Variability in 24-hour urine sodium excretion in children

Sodium and Health: Old Myths and a Controversy Based on Denial

PURPOSE OF REVIEW

The scientific consensus on which global health organizations base public health policies is that high sodium intake increases blood pressure (BP) in a linear fashion contributing to cardiovascular disease (CVD). A moderate reduction in sodium intake to 2000 mg per day helps ensure that BP remains at a healthy level to reduce the burden of CVD.

RECENT FINDINGS

Yet, since as long ago as 1988, and more recently in eight articles published in the European Heart Journal in 2020 and 2021, some researchers have propagated a myth that reducing sodium does not consistently reduce CVD but rather that lower sodium might increase the risk of CVD. These claims are not well-founded and support some food and beverage industry's vested interests in the use of excessive amounts of salt to preserve food, enhance taste, and increase thirst. Nevertheless, some researchers, often with funding from the food industry, continue to publish such claims without addressing the numerous objections. This article analyzes the eight articles as a case study, summarizes misleading claims, their objections, and it offers possible reasons for such claims. Our study calls upon journal editors to ensure that unfounded claims about sodium intake be rigorously challenged by independent reviewers before publication; to avoid editorial writers who have been co-authors with the subject paper's authors; to require statements of conflict of interest; and to ensure that their pages are used only by those who seek to advance knowledge by engaging in the scientific method and its collegial pursuit. The public interest in the prevention and treatment of disease requires no less.

What methods have been used to estimate salt intake? A systematic review

The relationship between salt intake and cardiovascular diseases is a contemporary scientific controversy, which has been attributed to the limits of the measures of salt intake used in the studies. Thus, this article sought to systematically review the literature on the methods used to estimate salt intake in different study designs. Of the 124 articles, 60.5% used only biochemical measures, 26.6% only self-report measures and 12.9% reported the combined use of both methods. The 24-hour urinary sodium excretion was the predominant biochemical method (79.1%) and the Food Frequency Questionnaire was the predominant self-report measure (36.4%). Interventional studies used mostly 24-hour urinary sodium excretion; while longitudinal studies used self-report measures. The question guiding the study and its design, as well as constraints related to costs, sample size and feasibility seems to influence the choice of the type of measurement.

The International Consortium for Quality Research on Dietary Sodium/Salt (TRUE) position statement on the use of 24-hour, spot, and short duration (<24 hours) timed urine collections to assess dietary sodium intake

The International Consortium for Quality Research on Dietary Sodium/Salt (TRUE) is a coalition of intentional and national health and scientific organizations formed because of concerns low-quality research methods were creating controversy regarding dietary salt reduction. One of the main sources of controversy is believed related to errors in estimating sodium intake with urine studies. The recommendations and positions in this manuscript were generated following a series of systematic reviews and analyses by experts in hypertension, nutrition, statistics, and dietary sodium. To assess the population's current 24-hour dietary sodium ingestion, single complete 24-hour urine samples, collected over a series of days from a representative population sample, were recommended. To accurately estimate usual dietary sodium at the individual level, at least 3 non-consecutive complete 24-hour urine collections obtained over a series of days that reflect the usual short-term variations in dietary pattern were recommended. Multiple 24-hour urine collections over several years were recommended to estimate an individual's usual long-term sodium intake. The role of single spot or short duration timed urine collections in assessing population average sodium intake requires more research. Single or multiple spot or short duration timed urine collections are not recommended for assessing an individual's sodium intake especially in relationship to health outcomes. The recommendations should be applied by scientific review committees, granting agencies, editors and journal reviewers, investigators, policymakers, and those developing and creating dietary sodium recommendations. Low-quality research on dietary sodium/salt should not be funded, conducted, or published.

Association of usual 24-h sodium excretion with measures of adiposity among adults in the United States: NHANES, 2014

Background

Both excessive sodium intake and obesity are risk factors for hypertension and cardiovascular disease. The association between sodium intake and obesity is unclear, with few studies assessing sodium intake using 24-h urine collection.

Objectives

Our objective was to assess the association between usual 24-h sodium excretion and measures of adiposity among US adults.

