Estimation of Daily Sodium and Potassium Excretion Using Spot Urine and 24-Hour Urine Samples in a Black Population (Benin)

Is a spot urine sample a good substitution to estimate 24-h urinary sodium excretion in a population ≥ 50 years old? A validation study

PURPOSE

A variety of prediction equations have been able to estimate 24-h urinary sodium excretion from spot urine samples; however, Iranians over the age of 50 have not been compared and verified. Using spot urine samples as a substitute for 24-h urine samples to estimate 24-h urine sodium excretion among the population age 50 and older are the purpose of this study.

METHODS

A 24-h urinary sodium excretion was studied by well-known Kawasaki, INTERSALT, Tanaka, and World Health Organization/Pan American Health Organization (WHO/PAHO) formulas. On 360 individuals, the mean bias, agreements between estimated and measured values, correlation, absolute and relative differences, and misclassification rates were evaluated for four equations.

RESULTS

As a result, the mean urinary sodium excretion for a 24-h period was 136.3 ± 52.21 mmol/24-h, which corresponds to a calculated intake of 9.1 ± 3.8 g of salt per day. According to the WHO/PAHO formula, the mean bias between measured values and estimated 24-h urinary sodium excretion is - 21.6 mg/day (95% confidence interval (CI) - 144.8, 101.6 mg/day), which is the smallest difference compared with the other three formulas. The lowest rate of individual misclassification of salt intake was 40% for WHO/PAHO, especially for those who consumed less than 9 g/day, while Kawasaki had the lowest misclassification rate at higher levels of salt intake.

CONCLUSION

As a result of our research, the WHO/PAHO equations accurately predict 24-h urinary sodium excretion among Iranians aged ≥ 50 more than other equations, both at the population level and at the individual level. However, further study is needed in regard to different ages in Iran.

The damaging duo: Obesity and excess dietary salt contribute to hypertension and cardiovascular disease

Hypertension is a primary risk factor for cardiovascular disease. Cardiovascular disease is the leading cause of death among adults worldwide. In this review, we focus on two of the most critical public health challenges that contribute to hypertension-obesity and excess dietary sodium from salt (i.e., sodium chloride). While the independent effects of these factors have been studied extensively, the interplay of obesity and excess salt overconsumption is not well understood. Here, we discuss both the independent and combined effects of excess obesity and dietary salt given their contributions to vascular dysfunction, autonomic cardiovascular dysregulation, kidney dysfunction, and insulin resistance. We discuss the role of ultra-processed foods-accounting for nearly 60% of energy intake in America-as a major contributor to both obesity and salt overconsumption. We highlight the influence of obesity on elevated blood pressure in the presence of a high-salt diet (i.e., salt sensitivity). Throughout the review, we highlight critical gaps in knowledge that should be filled to inform us of the prevention, management, treatment, and mitigation strategies for addressing these public health challenges.

Estimating population level 24-h sodium excretion using spot urine samples in older adults in rural South Africa

BACKGROUND

South Africa has introduced regulations to reduce sodium in processed foods. Assessing salt consumption with 24-h urine collection is logistically challenging and expensive. We assess the accuracy of using spot urine samples to estimate 24-h urine sodium (24hrUNa) excretion at the population level in a cohort of older adults in rural South Africa.

METHODS

24hrUNa excretion was measured and compared to that estimated from matched spot urine samples in 399 individuals, aged 40-75 years, from rural Mpumalanga, South Africa. We used the Tanaka, Kawasaki, International Study of Sodium, Potassium, and Blood Pressure (INTERSALT), and Population Mean Volume (PMV) method to predict 24hrUNa at the individual and population level.

