Long term effects of dietary sodium reduction on cardiovascular disease outcomes: observational follow-up of the trials of hypertension prevention (TOHP)

Patient characteristics associated with receipt of lifestyle behavior advice

BACKGROUND

Lifestyle behaviors such as reducing weight if overweight or obese, reducing salt intake, exercising, reducing alcohol intake, quitting smoking, and eating a healthy diet are related to the prevention and control of chronic diseases. However the amount of lifestyle advice provided by clinicians has been declining over the last decade.

METHODS

In 2002, a telephone survey was conducted to assess the quality of preventive care offered by health care providers. The study was a cross-sectional observational study of a randomly selected sample of 516 diverse individuals in Durham County, North Carolina. Information regarding age, sex, race, education, health conditions, and self-reported receipt of lifestyle advice was examined in the study.

RESULTS

The odds of receiving advice to engage in preventive lifestyle behaviors were significantly higher for those with a pre-existing diagnosis of diabetes or hypertension and for participants reporting poor health status. For example, the odds of receiving advice to control or lose weight was 8.32 (95% CI, 2.65, 26.75) among individuals reporting a diagnosis of diabetes. Similarly, the odds of reporting "receiving advice to reduce salt intake" was 6.97 (95% CI, 3.74, 13.00) among subjects reporting a diagnosis of hypertension.

LIMITATIONS

The results are from a cross-sectional study of a sample of individuals in only one county. Additionally, the results are based on patient self-reported information, which could be subject to recall and social desirability bias.

CONCLUSION

Patients with identified health problems were more likely than others to report being advised to adopt healthy lifestyle recommendations. Future research should examine methods to encourage health care providers to offer lifestyle advice to those without pre-existing illness.

Compound ion salt, a novel low-sodium salt substitute: from animal study to community-based population trial

BACKGROUND

Salt restriction, an important approach for primary and secondary prevention of hypertension, is undermined by unsatisfactory adherence. A salt-restriction study tested the efficacy and safety of a compound ion salt (CISalt) with low sodium content in an animal model and in a community-based population.

METHODS

In part 1, 8-week-old male spontaneously hypertensive rats (SHRs) were fed 1% CISalt in the study group and 8% or 1% normal salt (NSalt) in controls (n = 10 each) for 12 weeks. Blood pressure (BP) and urinary electrolytes were measured every 3 weeks. After 12 weeks, collagen deposition in the heart and kidney and the levels of angiotensin II (Ang II) and nitric oxide (NO) in plasma and renal cortex were measured. In part 2, a single-blind, randomized, 6-month controlled trial with CISalt was conducted in 248 persons (age >or=65 years) in 10 rural communities. Plasma renin activity and Ang II were included in blood and urinary measures at baseline and 6 months.

RESULTS

Reduced BP urinary protein excretion and reduced collagen in the heart and kidneys were significantly different in animals fed CISalt compared to controls. In human studies, at 6 months, mean systolic BP (SBP) was decreased by 9.6 mm Hg (95% confidence interval (CI): 13.1 to 6.1, P < 0.001) and diastolic BP (DBP) by 5.3 mm Hg (95% CI: 7.9 to 2.6, P < 0.001), respectively, compared to controls; urinary sodium excretion also decreased by 67.4 mmol/24 h (95% CI: 84.8 to 50.0, P < 0.001), and plasma renin activity was slightly increased by 0.19 ng/ml/h (95% CI: 0.04-0.33, P = 0.013). No adverse cardiovascular events were reported.

CONCLUSIONS

In these studies, CISalt lowered BP and showed end-organ protection in hypertensive animals and BP reduction in humans. CISalt appears to be a safe and acceptable strategy to reduce BP.

