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

Longitudinal Studies of Aging in Sub-Saharan Africa: Review, Limitations, and Recommendations in Preparation of Projected Aging Population

Background and Objectives

The United Nations has projected a 218% increase in older people in Sub-Saharan Africa (SSA) between 2019 and 2050, underscoring the need to explore changes that would occur over this time. Longitudinal studies are ideal for studying and proffering solutions to these changes. This review aims to understand the breadth and use of longitudinal studies on aging in the SSA regions, proffering recommendations in preparation for the projected aging population.

Research Design and Methods

This paper is the third of a four-part series paper of a previous systematic mapping review of aging studies in SSA. We updated the search (between 2021 and 2023) and screened the titles/abstracts and full-text articles by a pair of independent reviewers. Data were extracted using a standardized data-charting form, identifying longitudinal studies in SSA.

Results

We identified 193 studies leveraging 24 longitudinal study data sets conducted at 28 unique sites. The World Health Organization's Study on Global AGEing and Adult Health (WHO-SAGE) (n = 59, 30.5%) and Health and Aging in Africa: A Longitudinal Study of an INDEPTH Community in South Africa (HAALSI) (n = 51, 26.4%) were the most used longitudinal data sets. Four studies used more than one longitudinal study data set. Eighteen of the longitudinal study data sets were used only in 1-4 studies. Most (n = 150, 77.7%) of the studies used a cross-sectional analytical approach.

Discussion and Implications

Longitudinal studies on aging are sparingly being utilized in SSA. Most analyses conducted across the longitudinal data set were cross-sectional, which hindered the understanding of aging changes that occurred over time that could better inform aging policy and interventions. We call for funding bodies, such as WHO-SAGE, to develop funding competitions that focus on conducting longitudinal analyses, such as structural equation modeling, highlighting changes occurring among the aging population in SSA.

It is strongly recommended to not conduct, fund, or publish research studies that use spot urine samples with estimating equations to assess individuals' sodium (salt) intake in association with health outcomes: a policy statement of the World Hypertension League, International Society of Hypertension and Resolve to Save Lives

Spot urine samples with estimating equations have been used to assess individuals' sodium (salt) intake in association with health outcomes. There is large random and systematic error in estimating sodium intake using this method and spurious health outcome associations. Substantial controversy has resulted from false claims the method is valid. Hence, the World Hypertension League, International Society of Hypertension and Resolve to Save Lives, supported by 21 other health organizations, have issued this policy statement that strongly recommends that research using spot urine samples with estimating equations to assess individuals' sodium (salt) intake in association with health outcomes should not be conducted, funded or published. Literature reviews on the health impacts of reducing dietary sodium that include studies that have used spot and short duration timed urine samples with estimating equations need to explicitly acknowledge that the method is not recommended to be used and is associated with spurious health outcome associations.

Variability of 24-Hour Sodium Urinary Excretion in Young Healthy Males Based on Consecutive Urine Collections: Impact on Categorization of Salt Intake

OBJECTIVE

Several nonconsecutive 24-h urinary collections are considered the gold standard for estimating dietary salt intake. As those samples are logistically demanding, we aimed to describe the variability of 24-h sodium urinary excretion over consecutive days and report its adequacy with sodium intake.

METHODS

We enrolled 16 healthy male volunteers in a prospective controlled study. All participants randomly received a low salt diet (LSD) (3 g/day of NaCl), a normal salt diet (NSD) (6 g/day of NaCl), and a high salt diet (HSD) (15 g/day of NaCl) for 7 days in a crossover design without wash-out period.

RESULTS

On day 6, median sodium urinary excretion was 258 (216-338), 10 (8-18), and 87 (69-121) mmol/day for HSD, LSD, and NSD, respectively (P < .001). When considering days 4-6, sodium urinary excretion was in steady state as models with and without interaction term "diet type X sample day" were not significantly different (P = .163). On day 6, area under the curve (AUC) of receiver operating characteristic for urinary sodium excretion to detect HSD was 1.0 (1.0-1.0) and a cut-point of 175 mmol/day was 100% sensitive and specific to detect HSD. On day 6, receiver operating characteristic AUC to detect LSD was 0.993 (0.978-1.0) and a cut-point of 53 mmol/day was 96.4% sensitive and 100% specific to detect LSD.