RESULTS

The population median 24hrUNa excretion from our samples collected in 2017 was 2.6 g (interquartile range: 1.53-4.21) equal to an average daily salt intake of 6.6 g, whereas 65.4% of participants had a salt excretion above the WHO recommended 5 g/day. Estimated population median 24hrUNa derived from the INTERSALT, both with and without potassium, showed a nonsignificant difference of 0.25 g (P = 0.59) and 0.21 g (P = 0.67), respectively. In contrast, the Tanaka, Kawasaki, and PMV formulas were markedly higher than the measured 24hrUNa, with a median difference of 0.51 g (P = 0.004), 0.99 g (P = 0.00), and 1.05 g (P = 0.00) respectively. All formulas however performed poorly when predicting an individual's 24hrUNa.

CONCLUSION

In this population, the INTERSALT formulas are a well suited and cost-effective alternative to 24-h urine collection for the evaluation of population median 24hrUNa excretion. This could play an important role for governments and public health agencies in evaluating local salt regulations and identifying at-risk populations.

Estimation of mean population salt intakes using spot urine samples and associations with body mass index, hypertension, raised blood sugar and hypercholesterolemia: Findings from STEPS Survey 2019, Nepal

Background

High dietary salt intake is recognized as a risk factor for several non-communicable diseases (NCDs), in particular cardiovascular diseases (CVDs), including heart attack and stroke. Accurate measurement of population level salt intake is essential for setting targeted goals and plans for salt reduction strategies. We used a spot urine sample to estimate the mean population salt intake in Nepal and evaluated the association of salt intake with excess weight, hypertension, raised blood sugar and hypercholesterolemia, and a number of socio-demographic characteristics.

Methods

A population-based cross-sectional study was carried out from February to May 2019 using a WHO STEPwise approach to surveillance. Spot urine was collected from 4361 participants aged 15–69 years for the analysis of salt intake. We then used the INTERSALT equation to calculate population salt intake. Student’s ‘t’ test, one-way ANOVA and multivariable linear regression were used to assess the association between salt intake and a number of factors. Statistical significance was accepted at P < .05.

Results

The average (±SD) age of participants was 40 (14.1) years. Mean salt intake, derived from spot urine samples, was estimated to be 9.1g/d. A total of 70.8% of the population consumed more than the WHO’s recommended amount of 5g salt per day, with almost one third of the population (29%) consuming more than 10g of salt per day. Higher salt intake was significantly associated with male gender (β for male = 0.98g; 95%CI:0.87,1.1) and younger age groups (β25–39 years = 0.08; 95%CI:-0.08,0.23) and higher BMI (β = 0.19; 95%CI:0.18,0.21). Participants who were hypertensive and had raised blood cholesterol consumed less salt than people who had normal blood pressure and cholesterol levels (P<0.001).

Conclusions

Salt consumption in Nepal is high, with a total of 70.8% of the population having a mean salt intake >5g/d, well above the World Health Organization recommendation. High salt intake was found to be associated with sex, age group, education, province, BMI, and raised cholesterol level of participants These findings build a strong case for action to reduce salt consumption in Nepal in order to achieve the global target of 30% reduction in population salt intake by 2025.

Potassium

Potassium is an essential nutrient that performs a vital role in cellular functions including maintaining fluid balance and osmolality of cells. Potassium balance is maintained by the kidney and the majority of ingested potassium is excreted in the urine. There is strong evidence of a negative association between dietary potassium and blood pressure, and some evidence (much of it indirect) of negative associations between dietary potassium and cardiovascular disease (particularly stroke and coronary heart disease) and kidney disease (chronic renal failure, and kidney stones). Blood pressure lowering is particularly associated with high potassium and low sodium diets. Important dietary sources of potassium include fruit and vegetables (including rice, potatoes, legumes and wholegrains), dairy products, and animal proteins. Worldwide, diets are low in potassium compared to dietary guidelines. Interventions focused on increasing dietary potassium will have major benefits including improvements in diet, reducing non-communicable disease and enhancing planetary health.

