Association of urinary sodium and potassium excretion with systolic blood pressure in the Dietary Approaches to Stop Hypertension Sodium Trial

Urinary sodium-potassium ratio as a genetic predictor of myocardial infarction

BACKGROUND

The relationship between the urinary sodium-potassium ratio (USPR) and risk factors for heart disease has been observed over time. We evaluated the relationship between USPR and myocardial infarction (MI).

METHODS

Causal relationships were estimated based on USPR and MI data from genome-wide association studies. The main analysis method for bidirectional two-sample Mendelian randomization was inverse-variance weighting (IVW), with four other supplementary methods used.

RESULTS

The IVW method indicated a positive correlation between USPR levels and MI (IVW, odds ratio = 1.504, 95% confidence interval: 1.108-2.041, P = 0.009). In contrast, the inverse analysis provided evidence suggesting that MI affected USPR (P > 0.05). The Cochran Q test showed heterogeneity, while the intercept test revealed no horizontal pleiotropy, and the leave-one-out analysis demonstrated that the analyses were reliable.

CONCLUSIONS

This study provides evidence for the causal effect of the USPR on MI; however, this was not the case in the opposite situation. It is plausible that the USPR serves as a promoting factor for MI.

Using Genetics to Inform Interventions Related to Sodium and Potassium in Hypertension

BACKGROUND

Hypertension is a key risk factor for major adverse cardiovascular events but remains difficult to treat in many individuals. Dietary interventions are an effective approach to lower blood pressure (BP) but are not equally effective across all individuals. BP is heritable, and genetics may be a useful tool to overcome treatment response heterogeneity. We investigated whether the genetics of BP could be used to identify individuals with hypertension who may receive a particular benefit from lowering sodium intake and boosting potassium levels.

METHODS

In this observational genetic study, we leveraged cross-sectional data from up to 296 475 genotyped individuals drawn from the UK Biobank cohort for whom BP and urinary electrolytes (sodium and potassium), biomarkers of sodium and potassium intake, were measured. Biologically directed genetic scores for BP were constructed specifically among pathways related to sodium and potassium biology (pharmagenic enrichment scores), as well as unannotated genome-wide scores (conventional polygenic scores). We then tested whether there was a gene-by-environment interaction between urinary electrolytes and these genetic scores on BP.

RESULTS

Genetic risk and urinary electrolytes both independently correlated with BP. However, urinary sodium was associated with a larger BP increase among individuals with higher genetic risk in sodium- and potassium-related pathways than in those with comparatively lower genetic risk. For example, each SD in urinary sodium was associated with a 1.47-mm Hg increase in systolic BP for those in the top 10% of the distribution of genetic risk in sodium and potassium transport pathways versus a 0.97-mm Hg systolic BP increase in the lowest 10% (P=1.95×10-3). This interaction with urinary sodium remained when considering estimated glomerular filtration rate and indexing sodium to urinary creatinine. There was no strong evidence of an interaction between urinary sodium and a standard genome-wide polygenic score of BP.

CONCLUSIONS

The data suggest that genetic risk in sodium and potassium pathways could be used in a precision medicine model to direct interventions more specifically in the management of hypertension. Intervention studies are warranted.

Primary Role of the Kidney in Pathogenesis of Hypertension

Previous transplantation studies and the concept of 'nephron underdosing' support the idea that the kidney plays a crucial role in the development of essential hypertension. This suggests that there are genetic factors in the kidney that can either elevate or decrease blood pressure. The kidney normally maintains arterial pressure within a narrow range by employing the mechanism of pressure-natriuresis. Hypertension is induced when the pressure-natriuresis mechanism fails due to both subtle and overt kidney abnormalities. The inheritance of hypertension is believed to be polygenic, and essential hypertension may result from a combination of genetic variants that code for renal tubular sodium transporters or proteins involved in regulatory pathways. The renin-angiotensin-aldosterone system (RAAS) and sympathetic nervous system (SNS) are the major regulators of renal sodium reabsorption. Hyperactivity of either the RAAS or SNS leads to a rightward shift in the pressure-natriuresis curve. In other words, hypertension is induced when the activity of RAAS and SNS is not suppressed despite increased salt intake. Sodium overload, caused by increased intake and/or reduced renal excretion, not only leads to an expansion of plasma volume but also to an increase in systemic vascular resistance. Endothelial dysfunction is caused by an increased intracellular Na+ concentration, which inhibits endothelial nitric oxide (NO) synthase and reduces NO production. The stiffness of vascular smooth muscle cells is increased by the accumulation of intracellular Na+ and subsequent elevation of cytoplasmic Ca++ concentration. In contrast to the hemodynamic effects of osmotically active Na+, osmotically inactive Na+ stimulates immune cells and produces proinflammatory cytokines, which contribute to hypertension. When this occurs in the gut, the microbiota may become imbalanced, leading to intestinal inflammation and systemic hypertension. In conclusion, the primary cause of hypertension is sodium overload resulting from kidney dysregulation.