Methods

Cross-sectional data were analyzed from a sample of 730 nonpregnant participants aged 20-69 y who provided up to 2 complete 24-h urine specimens in the NHANES 2014 and had data on overweight or obesity [body mass index (kg/m2) ≥25] and central adiposity [waist circumference (WC): >88 cm for women, >102 cm for men]. Measurement error models were used to estimate usual sodium excretion, and multiple linear and logistic regression models were used to assess its associations with measures of adiposity, adjusting for sociodemographic, health, and dietary variables [i.e., energy intake or sugar-sweetened beverage (SSB) intake]. All analyses accounted for the complex survey sample design.

Results

Unadjusted mean ± SE usual sodium excretion was 3727 ± 43.5 mg/d and 3145 ± 55.0 mg/d among participants with and without overweight/obesity and 3653 ± 58.1 mg/d and 3443 ± 35.3 mg/d among participants with or without central adiposity, respectively. A 1000-mg/d higher sodium excretion was significantly associated with 3.8-units higher BMI (95% CI: 2.8, 4.8) and a 9.2-cm greater WC (95% CI: 6.9, 11.5 cm) adjusted for covariates. Compared with participants in the lowest quartile of sodium excretion, the adjusted prevalence ratios in the highest quartile were 1.93 (95% CI: 1.69, 2.20) for overweight/obesity and 2.07 (95% CI: 1.74, 2.46) for central adiposity. The associations also were significant when adjusting for SSBs, instead of energy, in models.

Conclusions

Higher usual sodium excretion is associated with overweight/obesity and central adiposity among US adults.

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.

Estimated 24-Hour Urinary Sodium and Potassium Excretion in US Adults

Importance

In 2010, the Institute of Medicine (now the National Academy of Medicine) recommended collecting 24-hour urine to estimate US sodium intake because previous studies indicated 90% of sodium consumed was excreted in urine.

Objective

To estimate mean population sodium intake and describe urinary potassium excretion among US adults.

Design, Setting, and Participants

In a nationally representative cross-sectional survey of the US noninstitutionalized population, 827 of 1103 (75%) randomly selected, nonpregnant participants aged 20 to 69 years in the examination component of the National Health and Nutrition Examination Survey (NHANES) collected at least one 24-hour urine specimen in 2014. The overall survey response rate for the 24-hour urine collection was approximately 50% (75% [24-hour urine component response rate] × 66% [examination component response rate]).

Exposures

24-hour collection of urine.

Main Outcomes and Measures

Mean 24-hour urinary sodium and potassium excretion. Weighted national estimates of demographic and health characteristics and mean electrolyte excretion accounting for the complex survey design, selection probabilities, and nonresponse.

Results

The study sample (n = 827) represented a population of whom 48.8% were men; 63.7% were non-Hispanic white, 15.8% Hispanic, 11.9% non-Hispanic black, and 5.6% non-Hispanic Asian; 43.5% had hypertension (according to 2017 hypertension guidelines); and 10.0% reported a diagnosis of diabetes. Overall mean 24-hour urinary sodium excretion was 3608 mg (95% CI, 3414-3803). The overall median was 3320 mg (interquartile range, 2308-4524). In secondary analyses by sex, mean sodium excretion was 4205 mg (95% CI, 3959-4452) in men (n = 421) and 3039 mg (95% CI, 2844-3234) in women (n = 406). By age group, mean sodium excretion was 3699 mg (95% CI, 3449-3949) in adults aged 20 to 44 years (n = 432) and 3507 mg (95% CI, 3266-3748) in adults aged 45 to 69 years (n = 395). Overall mean 24-hour urinary potassium excretion was 2155 mg (95% CI, 2030-2280); by sex, 2399 mg (95% CI, 2253-2545) in men and 1922 mg (95% CI, 1757-2086) in women; and by age, 1986 mg (95% CI, 1878-2094) in adults aged 20 to 44 years and 2343 mg (95% CI, 2151-2534) in adults aged 45 to 69 years.

Conclusions and Relevance

In cross-sectional data from a 2014 sample of US adults, estimated mean sodium intake was 3608 mg per day. The findings provide a benchmark for future studies.