Sensing of electrolytes in urine using a miniaturized paper-based device

Analyzing electrolytes in urine, such as sodium, potassium, calcium, chloride, and nitrite, has significant diagnostic value in detecting various conditions, such as kidney disorder, urinary stone disease, urinary tract infection, and cystic fibrosis. Ideally, by regularly monitoring these ions with the convenience of dipsticks and portable tools, such as cellphones, informed decision making is possible to control the consumption of these ions. Here, we report a paper-based sensor for measuring the concentration of sodium, potassium, calcium, chloride, and nitrite in urine, accurately quantified using a smartphone-enabled platform. By testing the device with both Tris buffer and artificial urine containing a wide range of electrolyte concentrations, we demonstrate that the proposed device can be used for detecting potassium, calcium, chloride, and nitrite within the whole physiological range of concentrations, and for binary quantification of sodium concentration.

Impact of fractional excretion of sodium on a single morning void urine collection as an estimate of 24-hour urine sodium

The standard for assessing dietary sodium intake is to measure 24-hour urine sodium. On average, 93% of daily sodium intake is excreted over 24-hours. Expense and difficulties in obtaining complete 24-hour collections have led to the measurement of sodium concentration in spot and single-void urine samples, using predictive equations to estimate 24-hour urine sodium. Although multiple predictive equations have been developed, in addition to having an average bias, all the equations overestimate 24-hour sodium at lower levels of 24-hour sodium and underestimate 24-hour urine sodium at higher levels of 24-hour sodium. One of the least biased estimating equations is the INTERSALT equation, which incorporates a spot urine creatinine concentration. The authors hypothesized that differential fractional excretion of sodium (FeNa)(derived from a morning void collection) relative to creatinine would impact on the accuracy of the INTERSALT equation in estimating 24-hour urine sodium. In a prospective study of 139 adults aged 65 years and over, three sequential morning void and 24-hour urine samples were examined. There was a significant correlation between increasing FENa and the difference between estimated and measured 24-hours urine sodium (r = 0.358, P < .01). In the lowest quartile of FENa, the INTERSALT equation overestimated 24-hour urine sodium, but underestimated 24-hour urine sodium with greater magnitude in each of the subsequent quartiles of FENa. Differential excretion of sodium relative to creatinine, potentially impacted by renal blood flow and hydration, among other factors, affected the accuracy of the INTERSALT equation. Additional research may refine the INTERSALT and other predictive equations to increase their accuracy.

Estimating mean population salt intake in Fiji and Samoa using spot urine samples

BACKGROUND

There is an increasing interest in finding less costly and burdensome alternatives to measuring population-level salt intake than 24-h urine collection, such as spot urine samples. However, little is known about their usefulness in developing countries like Fiji and Samoa. The purpose of this study was to evaluate the capacity of spot urine samples to estimate mean population salt intake in Fiji and Samoa.

METHODS

The study involved secondary analyses of urine data from cross-sectional surveys conducted in Fiji and Samoa between 2012 and 2016. Mean salt intake was estimated from spot urine samples using six equations, and compared with the measured salt intake from 24-h urine samples. Differences and agreement between the two methods were examined through paired samples t-test, intraclass correlation coefficient analysis, and Bland-Altman plots and analyses.

RESULTS

A total of 414 participants from Fiji and 725 participants from Samoa were included. Unweighted mean salt intake based on 24-h urine collection was 10.58 g/day (95% CI 9.95 to 11.22) in Fiji and 7.09 g/day (95% CI 6.83 to 7.36) in Samoa. In both samples, the INTERSALT equation with potassium produced the closest salt intake estimate to the 24-h urine (difference of - 0.92 g/day, 95% CI - 1.67 to - 0.18 in the Fiji sample and + 1.53 g/day, 95% CI 1.28 to 1.77 in the Samoa sample). The presence of proportional bias was evident for all equations except for the Kawasaki equation.

CONCLUSION

These data suggest that additional studies where both 24-h urine and spot urine samples are collected are needed to further assess whether methods based on spot urine samples can be confidently used to estimate mean population salt intake in Fiji and Samoa.

