Development of a formula for estimation of sodium intake from spot urine in people with chronic kidney disease

Spot urinary sodium in CKD patients: correlation with 24h-excretion and evaluation of commonly used prediction equations

BACKGROUND

Salt intake in CKD patients can affect cardiovascular risk and kidney disease progression. Twenty-four hour (24h) urine collections are often used to investigate salt metabolism but are cumbersome to perform. We assessed urinary sodium (U-Na) concentration in spot urine samples and investigated the correlation with 24h U-Na excretion and concentration in CKD patients under nephrological care. Further, we studied the role of CKD stage and diuretics and evaluated the performance of commonly used formulas for the prediction of 24h U-Na excretion from spot urine samples.

METHODS

One hundred eight patients of the German Chronic Kidney Disease (GCKD) study were included. Each participant collected a 24h urine and two spot urine samples within the same period. The first spot urine sample (AM) was part of the second morning urine. The second urine sample was collected before dinner (PM). Patients were advised to take their medication as usual without changing dietary habits. U-Na concentrations in the two spot urine samples and their average ((AM + PM)/2) were correlated with U-Na concentration and total Na excretion in the 24h urine collections. Correlations were subsequently studied after stratification by CKD stage and diuretic intake. The usefulness of three commonly applied equations to estimate 24h U-Na excretion from spot urine samples (Kawasaki, Tanaka and Intersalt) was determined using Bland-Altman plots, analyses of sensitivity, specificity, as well as positive (PPV) and negative predictive values (NPV).

RESULTS

Participants (42 women, 66 men) were on average (± SD) 62.2 (± 11.9) years old, with a mean serum creatinine of 1.6 (± 0.5) mg/dl. 95% had arterial hypertension, 37% diabetes mellitus and 55% were on diuretics. The best correlation with 24h U-Na total excretion was found for the PM spot U-Na sample. We also found strong correlations when comparing spot and 24h urine U-Na concentration. Correction of spot U-Na for U-creatinine did not improve strength of correlations. Neither CKD stage, nor intake of diuretics had significant impact on these correlations. All examined formulas revealed a significant mean bias. The lowest mean bias and the strongest correlation between estimated and measured U-Na excretion in 24h were obtained using the Tanaka-formula. Also, application of the Tanaka-formula with PM U-Na provided best sensitivity, specificity, PPV and NPV to estimate U-Na excretion > 4g/d corresponding to a salt consumption > 10g/d.

CONCLUSION

U-Na concentration of spot urine samples correlated with 24h U-Na excretion especially when PM spot U-Na was used. However, correlation coefficients were relatively low. Neither CKD stage nor intake of diuretics appeared to have an influence on these correlations. There was a significant bias for all tested formulas with the Tanaka-formula providing the strongest correlation with measured 24h U-Na excretion. In summary, using spot urine samples together with the Tanaka-formula in epidemiological studies appears feasible to determine associations between approximate salt intake and outcomes in CKD patients. However, the usefulness of spot-urine samples to guide and monitor salt consumption in individual patients remains limited.

Lower 24-h urinary potassium excretion is associated with higher prevalent depression and anxiety status in general population

BACKGROUND

Uncertainty remains about the association of potassium (K) intake with depression and anxiety status. We explored their relationship using 24-h urinary K, reflecting K intake, in general population.

METHODS

We collected 24-h urine and performed self-rating depression and anxiety scales (SDS, SAS) cross-sectionally in adults selected by random sampling in China. SDS and SAS standard score ≥50 defined depression and anxiety status. Participants were divided into three groups (T1, T2, and T3) by 24-h urinary K tertile. Odds ratios (OR) and 95% confidence intervals were calculated. Sensitivity analysis was performed by excluding anti-hypertensive agent takers.