CONCLUSION

A steady state of sodium balance, where sodium intake is proportional to its excretion, is reached within a few days under a constant diet in the real-life setting. Categorization of salt consumption into low (3 g/day), normal (6 g/day), or high (15 g/day) based on a single 24-h urine collection is nearly perfect. Based on these results, repeated nonconsecutive urine collection might prove unnecessary to estimate sodium intake in daily clinical practice provided that diet is rather constant over time.

Urinary metabolomics, dietary salt intake and blood pressure: the African-PREDICT study

In Black populations excessive salt intake may exacerbate the genetic predisposition to hypertension and promote the early onset of cardiovascular disease. Ethnic differences in the interaction between sodium intake and the metabolome may play a part in hypertension and cardiovascular disease development. We determined (1) urinary amino acid and acylcarnitine profiles of young Black and White adults according to low, moderate, and high dietary salt intake, and (2) investigated the triad of salt intake, systolic blood pressure (SBP), and the associated metabolomics profile. This study included 447 White and 380 Black adults aged 20-30 years from the African-PREDICT study. Estimated salt intake was determined from 24-hour urinary sodium levels. Urinary amino acids and acylcarnitines were measured using liquid chromatography-tandem mass spectrometry. Black adults exhibited no significant differences in SBP, amino acids, or acylcarnitines across low (<5g/day), moderate (5-10g/day), and high (>10g/day) salt intake. White adults with a high salt intake had elevated SBP compared to those with low or moderate intakes (p < 0.001). Furthermore, gamma-aminobutyric acid (GABA) (q = 0.020), citrulline (q = 0.020), glutamic acid (q = 0.046), serine (q = 0.054) and proline (q = 0.054) were lowest in those with higher salt intake. Only in White and not Black adults did we observe inverse associations of clinic SBP with GABA (Adj. R2 = 0.34; Std. β = -0.133; p = 0.003), serine (Adj. R2 = 0.33; Std. β = -0.109; p = 0.014) and proline (Adj. R2 = 0.33; Std. β = -0.109; p = 0.014). High salt intake in White, but not in black adults, were related to metabolomic changes and may contribute to pathophysiological mechanisms associated with increased BP.

Early evidence for the effectiveness of South Africa's legislation on salt restriction in foods: the African-PREDICT study

South Africa was among the first countries to adopt mandatory regulation in 2016 to lower the salt content in processed foods, aiming to reduce population salt intake to <5 g/day. To assess the effectiveness of this regulation in 20-30 year-old adults, we determined the change in salt intake over a mean follow-up time of 4.56-years spanning the implementation of the regulation. This observational study included baseline (2013-2016; N = 668; 24.9 ± 3 years; 47.8% black; 40.7% men) and follow-up data (2018-ongoing; N = 311; 25.4 ± 3.05 years; 51.1% black; 43.4% men) for participants of the African-PREDICT study. Salt intake was estimated from 24-h urinary sodium excretion. Median salt intake at baseline (N = 668) was 7.88 g/day (IQR: 5.67). In those followed (N = 311), salt intake reduced from baseline [median (IQR): 7.91 g/day (5.83)] to follow-up [7.26 g/day (5.30)] [unadjusted median: -0.82 g/day]. After adjusting for baseline salt intake to address regression to the mean, the mean salt reduction was -1.2 g/day. The greatest reductions were in men [mean difference: -1.47 g/day], black adults [mean difference: -2.04 g/day], and participants from low [mean difference: -1.89 g/day] or middle [mean difference: -1.84 g/day] socio-economic status groups, adjusting for baseline salt intake. Our preliminary findings suggest that South Africa's salt regulation has been effective in lowering salt intake in young adults by ~1.2 g salt/day. Our study supports the effectiveness of upstream interventions to lower population salt intake, particularly for vulnerable groups who may typically consume more processed foods. It needs to be determined if the legislation has the anticipated population health gains.