Individual variation in urinary sodium excretion among adolescent girls on a fixed intake

BACKGROUND

According to traditional understanding of sodium homeostasis, nearly all of daily sodium intake is excreted in urine, with intraindividual variability attributed to variability in dietary sodium intake and urine collection errors.

OBJECTIVE

To analyze the variability of urinary sodium in excretion from a balance study with fixed sodium intakes.

METHODS

Daily 24-h urine collections were assessed for sodium, potassium, and creatinine in 22 black and 13 white adolescent girls (11-15 year, BMI 15-29 kg/m) in a randomized, crossover design with controlled diets containing either low (57 mmol/day) or high (167 mmol/day) sodium, each fed for 3 weeks.

RESULTS

Coefficient of variation analysis indicated higher variation in urinary sodium excretion about the mean on low (vs high) sodium (40 vs 32%, P = 0.02) and in black (vs white) girls (42 vs 30%, P < 0.001). A mixed model showed no sodium intake × race interaction. Urinary sodium excretion was not correlated with urinary potassium or creatinine excretion. Excretion of 65 mmol/day (adequate intake) or less was documented on 16% on the days during the high-sodium diet. Reliability of the mean of several urine sodium samples varied from 23% for one sample to 75% for 10 samples for the high-sodium diet.

CONCLUSION

The high intraindividual variability in urinary sodium excretion on a fixed diet highlights the potential for substantial error in (a) using a single 24-h urine collection to estimate an individual's usual sodium intake and (b) relating sodium excretion from a single 24-h collection with outcomes. Further research is warranted to understand the causes of such variation.

Reproducibility of urinary biomarkers in multiple 24-h urine samples

BACKGROUND

Limited knowledge regarding the reproducibility of biomarkers in 24-h urine samples has hindered the collection and use of the samples in epidemiologic studies.

OBJECTIVE

We aimed to evaluate the reproducibility of various markers in repeat 24-h urine samples.

DESIGN

We calculated intraclass correlation coefficients (ICCs) of biomarkers measured in 24-h urine samples that were collected in 3168 participants in the NHS (Nurses' Health Study), NHSII (Nurses' Health Study II), and Health Professionals Follow-Up Study.

RESULTS

In 742 women with 4 samples each collected over the course of 1 y, ICCs for sodium were 0.32 in the NHS and 0.34 in the NHSII. In 2439 men and women with 2 samples each collected over 1 wk to ≥1 mo, the ICCs ranged from 0.33 to 0.68 for sodium at various intervals between collections. The urinary excretion of potassium, calcium, magnesium, phosphate, sulfate, and other urinary markers showed generally higher reproducibility (ICCs >0.4). In 47 women with two 24-h urine samples, ICCs ranged from 0.15 (catechin) to 0.75 (enterolactone) for polyphenol metabolites. For phthalates, ICCs were generally ≤0.26 except for monobenzyl phthalate (ICC: 0.55), whereas the ICC was 0.39 for bisphenol A (BPA). We further estimated that, for the large majority of the biomarkers, the mean of three 24-h urine samples could provide a correlation of ≥0.8 with true long-term urinary excretion.

CONCLUSIONS

These data suggest that the urinary excretion of various biomarkers, such as minerals, electrolytes, most polyphenols, and BPA, is reasonably reproducible in 24-h urine samples that are collected within a few days or ≤1 y. Our findings show that three 24-h samples are sufficient for the measurement of long-term exposure status in epidemiologic studies.

Use of Urine Biomarkers to Assess Sodium Intake: Challenges and Opportunities

This article summarizes current data and approaches to assess sodium intake in individuals and populations. A review of the literature on sodium excretion and intake estimation supports the continued use of 24-h urine collections for assessing population and individual sodium intake. Since 2000, 29 studies used urine biomarkers to estimate population sodium intake, primarily among adults. More than half used 24-h urine; the rest used a spot/casual, overnight, or 12-h specimen. Associations between individual sodium intake and health outcomes were investigated in 13 prospective cohort studies published since 2000. Only three included an indicator of long-term individual sodium intake, i.e., multiple 24-h urine specimens collected several days apart. Although not insurmountable, logistic challenges of 24-h urine collection remain a barrier for research on the relationship of sodium intake and chronic disease. Newer approaches, including modeling based on shorter collections, offer promise for estimating population sodium intake in some groups.