RESULTS

546 participants comprised current analytical sample. First, T1 and T2 groups showed higher SDS scores (40.0 vs 40.0 vs 36.0, p = .001), prevalence (19.8 vs 15.9 vs 7.1%, p = .002), whereas increased adjusted odds for depression status only in T1 group (OR = 2.71, p = .017), compared with T3 group. Second, T1 and T2 groups showed higher SAS scores (38.0 vs 40 vs 35.0, p < .001) and prevalence (14.8 vs 21.4 vs 8.8%, p = .003), whereas increased adjusted odds for anxiety status only in T2 group (OR = 2.07, p = .042), compared with T3 groups. Third, T1 and T2 groups showed higher prevalence (10.4% vs 11.5% vs 2.7%, p = .004) and adjusted odds (OR = 3.71, p = .013; OR = 3.66, p = .014) for co-existent anxiety and depression status, compared with T3 group. Most results remained consistent in sensitivity analysis.

CONCLUSIONS

Lower K intake is implicated in presence of anxiety and depression status in general population; this may provide basis for programs to increase K intake and prevent disease.

Sodium Management in Kidney Disease: Old Stories, New Tricks

Excessive dietary sodium intake is associated with an increased risk of hypertension, especially in the setting of chronic kidney disease (CKD). Although implementation of a low-sodium diet in patients with CKD generally is recommended, data supporting the efficacy of this practice is mostly opinion-based. Few controlled studies have investigated the specific association of dietary sodium intake and cardiovascular events and mortality in CKD. Furthermore, in epidemiologic studies, the association of sodium intake with CKD progression, cardiovascular risk, and mortality is not homogeneous, and both low- and high-sodium intake has been associated with adverse health outcomes in different studies. In general, the adverse effects of high dietary sodium intake are more apparent in the setting of advanced CKD. However, there is no established definitive target level of dietary sodium intake in different CKD stages based on glomerular filtration rate and albuminuria/proteinuria. This review discusses the current challenges regarding the rationale of sodium restriction, target levels and assessment of sodium intake, and interventions for sodium restrictions in CKD in relation to clinical outcomes.

24-hour urinary potassium excretion is negatively associated with self-reported sleep quality in the general population, independently of sleep-disordered breathing

STUDY OBJECTIVES

To investigate the association of 24-hour urinary potassium excretion with self-reported sleep quality in the general population.

METHODS

In this cross-sectional study, a population of patients aged 18 years or older was randomly selected from Xinjiang, China in 2019, 24-hour urine samples collected, and Pittsburgh Sleep Quality Index (PSQI) questionnaires assessed. Participants were divided into 2 groups (upper and lower median of 24-hour urinary potassium excretion). Poor sleep quality was defined as PSQI global score ≥ 6. Associations between 24-hour urinary potassium excretion and [24.8 mmol/L] sleep quality were assessed by multiple logistic regression analysis in total participants and those stratified by sex.

RESULTS

In total, 24-hour urine samples were collected from 1,147 participants, of whom data for those with complete urine samples and PSQI data were analyzed (n = 727; mean age = 48.7 years; percentage of women = 62%). Compared with the upper median group for 24-hour urinary potassium excretion, the lower median group showed a significantly higher PSQI global score (6 vs 5, P = .011), and prevalence of poor sleep quality (51.7% vs 42.2%, P = .011). In a fully-adjusted model of multivariate logistic regression, the lower median group showed 1.50-fold increased odds for presence of poor sleep quality (95% confidence interval: 1.01-2.24, P = .045). Sex-specific analyses translated these results to women, but not to men.

CONCLUSIONS

These results suggest that low potassium intake, indicated by lower potassium excretion, is associated with poor sleep quality in the general population, especially among women. Therefore, additional research is necessary to clarify the effect of increasing potassium intake to improve sleep quality.

CITATION

Li M, Heizhati M, Wang L, et al. 24-hour urinary potassium excretion is negatively associated with self-reported sleep quality in the general population, independently of sleep-disordered breathing. J Clin Sleep Med. 2022;18(11):2589-2596.

