Overnight urine collections to estimate sodium intake

Rationale and validation of predicting high sodium intake by spot urinary chloride in patients with chronic kidney disease

OBJECTIVE

To analyze the rationale and evaluate the validity of spot urinary chloride or derived formulas to predict high sodium intake in patients with chronic kidney disease (CKD).

METHODS

We collected consecutive CKD patients at stages 1-4 who were admitted to our Nephrology department in a single center from January 01, 2014, to December 31, 2017, and tested spot and 24-hour urinary analysis on the same day. The feasibility of urinary chloride to predict urinary sodium was firstly analyzed by calculating their correlations. The validity of predicting excessive sodium intake by spot urinary sodium and chloride, two derived formulas based on spot urinary sodium or chloride, and our previous "CKDSALT" equation were accessed. We finally conducted Receiver operating characteristic (ROC) curves to compare their performance in detecting high sodium intake.

RESULTS

All 5204 patients were eventually analyzed. In the derivation cohort (n = 2447), a strong positive linear correlation existed between urinary sodium and chloride in both spot urine (R² = 0.804) and 24-hour urine samples (R² = 0.905), and two predictive equations based on spot urinary sodium or chloride were derived. In the validation cohort (n = 2757), spot urinary sodium and chloride only showed "fair" performance. However, both urinary sodium and chloride equations had a "good" performance in ICC, Pearson's correlation, Bland-Altman plots, and ROC curves, while and CKDSALT equation showed the best performance.

CONCLUSIONS

Spot urinary chloride is a feasible method to predict and monitor high sodium intake in CKD patients, while a novel derived formula could elevate its diagnostic accuracy.

The Urine Anion Gap: Common Misconceptions

Two papers, one in 1986 and another one in 1988, reported a strong inverse correlation between urinary anion gap (UAG) and urine ammonia excretion (UNH₄) in patients with metabolic acidosis and postulated that UAG could be used as an indirect measure of UNH₄ This postulation has persisted until now and is widely accepted. In this review, we discuss factors regulating UAG and examine published evidence to uncover errors in the postulate and the design of the original studies. The essential fact is that, in the steady state, UAG reflects intake of Na, K, and Cl. Discrepancy between intake and urinary output of these electrolytes (i.e, UAG) indicates selective extrarenal loss of these electrolytes or nonsteady state. UNH₄ excretion, which depends, in the absence of renal dysfunction, mainly on the daily acid load, has no consistent relationship to UAG either theoretically or in reality. Any correlation between UAG and UNH₄, when observed, was a fortuitous correlation and cannot be extrapolated to other situations. Furthermore, the normal value of UAG has greatly increased over the past few decades, mainly due to increases in dietary intake of potassium and widespread use of sodium salts with anions other than chloride as food additives. The higher normal values of UAG must be taken into consideration in interpreting UAG.

At-home determination of 24-h urine sodium excretion: Validation of chloride test strips and multiple spot samples

Sodium intake and compliance with dietary sodium modification are typically assessed using a 24-h urine collection analyzed using flame photometry, but this is inconvenient. Spot urine samples have been investigated as alternatives to 24-h collections, but their accuracy is poor. Since sodium and chloride are present in equal concentrations in dietary salt, chloride test strips may provide a suitable proxy for at-home measurement of urine sodium concentrations. We aimed to determine whether (i) chloride test strips provide a reliable measure of urinary sodium compared to the gold standard flame photometry and (ii) multiple spot samples accurately reflect 24-h urine sodium. We recruited 43 participants (19 males) aged 23.6 ± 0.6 years to complete multiple consecutive spot samples (morning and evening) along with a 24-h urine sodium collection. Urine 24-h sodium estimates using chloride test strips (114.6 ± 7.5 mmol/day) were highly correlated (r = 0.900, p < 0.0001) with flame photometry (121.1 ± 7.7 mmol/day) with a bias of -6.53 ± 22.2 mmol/day. Use of a three-spot sample average (both morning and evening spot samples) with a correction factor applied (122.9 ± 4.1 mmol/day) provided a good approximation of 24-h sodium measured by flame photometry (125.6 ± 9.0 mmol/day), with a bias of -2.55 ± 43.9 mmol/day. Chloride test strips applied to a 24-h urine collection provide a highly accurate measure of urinary sodium excretion, permitting convenient at-home sample collection and analysis. Their application to multiple spot samples provides a reasonable approximation of sodium excretion that can be used to conveniently monitor attempts at dietary sodium manipulation, without the inconvenience of completing a 24-h urine sample.

Evaluation of urinary chloride dipsticks for the rapid estimation of hydration status in patients receiving artificial nutrition: Feasibility study

BACKGROUND AND AIMS

The home parenteral nutrition (HPN) population face many challenges, especially with respect to fluid balance management. A low urinary sodium concentration of <20 mmol/L is commonly used as an indicator of dehydration that requires clinical assessment in these patients. The Quantab titrator dipstick measures chloride concentration of a solution and correlates with sodium concentration. We assessed whether it would be feasible to use the Quantab dipstick in the HPN population and explored relationships between Quantab dipstick estimated chloride concentration and quality of life (QOL).

METHODS

Patients on HPN were asked to collect urine samples at 5 specific times points (day 0,7,14, 21 and 28) to send to the laboratory for formal electrolyte analysis. The participant and a member of laboratory staff tested these samples with the Quantab dipstick to estimate urinary chloride concentration. Participants were instructed to complete a QOL questionnaire at each of the 5 time-points in addition to a baseline demographic questionnaire and an end-of-study questionnaire. Six participants completed an interview at the end of the study period. The relationship between participant-derived and laboratory-derived data was assessed using rank correlation coefficients. QOL assessment was correlated with urine dipstick measurements.