A Systematic Review of the Impact of Dietary Sodium on Autoimmunity and Inflammation Related to Multiple Sclerosis

Multiple sclerosis (MS) is an autoimmune disease of the central nervous system. Current research into potential causes, risk factors, and treatment is largely based around the immune response involved in the pathophysiology of the disease, including factors that contribute to the augmentation of this immune response. This review aimed to determine the role of sodium as a risk factor for increased autoimmunity and inflammation in relation to MS pathogenesis. This systematic review searched the Scopus, MEDLINE, and PubMed scientific databases for studies related to MS and sodium. Studies were included if they addressed sodium intake and MS but were not limited to a disease type or to a study design. Study quality was assessed through the use of the quality rating checklist of the Academy of Nutrition and Dietetics. A total of 12 studies were included in the review, including human, animal, and cellular studies. The studies related to the proinflammatory effect of sodium, the blood-brain barrier, and an effect on autoimmunity. The data presented throughout this review provide insight into the emerging evidence base for sodium intake as a risk factor for MS disease progression and potentially onset of disease. More studies are needed to determine if the influence of sodium is as a single nutrient or has a combined effect as part of an overall eating pattern. This review was registered at PROSPERO as CRD42016039174.

Prediction of 24-hour sodium excretion from spot urine samples in South African adults: a comparison of four equations

Repeated 24-hour urine collection is considered to be the gold standard for assessing salt intake. This is often impractical in large-population studies, especially in low-middle-income countries. Equations to estimate 24-hour urinary salt excretion from a spot urine sample have been developed, but have not been widely validated in African populations. This study aimed to systematically assess the validity of four existing equations to predict 24-hour urinary sodium excretion (24UNa) from spot urine samples in a nationally representative sample of South Africans. Spot and 24-hour urine samples were collected in a subsample (n = 438) of participants from the World Health Organisation Study on global AGEing and adult health (SAGE) Wave 2 in South Africa in 2015. Measured 24UNa values were compared with predicted 24UNa values from the Kawasaki, Tanaka, INTERSALT and Mage equations using Bland-Altman plots. In this subsample (mean age 52.8 ± 16.4 years; body mass index 30.2 ± 8.2 kg/m²; 76% female; 73% black African; 42% hypertensive), all four equations produced a significantly different population estimate compared with the measured median value of 6.7 g salt/day (IQR 4.4-10.5). Although INTERSALT underestimated salt intake (-3.77 g/d; -1.64 to -7.09), the other equations overestimated by 1.28 g/d (-3.52; 1.97), 6.24 g/d (2.22; 9.45), and 17.18 g/d (8.42; 31.96) for Tanaka, Kawasaki, and Mage, respectively. Bland-Altman curves indicated unacceptably wide levels of agreement. Use of these equations to estimate population level salt intake from spot urine samples in South Africans is not recommended.

Dietary sodium intake in urban and rural Malawi, and directions for future interventions

Background

High dietary sodium intake is a major risk factor for hypertension. Data on population sodium intake are scanty in sub-Saharan Africa, despite a high hypertension prevalence in most countries.

Objective

We aimed to determine daily sodium intake in urban and rural communities in Malawi.

Design

In an observational cross-sectional survey, data were collected on estimated household-level per capita sodium intake, based on how long participants reported that a defined quantity of plain salt lasts in a household. In a subset of 2078 participants, 24-h urinary sodium was estimated from a morning spot urine sample.

Results

Of 29,074 participants, 52.8% of rural and 50.1% of urban individuals lived in households with an estimated per capita plain salt consumption >5 g/d. Of participants with urinary sodium data, 90.8% of rural and 95.9% of urban participants had estimated 24-h urinary sodium >2 g/d; there was no correlation between household per capita salt intake and estimated 24-h urinary sodium excretion. Younger adults were more likely to have high urinary sodium and to eat food prepared outside the home than were those over the age of 60 y. Households with a member with previously diagnosed hypertension had reduced odds (OR: 0.59; 95% CI: 0.51, 0.68) of per capita household plain salt intake >5 g/d, compared with those where hypertension was undiagnosed.

