Advantage of multiple spot urine collections for estimating daily sodium excretion: comparison with two 24-h urine collections as reference

Feasibility of Assessment of Habitual Salt Intake Using a 24-h Urinary Salt Excretion Self-Measuring Device

INTRODUCTION

To assess habitual salt intake, tools are needed to measure 24-h urinary salt excretion repeatedly. We developed and validated a new portable salt monitor, which measures salt excreted per urination and sums the values to provide an accurate estimate of urinary salt excretion over 24 h.

METHODS

A previously developed salt monitor was improved with respect to the capacity, volume sensors, and equation for urinary sodium chloride concentration estimation. In 20 healthy Japanese female volunteers, 24-h urinary salt excretion was measured using the salt monitor and a conventional 24-h urine collection method on eight nonconsecutive days.

RESULTS

In a total of 157 days, there were no fixed or proportional errors between the methods. The mean salt intake over 8 days was 8.5 ± 2.0 g/day for the 24-h urine collection and 8.3 ± 2.3 g/day for the salt monitor, showing a strong correlation (r = 0.912, p < 0.001). At a cut-off value of 6 g, the salt monitor was able to completely classify individuals by habitual salt intake.

CONCLUSION

The validity of the new salt monitor was confirmed. The device can be considered an alternative to the traditional 24-h urine collection for repeated surveys and self-management of daily salt intake.

Estimating mean population salt intake using spot urine samples in Nepal: a cross-sectional study

INTRODUCTION

Little is known about the usefulness of spot urine testing compared with 24-h urine samples to estimate salt intake in low-income settings. This is given 24-h urinary collection can be costly, burdensome, and impractical in population surveys. The primary objective of the study was to compare urinary sodium levels (as an estimate of salt intake) of Nepalese population between 24-h urine and spot urine using previously established spot urine-based equations. Additionally, this study explored the 24-h prediction of creatinine and potassium excretion from spot urine samples using available prediction equations.

METHODS

The sample population was derived from the community-based survey conducted in Nepal in 2018. Mean salt intake was estimated from spot urine samples comparing previously published equations, and this was then contrasted with mean salt intake estimations from 24-h urine samples, using paired t test, Pearson correlation coefficient, intraclass correlation coefficient, and Bland-Altman plots.

RESULTS

A total of 451 participants provided both complete 24-h and morning spot urine samples. Unweighted mean (±SD) salt intake based on 24-h urine collection was 13.28 ± 4.72 g/day. The corresponding estimates were 15.44 ± 5.92 g/day for the Kawasaki, 11.06 ± 3.17 g/day for the Tanaka, 15.22 ± 16.72 g/day for the Mage, 10.66 ± 3.35 g/day for the Toft, 8.57 ± 1.72 g/day for the INTERSALT with potassium, 8.51 ± 1.73 g/day for the INTERSALT without potassium, 7.88 ± 1.94 g/day for the Whitton, 18.13 ± 19.92 g/day for the Uechi simple-mean and 12.07 ± 1.77 g/day using the Uechi regression. As compared with 24-h urine estimates, all equations showed significant mean differences (biases); the Uechi regression had the least difference with 9% underestimation (-1.21 g/day, P  < 0.001).Proportional biases were evident for all equations depending on the level of salt intake in the Bland-Altman plots.

CONCLUSION

None of the included spot urine-based equations accurately corresponded to 24-h salt intake in the present study. These equations may be useful for longitudinal monitoring of population salt intake in Nepal, our study highlights that there are limitations on using existing equations for estimating mean salt intake in Nepali population. Further studies are warranted for accuracy and validation.

Development and application of the sodium index to estimate and assess sodium intake for Korean adults

BACKGROUND/OBJECTIVES

The purpose of this study was to develop a sodium index, which is a tool for estimating and assessing sodium intake easily and quickly, to assist in the prevention of various diseases induced by excess sodium intake in Korean adults.

SUBJECTS/METHODS

The 24-h urine collection and dietary behavior surveys were performed on 640 healthy people in 4 regions of South Korea, and an equation for the estimation of 24-h sodium intake was developed. The validity and reliability of the equation were verified with 200 adults. The sodium index was developed by converting the estimated sodium intake using the equation. Finally, the sodium intake status of 1,600 adults was assessed using the sodium index.