RESULTS

10 patients on HPN completed the study. Data on chloride concentration as estimated by the dipstick (assessed by participants and by the laboratory) and sodium concentration from the laboratory were available for 47 urine samples. There was a positive relationship between participant dipstick estimated chloride concentration and laboratory sodium (Kendall's τ = 0.45; P < 0.001; Spearman's r_s = 0.58 P < 0.001; 47 pairs). There was a strong correlation between chloride concentrations estimated by dipstick in the laboratory and by participants (Kendall 0.58 p < 0.001, Spearman's 0.69 p < 0.001; 47 pairs). In exploratory analyses, there was no relationship between QOL and dipstick estimated chloride concentration. Participants had no issues collecting urine samples but some difficulties were reported with determining the dipstick reading.

CONCLUSIONS

Patients on HPN are able to collect urine specimens, complete QOL questionnaires, and are capable of using the Quantab dipstick to estimate urinary chloride concentration. The Quantab dipstick correlates with laboratory measured sodium and chloride concentrations. Further work is required to fully establish whether this point-of-care test could be used to guide fluid balance management in the HPN population.

Reducing salt intake by urine chloride self-measurement in non-compliant patients with chronic kidney disease followed in nephrology clinics: a randomized trial

BACKGROUND

Adherence to low salt diets and control of hypertension remain unmet clinical needs in chronic kidney disease (CKD) patients.

METHODS

We performed a 6-month multicentre randomized trial in non-compliant patients with CKD followed in nephrology clinics testing the effect of self-measurement of urinary chloride (69 patients) as compared with standard care (69 patients) on two primary outcome measures, adherence to a low sodium (Na) diet (<100 mmol/day) as measured by 24-h urine Na (UNa) excretion and 24-h ambulatory blood pressure (ABPM) monitoring.

RESULTS

In the whole sample (N = 138), baseline UNa and 24-h ABPM were143 ± 64 mmol/24 h and 131 ± 18/72 ± 10 mmHg, respectively, and did not differ between the two study arms. Patients in the active arm of the trial used >80% of the chloride strips provided to them at the baseline visit and at follow-up visits. At the third month, UNa was 35 mmol/24 h (95% CI 10.8-58.8 mmol/24 h; P = 0.005) lower in the active arm than the control arm, whereas at 6 months the between-arms difference in UNa decreased and was no longer significant [23 mmol/24 h (95% CI -5.6-50.7); P = 0.11]. The 24-h ABPM changes as well as daytime and night-time BP changes at 3 and 6 months were similar in the two study arms (Month 3, P = 0.69-0.99; Month 6, P = 0.73-0.91). Office BP, the use of antihypertensive drugs, estimated Glomerular Filtration Rate (eGFR) and proteinuria remained unchanged across the trial.

CONCLUSIONS

The application of self-measurement of urinary chloride to guide adherence to a low salt diet had a modest effect on 24-h UNa and no significant effect on 24-h ABPM.

Change in mean salt intake over time using 24-h urine versus overnight and spot urine samples: a systematic review and meta-analysis

Background

Little is known about the capacity of overnight and spot urine samples to estimate changes in mean salt intake over time. The objective of this review was to compare the estimates of change in mean population salt intake based on 24-h urine and overnight/spot urine samples.

Methods

Studies were systematically identified through searches of peer-reviewed databases (Medline, Embase, Global Health, Cochrane Central Register of Controlled Trials, and Cochrane Database of Systematic Reviews) and grey literature. Studies that reported estimates of mean salt intake for at least two time points based on both 24-h and overnight/spot urines were deemed eligible. The capacity of overnight/spot urine samples to estimate the change in mean salt intake was assessed both at the individual-study level and overall through random-effects meta-analyses. The level of heterogeneity was assessed through the I² statistic. Subgroup and sensitivity analyses were conducted to explore possible sources of heterogeneity, and check the robustness of the findings from the primary analysis.

Results

A total of 1244 records were identified, 50 were assessed as full text, and 14 studies met the criteria, capturing data on 7291 participants from seven countries. Nine and five studies collected overnight and spot urines, respectively. The comparison of the change in mean salt intake between 24-h and overnight/spot urines showed some inconsistencies at the individual study-level. The pooled mean change in salt intake was − 0.43 g/day (95% CI − 1.16 to 0.30; I² = 95%) using 24-h urines, and − 0.22 g/day (− 0.65 to 0.20; I² = 87%) using overnight/spot urines, with a pooled difference-in-differences between the two methods of 0.27 g/day (− 0.23 to 0.77; I² = 89%). Subgroup analyses showed substantial heterogeneity for most subgroups. Sensitivity analyses did not change the effect observed in the primary analysis.

Conclusion

The evidence for the capacity of overnight/spot urines to estimate changes in mean salt intake over time is uncertain. More research where overnight/spot urines are collected in parallel with 24-h urines is needed to enable a more in-depth evaluation of these alternative approaches to estimating change in mean salt intake.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12937-020-00651-8.

Urine chloride self-measurement to monitor sodium chloride intake in patients with chronic kidney disease

Background Excessive sodium intake is a risk factor for hypertension, cardiovascular disease and the risk for kidney failure in chronic kidney disease (CKD) patients. Methods We tested the diagnostic performance and the feasibility of an inexpensive method based on urine chloride strips for self-monitoring sodium intake in a series of 72 CKD patients. Results Twenty-four hour urinary chloride as measured by the reactive strips and 24 h urinary sodium were interrelated (r=0.59, p<0.001). Forty-nine out of 72 patients (78%) had a 24 h urinary sodium >100 mmol/24 h, i.e. the upper limit recommended by current CKD guidelines. The strip method had 75.5% sensitivity and 82.6% specificity to correctly classify patients with urine sodium >100 mmol/24 h. The positive and the negative predictive values were 90.2% and 61.3%, respectively. The overall accuracy (ROC curve analysis) of urine chloride self-measurement for the >100 mmol/24 h sodium threshold was 87% (95% CI: 77%-97%). The large majority of patients (97%) perceived the test as useful to help compliance with the prescribed dietary sodium and considered the test as simple and of immediate application (58%) or feasible but requiring attention (39%). Conclusions A simple and inexpensive test for urine chloride measurement has a fairly good performance for the diagnosis of excessive sodium intake. The test is feasible and it is perceived by CKD patients as helpful for enhancing compliance to the dietary sodium recommendations. The usefulness of this test for improving hypertension control in CKD patients will be tested in a clinical trial (Clinicaltrials.gov RF-2010-2314890).