Dissociation of sodium-chloride cotransporter expression and blood pressure during chronic high dietary potassium supplementation

Dietary potassium (K+) supplementation is associated with a lowering effect in blood pressure (BP), but not all studies agree. Here, we examined the effects of short- and long-term K+ supplementation on BP in mice, whether differences depend on the accompanying anion or the sodium (Na+) intake and molecular alterations in the kidney that may underlie BP changes. Relative to the control diet, BP was higher in mice fed a high NaCl (1.57% Na+) diet for 7 weeks or fed a K+-free diet for 2 weeks. BP was highest on a K+-free/high NaCl diet. Commensurate with increased abundance and phosphorylation of the thiazide sensitive sodium-chloride-cotransporter (NCC) on the K+-free/high NaCl diet, BP returned to normal with thiazides. Three weeks of a high K+ diet (5% K+) increased BP (predominantly during the night) independently of dietary Na+ or anion intake. Conversely, 4 days of KCl feeding reduced BP. Both feeding periods resulted in lower NCC levels but in increased levels of cleaved (active) α and γ subunits of the epithelial Na+ channel ENaC. The elevated BP after chronic K+ feeding was reduced by amiloride but not thiazide. Our results suggest that dietary K+ has an optimal threshold where it may be most effective for cardiovascular health.

The perspective of hypertension and salt intake in Chinese population

Salt intake is too high nowadays. It has been widely recognized that there is a close relationship between hypertension (HTN) and dietary salt intake. Investigations reveal that long-term high salt intake, mainly sodium intake, induces a relevant increase in blood pressure in hypertensive and normotensive individuals. According to most scientific evidence, a diet with high salt intake in public increases cardiovascular risk, salted-related HTN, and other HTN-associated outcomes. Given the clinical importance, this review aims to present the prevalence of HTN and trends in salt intake in the Chinese population and will comprehensively discuss the risk factors, causes, and mechanisms of the association between salt intake and HTN. The review also highlights the education of Chinese people regarding salt intake and the cost-effectiveness of salt reduction from a global perspective. Finally, the review will emphasize the need to customize the unique Chinese practices to reduce salt intake and how awareness changes people's eating lifestyle and helps adopt diet salt reduction strategies.

The World Hypertension League Science of Salt: a regularly updated systematic review of salt and health outcomes studies (Sept 2019 to Dec 2020)

The World Hypertension League Science of Salt health outcomes review series highlights high-quality publications relating to salt intake and health outcomes. This review uses a standardised method, outlined in previous reviews and based on methods developed by WHO, to identify and critically appraise published articles on dietary salt intake and health outcomes. We identified 41 articles published between September 2019 to December 2020. Amongst these, two studies met the pre-specified methodological quality criteria for critical appraisal. They were prospective cohort studies and examined physical performance and composite renal outcomes as health outcomes. Both found an association between increased/higher sodium intake and poorer health outcomes. Few studies meet criteria for high-quality methods. This review adds further evidence that dietary salt reduction has health benefits and strengthens evidence relating to health outcomes other than blood pressure and cardiovascular disease. We observe that most studies on dietary sodium do not have adequate methodology to reliably assess sodium intake and its association with health outcomes.

Potassium homeostasis: sensors, mediators, and targets

Transmembrane potassium (K) gradients are key determinants of membrane potential that can modulate action potentials, control muscle contractility, and influence ion channel and transporter activity. Daily K intake is normally equal to the amount of K in the entire extracellular fluid (ECF) creating a critical challenge - how to maintain ECF [K] and membrane potential in a narrow range during feast and famine. Adaptations to maintain ECF [K] include sensing the K intake, sensing ECF [K] vs. desired set-point and activating mediators that regulate K distribution between ECF and ICF, and regulate renal K excretion. In this focused review, we discuss the basis of these adaptions, including (1) potential mechanisms for rapid feedforward signaling to kidney and muscle after a meal (before a rise in ECF [K]), (2) how skeletal muscles sense and respond to changes in ECF [K], (3) effects of K on aldosterone biosynthesis, and (4) how the kidney responds to changes in ECF [K] to modify K excretion. The concepts of sexual dimorphisms in renal K handling adaptation are introduced, and the molecular mechanisms that can account for the benefits of a K-rich diet to maintain cardiovascular health are discussed. Although the big picture of K homeostasis is becoming more clear, we also highlight significant pieces of the puzzle that remain to be solved, including knowledge gaps in our understanding of initiating signals, sensors and their connection to homeostatic adjustments of ECF [K].

Dietary Management of Heart Failure: DASH Diet and Precision Nutrition Perspectives

Heart failure (HF) is a major health care burden increasing in prevalence over time. Effective, evidence-based interventions for HF prevention and management are needed to improve patient longevity, symptom control, and quality of life. Dietary Approaches to Stop Hypertension (DASH) diet interventions can have a positive impact for HF patients. However, the absence of a consensus for comprehensive dietary guidelines and for pragmatic evidence limits the ability of health care providers to implement clinical recommendations. The refinement of medical nutrition therapy through precision nutrition approaches has the potential to reduce the burden of HF, improve clinical care, and meet the needs of diverse patients. The aim of this review is to summarize current evidence related to HF dietary recommendations including DASH diet nutritional interventions and to develop initial recommendations for DASH diet implementation in outpatient HF management. Articles involving human studies were obtained using the following search terms: Dietary Approaches to Stop Hypertension (DASH diet), diet pattern, diet, metabolism, and heart failure. Only full-text articles written in English were included in this review. As DASH nutritional interventions have been proposed, limitations of these studies are the small sample size and non-randomization of interventions, leading to less reliable evidence. Randomized controlled interventions are needed to offer definitive evidence related to the use of the DASH diet in HF management.