Angiotensin II maintains cerebral vascular relaxation via EGF receptor transactivation and ERK1/2

This study identified, on the integrative level, two components of the ANG II signaling pathway that lay downstream from the ANG II type 1 (AT(1)) receptor and are critically involved in maintaining vascular relaxation in cerebral resistance arteries. In these experiments, the relaxation of isolated middle cerebral arteries (MCA) in response to ACh (10(-9)-10(-5) M), iloprost (10(-16)-10(-11) g/ml), and reduced PO(2) was lost and the ratio of phospho-ERK/ERK1/2 was significantly reduced in aortas of male Sprague-Dawley rats fed a high-salt (HS; 4% NaCl) diet to suppress plasma ANG II levels. In salt-fed rats, relaxation of MCA in response to these vasodilator stimuli was restored by chronic (3 days) intravenous infusion of either ANG II (5 ngxkg(-1)xmin(-1)) or epidermal growth factor (EGF; 2 microg/h). The protective effect of ANG II infusion to restore vascular relaxation was eliminated by coinfusion of either the EGF receptor kinase inhibitor AG-1478 (20 microg/h), the ERK1/2 inhibitor PD-98059 (10 microg/h), or the protein synthesis inhibitor cycloheximide (5 microg/h). In rats fed a low-salt (0.4% NaCl) diet, MCA relaxation in response to ACh, reduced PO(2), and iloprost was eliminated by intravenous infusion of AG-1478, PD-98059, or cycloheximide. In ANG II-infused rats fed HS diet, and in rats fed LS diet, vasodilator responses to reduced PO(2) and iloprost were unaffected by the p38 MAP kinase inhibitor SB-203580 and the phosphatidylinositol 3-kinase inhibitor wortmannin. These findings indicate that maintenance of normal vascular relaxation mechanisms by ANG II in rat MCA requires activation of the EGF receptor kinase and ERK1/2.

Sociology meets genetics: sociogenetic implications for future management of hypertension and heart failure

Hypertension and heart failure contribute significantly to morbidity and mortality in the United States. Suboptimal control of these disease processes is multifactorial and involves poorly understood mechanisms affected by the environment (socioeconomic factors) and genetics (cell biology). Dietary sodium is an illustrative case. Although physicians intuitively accept that sodium affects renal and cardiovascular physiology, the complex overlay of genetics, environment, and culture is not practically addressed to make a meaningful difference in patient care. Optimal control of hypertension and heart failure will require a personalized care plan for each patient that includes lifestyle changes and carefully selected pharmacotherapy and also accounts for sociogenetic factors that affect each patient's life and thus his or her disease process. Physicians' cultural biases and perceptions also must be factored into this complex patient care equation.

Effect of modest salt reduction on blood pressure, urinary albumin, and pulse wave velocity in white, black, and Asian mild hypertensives

A reduction in salt intake lowers blood pressure. However, most previous trials were in whites with few in blacks and Asians. Salt reduction may also reduce other cardiovascular risk factors (eg, urinary albumin excretion, arterial stiffness). However, few well-controlled trials have studied these effects. We carried out a randomized double-blind crossover trial of salt restriction with slow sodium or placebo, each for 6 weeks, in 71 whites, 69 blacks, and 29 Asians with untreated mildly raised blood pressure. From slow sodium to placebo, urinary sodium was reduced from 165+/-58 (+/-SD) to 110+/-49 mmol/24 hours (9.7 to 6.5 g/d salt). With this reduction in salt intake, there was a significant decrease in blood pressure from 146+/-13/91+/-8 to 141+/-12/88+/-9 mm Hg (P<0.001), urinary albumin from 10.2 (IQR: 6.8 to 18.9) to 9.1 (6.6 to 14.0) mg/24 hours (P<0.001), albumin/creatinine ratio from 0.81 (0.47 to 1.43) to 0.66 (0.44 to 1.22) mg/mmol (P<0.001), and carotid-femoral pulse wave velocity from 11.5+/-2.3 to 11.1+/-1.9 m/s (P<0.01). Subgroup analysis showed that the reductions in blood pressure and urinary albumin/creatinine ratio were significant in all groups, and the decrease in pulse wave velocity was significant in blacks only. These results demonstrate that a modest reduction in salt intake, approximately the amount of the current public health recommendations, causes significant falls in blood pressure in all 3 ethnic groups. Furthermore, it reduces urinary albumin and improves large artery compliance. Although both could be attributable to the falls in blood pressure, they may carry additional benefits on reducing cardiovascular disease above that obtained from the blood pressure falls alone.