Dietary reference values for chloride

Following a request from the European Commission, the EFSA Panel on Nutrition, Novel Foods and Food Allergens (NDA) has derived dietary reference values (DRVs) for chloride. There are no appropriate biomarkers of chloride status, no balance studies and no adequate evidence on the relationship between chloride intake and health outcomes that can be used to set DRVs for chloride. There is a close relationship between sodium and chloride balances in the body. Sodium chloride is the main source of both electrolytes in European diets and similar urinary excretion levels of sodium and chloride (on a molar basis) are typically observed in Western populations. Hence, the Panel considered that reference values for chloride can be set at values equimolar to the reference values for sodium for all population groups, and are as follows: 1.7 g/day for children aged 1–3 years, 2.0 g/day for children aged 4–6 years, 2.6 g/day for children aged 7–10 years, 3.1 g/day for children aged 11–17 years and 3.1 g/day for adults including pregnant and lactating women. Consistent with the reference values for sodium, these levels of chloride intake are considered to be safe and adequate for the general EU population, under the consideration that the main dietary source of chloride intake is sodium chloride. For infants aged 7–11 months, an adequate intake of 0.3 g/day is set.

This publication is linked to the following EFSA Supporting Publications articles: http://onlinelibrary.wiley.com/doi/10.2903/sp.efsa.2019.EN-1679/full, http://onlinelibrary.wiley.com/doi/10.2903/sp.efsa.2017.e15121/full

This publication is linked to the following EFSA Journal article: http://onlinelibrary.wiley.com/doi/10.2903/j.efsa.2019.5778/full

Can Quantab titrator sticks reliably predict urinary sodium?

BACKGROUND & AIMS

Urinary sodium concentration is a commonly used marker for extracellular fluid depletion which is often associated with dehydration. A point of care test for urinary sodium may reduce delays in clinical decision making by offering more timely guidance leading to improved salt and fluid management. We compared laboratory assessed urinary sodium with a potential point of care measure of urinary chloride in a variety of in- and outpatient specialities, to explore its use as an indicator of low urine sodium.

METHODS

Urinary chloride concentrations were estimated using a Quantab titrator stick in samples from patients that had been sent for urinary sodium assays. We validated the results of this titrator stick with laboratory-assessed sodium concentrations by deriving correlation coefficients between these methods and using limits of agreement testing. We determined the optimal titrator stick cut-point for identifying low urinary sodium (urinary sodium <20 mmol/L) by maximising the product of the sensitivity and specificity. This level of urinary sodium was used to mirror the British Society of Gastroenterology guidance on short bowel patients Nightingale and Woodward, 2006.

RESULTS

We obtained laboratory urinary sodium concentration and Quantab stick chloride measures on 127 samples. Twenty three percent had a urinary sodium below 20 mmol/L so were regarded as biochemically dehydrated. A threshold of <4.3 on the Quantab scale had a positive predictive value for low sodium of 56% (95%CI 40%-71%) and a negative predictive value of 94% (95%CI 87%-98%).

CONCLUSIONS

These data suggest that the Quantab stick could be used as a point of care test to aid fluid and salt management decisions in an outpatient setting. Further work to explore the use of the titrator stick in specific patient populations at risk of salt and water depletion is justified.

Increased Aldosterone Release During Head-Up Tilt in Early Primary Hypertension

BACKGROUND

Hyperaldosteronism is well known cause of secondary hypertension. However, the importance of aldosterone for the much larger group of patients with primary hypertension is less clear. We hypothesized that in young subjects with primary hypertension, the rise of plasma aldosterone levels in response to head-up tilt testing as a stress stimulus is exaggerated.

METHODS

Hemodynamics (blood pressure (BP), heart rate (HR), cardiac index (CI), and total peripheral vascular resistance index (TPRI), all by TaskForce monitor) and hormones (plasma renin activity (PRA), angiotensin II (Ang II), aldosterone) were measured before and during 30 minutes of head-up tilt in 45 young hypertensive and 45 normotensive subjects.

RESULTS

BP, HR, CI, and TPRI all increased in response to head-up tilt, with no difference between groups. There was no difference in baseline PRA, Ang II, and aldosterone between groups. During head-up tilt, PRA, and Ang II levels increased similarly. However, aldosterone levels increased to a greater extent in the hypertensive vs. normotensive subjects (P = 0.0021).

CONCLUSIONS

Our data suggest that an increased release of aldosterone in response to orthostatic stress is a feature of early primary hypertension. The similar increase in PRA and Ang II suggests a potential role for secretagogues of aldosterone other than Ang II in this response. In addition to its established role in secondary hypertension, dysregulation of aldosterone release might contribute to the development of primary arterial hypertension.

Educating restaurant owners and cooks to lower their own sodium intake is a potential strategy for reducing the sodium contents of restaurant foods: a small-scale pilot study in South Korea

BACKGROUND/OBJECTIVES

This study was conducted to evaluate the feasibility of a sodium reduction program at local restaurants through nutrition education and examination of the health of restaurant owners and cooks.