Salt intake in children 10-12 years old and its modification by active working practices in a school garden

OBJECTIVE

The aim of the study was to evaluate the 24-h urinary sodium excretion in children of 10-12 years at a school in the north of Portugal and to examine the influence on salt intake and blood pressure of three different educational interventions for 6 months.

METHODS

Blood pressure (BP) and sodium excretion in 24-h urinary samples (UNa) validated with urinary creatinine were measured in 155 children 10-12 years old belonging to nine classes at baseline and after 6 months of three educational interventions in students from three classes each after parents consent was obtained. Interventions consisted in no additional action [control (CTR)], weekly lessons about the dangers of high salt intake [Theoretical (THEOR)] and both lessons and working practices in the school garden of planting, collection of herbs for salt substitution at home [practical (PRACT)].

RESULTS

At baseline 139 students (76 girls and 63 boys) were eligible showing average 24-h UNa of 132±43 mmol/24 h (mean salt intake of 7.8±2.5 g per day) and BP of 118/62 (13/9) mmHg that did not correlate to each other. At the end of the study, versus baseline, BP decreased by 8.2/6.5 mmHg in CTR (n=31), by 3.8/0.6 mmHg in THEOR (n=43) and by 3.5/0.7 mmHg in PRACT (n=53) and salt intake was reduced by 0.4±2.4 g per day in CTR, by 0.6±3.2 g per day in THEOR and by 1.1±2.5 g per day in PRACT. It was observed that salt intake variation was not independent of the group (CRT, THEOR and PRACT) (χ, 9.982, P=0.041). Salt intake was significantly reduced only in the PRACT group (1.1 g per day) and in the PRACT group the percentage of children who reduced salt intake by at least 1g per day from baseline to the end of the study was significantly higher (50.9%) than that of the other groups, THEOR, 48.8% and CTR, 32.2%.

CONCLUSION

Our data indicates that children 10-12 years old have a high salt intake that is well above the proposed recommendations and that a strategy based on theoretical and practical education may achieve in some children an important reduction in daily salt intake which, if maintained over time, may assume important public health implications. These results suggest that in those children a more complete theoretical and practical intervention is more productive and efficient towards reduction of salt intake than single theoretical or no intervention.

Urinary excretion of sodium and potassium in a screened cohort in Okinawa, Japan

Information regarding daily intake of sodium (Na) is useful for both normotensive and hypertensive subjects. We measured urinary excretion of sodium (U-Na) and urinary excretion of potassium (U-K) to estimate daily salt intake in a cohort of health screening subjects in Okinawa, Japan. Urine samples were obtained from 2,411 subjects (1,554 men and 857 women) who were examined on a half-day dry-doc at the Okinawa General Health Maintenance Association (OGHMA). Four hundred and one subjects were examined twice, once between September and November in 1997, and once between September and November in 1998. The mean U-Na was 182 mEq/day for men and 176 mEq/day for women. The mean U-K was 54 mEq/day for men and 50 mEq/day for women. U-Na was higher in young men, and U-K was lower in young women. In both men and women, smokers had a significantly lower Na excretion compared to nonsmokers. Subjects treated for hypertension had a significantly lower Na excretion (173 mEq/day) compared to subjects not treated for hypertension (192 mEq/day). Our findings suggest that Na excretion in screened subjects in Okinawa is lower than the national average. Sodium excretion, however, was higher in young men than in elderly subjects, and K excretion was lower in young women than in elderly subjects. Both trends are disadvantageous for controlling hypertension.

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.