RESULTS

The equation included sex, age, body mass index, eating habit and dietary behaviors related to sodium intake. In validity test of the equation, the mean bias between sodium intake using 24-h urine analysis and using the equation from the Bland-Altman plots was −1.5 mg/day. The sensitivity and specificity of the equation for estimation of sodium intake were 80.5% and 64.4%, respectively. In the reliability test of the equation, there was no significant difference between the first and second sodium intakes calculated using the equations, and Spearman's correlation coefficient between the 2 sodium intakes was 0.98. Sodium intake can be assessed as ‘very moderate’ for 75–100 on the sodium index, ‘moderate’ for 100–150, ‘careful’ for less than 75 or 150–200, and ‘severe’ for 250 or more. When sodium intake was assessed using the sodium index in 1,600 subjects, 54.3% and 24.3% of the subjects were assessed to be in the ‘careful’ and ‘severe’ categories, respectively.

CONCLUSIONS

Using a simple questionnaire, the sodium index can be used to monitor and assess sodium intake status, assisting in nutrition education and counseling in a large population.

High Iodine Nutrition May Be a Risk Factor for Cervical Lymph Node Metastasis in Papillary Thyroid Cancer Patients

PURPOSE

The aim of this study was to retrospectively identify the effect of iodine on the papillary thyroid cancer (PTC) process and investigate the risk clinicopathologic characteristics of cervical lymph node metastasis (CLNM) for achieving a better preventive strategy of PTC.

METHODS

Totally 187 patients with CLNM and 279 without CLNM (NCLNM) were enrolled, and their urinary iodine concentration (UIC) and serum iodine concentration (SIC) were measured. Logistic regressions were used to reveal the effects of iodine nutrition on the CLNM status of PTC.

RESULTS

The levels of thyroid-stimulating hormone (TSH) and thyroglobulin (TG) were higher in the CLNM group than in the NCLNM group. UIC and SIC were positively correlated, and both of them were correlated with TSH, free thyroxine, and TG. The proportions of UIC >300 μg/L and of SIC >90 μg/L were higher in the CLNM than in the NCLNM. Logistic analysis showed that SIC >90 μg/L was an independent predictor for CLNM in PTC. Additionally, age ≥45, female, TG, multifocality, and diameter of cancer invasion >1 cm also affected CLNM status in PTC, and their logistic regression model showed a certain diagnostic accuracy (area under the receiver-operating characteristic curve = 0.72).

CONCLUSIONS

Relatively high iodine nutrition seemed to be a significant risk factor for the occurrence of CLNM in PTC and may promote lymphatic metastasis in PTC.

Validity of five formulas in estimating 24-h urinary sodium via spot urine sampling in hypertensive patients living in Northeast China

OBJECTIVE

The objective was to evaluate the accuracy of five formulas -- the Kawasaki, Tanaka, INTERSALT, Mage, and Uechi methods -- using spot urinary sampling for 24-h urinary sodium (UNa) prediction in hypertensive patients living in northeast China.

METHODS

There were 1154 hypertensive patients enrolled from multiple centers. Five different formulas were used to predict 24-h UNa excretion via spot morning urinary samples. Actual UNa excretion was measured from 24-h urine samples. The estimated value was compared with the actual value by examining biases, the intraclass correlation coefficients (ICC), and Bland-Altman plots.

RESULTS

The average excretion of sodium was 2.97 ± 1.26 g/day. The formula-produced mean biases for actual UNa were 0.31 g/day for INTERSALT, 0.80 g/day for Mage, 0.88 g/day for Tanaka, 1.14 g/day for Uechi, and 1.95 g/day for Kawasaki. The ICC was 0.511 for Kawasaki, 0.499 for INTERSALT, 0.468 for Tanaka, 0.402 for Mage, and 0.378 for Uechi. The least mean bias in the lower and moderate salt intake subgroups was 1.22 and 0.07 g/day, respectively, which was calculated using the Mage and INTERSALT methods. The least mean bias in the higher salt intake subgroup was 0.10 g/day for the Uechi method. The INTERSALT method was more efficiency at the individual level, with 17.4% of participants having relative differences within 10%, and 22.3% participants having absolute differences within 393 mg.