SUBJECTS/METHODS

The study was a single-arm pilot intervention using a pre-post design in one business district with densely populated restaurants in Seoul, South Korea. The intervention focused on improving nutrition behaviors and psychosocial factors through education, health examination, and counseling of restaurant personnel. Forty-eight restaurant owners and cooks completed the baseline survey and participated in the intervention. Forty participants completed the post-intervention survey.

RESULTS

The overweight and obesity prevalences were 25.6% and 39.5%, respectively, and 74.4% of participants had elevated blood pressure. After health examination, counseling, and nutrition education, several nutrition behaviors related to sodium intake showed improvement. In addition, those who consumed less salt in their baseline diet (measured with urine dipsticks) were more likely to agree that providing healthy foods to their customers is necessary. This study demonstrated the potential to reduce the sodium contents of restaurant foods by improving restaurant owners' and cooks' psychological factors and their own health behaviors.

CONCLUSIONS

This small pilot study demonstrated that working with restaurant owners and cooks to improve their own health and sodium intake may have an effect on participation in restaurant-based sodium reduction initiatives. Future intervention studies with a larger sample size and comparison group can focus on improving the health and perceptions of restaurant personnel in order to increase the feasibility and efficacy of restaurant-based sodium reduction programs and policies.

Reliable Quantification of the Potential for Equations Based on Spot Urine Samples to Estimate Population Salt Intake: Protocol for a Systematic Review and Meta-Analysis

Background

Methods based on spot urine samples (a single sample at one time-point) have been identified as a possible alternative approach to 24-hour urine samples for determining mean population salt intake.

Objective

The aim of this study is to identify a reliable method for estimating mean population salt intake from spot urine samples. This will be done by comparing the performance of existing equations against one other and against estimates derived from 24-hour urine samples. The effects of factors such as ethnicity, sex, age, body mass index, antihypertensive drug use, health status, and timing of spot urine collection will be explored. The capacity of spot urine samples to measure change in salt intake over time will also be determined. Finally, we aim to develop a novel equation (or equations) that performs better than existing equations to estimate mean population salt intake.

Methods

A systematic review and meta-analysis of individual participant data will be conducted. A search has been conducted to identify human studies that report salt (or sodium) excretion based upon 24-hour urine samples and spot urine samples. There were no restrictions on language, study sample size, or characteristics of the study population. MEDLINE via OvidSP (1946-present), Premedline via OvidSP, EMBASE, Global Health via OvidSP (1910-present), and the Cochrane Library were searched, and two reviewers identified eligible studies. The authors of these studies will be invited to contribute data according to a standard format. Individual participant records will be compiled and a series of analyses will be completed to: (1) compare existing equations for estimating 24-hour salt intake from spot urine samples with 24-hour urine samples, and assess the degree of bias according to key demographic and clinical characteristics; (2) assess the reliability of using spot urine samples to measure population changes in salt intake overtime; and (3) develop a novel equation that performs better than existing equations to estimate mean population salt intake.

Results

The search strategy identified 538 records; 100 records were obtained for review in full text and 73 have been confirmed as eligible. In addition, 68 abstracts were identified, some of which may contain data eligible for inclusion. Individual participant data will be requested from the authors of eligible studies.

Conclusions

Many equations for estimating salt intake from spot urine samples have been developed and validated, although most have been studied in very specific settings. This meta-analysis of individual participant data will enable a much broader understanding of the capacity for spot urine samples to estimate population salt intake.

Effects of a behavioral intervention that emphasizes spices and herbs on adherence to recommended sodium intake: results of the SPICE randomized clinical trial

BACKGROUND

For decades, dietary sodium intake in the United States has remained high, and few studies have examined strategies for maintaining recommended intakes.

OBJECTIVE

We examined the effects of a behavioral intervention, which emphasized spices and herbs, on the maintenance of sodium intake at the recommended intake of 1500 mg/d in individuals to whom the US Dietary Guidelines for Americans apply.

DESIGN

We conducted a 2-phase study that included adults ≥18 y of age for whom Dietary Guidelines for Americans recommends 1500 mg Na/d. The study was conducted in Baltimore, Maryland, from 2012 to 2014. In phase 1, 55 individuals consumed a low-sodium diet for 4 wk. Participants were provided all foods, snacks, and calorie-containing drinks. In phase 2, 40 participants from phase 1 were randomly assigned to either a behavioral intervention to reduce sodium intake (n = 20) or a self-directed control group (n = 20) for 20 wk. The primary study outcome was the change in mean 24-h urinary sodium excretion during phase 2. Linear regression analyses were used to determine intervention effects on urinary sodium excretion.

RESULTS

Participant characteristics were as follows: women: 65%; African American: 88%; hypertension: 63%; diabetes: 18%; mean age: 61 y; and mean body mass index (in kg/m(2)): 30. At the end of phase 2, mean 24-h sodium excretion was lower in the behavioral intervention than in the self-directed group (mean difference: -956.8 mg/d; 95% CI: -1538.7, -374.9 mg/d) after sodium intake at screening was controlled for (P = 0.002). These findings persisted in sensitivity analyses that excluded potentially incomplete urine collections [Mage's equation mean difference: -1090 mg/d (P = 0.001); Joosens' equation mean difference: -796 mg/d (P = 0.04)].

CONCLUSIONS

A multifactorial behavioral intervention emphasizing spices and herbs significantly reduced sodium intake. Because of the ubiquity of sodium in the US food supply, multilevel strategies addressing individual behaviors and the food supply are needed to improve adherence to recommendations. This trial was registered at clinicaltrials.gov as NCT01615159.