A Systematic Review of Salt Taste Function and Perception Impairments in Adults with Chronic Kidney Disease

Individuals with chronic kidney disease (CKD) experience physiological changes that likely impair salt taste function and perception. Sodium restriction is a cornerstone of CKD management but dietary sodium plays an important role in food enjoyment and may interfere with compliance to this intervention. Therefore, confirming that taste deficits are present in CKD will improve our understanding of how taste deficits can affect intake, and inform dietary counselling in the future. A systematic review was conducted. Studies that included adults with CKD and healthy controls, and assessed salt taste sensitivity, perceived intensity, and/or hedonic ratings were included. Study quality was assessed using the Academy of Nutrition and Dietetics Evidence Analysis Library Quality Criteria Checklist: Primary Research. Of the 16 studies, the majority reported decreased salt taste sensitivity, but no consistent differences in intensity or hedonic ratings were observed. Higher recognition thresholds in CKD patients were associated with higher sodium intake, but results should be interpreted with caution as the measures used were subject to error in this population. In conclusion, salt taste sensitivity is decreased in CKD, but intensity and hedonic evaluations appear to be more robust. Given that hedonic assessments are better predictors of intake, and that salt taste preferences can be changed over time, dietary counselling for low-sodium intake is likely to be effective for this population.

Association between 24 h Urinary Sodium and Potassium Excretion and Dietary Intake in Japanese Male Adolescent Football Players

High urinary sodium-to-potassium ratio is considered a strong risk factor for hypertension. This study aimed to evaluate urinary excretion of sodium and potassium, and we analyzed these levels associated with dietary intake in Japanese adolescent football players. This cross-sectional study included 120 Japanese male adolescent football players. Over 24 h, urine was collected and measured for creatinine, sodium, and potassium levels. A dietary assessment was performed using a self-administered diet history questionnaire. The study analyzed 79 participants. The mean urinary sodium was 143.2 mmol/day, urinary potassium was 42.8 mmol/day, and the mean urinary sodium-to-potassium ratio was 3.6. Compared with the Japanese Dietary Reference Intakes, the estimated salt intake was 73.4% for the participants who exceeded the sodium intake, and the estimated potassium intake was 73.4% for the participants who did not satisfy it. Multiple regression analysis revealed that milk and dairy product intake was independently and positively associated with urinary potassium (β = 0.252) and independently and negatively associated with the urinary sodium-to-potassium ratio (β = −0.254). Adolescent football players had a high-sodium and low-potassium diet, well above the Japanese Dietary Reference Intakes recommendations. Milk and dairy products could be effective for increasing urinary potassium and decreasing the urinary sodium-to-potassium ratio.

Effect of South Africa's interim mandatory salt reduction programme on urinary sodium excretion and blood pressure

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Thirty percent reduction in population salt intake by 2025 is recommended by WHO.

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South Africa introduced mandatory maximum sodium limits in processed foods in 2016.

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A countrywide impact evaluation assessed change in salt intake after two years.

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Salt intake measured using 24hr Na excretion dropped by 1.15 g per day.

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Ongoing evaluation is necessary as more stringent targets were implemented in 2019.

South Africa implemented legislation in June 2016 mandating maximum sodium (Na) levels in processed foods. A pre-post impact evaluation assessed whether the interim legislative approach reduced salt intake and blood pressure. Baseline Na intake was assessed in a nested cohort of the WHO Study on global AGEing and adult health (WHO-SAGE) Wave 2 (Aug-Dec 2015). 24-hour urine samples were collected in a random subsample (n = 1,299; of which n = 750 were considered valid (volume ≥ 300 mL and creatinine ≥ 4 mmol/day (women) or ≥ 6 mmol/day (men))). Follow-up urine samples were collected in Wave 3 (Jun 2018-Jun 2019), with replacements included for those lost to follow-up (n = 1,189; n = 548 valid). In those aged 18 − 49y, median salt intake was 7.8 (4.7, 12.0) g/day in W2 (n = 274), remaining similar in the W3 sample (7.7 (4.9, 11.3) g salt/day (n = 92); P = 0.569). In older adults (50 + y), median salt intake was 5.8 (4.0, 8.5) g/day (n = 467) in W2, and 6.0 (4.0, 8.6) g/day (n = 455) in W3 (P = 0.721). Controlling for differences in background characteristics, overall salt intake dropped by 1.15 g/day (P = 0.028). 24hr urinary Na concentrations from a countrywide South African sample suggest that salt intakes have dropped during the interim phase of mandatory sodium legislation. Further measurement of population level salt intake following stricter Na targets, enforced from June 2019, is necessary.

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.