CONCLUSION

The INTERSALT method may exhibit a good performance in estimating 24-h urinary sodium level for the hypertensive population living in northeast China.

Can spot urine measurement be a substitute for 24-hour urine measurement to estimate sodium intake in adolescents?

IMPORTANCE

Several methods have been established in recent decades that allow use of spot urine to estimate dietary sodium intake. However, their accuracies have been controversial in children.

OBJECTIVE

To validate the performance of three commonly used methods-the Kawasaki, Tanaka, and International Cooperative Study on Salt, Other Factors, and Blood Pressure (INTERSALT) methods. Additionally, this study explored the accuracies of the Tanaka and INTERSALT methods by using spot urine samples taken at four separate times.

METHOD

Forty-one adolescents aged 14 to 16 years completed two non-consecutive 24-hour urine collections and their mean values were used as reference data. The second-morning urine was used for assessment with the Kawasaki method; a casual spot urine and spot urine samples taken at four separate times (morning, afternoon, evening, and overnight) were used for assessment with the Tanaka and INTERSALT methods.

RESULTS

The mean differences were 1801 mg, 542 mg, 47 mg, and -31 mg for the Kawasaki, Tanaka, INTERSALT1 (with potassium), and INTERSALT2 (without potassium) methods with their required spot urine, respectively. The proportions of relative difference levels within ± 10% were 4.9% for the Kawasaki method, 19.5% for the Tanaka method, 36.6% for the INTERSALT1 method, and 36.6% for the INTERSALT2 method.

INTERPRETATION

The INTERSALT method seemed to provide minimally biased estimations of mean population sodium intake with casual spot urine. However, there is a need to be cautious regarding inconsistencies in estimation among different levels of sodium intake. The methods assessed in this study were unable to accurately estimate sodium intake at the individual level.

Effect of workplace dietary intervention on salt intake and sodium-to-potassium ratio of Japanese employees: A quasi-experimental study

OBJECTIVES

Excess salt intake is a major risk factor for hypertension and cardiovascular disease. Modifying workplace environments has been recognized to be important for reducing salt intake. However, studies examining the effects of improving the workplace environment regarding salt reduction are limited. This study aimed to evaluate the effects of workplace dietary intervention on employees' salt intake and sodium-to-potassium (Na/K) ratio.

METHODS

A quasi-experimental study was conducted. Two small business establishments in Saitama Prefecture, Japan, were allocated as the intervention (n = 69) and comparison (n = 68) workplaces, respectively. The 1-year intervention involving healthy lunch and nutrition education was implemented in the intervention workplace. Spot urine samples, physical assessments, and self-administered questionnaire data were collected at baseline, 6 months, and 1 year after the start of the intervention. Analysis of covariance was conducted to investigate differences in the salt intake or Na/K ratio between the study workplaces at year 1. Educational status and rotating work schedules were included as covariates.

RESULTS

Salt intake in the intervention workplace decreased significantly from 10.7 to 9.3 g (-1.4 g change; 95% confidence interval [CI]: "-2.4, -0.5"). The adjusted difference in changes in salt intake between workplaces was statistically significant (-3.7 g change; 95% CI: "-5.2, -2.3"). Although no significant change was observed in the Na/K ratio in the intervention workplace (3.37-3.08; -0.29 change; 95% CI: "-0.59, 0.01"), the adjusted difference in changes between the workplaces was statistically significant (-0.60 change; 95% CI: "-1.03, -0.17").

CONCLUSIONS

Providing healthy lunch and nutrition education may be effective approaches to reduce employees' salt intake and Na/K ratio.

Estimation of daily sodium and potassium excretion from overnight urine of Japanese children and adolescents

BACKGROUND

Estimates of daily sodium (Na) and potassium (K) excretion were explicitly biased when using equations for adults. We aimed to develop equations to estimate them using overnight urine from Japanese children and adolescents.