A pilot study to validate a standardized one-week salt estimation method evaluating salt intake and its sources for family members in China

The objective of this study was to develop a new method named the “one-week salt estimation method” that could estimate an individual’s salt intake and the sources of salt in the diet, and to evaluate this new method with a 24-h urine collection. The new method estimates salt intake from: (1) household cooking by weighing the family salt container and other high-salt condiments or sauces at the beginning and end of a week; (2) processed food according to established China food composition figures; and (3) cafeteria or restaurant meals using the results of previous studies. Consumption of salt additives and major salt contained foods and salt intake related eating habits were collected using a structured simple seven-day questionnaire. In order to validate the method, we studied 37 individuals from 11 families using the new method and 26 of these participants collected seven concurrent 24-h urine samples. The average salt intake for the 26 participants was 15.6 ± 5.5 g/person/day (mean ± standard deviation) by the 24-h urine collection and 13.7 ± 6.5 g/person/day by the new method. The difference was 1.8 ± 4.2 g/day/person (p = 0.037). The Pearson correlation coefficient was 0.762 (p < 0.001) and the partial correlation coefficient was 0.771 (p < 0.001) when adjusted for family code. Bland-Altman Plot showed the average of the difference between the two methods was −1.83, with 95% limits of −10.1 to 6.5 g/person/day. The new method showed that 43.7% of salt intake came from household cooking (33.5% from cooking salt, 10.2% from other condiments and sauces), 12.9% from processed food, and 43.4% from eating out. In conclusion, despite its limitations of underestimating salt intake, the “one-week salt estimation method” is easier for people to implement and is likely to provide useful information that highlights the excessively high intake of salt and its sources, and in turn is helpful in guiding dietary salt reduction.

Genetic and environmental influences on sodium intake determined by using half-day urine samples: the Healthy Twin Study

BACKGROUND

Salt is essential in our diet, but excess intake is a well-established risk factor for hypertension. The presence and importance of genetic contributions to salt intake, however, are not well understood.

OBJECTIVE

The aim of this study was to examine whether a genetic predisposition and an environmental influence exist for sodium intake and salt habit.

DESIGN

In a twin-family cohort, half-day urine samples from 1204 individuals (133 pairs of monozygotic twins, 29 pairs of dizygotic twins, and 880 singletons) were collected to assess 24-h sodium intakes. Daily total sodium intake, sodium density per calorie (Na-D), and salt habit questions were analyzed with adjustment for other epidemiologic characteristics. We calculated heritability (h2) and intraclass correlations to examine the genetic and shared environmental contributions to total sodium intake traits.

RESULTS

The average sodium intake was 208.4 ± 107.0 mmol/d. Men had a higher absolute sodium intake (242.6 ± 117.4 mmol/d), but Na-D did not differ by sex. Moderate genetic influences existed (h2 = 0.31-0.34) for sodium intake and Na-D. We also found that sharing current residence rather than being a family member explained 22% of the variance in Na-D.

CONCLUSION

Our findings suggest that both genetic predisposition and shared environment contribute to sodium intakes and salt habits alike.

Reducing salt intake for prevention of cardiovascular diseases in high-risk patients by advanced health education intervention (RESIP-CVD study), Northern Thailand: study protocol for a cluster randomized trial

BACKGROUND

Decreasing salt consumption can prevent cardiovascular diseases (CVD). Practically, it is difficult to promote people's awareness of daily salt intake and to change their eating habits in terms of reducing salt intake for better cardiovascular health. Health education programs visualizing daily dietary salt content and intake may promote lifestyle changes in patients at high risk of cardiovascular diseases.

METHODS/DESIGN

This is a cluster randomized trial. A total of 800 high-CVD-risk patients attending diabetes and hypertension clinics at health centers in Muang District, Chiang Rai province, Thailand, will be studied with informed consent. A health center recruiting 100 participants is a cluster, the unit of randomization. Eight clusters will be randomized into intervention and control arms and followed up for 1 year. Within the intervention clusters the following will be undertaken: (1) salt content in the daily diet will be measured and shown to study participants; (2) 24-hour salt intake will be estimated in overnight-collected urine and the results shown to the participants; (3) a dietician will assist small group health education classes in cooking meals with less salt. The primary outcome is blood pressure change at the 1-year follow-up. Secondary outcomes at the 1-year follow-up are estimated 24-hoursalt intake, incidence of CVD events and CVD death. The intention-to-treat analysis will be followed.Blood pressure and estimated 24-hour salt intake will be compared between intervention and control groups at the cluster and individual level at the 1-year follow-up. Clinical CVD events and deaths will be analyzed by time-event analysis. Retinal blood vessel calibers of CVD-risk patients will be assessed cross-sectionally. Behavioral change to reduce salt intake and the influencing factors will be determined by structured equation model (SEM). Multilevel regression analyses will be applied. Finally, the cost effectiveness of the intervention will be analyzed.

DISCUSSION

This study is unique as it will recruit the individuals most vulnerable to CVD morbidity and mortality by applying the general Framingham CVD risk scoring system. Dietary salt reduction will be applied as a prioritized, community level intervention for the prevention of CVD in a developing country.

TRIAL REGISTRATION

ISRCTN39416277.

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.

Are overnight urinary indicators associated with morning blood pressure in the elderly?