The internist's role in treating hypertension in hemodialysis patients

Hypertension in hemodialysis patients is typically treated with a combination of volume removal with dialysis--although limited by current dialysis paradigms--and hypertension medications. Unfortunately, most patients treated in this manner remain hypertensive. This contrasts with superior results obtained in clinical studies in which salt restriction and augmented dialytic volume removal normalized blood pressure without requiring medicines. These results are consistent with the role of excess volume as the main etiology of hypertension in end-stage renal disease (ESRD). Interdialytic blood pressure is now recognized as important to patient prognosis. These measurements are frequently obtained by internists at office visits. Internists and nephrologists should address both peri-dialysis and interdialysis hypertension in a collaborative manner. This strategy should focus on, as much as reasonably possible, salt restriction and dialytic volume removal rather than hypertension medicines.

Salt and high blood pressure

HBP (high blood pressure) is the leading risk of death in the world. Unfortunately around the world, blood pressure levels are predicted to become even higher, especially in developing countries. High dietary salt is an important contributor to increased blood pressure. The present review evaluates the association between excess dietary salt intake and the importance of a population-based strategy to lower dietary salt, and also highlights some salt-reduction strategies from selected countries. Evidence from diverse sources spanning animal, epidemiology and human intervention studies demonstrate the association between salt intake and HBP. Furthermore, animal studies indicate that short-term interventions in humans may underestimate the health risks associated with high dietary sodium. Recent intervention studies have found decreases in cardiovascular events following reductions in dietary sodium. Salt intake is high in most countries and, therefore, strategies to lower salt intake could be an effective means to reduce the increasing burden of HBP and the associated cardiovascular disease. Effective collaborative partnerships between governments, the food industry, scientific organizations and healthcare organizations are essential to achieve the WHO (World Health Organization)-recommended population-wide decrease in salt consumption to less than 5 g/day. In the milieu of increasing cardiovascular disease worldwide, particularly in resource-constrained low- and middle-income countries, salt reduction is one of the most cost-effective strategies to combat the epidemic of HBP, associated cardiovascular disease and improve population health.

Dietary sodium alters the prevalence of electrocardiogram determined left ventricular hypertrophy in hypertension

BACKGROUND

Determination of left ventricular hypertrophy (LVH) via electrocardiogram (ECG) is a known independent risk factor for cardiovascular morbidity and mortality in hypertension (HTN). Dietary sodium and HTN are both associated with unfavorable alterations in left ventricular mass, however, to what extent their interplay affects ECG screening for LVH is unclear.

METHODS

The effects of controlled dietary sodium manipulation on ECG determinants of LVH in hypertensive subjects were evaluated using well-established voltage criteria for LVH. ECGs from 80 hypertensive subjects were evaluated following random sequence assignment to 7 days of high sodium (HS) intake (200 mEq/24 h), and then 7 days of low sodium (LS) intake (10 mEq/24 h).

RESULTS

Sodium restriction over 7 days resulted in significant decreases in overall, and LVH-specific, ECG voltages. Most subjects exhibited decrements in overall ECG voltage with sodium restriction (72%); however, a smaller subset displayed higher voltages when on LS intake (28%). The prevalence of ECG-determined LVH was significantly lowered with LS diet (HS diet 22/80 (28%) vs. LS diet 8/80 (10%), P < 0.05). Subjects exhibiting reversal of LVH status with sodium restriction were younger, demonstrated salt sensitivity of blood pressure, and lower LVH-specific ECG voltage.

CONCLUSIONS

Short-term dietary sodium fluctuations can significantly alter overall ECG voltage and the prevalence of ECG-determined LVH in hypertensive individuals. Inclusion of dietary sodium assessment when screening hypertensive subjects for LVH by ECG may improve the consistency of cardiac risk assessment.

Teores de sódio e lipídios em refeições almoço consumidas por trabalhadores de uma empresa do município de Suzano, SP

OBJETIVO: Avaliar os valores de sódio e lipídios em refeições almoço consumidas por usuários de uma unidade de alimentação e nutrição. MÉTODOS: Análise laboratorial das porções médias consumidas, utilizando-se o método de fotometria de chama para determinação de sódio e o método de extração de lipídios totais por meio de solventes orgânicos. Os resultados foram comparados com as recomendações da Organização Mundial da Saúde e com as novas recomendações do Programa de Alimentação do Trabalhador. RESULTADOS: Observaram-se valores de sódio e lipídios acima das recomendações do Programa de Alimentação do Trabalhador. Neste estudo, o valor médio de sódio foi de 2435mg (DP=518mg) e o valor energético médio de lipídios foi de 329kcal (DP=40kcal) em uma porção média de refeição - 745g (DP=60g). CONCLUSÃO: São necessárias mudanças para que haja uma adequação das quantidades de sal e de lipídios utilizadas nas refeições, uma redução da utilização de alimentos que contenham grande quantidade de sódio e/ou gordura, e que se programem ações educativas junto aos usuários da unidade de alimentação e nutrição, para a melhoria da qualidade de vida de quem representa a força produtiva da empresa.