Conclusions

Sodium consumption exceeds the recommended amounts for most of the population in rural and urban Malawi. Population-level interventions for sodium intake reduction with a wide focus are needed, targeting both sources outside the home as well as home cooking. This trial was registered at clinicaltrials.gov as NCT03422185.

Comparison of sodium, potassium, calcium, magnesium, zinc, copper and iron concentrations of elements in 24-h urine and spot urine in hypertensive patients with healthy renal function

Sodium, potassium, calcium, magnesium, zinc, copper and iron are associated with the sequela of hypertension. The most reliable method for testing those elements is by collecting 24-h urine samples. However, this is cumbersome and collection of spot urine is more convenient in some circumstance. The aim of this study was to compare the concentrations of different elements in 24-h urine and spot urine.

METHODS

Data was collected from a sub-study of China Salt Substitute and Stroke Study. 240 participants were recruited randomly from 12 villages in two counties in Ningxia, China. Both spot and 24-h urine specimens were collected from each patient. Routine urine test was conducted, and concentration of elements was measured using microwave digestion and Inductively Coupled Plasma-Optical Emission Spectrometry. Partial correlation analysis and Spearman correlation analysis were used to investigate the concentration of different elements and the relationship between 24- h urine and spot urine.

RESULTS

A partial correlation in sodium, potassium, calcium, magnesium and iron was found between paired 24-h urine and spot urine samples except copper and zinc: 0.430, 0.426, 0.550, 0.221 and 0.191 respectively.

CONCLUSIONS

Spot urine can replace 24-h urine for estimating some of the elements in hypertensive patients with normal renal function.

Associations of urinary sodium and sodium to potassium ratio with hypertension prevalence and the risk of cardiovascular events in patients with prehypertension

The aim of this study was to investigate the effects of urinary sodium and sodium to potassium ratio on inflammatory cytokines, hypertension, and cardiovascular disease in patients with prehypertension. The authors observed 627 patients with prehypertension in the General Hospital of Shenyang Military Region. Rank correlation analysis revealed that interleukin 6 expression exhibited significant positive correlations with urinary sodium (R = .13) and sodium to potassium ratio (R = .13). The multivariate-adjusted hazard ratio of 24-hour urinary sodium was 1.01 (95% confidence interval, 1.00 - 1.01) for hypertension and 1.01 (95% confidence interval, 1.00 - 1.02) for cardiovascular disease, whereas the hazard ratio for 24-hour urinary sodium to potassium ratio was 1.13 (95% confidence interval, 1.08 - 1.19) for hypertension and 1.10 (95% confidence interval, 1.04 - 1.17) for cardiovascular disease. The study suggests that a high-salt diet may lead to increased interleukin 6 levels and may contribute to hypertension. In addition, a high sodium to potassium ratio and high sodium levels are associated with increased risks of cardiovascular disease and hypertension in patients with prehypertension.

Diagnostic value of potassium level in a spot urine sample as an index of 24-hour urinary potassium excretion in unselected patients hospitalized in a hypertension unit

BACKGROUND

Primary hyperaldosteronism may be associated with elevated 24-hour urinary potassium excretion. We evaluated the diagnostic value of spot urine (SU) potassium as an index of 24-hour urinary potassium excretion.

METHODS

We measured SU and 24-hour urinary collection potassium and creatinine in 382 patients. Correlations between SU and 24-hour collections were assessed for potassium levels and potassium/creatinine ratios. We used the PAHO formula to estimate 24-hour urinary potassium excretion based on SU potassium level. The agreement between estimated and measured 24-hour urinary potassium excretion was evaluated using the Bland-Altman method. To evaluate diagnostic performance of SU potassium, we calculated areas under the curve (AUC) for SU potassium/creatinine ratio and 24-hour urinary potassium excretion estimated using the PAHO formula.

