Dietary sodium and health: more than just blood pressure

Editor-in-Chief's Top Picks From 2015: Part One

Each week, I record audio summaries for every article in JACC, as well as an issue summary. While this process has been time-consuming, I have become very familiar with every paper that we publish. Thus, I have personally selected the papers (both original investigations and review articles) from 13 distinct specialties for your review. In addition to my personal choices, I have included manuscripts that have been the most accessed or downloaded on our websites, as well as those selected by the JACC Editorial Board members. There are approximately 130 articles selected across this 2-part series, which represent less than 3% of the papers submitted to the Journal in 2015. In order to present the full breadth of this important research in a consumable fashion, we will present these manuscripts over the course of 2 issues in JACC. Part One includes the sections: Congenital Heart Disease, Coronary Disease & Interventions, CVD Prevention & Health Promotion, Cardiac Failure, Cardiomyopathies, Genetics, Omics, & Tissue Regeneration, and Hypertension (1-60). Part Two includes the sections: Imaging, Metabolic Disorders & Lipids, Rhythm Disorders, Statistics, Valvular Heart Disease, and Vascular Medicine.

The health gains and cost savings of dietary salt reduction interventions, with equity and age distributional aspects

BACKGROUND

A "diet high in sodium" is the second most important dietary risk factor for health loss identified in the Global Burden of Disease Study 2013. We therefore aimed to model health gains and costs (savings) of salt reduction interventions related to salt substitution and maximum levels in bread, including by ethnicity and age. We also ranked these four interventions compared to eight other modelled interventions.

METHODS

A Markov macro-simulation model was used to estimate QALYs gained and net health system costs for four dietary sodium reduction interventions, discounted at 3 % per annum. The setting was New Zealand (NZ) (2.3 million adults, aged 35+ years) which has detailed individual-level administrative cost data.

RESULTS

The health gain was greatest for an intervention where most (59 %) of the sodium in processed foods was replaced by potassium and magnesium salts. This intervention gained 294,000 QALYs over the remaining lifetime of the cohort (95 % UI: 238,000 to 359,000; 0.13 QALY per 35+ year old). Such salt substitution also produced the highest net cost-savings of NZ$ 1.5 billion (US$ 1.0 billion) (95 % UI: NZ$ 1.1 to 2.0 billion). All interventions generated relatively larger per capita QALYs for men vs women and for the indigenous Māori population vs non-Māori (e.g., 0.16 vs 0.12 QALYs per adult for the 59 % salt substitution intervention). Of relevance to workforce productivity, in the first 10 years post-intervention, 22 % of the QALY gain was among those aged <65 years (and 37 % for those aged <70).

CONCLUSIONS

The benefits are consistent with the international literature, with large health gains and cost savings possible from some, but not all, sodium reduction interventions. Health gain appears likely to occur among working-age adults and all interventions contributed to reducing health inequalities.

Modeling health gains and cost savings for ten dietary salt reduction targets

BACKGROUND

Dietary salt reduction is included in the top five priority actions for non-communicable disease control internationally. We therefore aimed to identify health gain and cost impacts of achieving a national target for sodium reduction, along with component targets in different food groups.

METHODS

We used an established dietary sodium intervention model to study 10 interventions to achieve sodium reduction targets. The 2011 New Zealand (NZ) adult population (2.3 million aged 35+ years) was simulated over the remainder of their lifetime in a Markov model with a 3 % discount rate.

RESULTS

Achieving an overall 35 % reduction in dietary salt intake via implementation of mandatory maximum levels of sodium in packaged foods along with reduced sodium from fast foods/restaurant food and discretionary intake (the "full target"), was estimated to gain 235,000 QALYs over the lifetime of the cohort (95 % uncertainty interval [UI]: 176,000 to 298,000). For specific target components the range was from 122,000 QALYs gained (for the packaged foods target) down to the snack foods target (6100 QALYs; and representing a 34-48 % sodium reduction in such products). All ten target interventions studied were cost-saving, with the greatest costs saved for the mandatory "full target" at NZ$1260 million (US$820 million). There were relatively greater health gains per adult for men and for Māori (indigenous population).