Is higher sodium intake associated with elevated systemic inflammation? A population-based study

BACKGROUND

Observational epidemiologic studies have suggested that a low-sodium diet is associated with reduced mortality.

OBJECTIVE

The objective was to test the hypothesis that a higher dietary intake of sodium is associated with increased systemic inflammation--a potential risk factor for both cardiovascular disease and cancer.

DESIGN

The study design consisted of a randomly selected, cross-sectional, population-based study of 2633 individuals surveyed in 1991, of whom 1597 participants provided paired urinary and blood samples permitting measurement of 24-h urinary sodium excretion and serum C-reactive protein (CRP) concentrations.

RESULTS

The mean (+/-SD) 24-h sodium intake for the population was 177 +/- 69 mmol. In the basic model adjusted for age, sex, and smoking, higher levels of 24-h sodium excretion were directly associated with serum CRP, with an increase in serum CRP of 1.20 mg/L per 100-mmol increment in sodium excretion (95% CI: 1.11, 1.30). However, this association was reduced after adjustment for body mass index, with an increase in serum CRP of 1.06 mg/L per 100-mmol increment in sodium excretion (95% CI: -1.02, 1.15).

CONCLUSIONS

We observed a linear association between an objective measure of sodium intake and serum CRP that may be influenced by confounding by body mass index. The magnitude of these associations suggests that dietary sodium consumption is unlikely to be an important modifiable risk factor for increased systemic inflammation.

High protein intake associates with cardiovascular events but not with loss of renal function

The long-term effects of higher dietary protein intake on cardiovascular and renal outcomes in the general population are not clear. We analyzed data from 8461 individuals who did not have renal disease and participated in two or three subsequent screenings (6.4-yr follow-up) in a prospective, community-based cohort study (Prevention of Renal and Vascular ENd-stage Disease [PREVEND]). We calculated daily protein intake from 24-h urinary urea excretion (Maroni formula) and used Cox proportional hazard models to analyze the associations between protein intake, cardiovascular events, and mortality. We used mixed-effects models to investigate the association between protein intake and change in renal function over time. The mean +/- SD daily protein intake was 1.20 +/- 0.27 g/kg. Protein intake was significantly associated with cardiovascular events during follow-up. The associations seemed U-shaped; compared with intermediate protein intake, individuals with either higher or lower protein intake had higher event rates. All-cause mortality and noncardiovascular mortality also were significantly associated with protein intake; individuals with low protein intake had the highest event rates. We found no association between baseline protein intake and rate of renal function decline during follow-up. In summary, in the general population, high protein intake does not promote accelerated decline of renal function but does associate with an increased risk for cardiovascular events.

Current challenges and unresolved problems in hypertensive disease

Over the past four or five decades, hypertension and cardiovascular medicine has experienced dramatic and innovative changes that have significantly reduced morbidity and mortality. A vast array of new antihypertensive compounds have been developed, which are able to inhibit many pathophysiologic mechanisms of the disease and prevent many of the outcomes in patients with hypertension. Much of this series of therapeutic breakthroughs have been the result of active participation of clinical scientists with tremendous and remarkable knowledge of and experience with the fundamental mechanisms of disease. In more recent years, much new information has appeared concerning the basis genetic and biologic mechanisms involved in cardiovascular and renal diseases. What remains of utmost importance is for members of the academic community with a wide spectrum of experience and points of view to continue to work with the fundamental problems and mechanisms of the diseases.

A translational framework for public health research

BACKGROUND

The paradigm of translational medicine that underpins frameworks such as the Cooksey report on the funding of health research does not adequately reflect the complex reality of the public health environment. We therefore outline a translational framework for public health research.