Recent reports suggest that high blood pressure (BP) during the night is associated with hypertensive organ damage, and that increased BP in the morning is closely related to the incidence of stroke and ischemic heart disease. The aim of this study was to investigate the relationships between overnight urinary indicators and 24-hour (24-h) BP, especially in the morning and during sleep in the elderly. A total of 85 volunteers (males 43, females 42), aged between 51 and 76 years and not taking any antihypertensive medications, participated in this study. Their 24-h BP was measured by ambulatory BP monitoring every 30-minute using a TERUMO ES-H531 system. Overnight urine samples were collected using a proportional urine-sampling device, Urine mate P. Overnight sodium (UNa(n)) and potassium (UKn) excretions were measured by an ion electrode method. Simple linear regression analyses showed that systolic blood pressure (SBP) in the morning and diastolic blood pressure (DBP) during sleep were negatively related with overnight urinary weight standardized for body weight (UW(n)/BW). Multiple regression analyses showed that SBP during the morning and during sleep was positively related to UNa(n) and negatively related to UW(n)/BW. We also found a negative relationship between SBP during sleep and UK(n). The study suggested that urine weight adjusted for BW was negatively related with 24-h BP, especially morning BP. Sodium excretion combined with a large volume of urine proportional to body weight may prevent increases in BP, especially in the morning.

Trial design: blood pressure control and weight gain prevention in prehypertensive and hypertensive smokers: the treatment and prevention study

BACKGROUND

Cigarette smokers with elevated blood pressure (BP) are at substantially higher risk for cardiovascular events compared to normotensive smokers. Although smoking cessation should be a primary treatment goal for these patients, increases in body weight accompanying smoking abstinence may further increase BP. Intervention strategies that facilitate smoking cessation and modify adverse changes in body weight and BP are needed.

METHODS

We describe an ongoing multi-site, two-phase, five-year randomized clinical trial. Participants are cigarette smokers with Prehypertension or Stage I Hypertension. In the first phase, participants receive a smoking cessation intervention combining behavioral counseling and nicotine replacement in an open-label fashion. In the second phase, participants who successfully quit smoking are randomly assigned to one of three lifestyle interventions: 1) weight gain prevention, 2) blood pressure control, or 3) usual lifestyle. Participants are followed for one year to assess changes in blood pressure, body weight, dietary intake, and physical activity.

CONCLUSIONS

Results from the proposed study will provide important insights into the efficacy of various approaches to lifestyle modification in smokers at increased risk for cardiovascular events.

A 4-Day Sodium-Controlled Diet Reduces Variability of Overnight Sodium Excretion in Free-Living Normotensive Adolescents

The present analysis examined changes in the variability of overnight sodium excretion in 84 free-living adolescents (ages 15 to 19 years) on a 4-day sodium-controlled diet in which foods provided were selected by adolescents from an extensive list of menu items. The only selection criterion imposed was that foods selected for each day contain 4,000+/-200 mg sodium. Adolescents collected overnight urine samples. Repeated measures analysis of variance tested the effect of diet day on overnight sodium excretion, overnight urinary sodium concentration, and overnight urinary volume. Variance ratio test evaluated changes in overnight sodium excretion variance across days. Day 4 overnight sodium excretion was statistically lower than days 1 to 3 (1.84 vs 6.54, 5.94, and 5.52 mEq/h [1.84 vs 6.54, 5.94, and 5.52 mmol/h]). Day 4 overnight urinary sodium concentration was lower than days 1 to 3 (32.16 vs 119.64, 109.61, and 111.32 mEq/L [32.16 vs 119.64, 109.61, and 111.32 mmol/L]). The variance of overnight sodium excretion from day 1 to day 4 was reduced 10-fold from 20.1 mEq/h (20.1 mmol/h) to 1.90 mEq/h (1.90 mmol/h). Daily overnight urine volumes remained constant, averaging 451.7 mL/day. The dietary protocol successfully reduced the variability of sodium intake as estimated by overnight sodium excretion in free-living adolescents. The protocol could be expanded to include baseline values, additional days of sodium control, and varying levels of dietary sodium intake.

Self-monitoring of home blood pressure with estimation of daily salt intake using a new electrical device

We investigated a simple device to monitor daily salt intake at home and examined the relationship between salt excretion and morning blood pressure in order to enable patients to better manage daily salt intake and hypertension. The correlation between 24-h urinary salt excretion and measured value with salt monitor from overnight urine was significant (n = 224, r = 0.72, P < 0.001). A total of 46 volunteers participated for more than 3 weeks by measuring daily salt intake and morning blood pressure. The relationship between predicted daily salt excretion and blood pressure was examined with use of 3-day moving average. Mean salt excretion and systolic blood pressure (SBP) significantly decreased by the end of the trial (i.e., salt excretion decreased from 158+/-31 to 149+/-30 mmol/day and SBP from 137+/-17 to 133+/-16 mm Hg). Of 46 participants, 18 (39%) had a significant correlation between predicted daily salt excretion and blood pressure (r > 0.4, P < 0.05, n > 21), indicating sodium sensitivity. An additional 17% had a positive correlation that did not reach statistical significance (0.2 < r < or = 0.4), and the remaining 44% had no correlation (r < or = 0.2). Mean decrease in blood pressure per decrease in salt (g) (17 mmol) intake in the 18 participants with a significant correlation was 3.3 mm Hg (SBP) and 1.5 mm Hg (diastolic blood pressure), which was higher than that reported for other studies. Hypertensive patients not using medication showed the largest decrease. We conclude that daily monitoring of salt intake and morning blood pressure will be useful for management of hypertension.

Estimation of 24-h urinary sodium excretion using lean body mass and overnight urine collected by a pipe-sampling method

BACKGROUND Although salt intake can be estimated from 24-h urinary sodium excretion (Na24 ), for a long time there has been no precise and easy method for its measurement.

OBJECTIVE

To investigate the possibility of estimating Na24 using pipe-sampling of overnight urine and lean body mass.

PARTICIPANTS AND METHODS

Body height, body weight and body fat determined by bioelectrical impedance (lean body mass = body weight body fat) was measured in 351 healthy individuals (126 men, 225 women). Twenty-four-hour urine was collected and creatinine and sodium were measured. To predict 24-h urinary creatinine excretion (Cr24 ), the relationship between Cr24 and lean body mass was investigated. Both 24-h urine and overnight urine specimens were collected in 149 individuals (71 men, 78 women) using a sampling pipe (semi-automatic proportional urine sampling device; height 16 cm, width 1.5 cm). Multiple regression analysis was used to estimate Na24.