A Method for Estimating 24 h Urinary Sodium and Potassium Excretion by Spot Urine Specimen in Stroke Patients

Spot urine specimens have been used to estimate 24 h urinary sodium (Na) excretion (24UNaV) and potassium (K) excretion (24UKV). However, the validity is limited for 24UNaV and unknown for 24UKV in stroke patients, using the existing formulas. Herein, we developed and validated a new formula for 24UNaV and 24UKV by spot urine specimens in stroke patients. Spot and 24 h urine samples were collected from 970 stroke patients. The models of 24UNaV and 24UKV were developed using stepwise multivariate linear regression in 689 patients. The performance of different formulas was internally validated in 281 patients at the population and individual levels. The obtained new formulas were: (1) estimated 24UNaV (mmol/day): -0.191 × Age + 4.349 × BMI + 0.229 × Spot_Na + 1.744 × Spot_Na/Spot creatinine (Cr) + 41.492 (for male); -1.030 × Age + 2.011 × BMI + 0.143 × Spot_Na + 1.035 × Spot_Na/Spot_Cr + 147.159 (for female); and (2) estimated 24UKV (mmol/day): -0.052 × Age + 0.410 × BMI + 0.031 × Spot_K + 33.280 × Ln (spot_K/spot _Cr) - 5.789 × Ln (spot_Na/spot _Cr) - 1.035 (for male); -0.235 × Age + 0.530 × BMI + 0.040 × Spot_K + 30.990 × Ln (spot _K/spot _Cr) - 7.837 × Ln (spot_Na/spot_Cr) + 4.318 (for female). The new formula obtained the lowest mean bias (5.17 mmol/day for 24UNaV and 0.85 mmol/day for 24UKV) and highest proportion at the cutoff under the ±30% level for the estimation of 24UNaV (59.43%) and 24UKV (70.11%). The new formula provides a meaningful exploration to estimate 24UNaV and 24UKV in stroke patients by using spot urine specimens.

Validation and reproducibility of a semi-qualitative food frequency questionnaire for assessment of sodium intake in Iranian population

Background

Few semi-quantitative food frequency questionnaires (SFFQ)s has yet been developed to assess sodium intake in Middle East region. This study was performed to validate a SFFQ for assessment of sodium consumption and food groups΄ contribution to sodium intake.

Methods

This study was performed on 219 healthy participants including 113 adults aged ≥19 years and 106 children aged 6–18 years in Isfahan, Iran. They were administered two SFFQ at the beginning and after 1 year to evaluate the reproducibility. The validity of SFFQ for assessment of sodium intake was compared with 24-h urine sodium and twelve 24-h dietary recalls which were completed monthly during a year as two standard methods.

Results

Correlation coefficient between the contribution of food groups to sodium intake based on SFFQ and 24-h dietary recalls varied from 0.04 for legumes (P = 0.667) to 0.47 for added salt (P < 0.001). There was a significant correlation between the estimated total sodium intake based on SFFQ and both standard methods (P < 0.01). Intraclass correlation coefficient (95% CI) between first and second SFFQ had a diverse range from 0.10 (-0.05, 0.17) for fats and oils to 0.49 (0.28, 0.69) for bread. According to the Bland-Altman plots, we observed an acceptable level of agreement between the two methods for sodium intake.

Conclusions

The SFFQ was a relatively valid and reproducible method for estimating sodium intake. Combination of this SFFQ with a valid prediction of 24-h urinary sodium excretion can be useful in achieving more accurate results.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12937-021-00749-7.