Avoidance of dietary sodium--a simple questionnaire

Patients who are advised to reduce their sodium intake need intensive counselling and regular feedback on their progress. Urinary tests can indicate a high sodium intake, but the dietary source remains unknown until the patient has answered detailed questions. We have developed a sodium-intake check-list for this purpose and have investigated whether it is comprehensive enough to replace the urinary test. The most heavily-salted foods in the typical Western diet are listed in 21 questions, which are to be answered in relation to the previous three days' intake with a frequency rating of "zero" to "eight or more"; the check-list score is the sum of the scores for all 21 items. For 190 college students who were eating their regular diet, the scores were distributed normally and internally were reliable (Cronbach coefficient alpha = 0.75). They were significantly different (P less than 0.001) from the scores of the 40 persons who were attending a low-sodium advisory service. The range of the urinary sodium excretion rate for 39 persons in the latter group was 9-181 mmol/24 h. The correlation between the urinary sodium excretion results and those of the check-list was r = 0.701, which is an acceptable figure considering that the urine excretion data were, for practical reasons, derived from a single 24-h sample. As the absolute sodium excretion is itself only an estimate of dietary behaviour, we consider that this simple questionnaire, as based on a three-day recall, is useful in the management of patients who are ingesting "salt-free" diets, both as an adjunct and as an alternative to urinary testing in routine clinical use.

Electrolyte excretion in 12-hour urine and in spot urine. Relationship to plasma renin activity and aldosterone concentration in older children

Plasma renin activity (PRA) and urinary electrolyte excretion were measured in 137 healthy children aged 6 to 14 years. Plasma aldosterone concentration (PAC) was measured in 52 of the children. Nocturnal 12-hour urine was collected in 110 of the children. Spot urine was collected on two occasions, once just before lying down, once after 90-min supine rest in another 27. Na/K ratio and fractional Na excretion rate (FENa) in 12-hour urine showed a significant inverse correlation with PRA or PAC. Na excretion (mmol/min, mmol/mmol creatinine), Na/K ratio and FENa in the spot urine following 90 min in a supine position showed a significant inverse correlation with PRA or PAC, but they failed to show a significant relationship to PRA or PAC in the spot urine preceding supine rest. A spot urine after 90 min in the supine position is collected easily and hence most appropriate to study the relationship between Na excretion and PRA or PAC clinically.

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.

Interrelationships between blood pressure, sodium, potassium, serum cholesterol, and protein intake in Japanese

Interrelationships among blood pressure (BP), sodium (Na), potassium (K), dietary protein, and serum cholesterol level (Chol) were examined in 62% (1120) of 1818 Japanese inhabitants of both sexes aged over 30 years who lived in a rural village in Japan. Fasting single-spot urine specimens were collected in the morning to measure Na, K, urea nitrogen (UN), inorganic sulfate (SO4), and creatinine (Cr). The Cr ratios of Na, K, UN, SO4, Na/K, and SO4/UN were analyzed by multiple regression analysis to determine independent associations with BP together with age, obesity index, hematocrit (Hct), Chol, triglyceride (TG), and fasting serum glucose level (Glu). Except for Na/Cr in men, Na/Cr and Na/K were found to be independently and positively related to BP, particularly to systolic BP (SBP). In contrast, K/Cr and SO4/UN (an index related to the dietary score of sulphur-containing amino acids derived mainly from animal protein) were both negatively associated with SBP, and UN/Cr (an index of total protein intake) was positively associated with SBP in men. Chol was linked to BP negatively in men but positively in women. Age, obesity index, TG, and Hct were generally positively and significantly related to BP in both sexes. The results confirmed on epidemiological grounds the positive link of Na and the negative link of K to BP within a single population in Japan. They further suggest, although only in men, that there is a negative relationship of Chol and dietary animal protein with BP.

Left ventricular mass reduction during salt depletion in arterial hypertension

Long-term therapy with antihypertensive agents that reduce sympathetic nervous system activity has been demonstrated by echocardiographic measurements to reverse left ventricular hypertrophy. This investigation evaluated the effects of salt depletion obtained by both chlorthalidone (25 mg/day) and severe restriction of salt intake (about 1016 mg Na+/day) on left ventricular mass (LVM) in as short a time as 12 weeks. Before the study, the patients had been off medication and on a balanced diet without salt restriction for at least 2 weeks; they were then randomly allocated to either the diuretic or low-salt regimen for 6 weeks and finally to alternative treatment according to a crossover model. Blood pressure, body weight, myocardial mass, and noninvasive measurements of left ventricular function (LVF) were determined at baseline and at the end of both periods of treatment. Results were evaluated by two-way analysis of variance in randomized blocks. Systolic and diastolic blood pressure and LVM were significantly and similarly reduced by diuretic therapy or salt restriction. A significant correlation was demonstrated between noninvasive measurements of LVM, expressed as cross-sectional area, and systolic blood pressure. No impairment of LVF could be detected over the treatment period.