CONCLUSIONS

This work provides modeling-level evidence that achieving dietary sodium reduction targets (including specific food category targets) could generate large health gains and cost savings for a national health sector. Demographic groups with the highest cardiovascular disease rates stand to gain most, assisting in reducing health inequalities between sex and ethnic groups.

High Salt Intake Is Independently Associated With Hypertensive Target Organ Damage

The authors tested the hypothesis that high salt intake is associated with hypertensive target organ damage (TOD) independent of blood pressure (BP), and oxidative stress is a modifying factor of this association. A total of 369 community-dwelling Japanese adults (mean age, 67.5 years; 56.6% women) were examined in this observational study. At the patients' annual health check-ups, urinary salt excretion (U-SALT), 8-hydroxy-2'-deoxyguanosine (8-OHdG), and albumin-creatinine ratio (UACR) were measured from first morning urine. U-SALT (β=0.14, P=.016) and 8-OHdG (β=0.13, P=.018) were both independently associated with logUACR. U-SALT was associated with TOD independent of BP level, and oxidative stress may be a modifying factor in the association between high salt intake and TOD. The elevation of 8-OHdG may be involved in the pathophysiology of TOD induced by salt intake.

Legal Regulation of Sodium Consumption to Reduce Chronic Conditions

In the United States, tens of thousands of Americans die each year of heart disease, stroke, or other chronic conditions tied to hypertension from long-term overconsumption of sodium compounds. Major strides to lower dietary sodium have been made over decades, but the goal of reducing Americans' daily consumption is elusive. The Food and Drug Administration (FDA) has been urged to consider stronger regulatory limits on sodium, especially in processed and prepared foods. Still, FDA categorizes salt (and many other sodium compounds) as "generally recognized as safe," meaning they can be added to foods when ingested in reasonable amounts. Legal reforms or actions at each level of government offer traditional and new routes to improving chronic disease outcomes. However, using law as a public health tool must be assessed carefully, given potential trade-offs and unproven efficacy.

Renal Effects and Underlying Molecular Mechanisms of Long-Term Salt Content Diets in Spontaneously Hypertensive Rats

Several evidences have shown that salt excess is an important determinant of cardiovascular and renal derangement in hypertension. The present study aimed to investigate the renal effects of chronic high or low salt intake in the context of hypertension and to elucidate the molecular mechanisms underlying such effects. To this end, newly weaned male SHR were fed with diets only differing in NaCl content: normal salt (NS: 0.3%), low salt (LS: 0.03%), and high salt diet (HS: 3%) until 7 months of age. Analysis of renal function, morphology, and evaluation of the expression of the main molecular components involved in the renal handling of albumin, including podocyte slit-diaphragm proteins and proximal tubule endocytic receptors were performed. The relationship between diets and the balance of the renal angiotensin-converting enzyme (ACE) and ACE2 enzymes was also examined. HS produced glomerular hypertrophy and decreased ACE2 and nephrin expressions, loss of morphological integrity of the podocyte processes, and increased proteinuria, characterized by loss of albumin and high molecular weight proteins. Conversely, severe hypertension was attenuated and renal dysfunction was prevented by LS since proteinuria was much lower than in the NS SHRs. This was associated with a decrease in kidney ACE/ACE2 protein and activity ratio and increased cubilin renal expression. Taken together, these results suggest that LS attenuates hypertension progression in SHRs and preserves renal function. The mechanisms partially explaining these findings include modulation of the intrarenal ACE/ACE2 balance and the increased cubilin expression. Importantly, HS worsens hypertensive kidney injury and decreases the expression nephrin, a key component of the slit diaphragm.