Total Body Sodium Balance in Chronic Kidney Disease

Excess sodium intake is a leading but modifiable risk factor for mortality, with implications on hypertension, inflammation, cardiovascular disease, and chronic kidney disease (CKD). This review will focus mainly on the limitations of current measurement methods of sodium balance particularly in patients with CKD who have complex sodium physiology. The suboptimal accuracy of sodium intake and excretion measurement is seemingly more marked with the evolving understanding of tissue (skin and muscle) sodium. Tissue sodium represents an extrarenal influence on sodium homeostasis with demonstrated clinical associations of hypertension and inflammation. Measurement of tissue sodium has been largely unexplored in patients with CKD. Development and adoption of more comprehensive and dynamic assessment of body sodium balance is needed to better understand sodium physiology in the human body and explore therapeutic strategies to improve the clinical outcomes in the CKD population.

Association between 24-h urinary sodium to potassium ratio and mild cognitive impairment in community-based general population

OBJECTIVE

To explore the relationship between parameters of Na and K excretion using 24-h urine sample and mild cognitive impairment (MCI) in general population.

DESIGN

This is a cross-sectional study.

SETTING

Community-based general population in Emin China.

PARTICIPANTS

Totally, 1147 subjects aged ≥18 years were selected to complete the study, with a multistage proportional random sampling method. Cognitive status was assessed with Mini Mental State Examination (MMSE) questionnaire and timed 24-h urine specimens were collected. Finally, 561 participants aged ≥35 years with complete urine sample and MMSE data were included for the current analysis and divided into groups by tertiles of 24-h urinary sodium to potassium ratio (24-h UNa/K) as lowest (T1), middle (T2) and highest (T3) groups.

RESULTS

The MMSE score was significantly lower in T3, compared with the T1 group (26·0 v. 25·0, P = 0·002), and the prevalent MCI was significantly higher in T3 than in T1 group (11·7 % v. 25·8 %, P < 0·001). In multiple linear regression, 24-UNa/K (β: -0·184, 95 % CI -0·319, -0·050, P = 0·007) was negatively associated with MMSE score. In multivariable logistic regression, compared with T1 group, 24-h UNa/K in the T2 and T3 groups showed 2·01 (95 % CI 1·03, 3·93, P = 0·041) and 3·38 (95 % CI 1·77, 6·44, P < 0·001) fold odds for presence of MCI, even after adjustment for confounders. More augmented results were demonstrated in sensitivity analysis by excluding individuals taking anti-hypertensive agents.

CONCLUSIONS

Higher 24-h UNa/K is in an independent association with prevalent MCI.

Spot Urine Samples to Estimate Na and K Intake in Patients With Chronic Kidney Disease and Healthy Adults: A Secondary Analysis From a Controlled Feeding Study

OBJECTIVE

The objective of this study was to assess the agreement between estimated 24-hour urinary sodium excretion (e24hUNa) and estimated 24-hour urinary potassium excretion (e24hUK), calculated from a spot urine sample using several available equations and actual sodium and potassium intake from a controlled diet in both healthy participants and those with chronic kidney disease (CKD).

DESIGN AND METHODS

This study is a secondary analysis of a controlled feeding study in CKD patients matched to healthy controls. Participants (n = 16) consumed the controlled diet, which provided ∼2400 mg Na/day and ∼3000 mg K/day, for 8 days. On days 7 and 8, participants consumed all meals and collected all urine in an inpatient research setting, and they were discharged on day 9. The day 7 morning spot urine sample was used to calculate e24hUNa and e24hUK, which was compared with known sodium and potassium intake, respectively.

RESULTS

Average e24hUNa from the INTERSALT and Tanaka-Na equations were higher than actual sodium intake by 373 mg and 559 mg, respectively, though the differences were not significant. e24hUNa from the Nerbass-SALTED equation in CKD participants was significantly higher than actual sodium intake by ∼2000 mg (P < .001), though e24hUNa from the Nerbass-RRID equation was not different from intake. e24hUK from the Tanaka-K equation was significantly lower than actual potassium intake (P < .001). For both e24hUNa and e24hUK for all participants, agreement with actual intake was poor, and e24hUNa and e24hUK were not correlated with actual sodium or potassium intake, respectively.