Blood pressure in blacks and whites and its relationship to dietary sodium and potassium intake

The 24-hour dietary intake and blood pressure of 1928 black and 9739 white adults derived from the data sets of the first US National Health and Nutrition Examination Survey (NHANES I) of 1971-1974 were analyzed. Contrary to expectation, the absolute and relative intakes of sodium and potassium in blacks were less than those of whites. However, because the difference in potassium was greater than the difference in sodium, blacks did have a significantly higher sodium/potassium ratio than whites. Blacks had significantly higher blood pressure than whites even when adjusted for differences in sodium/potassium ratio. It is concluded that the higher blood pressure and prevalence of hypertension in blacks does not appear to be a function of an absolutely greater dietary sodium intake, but related to a relatively low intake of potassium. It is possible that blacks have a greater sensitivity than whites to the hypertensinogenic effects of sodium which, coupled with the relatively low dietary intake of potassium, accounts for their increased blood pressure.

Hypothesis: discrepancy between intra- and interpopulation studies of the relationship between dietary salt and blood pressure: fact or fiction?

It is a paradox that intra-population studies fail to show significant correlation between sodium excretion and blood pressure while a clear relationship exists in cross-cultural studies. Since daily variation of sodium excretion is high, the discrepancy between the two observations could be due to non-comparable data on sodium excretion. This is a discussion of the hypothesis that the finding of a significant correlation or not between sodium excretion and blood pressure depends on the statistical analysis of the data.

The selective lipid-lowering effect of vegetarianism on low density lipoproteins in a cross-over experiment

In a cross-over experiment the effect of short-term vegetarianism on serum lipids, lipoproteins and apoproteins was studied. The experimental diet was free of animal products, with the exception of skim milk, and consequently low in saturated fat and cholesterol. Fifteen free-living individuals were randomly assigned to 3-week periods on either the experimental diet or a control diet which closely approximated the usual intake in the U.S.A. Significant reductions in total cholesterol (12.5%), low density lipoprotein cholesterol (14.7%), and apo B (13.2%) were observed, accompanied by a non-significant decrease in high density lipoprotein cholesterol (10%), apo A-I (3%) and a non-significant increase in apo-II (4%). These data suggest that a fat-modified diet low in total fat, saturated fat and cholesterol, and moderate (not high) in polyunsaturated fat may not lower HDL-C or its apoproteins as much as a diet high in polyunsaturated fat, while having similar effects on LDL-C, and would therefore be preferable as the basis for primary prevention of atherosclerosis.

Methodological problems in characterizing an individual's plasma glucose level

Two methodological problems in characterizing an individual's plasma glucose level are examined in this study. First, how large is the intra-individual variation of an individual's 1-hr post-load glucose level and for this estimated intra-individual variation what are the probabilities of misclassifying individuals based on a one-time measurement only of glucose level? Second, do different tests-i.e. fasting, 1-hr, 2 hr post-load, GTT-yield consistent ranking for the same individual? The first of these was explored with data on subsamples from the Chicago Peoples Gas Company (PG) study and the Chicago Heart Association Detection Project in Industry (CHA) study; the second, with data from the Chicago Coronary Prevention Evaluation Program (CPEP). For both the PG and CHA studies, the estimated ratios of the intra- to inter-individual variances were generally higher for post-load plasma glucose than blood pressure, heart rate, weight and serum uric acid. The conditional probabilities of misclassifying individuals into quintiles or deciles based on one measurement of 1-hr post-load glucose were also estimated from these data. These estimated probabilities indicated that the possible attenuation due to intra-individual variation cannot abolish a strong association; however, it may create some problem if the relationship is not very strong. Furthermore, both rank correlation and quintile classification analyses show that fasting, 1-hr and 2-hr plasma glucose level characterize individuals differently. Thus it is possible that the inconsistent results of previous studies, all using a one-time measure of plasma glucose, are partially due to the large intra-individual variation of this variable, and the use of methods that are not highly consistent in their classification of individuals.