DISCUSSION

Our framework redefines the objective of translation from that of institutionalising effective interventions to that of improving population health by influencing both individual and collective determinants of health. It incorporates epidemiological perspectives with those of the social sciences, recognising that many types of research may contribute to the shaping of policy, practice and future research. It also identifies a pivotal role for evidence synthesis and the importance of non-linear and intersectoral interfaces with the public realm.

SUMMARY

We propose a research agenda to advance the field and argue that resources for 'applied' or 'translational' public health research should be deployed across the framework, not reserved for 'dissemination' or 'implementation'.

Salt intakes around the world: implications for public health

BACKGROUND

High levels of dietary sodium (consumed as common salt, sodium chloride) are associated with raised blood pressure and adverse cardiovascular health. Despite this, public health efforts to reduce sodium consumption remain limited to a few countries. Comprehensive, contemporaneous sodium intake data from around the world are needed to inform national/international public health initiatives to reduce sodium consumption.

METHODS

Use of standardized 24-h sodium excretion estimates for adults from the international INTERSALT (1985-87) and INTERMAP (1996-99) studies, and recent dietary and urinary sodium data from observational or interventional studies--identified by a comprehensive search of peer-reviewed and 'grey' literature--presented separately for adults and children. Review of methods for the estimation of sodium intake/excretion. Main food sources of sodium are presented for several Asian, European and Northern American countries, including previously unpublished INTERMAP data.

RESULTS

Sodium intakes around the world are well in excess of physiological need (i.e. 10-20 mmol/day). Most adult populations have mean sodium intakes >100 mmol/day, and for many (particularly the Asian countries) mean intakes are >200 mmol/day. Possible exceptions include estimates from Cameroon, Ghana, Samoa, Spain, Taiwan, Tanzania, Uganda and Venezuela, though methodologies were sub-optimal and samples were not nationally representative. Sodium intakes were commonly >100 mmol/day in children over 5 years old, and increased with age. In European and Northern American countries, sodium intake is dominated by sodium added in manufactured foods ( approximately 75% of intake). Cereals and baked goods were the single largest contributor to dietary sodium intake in UK and US adults. In Japan and China, salt added at home (in cooking and at the table) and soy sauce were the largest sources.

CONCLUSIONS

Unfavourably high sodium intakes remain prevalent around the world. Sources of dietary sodium vary largely worldwide. If policies for salt reduction at the population level are to be effective, policy development and implementation needs to target the main source of dietary sodium in the various populations.

Vascular consequences of dietary salt intake

Animal and human studies support an untoward effect of excess dietary NaCl (salt) intake on cardiovascular and renal function and life span. Recent work has promoted the concept that the endothelium, in particular, reacts to changes in dietary salt intake through a complex series of events that are independent of blood pressure and the renin-angiotensin-aldosterone axis. The cellular signaling events culminate in the intravascular production of transforming growth factor-beta (TGF-beta) and nitric oxide in response to increased salt intake. Plasticity of the endothelium is integral in the vascular remodeling consequences associated with excess salt intake, because nitric oxide serves as a negative regulator of TGF-beta production. Impairment of nitric oxide production, such as occurs with endothelial dysfunction in a variety of disease states, results in unopposed excess vascular TGF-beta production, which promotes reduced vascular compliance and augmented peripheral arterial constriction and hypertension. Persistent alterations in vascular function promote the increase in cardiovascular events and reductions in renal function that reduce life span during increased salt intake.

Salt and the metabolic syndrome

BACKGROUND AND AIMS

High blood pressure in subjects with the metabolic syndrome (MS) is largely related to dietary salt. We investigated in free-living men and women whether increase in dietary salt intake is associated with the presence and severity of the MS.

METHODS AND RESULTS

A total of 766 subjects (251M, 515F) of 44.9+/-0.5 years/age and SBP/DBP of 120+/-0.6/77+/-0.4 mmHg were studied. Twenty-four hour urinary sodium (UNa(+)) and potassium (UK(+)) excretions were 143+/-2.5 mmol (median: 131.5) and 48+/-0.9 mmol (median: 44). UNa(+) was higher in men than in women (median: 155.5 vs. 119.8 mmol/day; P<0.0001). UK(+) (r=0.34; P<0.0001), measures of obesity (r=0.26; P<0.0001) and BP (r=0.15; P<0.0001) were significantly associated with UNa(+). The association with BP was lost after adjusting for weight. Of the 766 subjects, 256 (33.4%) met the NCEP-ATPIII criteria for the MS. Median UNa(+) in men and women with no traits of the MS was 140 and 116.7 mmol/day, respectively (P<0.001), increasing to 176 in men and 135 mmol/day in women with 4-5 components of the syndrome (P<0.001). Weight, BMI and waist increased significantly across the quartiles of UNa(+) both in men and women; whereas, age, lipids and fasting glucose did not. SBP and DBP were associated with UNa(+) in men but not in women. UK(+) correlated with age in men and women (r=023; P<0.0001) and with obesity in women (r=0.14; P=0.001).