CONCLUSION

e24hUNa and e24hUK are poor indicators of true sodium and potassium intake, respectively, in both healthy and CKD participants. Findings should be confirmed in larger sample sizes with varying levels of dietary sodium and potassium.

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.

Trend of salt intake measured by 24-hour urine collection samples among Iranian adults population between 1998 and 2013: The Isfahan salt study

BACKGROUND AND AIM

Few population-based studies conducted in the Eastern Mediterranean region assessed salt intake by the measurement of 24-h sodium urine excretion (24-hUNa). The current study aimed to assess the trend of mean salt intake in Iranian adults between 1998 and 2013.

METHODS AND RESULTS

These cross-sectional studies were performed on 564, 157, 509 and 837 randomly selected healthy adults aged >18 years from Isfahan city, Iran, in 1998, 2001, 2007 and 2013, respectively. BP was measured using a mercury sphygmomanometer according to a standard protocol. Single 24-h urine was collected to assess 24-hUNa as a surrogate of salt intake, and 24-h urinary K (24-hUK). The estimated trend of salt intake was 9.5, 9.7, 9.6 and 10.2 g/day in total population (P < 0.001). The increase in salt intake between 1998 and 2013 was significant only in men, (P < 0.001). The risk of pre-hypertension was 21% and 18% significantly greater in the highest quartiles of UNa/UK after adjustment for potential confounders in 2001 and 2013, respectively, [OR (95% CI): 1.21 (1.03-1.64) and 1.18 (1.02-1.38), respectively].

CONCLUSIONS

This population-based study indicated that mean salt intake was about two times of recommendation in Isfahan city, Iran, and suggest that it would be essential to implement a salt reduction strategy program in Iranian population. Longitudinal national studies with larger samples examining the trend of salt intake are warranted.

Estimating the urinary sodium excretion in patients with chronic kidney disease is not useful in monitoring the effects of a low-salt diet

Background

Several epidemiologic studies have suggested that the urine sodium excretion (USE) can be estimated in lieu of performing 24-hour urine collection. However, this method has not been verified in patients with chronic kidney disease (CKD) or in an interventional study. The purpose of this study was to evaluate the usefulness of estimating USE in a prospective low-salt diet education cohort (ESPECIAL).

Methods

A new formula was developed on the basis of morning fasting urine samples from 228 CKD patients in the ESPECIAL cohort. This formula was compared to the previous four formulas in the prediction of 24-hour USE after treatment with olmesartan and low-salt diet education.

Results

Most previously reported formulas had low predictability of the measured USE based on the ESPECIAL cohort. Only the Tanaka formula showed a small but significant bias (9.8 mEq/day, P < 0.05) with a low correlation (r = 0.34). In contrast, a new formula showed improved bias (-0.1 mEq/day) and correlation (r = 0.569) at baseline. This formula demonstrated no significant bias (-1.2 mEq/day) with the same correlation (r = 0.571) after 8 weeks of treatment with olmesartan. Intensive low-salt diet education elicited a significant decrease in the measured USE. However, none of the formulas predicted this change in the measured urine sodium after diet adjustment.

Conclusion

We developed a more reliable formula for estimating the USE in CKD patients. Although estimating USE is applicable in an interventional study, it may be unsuitable for estimating the change of individual sodium intake in a low-salt intervention study.

Sodium Intake and Blood Pressure in Patients with Chronic Kidney Disease: A Salty Relationship

BACKGROUND

Hypertension affects almost all chronic kidney disease patients and is related to poor outcomes. Sodium intake is closely related to blood pressure (BP) levels in this population and decreasing its intake consistently improves the BP control particularly in short-term controlled trials. However, most patients struggle in following a controlled diet on sodium according to the guidelines recommendation due to several factors and barriers discussed in this article.

