High sodium intake: review of recent issues on its association with cardiovascular events and measurement methods

Protocol for a systematic review assessing the measurement of dietary sodium intake among adults with elevated blood pressure

INTRODUCTION

Accurate sodium intake estimates in adults with elevated blood pressure are essential for monitoring salt reduction progress and preventing cardiovascular diseases. However, sodium assessments are challenging in this high-risk population because many commonly used antihypertensive drugs alter urinary sodium excretion. Despite the high cost and substantial participant burden of gold-standard 24-hour urine collection, the relative performance of existing spot-urine based equations and dietary self-report instruments have not been well studied in this population, who will benefit from salt restriction. This systematic review aims to describe the current methods of assessing dietary sodium intake in adults with elevated blood pressure and determine what method can provide a valid and accurate estimate of sodium intake compared with the gold standard 24-hour urine collection.

METHODS AND ANALYSIS

Studies assessing sodium intake in adults aged 18 years and above with reported elevated blood pressure will be included. Five electronic databases (MEDLINE, Embase, Global Health, WoS and Cochrane CENTRAL) will be systematically searched from inception to March 2021. Also, a manual search of bibliographies and grey literature will be conducted. Two reviewers will screen the records independently for eligibility. One reviewer will extract all data, and two others will review the extracted data for accuracy. The methodological quality of included studies will be evaluated based on three scoring systems: (1) National Heart, Lung and Blood Institute for interventional studies; (2) Biomarker-based Cross-sectional Studies for biomarker-based observational studies and (3) European Micronutrient Recommendation Aligned Network of Excellence for validation studies of dietary self-report instruments.

ETHICS AND DISSEMINATION

As the proposed systematic review will collect and analyse secondary data associated with individuals, there will be no ethical approval requirement. Findings will be disseminated in a peer-reviewed journal or presented at a conference.

PROSPERO REGISTRATION NUMBER

CRD42020176137.

Unbalanced intakes of sodium and potassium among Tunisian adults: A cross-sectional study

The prevention and management of hypertension are untimely associated with a lowering of sodium intake. The present study aimed to evaluate the sodium and potassium intake levels of Tunisian population through measurement of 24-hr urinary sodium excretions. A randomly, multistage, cross-sectional study was conducted in an urban region (Bizerte) in Tunisia during 2015. The target population involved adults aged from 25 to 64 years. Sodium, potassium, and creatinine concentrations were determined in each urine sample using indirect potentiometric method. From the 420 selected participants, only 194 gave urine samples complying completeness criteria. A multivariate regression model was used to assess the variables related to sodium and potassium excretion. The daily mean excretion of sodium and potassium was 138.3 ± 46.5 mmol/d (corresponding to 8.1 ± 2.7 g/d of salt intake) and 61.0 ± 22.7 mmol/d, respectively. More than 87.1% of the participants (89.8% for men vs. 84.9% for women; p = .31) exceeded the WHO recommendation of 5 g/d. The upper limit of 10 g salt intake per day was still exceeded by 26.3%. After adjusted analysis, sex (for women, coef = -1.6; (95% CI: -2.4, -0.7)), level of instruction (≥30 kg/m2, coef = +1.1; (95% IC: 0.4-2.0)), and body mass index (≥30 kg/m2, coef = +1.1; (95% CI: 0.1, 2.0)) were associated with the sodium excretion. High sodium intake and inadequate potassium intake were found among participants. This consumption profile complies with the diet westernization context occurring in Tunisia. The initiated strategy focused on the downward of sodium in bread (the main source of salt intake) seems to be promising.

Sodium Intake, Blood Pressure and Cardiovascular Disease

Sodium intake reduction has been emphasized because sodium adversely impacts health, especially blood pressure (BP), and the cardiovascular (CV) disease risk. However, data obtained from several cohort studies have raised questions regarding the effects of high sodium intake on BP and the CV disease risk. In the present study, we systematically reviewed the literature to evaluate these associations. Studies showing negative associations between urine sodium and BP and CV outcomes relied on estimated 24-hour urine sodium from spot urine that is inappropriate for determining sodium intake at an individual level. Furthermore, controversy about the association between 24-hour urine sodium and BP may have been caused by different characteristics of study populations, such as age distribution, ethnicity, potassium intake and the inclusion of patients with hypertension, the different statistical methods and BP measurement methods. Regarding the association between sodium intake and the CV disease risk, studies showing negative or J- or U-shaped associations used a single baseline measurement of 24-hour urine sodium in their analyses. However, recent studies that employed average of subsequently measured 24-hour urine sodium showed positive, linear associations between sodium intake and CV outcomes, indicating that controversies are caused by the different sodium intake measurement methods and analytic designs. In conclusion, the study shows that positive associations exist between sodium intake and BP, CV outcomes, and mortality, and that the argument that reducing sodium intake is dangerous is invalid. Sodium intake reduction should be recommended to all, and not limited to patients with hypertension or CV disease.