CONCLUSIONS

UNa(+) a measure of dietary sodium intake in free-living subjects was markedly increased in subjects with the MS. Higher UNa(+) was associated with obesity and higher BP, but not with age, dyslipidemia or fasting glucose.

Effects of a low-salt diet on flow-mediated dilatation in humans

BACKGROUND

The effect of salt reduction on vascular function, assessed by brachial artery flow-mediated dilatation (FMD), is unknown.

OBJECTIVE

Our aim was to compare the effects of a low-salt (LS; 50 mmol Na/d) diet with those of a usual-salt (US; 150 mmol Na/d) diet on FMD.

DESIGN

This was a randomized crossover design in which 29 overweight and obese normotensive men and women followed an LS diet and a US diet for 2 wk. Both diets had similar potassium and saturated fat contents and were designed to ensure weight stability. After each intervention, FMD, pulse wave velocity, augmentation index, and blood pressure were measured.

RESULTS

FMD was significantly greater (P = 0.001) with the LS diet (4.89 +/- 2.42%) than with the US diet (3.37 +/- 2.10%), systolic blood pressure was significantly (P = 0.02) lower with the LS diet (112 +/- 11 mm Hg) than with the US diet (117 +/- 13 mm Hg), and 24-h sodium excretion was significantly lower (P = 0.0001) with the LS diet (64.1 +/- 41.3 mmol) than with the US diet (156.3 +/- 56.7 mmol). There was no correlation between change in FMD and change in 24-h sodium excretion or change in blood pressure. No significant changes in augmentation index or pulse wave velocity were observed.

CONCLUSIONS

Salt reduction improves endothelium-dependant vasodilation in normotensive subjects independently of the changes in measured resting clinic blood pressure. These findings suggest additional cardioprotective effects of salt reduction beyond blood pressure reduction. The trial is registered with the Australian and New Zealand Clinical Trials Registry (unique identifier: ANZCTR12607000381482; http://www.anzctr.org.au/trial_view.aspx?ID=82159).

Joint effects of sodium and potassium intake on subsequent cardiovascular disease: the Trials of Hypertension Prevention follow-up study

BACKGROUND

Previous studies of dose-response effects of usual sodium and potassium intake on subsequent cardiovascular disease (CVD) have largely relied on suboptimal measures of intake.

METHODS

Two trials of sodium reduction and other interventions collected 24-hour urinary excretions intermittently during 18 months from September 17, 1987, to January 12, 1990 (Trials of Hypertension Prevention [TOHP] I), and during 36 months from December 18, 1990, to April 7, 1995 (TOHP II), among adults with prehypertension aged 30 to 54 years. Among adults not assigned to an active sodium reduction intervention, we assessed the relationship of a mean of 3 to 7 twenty-four-hour urinary excretions of sodium and potassium and their ratio with subsequent CVD (stroke, myocardial infarction, coronary revascularization, or CVD mortality) through 10 to 15 years of posttrial follow-up.

RESULTS

Among 2974 participants, follow-up information was obtained on 2275 participants (76.5%), with 193 CVD events. After adjustment for baseline variables and lifestyle changes, there was a nonsignificant trend in CVD risk across sex-specific quartiles of urinary sodium excretion (rate ratio [RR] from lowest to highest, 1.00, 0.99, 1.16, and 1.20; P = .38 for trend) and potassium excretion (RR, 1.00, 0.94, 0.91, and 0.64; P = .08 for trend) but a significant trend across quartiles of the sodium to potassium excretion ratio (RR, 1.00, 0.84, 1.18, and 1.50; P = .04 for trend). In models containing both measures simultaneously, linear effects were as follows: RR, 1.42; 95% confidence interval (CI), 0.99 to 2.04 per 100 mmol/24 h of urinary sodium excretion (P = .05); and 0.67; 0.41 to 1.10 per 50 mmol/24 h of urinary potassium excretion (P = .12). A model containing the sodium to potassium excretion ratio (RR, 1.24; 95% CI, 1.05-1.46; P = .01) had the lowest Bayes information criterion (best fit).