METHODS

The subjects comprised 70 students aged 10.49-15.76 years: validation group, n = 34; and verification group, n = 36. Each subject performed two operations of overnight spot urine (U_m) and 24-h urine (U₂₄) sampling. Concentrations of Na, K, and creatinine (Cr) were measured, and anthropometrics were recorded. In the validation group, Na/Cr, and K/Cr (mEq L^-1/mg dL^-1) in 24-h urine were predicted from their correspondents in overnight urine. Daily Cr excretion (EstCr₂₄; mg d^-1) was estimated according to Mage's method.

RESULTS

In validation, we formulated Na excretion (mg d^-1) = 23 × exp (0.2085) × [(Na/CrU_m + 1)^1.0148 - 1] × 1.078 × EstCr₂₄/10; and K excretion (mg d^-1) = 39 × exp (0.0315) × [(K/CrU_m + 1)^1.3165 - 1] × 1.078 × EstCr₂₄/10. For verification, we compared estimates with the measured 24-h Na excretion 3596 ± 1058 mg d^-1, and K excretion 1743 ± 569 mg d^-1. The mean biases and intraclass correlations (3, 1) were -131 mg d^-1 and 0.60, respectively for Na excretion; and -152 mg d^-1 and 0.55 for K excretion.

CONCLUSION

We obtained validated equations to estimate daily Na and K excretion with accessible variables such as Na, K, and Cr concentrations of overnight urine, body height and weight, and age for children and adolescents. When using the obtained equations, caution should be paid to small but definite biases and measurement errors.

Correlations of spot urinary sodium and potassium with blood pressure in pregnant women: A longitudinal study in Southern Thailand

OBJECTIVE

To assess the changes of spot urinary sodium and potassium and blood pressure (BP) throughout pregnancy and their correlations in southern Thailand.

METHODS

A longitudinal study was conducted in southern Thailand from March 2018 to November 2019. Spot urinary excretion of sodium per creatinine (U[Na⁺ ]/[Cr]), potassium per creatinine (U[K⁺ ]/[Cr]) and U[Na⁺ ]/[K⁺ ] ratios, and BP were measured at four time points throughout pregnancy. A one-way analysis of variance with repeated measures and Bonferroni correction with post hoc analysis was used to identify significant differences between time points. The correlations were measured using Pearson's correlation coefficients.

RESULTS

A total of 327 pregnant women were included. Both systolic and diastolic BPs decreased gradually from up to 14 weeks of pregnancy to 18-22 weeks and then increased until 30-34 weeks. Mean spot U[Na⁺ ]/[Cr] ratios did not significantly change during the study period. Mean spot U[K⁺ ]/[Cr] ratios gradually increased, and spot U[Na⁺ ]/[K⁺ ] ratios gradually decreased. The correlation of spot U[Na⁺ ]/[Cr] and U[K⁺ ]/[Cr] ratios with BPs was weakly negative at all four time points.

CONCLUSIONS

Spot U[Na⁺ ]/[Cr] and U[K⁺ ]/[Cr] ratios are inversely correlated with BPs; weak correlations are found among pregnant women in southern Thailand. Further research in different populations is required to confirm its correlation and broader use.

Estimation of Sodium and Potassium Intake: Current Limitations and Future Perspectives

Globally, average dietary sodium intake is double the recommended amount, whereas potassium is often consumed in suboptimal amounts. High sodium diets are associated with increased cardiovascular and renal disease risk, while potassium may have protective properties. Consequently, patients at risk of cardiovascular and renal disease are urged to follow these recommendations, but dietary adherence is often low due to high sodium and low potassium content in processed foods. Adequate monitoring of intake is essential to guide dietary advice in clinical practice and can be used to investigate the relationship between intake and health outcomes. Daily sodium and potassium intake is often estimated with 24-h sodium and potassium excretion, but long-term balance studies demonstrate that this method lacks accuracy on an individual level. Dietary assessment tools and spot urine collections also exhibit poor performance when estimating individual sodium and potassium intake. Collection of multiple consecutive 24-h urines increases accuracy, but also patient burden. In this narrative review, we discuss current approaches to estimating dietary sodium and potassium intake. Additionally, we explore alternative methods that may improve test accuracy without increasing burden.