RESULTS

Strongest correlation between SU and 24-hour collection was found for potassium/creatinine ratio (r = 0.69, P<0.001). The PAHO formula underestimated 24-hour urinary potassium excretion by mean 8.3±18 mmol/d (95% limits of agreement -28 to +44 mmol/d). Diagnostic performance of SU potassium/creatinine ratio was borderline good only if 24-hour urinary potassium excretion was largely elevated (AUC 0.802 for 120 mmol K+/24 h) but poor with lower values (AUC 0.696 for 100 mmol K+/24 h, 0.636 for 80 mmol K+/24 h, 0.675 for 40 mmol K+/24 h). Diagnostic performance of 24-hour urinary potassium excretion estimated by the PAHO formula was excellent with values above 120 mmol/d and good with lower values (AUC 0.941 for 120 mmol K+/24 h, 0.819 for 100 mmol K+/24 h, 0.823 for 80 mmol K+/24 h, 0.836 for 40 mmol K+/24 h).

CONCLUSIONS

Spot urine potassium/creatinine ratio might be a marker of increased 24-hour urinary potassium excretion and a potentially useful screening test when reliable 24-hour urine collection is not available. The PAHO formula allowed estimation of the 24-hour urinary potassium excretion based on SU measurements with reasonable clinical accuracy.

The Science of Salt: A regularly updated systematic review of the implementation of salt reduction interventions (March-August 2016)

This review aims to identify, summarize, and appraise studies reporting on the implementation of salt reduction interventions that were published between March and August 2016. Overall, 40 studies were included: four studies evaluated the impact of salt reduction interventions, while 36 studies were identified as relevant to the design, assessment, and implementation of salt reduction strategies. Detailed appraisal and commentary were undertaken on the four studies that measured the impact of the interventions. Among them, different evaluation approaches were adopted; however, all demonstrated positive health outcomes relating to dietary salt reduction. Three of the four studies measured sodium in breads and provided consistent evidence that sodium reduction in breads is feasible and different intervention options are available. None of the studies were conducted in low- or lower middle-income countries, which stresses the need for more resources and research support for the implementation of salt reduction interventions in these countries.

Ultra-long-term human salt balance studies reveal interrelations between sodium, potassium, and chloride intake and excretion

BACKGROUND

The intake of sodium, chloride, and potassium is considered important to healthy nutrition and cardiovascular disease risk. Estimating the intake of these electrolytes is difficult and usually predicated on urine collections, commonly for 24 h, which are considered the gold standard. We reported on data earlier for sodium but not for potassium or chloride.

OBJECTIVE

We were able to test the value of 24-h urine collections in a unique, ultra-long-term balance study conducted during a simulated trip to Mars.

DESIGN

Four healthy men were observed while ingesting 12 g salt/d, 9 g salt/d, and 6 g salt/d, while their potassium intake was maintained at 4 g/d for 105 d. Six healthy men were studied while ingesting 12 g salt/d, 9 g salt/d, and 6 g salt/d, with a re-exposure of 12 g/d, while their potassium intake was maintained at 4 g/d for 205 d. Food intake and other constituents were recorded every day for each subject. All urine output was collected daily.

RESULTS

Long-term urine recovery rates for all 3 electrolytes were very high. Rather than the expected constant daily excretion related to daily intake, we observed remarkable daily variation in excretion, with a 7-d infradian rhythm at a relatively constant intake. We monitored 24-h aldosterone excretion in these studies and found that aldosterone appeared to be the regulator for all 3 electrolytes. We report Bland-Altman analyses on the value of urine collections to estimate intake.

CONCLUSIONS

A single 24-h urine collection cannot predict sodium, potassium, or chloride intake; thus, multiple collections are necessary. This information is important when assessing electrolyte intake in individuals.