sodium and slope (increase) of blood pressure with age across population samples. The weight of evidence from animal-experimental, clinical, intervention, and epidemiological data favors a causal relation. INTERSALT data from 52 centers in 32 countries permit an estimate of effect on average population blood pressure of lower sodium intake. Based on the sodium-blood pressure association in individuals, it was estimated that a habitual population sodium intake that was lower by 100 mmol/day (e.g., 70 vs. 170 mmol/day) would correspond to an average population systolic pressure that was lower by at least 2.2 mm Hg. This size difference in systolic blood pressure in major US and UK population studies is associated with 4% lower risk of coronary death and 6% lower risk of stroke death in middle age. If habitual diet is both lower in sodium and higher in potassium with lower alcohol intake and less obesity, INTERSALT data estimate average population systolic pressure would be lower by 5 mm Hg. This was calculated to correspond to a 9% lower risk of coronary death and a 14% lower risk of stroke death. INTERSALT cross-population data also suggest that, with a 100 mmol/day lower sodium intake over the life span, the average increase in population systolic pressure from age 25 to 55 years would be less by 9 mm Hg, corresponding at age 55 to a 16% lower risk of subsequent coronary death and 23% lower risk of stroke death.(ABSTRACT TRUNCATED AT 250 WORDS)

Intersalt: an international study of electrolyte excretion and blood pressure. Results for 24 hour urinary sodium and potassium excretion. Intersalt Cooperative Research Group

The relations between 24 hour urinary electrolyte excretion and blood pressure were studied in 10,079 men and women aged 20-59 sampled from 52 centres around the world based on a highly standardised protocol with central training of observers, a central laboratory, and extensive quality control. Relations between electrolyte excretion and blood pressure were studied in individual subjects within each centre and the results of these regression analyses pooled for all 52 centres. Relations between population median electrolyte values and population blood pressure values were also analysed across the 52 centres. Sodium excretion ranged from 0.2 mmol/24 h (Yanomamo Indians, Brazil) to 242 mmol/24 h (north China). In individual subjects (within centres) it was significantly related to blood pressure. Four centres found very low sodium excretion, low blood pressure, and little or no upward slope of blood pressure with age. Across the other 48 centres sodium was significantly related to the slope of blood pressure with age but not to median blood pressure or prevalence of high blood pressure. Potassium excretion was negatively correlated with blood pressure in individual subjects after adjustment for confounding variables. Across centres there was no consistent association. The relation of sodium to potassium ratio to blood pressure followed a pattern similar to that of sodium. Body mass index and heavy alcohol intake had strong, significant independent relations with blood pressure in individual subjects.

The association between blood pressure, age, and dietary sodium and potassium: a population study

We examined the relationship between blood pressure and dietary sodium and potassium intake estimated from 24 hr diet recall in a population of 584 men and 718 women 30 to 79 years old in Southern California. In men, but not women, age-adjusted systolic and diastolic blood pressure correlated significantly with dietary sodium intake. In both men and women, age-adjusted diastolic blood pressure significantly inversely correlated with dietary potassium intake. Age-adjusted systolic and diastolic blood pressure correlated significantly with the dietary sodium/potassium ratio in each sex; correlations were better for the ratio than for either sodium or potassium alone. The relationship was apparent over the whole range of blood pressure and dietary intake. A marked age gradient was apparent in men, the regression slope for blood pressure vs sodium/potassium ratio increasing with increasing age, suggesting increasing sensitivity to dietary sodium/potassium ratio with age. Adjusting for intake of other dietary variables, including calories, protein, carbohydrate, saturated fat, alcohol, calcium, and fiber, did not alter the relationships; adjusting for body mass index reduced the strength of the association in women but not in men. These results support the hypothesis that dietary sodium and potassium are related to blood pressure within a population.

Electrolytes and dietary fat in hypertensive cardiovascular disease

Nonpharmacologic measures have been increasingly applied to the management of patients with essential hypertension. Published findings concerning dietary factors and blood pressure are reviewed. Specifically, the impact of manipulations of dietary sodium, potassium, magnesium, calcium and dietary fat on blood pressure is considered. The data support a beneficial role for calcium supplementation and sodium restriction, a lesser role for potassium supplementation and a decrease in total and saturated fat intake in at least some hypertensive persons. At this time, no dietary alteration can be recommended for broad application to the population as a whole.