Correcting for Intra-Individual Variability in Sodium Excretion in Spot Urine Samples Does Not Improve the Ability to Predict 24 h Urinary Sodium Excretion

Given a global focus on salt reduction efforts to reduce cardiovascular risk, it is important to obtain accurate measures of salt intake on a population level. This study determined firstly whether adjustment for intra-individual variation in urinary sodium (Na) excretion using three repeated 24 h collections affects daily estimates and whether the use of repeated spot urine samples results in better prediction of 24 h Na compared to a single collection. Twenty three community-dwelling men and women from South Africa (mean age 59.7 years (SD = 15.6)) participating in the World Health Organization Study on global AGEing and adult health (WHO-SAGE) Wave 3 study collected 24 h and spot early morning urine samples over three consecutive days to assess urinary Na excretion. INTERSALT, Tanaka, and Kawasaki prediction equations, with either average or adjusted spot Na values, were used to estimate 24 h Na and compared these against measured 24 h urinary Na. Adjustment was performed by using the ratio of between-person (sb) and total (sobs) variability obtained from repeated measures analysis of variance. Sensitivity of the equations to predict daily urinary Na values below 5 g salt equivalent was calculated. The sb/sobs for urinary Na using three repeated samples for spot and 24 h samples were 0.706 and 0.798, respectively. Correction using analysis of variance for 3 × 24 h collections resulted in contraction of the upper end of the distribution curve (90th centile: 157 to 136 mmoL/day; 95th centile: 220 to 178 mmoL/day). All three prediction equations grossly over-estimated 24 h urinary Na excretion, regardless of whether a single spot urine or repeated collections corrected for intra-individual variation were used. Sensitivity of equations to detect salt intake equivalent values of ≤5 g/day was 13% for INTERSALT, while the other two equations had zero sensitivity. Correcting for intra-individual variability in Na excretion using three 24 h urine collections contracted the distribution curve for high intakes. Repeated collection of spot samples for urinary Na analysis does not improve the accuracy of predicting 24 h Na excretion. Spot urine samples are not appropriate to detect participants with salt intakes below the recommended 5 g/day.

Formulas developed based on the ratio of urea nitrogen to creatinine concentrations obtained from multiple spot urine samples are acceptable to predict protein intake at group level but not at individual level

In this study, we hypothesized that spot urine can be used to predict protein intake at both group and individual levels. Participants (n = 369) of this study were recruited from all 47 prefectures in Japan. Sex-specific formulas were developed based on the ratio of urea nitrogen to creatinine concentration obtained from 3 spot urine samples. Validity of the formulas was examined against two 24-hour urine collections for 7 combinations of spot urine (single and means of 2 or 3 samples) using t test (mean estimation), Spearman correlation, and Bland-Altman plot (individual bias). Means of measured protein intake based on 24-hour urinary excretions were 87.3 g/d (standard deviation 19.7) for men and 70.5 g/d (standard deviation 14.7) for women. Irrespective of sex, the predicted intakes were not significantly different (within 2.7% of differences) from those measured by urinary excretions. Predicted intakes were moderately correlated with measured intakes (men, 0.45-0.60; women, 0.35-0.53). Even after using the mean of 3 samples, Bland-Altman plots showed a considerably wide limit of agreement (men, -30 to 33 g/d; women, -27 to 24 g/d). Except for using single spot urine samples in women, the formula tended to overestimate intake at a lower and underestimate at a higher level of protein intake (slope: men, -0.47 [P < .0001]; women, -0.38 [P = .002]). In conclusion, predictive formulas developed in this study can be used to predict protein intake at group level or to rank individuals' intake but not to predict absolute intake at individual level.

Estimating sodium intake from spot urine samples at population level: a validation and application study in French adults