SUMMARY

This review article summarizes the current knowledge related to the associations between sodium consumption, BP, and the risk of cardiovascular disease and chronic kidney disease (CKD); it also provides recommendations of how to achieve sodium intake lowering. Key Messages: Evidences support the benefits in decreasing sodium intake on markers of cardiovascular and renal outcomes in CKD. Trials had shorter follow-up and to maintain long-term sodium intake control is a major challenge. Larger studies with longer follow-up looking at hard endpoints will be important to drive future recommendations.

Spot urine sodium measurements do not accurately estimate dietary sodium intake in chronic kidney disease

BACKGROUND

Sodium intake influences blood pressure and proteinuria, yet the impact on long-term outcomes is uncertain in chronic kidney disease (CKD). Accurate assessment is essential for clinical and public policy recommendations, but few large-scale studies use 24-h urine collections. Recent studies that used spot urine sodium and associated estimating equations suggest that they may provide a suitable alternative, but their accuracy in patients with CKD is unknown.

OBJECTIVE

We compared the accuracy of 4 equations [the Nerbass, INTERSALT (International Cooperative Study on Salt, Other Factors, and Blood Pressure), Tanaka, and Kawasaki equations] that use spot urine sodium to estimate 24-h sodium excretion in patients with moderate to advanced CKD.

DESIGN

We evaluated the accuracy of spot urine sodium to predict mean 24-h urine sodium excretion over 9 mo in 129 participants with stage 3-4 CKD. Spot morning urine sodium was used in 4 estimating equations. Bias, precision, and accuracy were assessed and compared across each equation.

RESULTS

The mean age of the participants was 67 y, 52% were female, and the mean estimated glomerular filtration rate was 31 ± 9 mL · min(-1) · 1.73 m(-2) The mean ± SD number of 24-h urine collections was 3.5 ± 0.8/participant, and the mean 24-h sodium excretion was 168.2 ± 67.5 mmol/d. Although the Tanaka equation demonstrated the least bias (mean: -8.2 mmol/d), all 4 equations had poor precision and accuracy. The INTERSALT equation demonstrated the highest accuracy but derived an estimate only within 30% of mean measured sodium excretion in only 57% of observations. Bland-Altman plots revealed systematic bias with the Nerbass, INTERSALT, and Tanaka equations, underestimating sodium excretion when intake was high.

CONCLUSION

These findings do not support the use of spot urine specimens to estimate dietary sodium intake in patients with CKD and research studies enriched with patients with CKD. The parent data for this study come from a clinical trial that was registered at clinicaltrials.gov as NCT00785629.

Reduction in sodium intake is independently associated with improved blood pressure control in people with chronic kidney disease in primary care

Decreasing sodium intake has been associated with improvements in blood pressure (BP) and proteinuria, two important risk factors for CVD and chronic kidney disease (CKD) progression. We aimed to investigate the role of sodium intake by examining the effect of changes in sodium intake over 1 year on BP and proteinuria in people with early stage CKD. From thirty-two general practices, 1607 patients with previous estimated glomerular filtration rate of 59-30 ml/min per 1.73 m² and mean age of 72.9 (sd 9.0) years were recruited. Clinical assessment, urine and serum biochemistry testing were performed at baseline and after 1 year. Sodium intake was estimated from early morning urine specimens using an equation validated for this study population. We found that compared with people who increased their sodium intake from ≤ 100 to >100 mmol/d over 1 year, people who decreased their intake from >100 to ≤ 100 mmol/d evidenced a greater decrease in all BP variables (Δmean arterial pressure (ΔMAP) = -7.44 (SD 10.1) v. -0.23 (SD 10.4) mmHg; P<0.001) as well as in pulse wave velocity (ΔPWV = -0.47 (SD 1.3) v. 0.08 (SD 1.88) m/s; P<0.05). Albuminuria improved only in albuminuric patients who decreased their sodium intake. BP improved in people who maintained low sodium intake at both times and in those with persistent high intake, but the number of anti-hypertensive increased only in the higher sodium intake group, and PWV improved only in participants with lower sodium intake. Decreasing sodium intake was an independent determinant of ΔMAP. Although more evidence is needed, our results support the benefits of reducing and maintaining sodium intake below 100 mmol/d (2.3-2.4 g/d) in people with early stages of CKD.