CONCLUSION

A higher sodium to potassium excretion ratio is associated with increased risk of subsequent CVD, with an effect stronger than that of sodium or potassium alone.

Salt restriction in kidney disease--a missed therapeutic opportunity?

The importance of salt restriction in the treatment of patients with renal disease has remained highly controversial. In the following we marshal the current evidence that salt plays a definite role in the genesis of hypertension and target organ damage, point to practical problems of salt restriction, and report on novel pathomechanisms of how salt affects blood pressure and causes target organ damage.

Salt, arterial pressure, and cardiovascular and renal damage

This brief review deals with some novel developments regarding the possible role of salt in the pathogenesis of cardiovascular and renal disorders. Studies in both humans and experimental animals are discussed. Increased salt intake is usually associated with an increase in arterial pressure although some controversies still exist. Salt sensitivity of arterial pressure (defined as an increase in arterial pressure on dietary salt overload) was demonstrated in many animal species as well as in humans. However, findings in rats, the most often used animal model, also demonstrated that this salt sensitivity was not uniform; some strains are salt sensitive, while other strains are salt resistant. Salt sensitivity of arterial pressure in humans is also not uniform; less than one-third of normotensive individuals and less than one-half of hypertensive individuals are salt sensitive. Of great importance are findings that excessive salt intake may damage target organs (cardiovascular system and kidneys) irrespective of arterial pressure. Together with an ever-growing consensus that sodium intake in acculturated societies is high, these findings also emphasize the need for reduction in salt intake. Therefore, the adverse cardiovascular and renal effects of salt continue to be a subject of intense study. Current data indicate that a reduction in salt intake should ameliorate, if not prevent, cardiovascular and renal morbidity and mortality, particularly among individuals with hypertension.

Salt restriction among hypertensive patients: modest blood pressure effect and no adverse effects

OBJECTIVE

Previous studies, mainly evaluating short-term very low salt diets, suggest that salt restriction may influence glucose and insulin metabolism, catecholamines, renin, aldosterone, and lipid levels adversely. The authors wanted to explore whether sodium restriction for eight weeks influenced insulin secretion unfavourably, and evaluate the efficacy and safety of such treatment also in terms of other parameters important in the management of hypertensive patients.

DESIGN

A double-blind randomized controlled parallel group designed trial. All participants received dietary advice aimed at a moderate salt-restricted diet. Half of the participants received salt capsules, the others received identical placebo capsules.

SETTING

General practice.

SUBJECTS

Forty-six hypertensive patients inadequately controlled by drug treatment.

MAIN OUTCOME MEASURES

Fasting serum insulin C-peptide and glucose and levels of these measures after oral glucose, blood pressure, serum aldosterone and lipids, peripheral resistance, and skin conductance.

RESULTS

Salt restriction did not influence glucose and insulin metabolism, aldosterone, or lipid levels adversely. We observed better blood pressure regulation in the low salt group than in the high salt group, with a systolic and diastolic blood pressure difference of 5/5 mmHg after eight weeks. The difference was only statistically significant for diastolic blood pressure, p 0.02.

CONCLUSION

This study revealed a modest diastolic blood pressure reducing effect of moderate sodium restriction. This reduction was obtained without any apparent unfavourable side effects such as increased insulin secretion, impaired glucose tolerance or dyslipidaemia.

An updated concept for left ventricular hypertrophy risk in hypertension

Left ventricular hypertrophy (LVH) was one of the first three "factors of risk" originally identified by the Framingham Heart Study predisposing the patient to premature morbidity and mortality resulting from coronary heart disease. Among the initial approaches toward specific risk reduction were antihypertensive agents that reduce left ventricular (LV) mass with control of arterial pressure. However, the indication to reduce risk from LVH has not been approved by the federal regulatory agency. All drugs that reduce arterial pressure are capable of decreasing LV mass. More recently, investigative efforts in the laboratory and clinic have focused on identifying specific epiphenomena that are responsible for risk; they include ischemia, fibrosis, apoptosis, dietary salt excess, and inflammatory factors. Newer clinical methods are becoming available to diagnose these alterations. Current antihypertensive therapy and management improve coronary blood flow and flow reserve, diminish ventricular fibrosis and apoptosis, employ established educational interventions to reduce dietary salt intake, and may prevent inflammatory factors (although the latter factor requires further study; and others, no doubt, will continue to be identified). Thus, present knowledge is available to apply this more current paradigm for the treatment of hypertension and to reduce risk from LVH.