Low correlation between morning spot and 24-hour urine samples for estimating sodium intake in an Iranian population: Isfahan Salt Study

Introduction: Although difficult, the 24-hour urine sodium excretion is still considered as the gold standard method to estimate salt intake. The current study aimed to assess the validity of using spot urine samples in comparison with the standard 24-hour urine collection to estimate sodium and potassium intake in healthy Iranian adults. Methods and subjects: This cross-sectional study was performed on 1099 healthy Iranians aged 18-69 years. Samples of 24-hour and fasting morning spot urine were collected to measure sodium and potassium excretions. Tanaka's formula was utilized to predict the 24-hour sodium and potassium urinary excretions based on the spot values. Results: The difference between measured and estimated sodium excretion values was 4265 mg/day (95% CI: 4106-4424; P < 0.001) and 2242 mg/day in case of potassium excretion (95% CI: 2140-2344; P < 0.001). There was a weak significant correlation between the 24-hour urine sodium and potassium excretion and the predicted values (intraclass correlations: 0.22 and 0.28, respectively; both P < 0.001). Conclusion: The weak association between the predicted and measured values of sodium and potassium along with the marked overestimation of daily sodium and potassium excretions based on the spot urine and using Tanaka formula indicates that Tanaka formula is not practical for the prediction of sodium and potassium or salt intake in Iranian adults. Using other spot urine sampling times and/or adopting a formula designed based on the characteristics of the Iranian population may increase the validity of spot urine tests.

Salt intake, blood pressure, and socioeconomic disparities among government employees in Sri Lanka: a cross-sectional study

Our study estimated salt intake, examined the association between blood pressure (BP) and salt intake, and explored the socioeconomic variations in salt intake among administrators (government employees). This is a cross-sectional study. We studied 168 randomly selected administrators aged 30-60 years attached to government offices in Colombo, Sri Lanka. Self-administered questionnaire gathered information on socio-demographic, work-related information, lifestyle practices, and medical history. BP, 24-hour urine collection, and anthropometric indices were measured. Mean salt intake levels measured by 24-hour Sodium (Na) excretion in hypertensives and non-hypertensives were 202.56 (SD ± 85.45) mmol/day and 176.79 (SD ± 82.02) mmol/day, respectively. A 100-mmol increase in sodium was associated with an average increase of 3.1 (95 per cent CI 2-4.2) mmHg in systolic BP and 1.8 (95 per cent CI 0.89-2.6) mmHg in diastolic BP. Higher salt intake was found in managerial assistants (12.38 ± 5.0 g) compared with senior officers (10.84 ± 4.9 g). Salt intake among these administrators was alarmingly high. High salt intake was positively associated with hypertension and more prevalent in lower socioeconomic strata.

Effects of Rubus occidentalis extract on blood pressure in patients with prehypertension: Randomized, double-blinded, placebo-controlled clinical trial

OBJECTIVE

Black raspberry (Rubus occidentalis) is known for improving vascular function. However, there has been no study evaluating its effects on 24-h systolic and diastolic blood pressure in prehypertensive patients. The aim of this study was to examine those effects.

METHODS

Patients with prehypertension (N = 45) were prospectively randomized into a moderate-dose black raspberry group (n = 15, 1500 mg/d), a high-dose black raspberry group (n = 15, 2500 mg/d), or a placebo group (n = 15) during an 8-wk follow-up period. Raspberries were consumed in the form of a dried powder extract that was fashioned into capsules. The capsules contained 187.5 and 312.5 mg of raspberry powder, which was equivalent to 1500 and 2500 mg raspberries. Ambulatory 24-h blood pressure (BP); central BP; pulse-wave velocity; abdominal visceral fat; serum renin; angiotensin-converting enzyme; and inflammatory cytokines such as interleukin-6, tumor necrosis factor-α, C-reactive protein, soluble intercellular adhesion molecule-1, soluble vascular cell adhesion molecule-1, and plasminogen activator inhibitor-1 were measured at baseline and at 8-wk follow-up.

RESULTS

High-dose black raspberry significantly reduced 24-h systolic blood pressure (SBP; 3.3 ± 10 mm Hg versus -6.7 ± 11.8 mm Hg; P < 0.05) and nighttime SBP (5.4 ± 10.6 mm Hg versus -4.5 ± 11.3 mm Hg; P < 0.05) compared with controls during the 8-wk follow-up. Black raspberry powder did not produce any significant changes in most of the parameters other than BP.

CONCLUSION

The use of black raspberry significantly lowered 24-h BP in prehypertensive patients during the 8-wk follow-up. Black raspberry used as a dietary supplement could be beneficial in reducing SBP in prehypertensive patients.