Over-salting ruins the balance of the immune menu

Regulatory components of the immune system are critical for preventing unintended activation of immune cells. Failure to prevent this unintended activation raises the risk of developing exaggerated inflammation and autoimmunity. In this issue of the JCI, Binger et al. and Hernandez et al. report that salt can play an important role in undermining regulatory mechanisms of the innate and adaptive immune systems. High salt levels interfere with alternative activation of macrophages (M2), which function in attenuating tissue inflammation and promoting wound healing. High salt also impairs Treg function by inducing IFNγ production in these cells. Together, these results provide evidence that environmental signals in the presence of high dietary salt enhance proinflammatory responses by interfering with both innate and adaptive regulatory mechanisms.

Resistant hypertension in type 2 diabetes: prevalence and patients characteristics

BACKGROUND AND AIMS

Resistant hypertension is defined as failure to achieve blood pressure lower than 140/90 mmHg when using three antihypertensive agents or controlled blood pressure with four or more drugs. We aimed at assessing the prevalence of resistant hypertension and to describe a type 2 diabetes population with resistant hypertension.

METHODS

The retrospective observational study included (n=73) type 2 diabetes subjects with resistant hypertension selected from (n=728) subjects admitted to the Centre of Diabetes, Cluj, Romania.

RESULTS

The subjects (70% women) had a mean age of 65.0±8.9 yrs. and diabetes duration 11(6-19) yrs. Prevalence of resistant hypertension was 10%. Chronic diabetes complications and cardiovascular disease were present in 77% and 56% of subjects respectively. On admission, antihypertensive drugs used were: angiotensin-converting enzyme inhibitors or angiotensin II receptors blockers 93%, β-blockers 88%, diuretics 78%, calcium channels blockers 59%, adrenergic α-antagonists 11%. Systolic and diastolic blood pressure were lower in the last compared to first admission day. Diuretics and calcium channels blockers were the most frequently newly added antihypertensive agents.

CONCLUSION

Although the prevalence of resistant hypertension in type 2 diabetes did not differ from the general population, we observed that these patients had increased frequency of chronic diabetic complications. Angiotensin-converting enzyme inhibitors or angiotensin II receptors and β-blockers were the most used antihypertensive drugs, while the most frequently newly prescribed drugs were diuretics and calcium channel blockers.

Salt Sensitivity and Hypertension: A Paradigm Shift from Kidney Malfunction to Vascular Endothelial Dysfunction

Hypertension is a complex trait determined by both genetic and environmental factors and is a major public health problem due to its high prevalence and concomitant increase in the risk for cardiovascular disease. With the recent large increase of dietary salt intake in most developed countries, the prevalence of hypertension increases tremendously which is about 30% of the world population. There is substantial evidence that suggests some people can effectively excrete high dietary salt intake without an increase in arterial BP, and another people cannot excrete effectively without an increase in arterial BP. Salt sensitivity of BP refers to the BP responses for changes in dietary salt intake to produce meaningful BP increases or decreases. The underlying mechanisms that promote salt sensitivity are complex and range from genetic to environmental influences. The phenotype of salt sensitivity is therefore heterogeneous with multiple mechanisms that potentially link high salt intake to increases in blood pressure. Moreover, excess salt intake has functional and pathological effects on the vasculature that are independent of blood pressure. Epidemiologic data demonstrate the role of high dietary salt intake in mediating cardiovascular and renal morbidity and mortality. Almost five decades ago, Guyton and Coleman proposed that whenever arterial pressure is elevated, pressure natriuresis enhances the excretion of sodium and water until blood volume is reduced sufficiently to return arterial pressure to control values. According to this hypothesis, hypertension can develop only when something impairs the excretory ability of sodium in the kidney. However, recent studies suggest that nonosmotic salt accumulation in the skin interstitium and the endothelial dysfunction which might be caused by the deterioration of vascular endothelial glycocalyx layer (EGL) and the epithelial sodium channel on the endothelial luminal surface (EnNaC) also play an important role in nonosmotic storage of salt. These new concepts emphasize that sodium homeostasis and salt sensitivity seem to be related not only to the kidney malfunction but also to the endothelial dysfunction. Further investigations will be needed to assess the extent to which changes in the sodium buffering capacity of the skin interstitium and develop the treatment strategy for modulating the endothelial dysfunction.