RESULTS

The prediction of Cr24 (Pr.UCr24 ) was derived from lean body mass. Using Pr.UCr24 and the overnight urinary Na/Cr excretion ratio (Na n /Cr n ), Na24 was estimated as 0.634 (Na n /Cr n ) Pr.UCr 24 + 104.7 mmol/day for men and 0.682 (Na n /Cr n ) Pr.UCr 24 + 62.6 mmol/day for women. The correlation coefficient (r) between true Na24 and Na24 estimated by these formulae was r = 0.78 ( P<0.001; mean difference SD-0.03 39.0 mmol/day).

CONCLUSIONS

A new pipe-sampling method using overnight urine and lean body mass was easy and reliable for the estimation of Na 24. Furthermore, this method is convenient and may enable counselling on salt intake.

Choose and prepare foods with less salt: dietary advice for all Americans

The Nutrition and Your Health: Dietary Guidelines for Americans have included dietary guidance on salt and sodium since they were first released in 1980. This paper briefly reviews the impetus for including sodium guidelines, changes in them over time and factors influencing these changes. Although guidance appears to have changed little over the five editions, differences in wording reflect changes in knowledge of the link between sodium and blood pressure, a shift in public health policy toward prevention and increased consumption of processed and prepared foods. We examine methods to monitor sodium intake and assess whether Americans are following these guidelines. Available data indicate that American adolescents and adults are consuming more sodium than recommended and are unable to judge whether the amount of sodium in their diet is appropriate. Although Americans avoid adding salt to food at the table, their efforts may have little effect given that the majority of salt consumed is added during commercial processing and preparation. Thus, changes to the Dietary Guidelines that emphasize the major sources of sodium in U.S. diets and advice to "choose and prepare foods with less salt" may help all Americans meet recommended sodium intake levels in the future.

Do hypertensive patients have a different diurnal pattern of electrolyte excretion?

Studies generally indicate that excretion of sodium, potassium, and water is greater during the day than during the night. To determine whether hypertensive patients exhibit this same pattern of excretion, diurnal variations in excretion of sodium, potassium, creatinine, and water were examined in 107 hypertensive men and women from a clinical trial on control of hypertension by nonpharmacological means--the Hypertension Control Program. Each participant provided two carefully timed 24-hour urine collections divided into daytime and overnight specimens. The median ratios of 24-hour to 8-hour overnight excretion were 2.84, 3.95, 2.99, and 2.77 for sodium, potassium, creatinine, and water, respectively. Thus, more than half of this hypertensive group exhibited a greater rate of sodium and water excretion during sleep than during daytime hours, a reversal of the usual pattern. When the group was subdivided based on age, sex, race, trial randomization group, use of diuretics, and hypertension severity, women had significantly lower ratios of 24-hour to overnight excretion for sodium and water than men and blacks had significantly lower 24-hour to overnight ratios for water and potassium than whites. When the 24-hour to overnight ratios for these hypertensive patients were compared with those for a group of 30 men and women with high-normal blood pressure, those with high-normal blood pressure had significantly larger ratios for sodium and water excretion than the hypertensive group. The results of this study suggest that hypertensive patients may have a different diurnal pattern of sodium and water excretion than normotensive subjects and that further research is needed to clarify this issue.

Bedside urinary chloride measurement: assessment in the acute setting

In 100 random urine samples from hospitalized patients, the results of a rapid bedside test for urinary chloride (Quantab chloride titrators) were compared with those of the hospital laboratory. Renal chloride retention (less than or equal to 20 mEq/L) was recognized using the titrator in 25 of 27 samples. There were no falsely low results in samples containing greater than 20 mEq/L by laboratory analysis. The titrator strips should aid in rapid diagnosis of conditions in which the recognition of renal salt retention is important.

Home testing of urine chloride to estimate dietary sodium intake: evaluation of feasibility and accuracy

To estimate the utility of quantab chloride titrators, a product of Ames Laboratories, in estimating urine and diet sodium, two study populations were examined. The first consisted of 56 normotensive individuals providing timed, overnight, urine collections and 24-hour food records as part of the baseline assessment for a hypertension prevention study. The second group consisted of 19 study employees, who were instructed to maintain a low sodium diet, and to self-assess diet sodium and urine chloride at home. Results showed that urine chloride measured by quantab was highly correlated with urine sodium. Neither urine chloride nor urine sodium correlated highly with the previous day's intake of dietary sodium as measured by food record. It is estimated that five overnight urine samples would be required to estimate food record sodium to within +/- 25 mEq in individuals with relatively stable diets. Home assessment of urine chloride is feasible. It seems likely that clinical procedures which combine self-monitoring of dietary sodium intake by food record and home measurement of urine chloride concentration would be an effective way of providing persons prescribed sodium restricted diets with continuous and convergent feedback about their success in dietary adherence.

Management of hypertension in high school students by using new salt titrator tape

In a blood pressure screening program involving 6589 high school students, 180 male (4.7%) and 17 female (0.6%) students were identified as borderline hypertensive. The 174 hypertensive male adolescents studied further showed pathophysiological features such as a significantly higher frequency of obesity, higher 24-hour urinary sodium excretion, higher hematocrit value, higher sodium and lower potassium concentration in red blood cells, and higher ouabain-sensitive sodium efflux compared with the control group (231 male students; p less than 0.05). When used alone, the ordinary 10-week period of counseling about a low salt diet failed to significantly reduce the blood pressure of hypertensive students. However, when education and counseling efforts were combined with self-monitoring of salt (chloride) excretion in overnight urine samples using a new salt titrator tape developed in our laboratory, 24-hour urinary sodium excretion, weight, and blood pressure decreased significantly over 10 weeks (mean reduction: 52 mEq/day for 24-hour urinary sodium excretion, 1.7 kg for weight, 12/7 mm Hg for blood pressure). These results indicate that blood pressure of borderline hypertensive adolescents could be effectively reduced with this nonpharmacological method of dietary education. Such systematic management might be of importance for the prevention of essential hypertension.