High sodium intake is associated with important risk factors in a large cohort of chronic kidney disease patients

BACKGROUND/OBJECTIVES

An increased risk of mortality and cardiovascular disease (CVD) is observed in people with chronic kidney disease (CKD) even in early stages. Dietary sodium intake has been associated with important CVD and CKD progression risk factors such as hypertension and proteinuria in this population. We aimed to investigate the relationship between sodium intake and CVD or CKD progression risk factors in a large cohort of patients with CKD stage 3 recruited from primary care.

SUBJECTS/METHODS

A total of 1733 patients with previous estimated glomerular filtration rate (eGFR) of 30-59 ml/min/1.73m(2), with a mean age 72.9±9.0 years, were recruited from 32 general practices in primary care in England. Medical history was obtained and participants underwent clinical assessment, urine and serum biochemistry testing. Sodium intake was estimated from three early-morning urine specimens using an equation validated for this study population.

RESULTS

Sixty percent of participants who had estimated sodium intake above recommendation (>100 mmol/day or 6 g salt/day) also had higher diastolic blood pressure, mean arterial pressure (MAP), urinary albumin-to-creatinine ratio, high-sensitive C-reactive protein and uric acid and used a greater number of anti-hypertensive drugs. In multivariable regression analysis, excessive sodium intake was an independent predictor of MAP (B=1.57, 95% confidence interval (CI) 0.41-2.72; P=0.008) and albuminuria (B=1.35, 95% CI 1.02-1.79; P=0.03).

CONCLUSIONS

High sodium intake was associated with CVD and CKD progression risk factors in patients with predominantly early stages of CKD followed up in primary care. This suggests that dietary sodium intake could afffect CVD risk even in early or mild CKD. Intervention studies are warranted to investigate the potential benefit of dietary advice to reduce sodium intake in this population.

Demographic associations of high estimated sodium intake and frequency of consumption of high-sodium foods in people with chronic kidney disease stage 3 in England

OBJECTIVE

The objective of this study was to investigate sodium intake in a cohort of people with chronic kidney disease (CKD) Stage 3 in England to identify demographic characteristics of subgroups with high sodium intake and specific foods that contribute to excessive sodium intake.

DESIGN AND METHODS

Study subjects (N = 1,729) included CKD patients from 32 general practices in the Renal Risk in Derby study. Patients had a glomerular filtration rate between 30 and 59 mL/min per 1.73 m(2) on 2 or more occasions at least 3 months apart before recruitment. Sodium excretion (assumed to be equal to intake) was estimated from early morning urine specimens using an equation validated for this study population. The frequency of intake of 12 salty foods was assessed by a food frequency questionnaire.

RESULTS

The mean estimated urinary sodium excretion was 110.5 ± 33.8 mmol/day; 60.1% had values above the National Kidney Foundation recommendation (<100 mmol/day). Subgroups with a greater percentage of participants having sodium excretion above the recommendation were as follows: men, those younger than 75 years of age, those with central obesity or diabetes, those with formal educational qualifications, and those who were previous or current smokers. In multivariable analysis, gender, younger age, waist-to-hip ratio, and diabetes mellitus status were the main independent determinants of excessive sodium excretion. Specific food items that contributed to excessive intake were table and cooking salt, salted snacks, hard cheeses, processed meat, and tinned fish. The most important source of sodium varied by subgroup.

CONCLUSION

A high prevalence of sodium excretion above the recommended value was detected, and independent determinants were gender, age, waist-to-hip ratio, and diabetes mellitus. Specific food items that contributed to excessive intake were also identified and varied in different subgroups. These data will be helpful in informing strategies to target dietetic advice to those most likely to have high sodium intake and will allow dietitians to focus on the most likely sources of sodium in different subgroups.