Promoting good nutrition for today and the year 2000

Present evidence and recommendations for promoting health and preventing disease by diet are summarized in this article. Progression studies relating to these issues over the past 6 years and relevant documents dealing with these and other public health measures are reviewed.

Factor analysis suggesting contrasting determinants for different blood pressure measurements

A multiple regression analysis was performed on statistically independent factors derived from blood pressure measurements and possible predictive variables in 618 Utah adults. Nine blood pressure factors obtained in a previous study composed the dependent variables; 35 anthropometric, questionnaire, and biochemical variables were reduced by factor analysis to 10 factors and used as independent variables. Body size and obesity had significant independent effects on different types of blood pressure: body size correlated most highly with systolic blood pressure, while obesity correlated most highly with sitting diastolic blood pressure measurements. Smoking did not correlate with sitting blood pressure but did show a significant positive correlation (after controlling for obesity) with tilt and supine diastolic pressure. Alcohol consumption correlated positively with sitting diastolic pressure when the effects of body size and obesity were controlled. No correlations were found between urinary potassium or sodium excretion and any blood pressure factors, but a significant positive correlation was seen between plasma sodium concentration and several different types of diastolic blood pressure measurements. Psychological stress showed a significant independent positive correlation with systolic blood pressure measurements that was strongest in adults over 35 years of age. The multiple correlation values for the multiple regression equations ranged from 0.19 to 0.52.

Is calcium more important than sodium in the pathogenesis of essential hypertension?

The hypothesis that abnormalities of calcium homeostasis at both an organ and cellular level are a primary factor in the pathogenesis of human and experimental hypertension forms the basis of this review. The rapidly expanding data base relating disordered calcium metabolism to altered vascular smooth muscle function and increased peripheral vascular resistance is summarized and integrated with the observations that reduced dietary calcium intake is the most consistent nutritional correlate of hypertension in the United States. The role of sodium and sodium chloride in pathogenesis of hypertension is reassessed in the light of new data from epidemiological clinical research, experimental models, and cell physiology investigations. The data supporting the thesis that the effects of sodium or chloride or both on blood pressure may represent, in selected situations, secondary influences mediated through induced changes in calcium homeostasis are presented. The interface between these nutritional factors and the normal regulation of vascular smooth muscle is discussed, providing a theoretical framework in which to assess the current information and to formulate the necessary future research.

The efficacy of quantitative and qualitative chloride titrators in the estimation of human salt intake

We evaluated the utility of chloride titrator sticks for facilitating the assessment of dietary salt intake, in a systematic series of clinical trials. These inexpensive devices were applied daily to 24-h or nocturnal urine specimens, thereby avoiding the inter- and intra-subject variability in salt excretion which confounds the use of occasional 24-h urine collections. Chloride and sodium concentrations in urine were highly correlated (r greater than 0.92) in either nocturnal, diurnal, or 24-h collections. The quantitative chloride titrator estimates and measured chloride concentrations were highly correlated as well (r greater than 0.99). The qualitative chloride titrator was graded on a simple scale, and was successfully employed by outpatients attempting to limit their salt intake. Commonly used antihypertensive medications did not interfere with the determinations. Additional chloride intake, such as supplemental potassium chloride, interfered with estimates of salt ingestion, but if the daily amount of potassium chloride supplement was constant, adjustments in interpretation could be made. Renal insufficiency introduced a systematic over-estimation of salt intake by the qualitative chloride tirator, but only at high salt intakes. Relative estimates of salt intake in subjects with renal failure were still possible. We conclude that chloride titrators can facilitate the management of patients who require a prescribed salt intake.

Blood pressure and nutrient intake in the United States

A data base of the National Center for Health Statistics, Health and Nutrition Examination Survey I (HANES I), was used to perform a computer-assisted, comprehensive analysis of the relation of 17 nutrients to the blood pressure profile of adult Americans. Subjects were 10,372 individuals, 18 to 74 years of age, who denied a history of hypertension and intentional modification of their diet. Significant decreases in the consumption of calcium, potassium, vitamin A, and vitamin C were identified as the nutritional factors that distinguished hypertensive from normotensive subjects. Lower calcium intake was the most consistent factor in hypertensive individuals. Across the population, higher intakes of calcium, potassium, and sodium were associated with lower mean systolic blood pressure and lower absolute risk of hypertension. Increments of dietary calcium were also negatively correlated with body mass. Even though these correlations cannot be accepted as proof of causation, they have implications for future studies of the association of nutritional factors and dietary patterns with hypertension in America.