Intra- and interindividual variability in sodium intake in normal subjects and in patients with renal insufficiency

To elucidate patterns of dietary sodium ingestion in free-living subjects, we collected 26 consecutive 24-hour urine specimens in 18 subjects who had not received instructions to limit the sodium content of their diets, and who were not aware that sodium intake would be estimated from the collections. Nine subjects with plasma creatinine values less than 2 mg/dL had a mean 24-hour UNaV of 156 mEq/d, with an interindividual variability of SD +/- 38 mEq. Their intraindividual variability was 61 mEq. Nine subjects with creatinine values greater than 2 mg/dL had a mean 24-hour UNaV of 108 mEq/d (P less than 0.05). The intraindividual variability of these subjects was 39 mEq/d. Subjects with normal renal function ingested more sodium than subjects with renal insufficiency, although the variability in both groups was extensive. These data confirm and extend earlier observations and illustrate the difficulty in identifying biologic correlations in the presence of considerable intraindividual variability. They underscore the futility of estimating mean dietary sodium intake with a single or occasional 24-hour urine collection in both normal subjects and patients with renal insufficiency.

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.

The effect of chloride-containing potassium supplements on chloride titrator estimates of dietary sodium intake

To examine the effect of chloride-containing potassium supplements on chloride titrator estimates of dietary sodium intake, we gave normal subjects diet containing 10, 100, or 200 mEq/d sodium in random order either as such, or supplemented with one of two potassium supplements. One regimen consisted of potassium 45 mEq/d with 12 mEq/d chloride and 33 mEq/d of citrate and gluconate; the other contained 48 mEq/d potassium and 48mEq/d chloride. Increased potassium intake with either supplemented regimen resulted in increased 24-hour potassium excretion, which was manifested in only the diurnal collections. Increased chloride intake resulted in increased urinary chloride excretion both during the day and at night. At all chloride intakes, urinary sodium and chloride excretion were highly correlated. The 48 mEq/d chloride intake generated a relationship with the same slope but with a different intercept from the other two regimens. The highest chloride intake resulted in a greater chloride titrator reading; however, the relationship was sufficiently predictable that adjustments in interpretation could be easily made. We conclude that if daily potassium chloride intake is known, chloride titrators continue to be reliable tools for estimating dietary sodium intake.

Salt taste and hypertension: a critical review of the literature

Studies of the salt taste sensitivity, responsiveness, preference, and appetite of normotensive and hypertensive individuals have yielded therapeutic, diagnostic, predictive, and mechanistic findings related to hypertension. Following a brief description of the nature of these taste parameters, findings pertaining to the association between each and hypertension are critically reviewed. Potential clinical implications of this information, as well as the need to exercise caution in the translation of taste data into dietary practice are also discussed.

Estimating dietary sodium intake in individuals receiving a randomly fluctuating intake

Previous investigations examining techniques to estimate sodium intake in free-living persons failed to consider a varying intake or were not conducted under circumstances in which the intake was actually known. To examine the utility of 24-hour and nocturnal urine collections as estimation of sodium intake under such conditions, we studied 43 white and black men and women ingesting a known sodium intake for 10 days that was randomly varied daily, with a mean intake of 150 mEq/day + 2 SD (range, 50 to 250 mEq/day). The mean 24-hour sodium excretion (UNaV) per day was and 24-hour UNaV estimated that day's sodium intake accurately for the entire 10 days, the average of several 24-hour collections was required. Nine collections were optimal (r = 0.75). Nocturnal specimens were not helpful; the average of all 10 collections correlated weakly (r = 0.30) with sodium intake. These data suggest that to estimate mean sodium intake accurately in free-living persons, only 24-hour collections are useful, although nocturnal collections are helpful in evaluating compliance with low sodium intake.

Sodium intake and essential hypertension

This review briefly considers the hypothesis that a generous dietary sodium intake contributes to the development or maintenance of essential hypertension. Three lines of evidence are presented that are not mutually exclusive. Epidemiological studies examining sodium intake, prevalence of hypertension, and increases of blood pressure with age provide circumstantial support for the concept that hypertension is related to sodium intake. Analyses of cellular electrolyte transport suggest that hypertensives and their relatives are at a disadvantage with respect to extruding sodium from cells. A conceptual framework indicates that blood pressure is determined by a balance between the natriuretic effect of increased blood pressure and the pressor effect of sodium retention. Clinical studies in humans support the sodium hypothesis. The kidney's ability to excrete sodium and its sodium regulatory system are genetically determined. In hypertensive humans, blood pressure is directly correlated with total body and exchangeable sodium, a relationship that increases with age. Groups at risk for hypertension excrete sodium less well then those at less risk. Yet both hypertensives and normotensives exhibit heterogeneous blood pressure responses when sodium-loaded or -depleted. It has not been shown that sodium restriction will prevent the development of hypertension in normal individuals; however, it is clear that sodium restriction is an important aspect of management. In three prospective randomized controlled trials, practical sodium restriction lowered blood pressure by 8 mm Hg. Such a decrease would lower cardiovascular morbidity by 10% to 15%. Were means available to detect "salt-sensitive" hypertensives, sodium restriction could be conducted in a more appropriate fashion.