The aim of this study was to assess the validity of the predictive INTERSALT equation using spot urine samples to estimate 24-h urinary Na (24-hUNa) excretion and daily Na intake among the French adult population. Among 193 French adults ('validation sample'), we assessed the validity by comparing predicted 24-hUNa excretion from spot urine and measured 24-hUNa excretion from 24-h urine collections. Spearman correlation coefficients and Bland-Altman plots were used and we calculated calibration coefficients. In a nationally representative sample of 1720 French adults ('application sample'), the calibrated predictive equation was then applied to the spot urine Na values to estimate 24-hUNa excretion and daily Na intake. In that sample, predicted Na intake was compared with that estimated from 24-h dietary recalls. Results were adjusted and corrected using calibration coefficients. In the validation sample, the measured 24-hUNa excretion was on average 14 % higher than the predicted 24-hUNa (+13 % for men and +16 % for women). Correlation between measured and predicted 24-hUNa excretion was moderate (Spearman r 0·42), and the Bland-Altman plots showed underestimation at lower excretion level and overestimation at higher level. In the application study, estimated daily salt intake was 8·0 g/d using dietary recalls, 8·1 g/d using predicted INTERSALT equation and 9·3 g/d after applying calibration coefficients calculated in the validation study. Despite overall underestimation of 24-hUNa excretion by spot urinary Na, the use of predictive INTERSALT equation remains an acceptable alternative in monitoring global Na intake/excreted in the French population but its use is not advised at the individual level.

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.

Accuracy Validation of 8 Equations to Estimate 24-Hour Sodium by Spot Urine in Young Adolescents

BACKGROUND

Several formulas using spot urine have been developed to estimate 24-hour sodium excretion, but none of them have been validated in pediatrics. We aimed to evaluate the performance of 8 formulas-Kawasaki; Tanaka; International Cooperative Study on Salt, Other Factors, and Blood Pressure (INTERSALT1); INTERSALT without potassium (INTERSALT2); Mage; Whitton; Uechi simple-mean; and Uechi regression-in estimating 24-hour sodium excretion at both population and individual levels in Chinese young adolescents.

METHODS

This cross-sectional study consisted of 284 students aged 10-15 years from Hunan, China. Two spot urine and 24-hour urine samples were collected from each participant.

RESULTS

The median 24-hour urinary sodium excretion was 2,742 mg. The mean differences (95% confidence intervals) of 24-hour sodium excretion by the 8 equations were 1,613 (1,491 to 1,735) mg for Kawasaki, -12 (-97 to 73) mg for Tanaka, -214 (-319 to -110) mg for INTERSALT1, -289 (-394 to -185) mg for INTERSALT2, -615 (-730 to -500) mg for Mage, 1,082 (967 to 1,198) mg for Whitton, -479 (-610 to -348) mg for Uechi simple-mean, and -620 (-716 to -525) mg for Uechi regression. The Tanaka formula performed best in relative and absolute difference distributions, with 35.2% participants having relative differences within 10%, and 45.8% participants having absolute differences within 393 mg. The misclassification rates were all >50% except for the Tanaka formula (43.7%).

CONCLUSIONS

In our study, Tanaka could offer a plausible alternative of mean populational 24-hour sodium estimation for young adolescents. However, the results did not support the use of these equations in pediatrics at individual levels.

Seasonal Variation in the Daily Urinary Sodium Excretion in Outpatients from the Morioka Region of Northern Japan

Objective Although the daily urinary sodium excretion (UNaV) is considered to provide the most reliable estimate of the daily sodium intake, it may be affected by salt loss due to sweating in summer. However, the seasonal variation in the daily UNaV associated with a normal lifestyle is unknown. Methods This study was performed in 348 outpatients from the Morioka region during three seasons: summer (summer 1), winter, and the following summer (summer 2). The daily UNaV (g salt/day) was estimated by the second morning urine method three times during each season. Seasonal variation was defined as a significant trend across the three seasons together with a significant difference between winter and both summers. Results In women, the daily UNaV was higher in winter (11.8±3.0 g salt/day) than in summer 1 (11.2±2.9 g salt/day) or summer 2 (11.0±2.9 g salt/day). In contrast, there was no marked seasonal variation in men. An analysis stratified by age (4 quartiles) identified seasonal variation in the older 2 quartiles of women (aged ≥68 years). In these women, the mean seasonal difference in the daily UNaV was 0.9 g of salt/day for both winter vs. summer 1 and winter vs. summer 2, while it was 0.1-0.8 g of salt/day in the other groups. Conclusion Seasonal variation in the daily UNaV only occurred in older female patients and was relatively small. This is evidence for restricting salt intake throughout the year and should reassure patients who are anxious about salt loss due to sweating in summer.