Methodological assessment of assays for red cell sodium concentration and sodium-dependent lithium efflux

Assays for red cell sodium concentration and sodium-dependent lithium efflux were studied from a methodological point of view. The technical errors for sodium concentration--based on concurrent analysis of randomized blind duplicate samples--was 2.5% and for lithium efflux 6.4%. Based on repeated measures in the same individual, the assays were stable over time and reproducible; individual differences at a mean interval of 16 days were not significantly different. A wait of two hours from time of phlebotomy to analysis yielded a slight (3.8%) but significant fall in the sodium concentration; no further change was found at four hours. No change occurred in the lithium efflux over time. A standardized breakfast containing 664 mg sodium did not affect the measurements when fasting and three-hour postprandial levels were compared. The ratios of intra- to inter-individual variance were small--0.04 for red cell sodium concentration and 0.09 for sodium-stimulated lithium efflux. These assays appear to be reproducible and stable and can be applied in large scale field trials.

The association between urinary sodium excretion and blood pressure in children

This study explored the association between sodium excretion and blood pressure (BP). A new method was used to minimize the measurement error introduced by the large intrinsic variability of 24-hour sodium excretion. The ratio of intra- to interindividual variation was used to estimate the number of measurements needed to characterize the individual. When seven consecutive 24-hour samples were collected from 73 children, ages 11-14 years, a significant correlation between mean individual sodium excretion and BP was demonstrated. The independent relationship persisted when controlling for height, weight, pulse, age, sex and race (p = 0.045), but was eliminated by simultaneously considering mean creatinine excretion. Although the cross-sectional association described is quantitatively weak, a linear relationship between BP and sodium over the range consumed in this society could be important for prevention.

Obesity, sodium intake, and blood pressure in adolescents

It has been postulated that increased dietary sodium associated with greater food intake by obese people is a mechanism for the relationship between obesity and blood pressure (BP). We have evaluated this hypothesis by exploring the interrelationships of measures of obesity, sodium intake, and BP in 248 "normal" adolescents, 16 to 17 years of age. As an index of sodium intake, the sodium excretion in three overnight urine collections was used. As a more specific index of saltiness of diet, we used a ratio of sodium excretion to calorie intake, with calories estimated from 3-day diet records and dietary interview. Body weight and other measures of obesity showed a positive relationship with systolic blood pressure (SBP), but not with diastolic (K5) blood pressure (DBP5). Measures of overnight sodium excretion were positively correlated with body weight and calculated body fat percentage, suggesting that heavier people indeed ingest more sodium. This may result not from increased intake of food per se, but from increased saltiness of diet, since calorie intake did not increase with body weight. No significant relationships were found between BP and concurrent measures of sodium excretion or diet saltiness.

A survey of patterns of nonpharmacologic care for hypertensive patients, including recommendations for their children

To ascertain current approaches of physicians to nutritional-hygienic management of hypertensive patients and their children, a survey was done among a random sample of Chicago-area generalists, internists, and cardiologists. Thirteen items related to advice for patients; two for their children. Of 713 physicians holding M.D. degrees in the sample, 573 (80%) responded. For hypertensive patients, the great majority of physicians indicated that they advise weight loss, avoidance of salt use at table, no smoking, regular exercise, limitation of alcohol intake, and avoidance of stressful situations. Although 98% advised weight loss, a minority responded positively to reduction of carbohydrate and/or fat intake. Only 25% recommended limiting the salt use of children, and only 19% recommended taking the blood pressure of children of hypertensive patients. These data indicate that the majority of Chicago-area practitioners advocate nutritional-hygienic measures for their hypertensive patients. Only a minority, however, apparently advocate primary preventive approaches for the children of hypertensive patients.