A comprehensive review on salt and health and current experience of worldwide salt reduction programmes

Cardiovascular disease (CVD) is the leading cause of death and disability worldwide. Raised blood pressure (BP), cholesterol and smoking, are the major risk factors. Among these, raised BP is the most important cause, accounting for 62% of strokes and 49% of coronary heart disease. Importantly, the risk is throughout the range of BP, starting at systolic 115 mm Hg. There is strong evidence that our current consumption of salt is the major factor increasing BP and thereby CVD. Furthermore, a high salt diet may have direct harmful effects independent of its effect on BP, for example, increasing the risk of stroke, left ventricular hypertrophy and renal disease. Increasing evidence also suggests that salt intake is related to obesity through soft drink consumption, associated with renal stones and osteoporosis and is probably a major cause of stomach cancer. In most developed countries, a reduction in salt intake can be achieved by a gradual and sustained reduction in the amount of salt added to food by the food industry. In other countries where most of the salt consumed comes from salt added during cooking or from sauces, a public health campaign is needed to encourage consumers to use less salt. Several countries have already reduced salt intake, for example, Japan (1960-1970), Finland (1975 onwards) and now the United Kingdom. The challenge is to spread this out to all other countries. A modest reduction in population salt intake worldwide will result in a major improvement in public health.

Urinary sodium and potassium excretion and risk of hypertension in Chinese: report from a community-based cohort study in Taiwan

BACKGROUND

Dietary sodium intake is associated with blood pressure and hypertension risk. However, most of the studies have been conducted in whites and it is not clear whether the effects exist in Asian populations.

OBJECTIVE

The purpose of the present study was to investigate the role of 24-h urinary sodium excretion and hypertension risk among ethnic Chinese.

DESIGN

A prospective cohort design on community.

SETTING AND PARTICIPANTS

One thousand five hundred and twenty middle-aged and elderly participants who were free from hypertension at baseline and had available urine electrolyte data.

MAIN OUTCOME MEASURES

Hypertension incidence.

RESULTS

During a median 7.93 years of follow-up (interquartile range = 4.07-9.04 years), we documented 669 cases of incident hypertension. The multivariate risk was 1.26 (95% confidence interval = 1.01-1.57; P = 0.043) for individuals in the highest quartile of urinary sodium excretion as compared with those in the second quartile. A significant J-shape relationship between urinary sodium excretion and the risk of hypertension was observed, with the test for linear relation being rejected (P = 0.046). Participants who were in the highest quartile of urinary sodium excretion and higher baseline blood pressure had a 2.43-fold increased risk of hypertension (95% confidence interval = 1.72-3.22) compared with those in the lowest quartiles of urinary sodium and lower blood pressure.

CONCLUSION

Urinary sodium excretion was associated with the risk of hypertension among ethnic Chinese. Urinary sodium excretion, as a marker of dietary sodium intake, can be useful for a comprehensive evaluation of hypertension risk in Asian populations.

Effect of comprehensive therapeutic lifestyle changes on prehypertension

Although national clinical guidelines promulgate therapeutic lifestyle changes (TLC) as a cornerstone in the management of prehypertension, there is a perceived ineffectiveness of TLC in the real world. In this study of 2,478 ethnically diverse (African Americans n = 448, Caucasians n = 1,881) men (n = 666) and women (n = 1,812) with prehypertension and no known atherosclerotic cardiovascular disease, diabetes mellitus, or chronic kidney disease, we evaluated the clinical effectiveness of TLC in normalizing blood pressure (BP) without antihypertensive medications. Subjects were evaluated at baseline and after an average of 6 months of participation in a community-based program of TLC. TLC included exercise training, nutrition, weight management, stress management, and smoking cessation interventions. Baseline BP (125 +/- 8/79 +/- 3 mm Hg) decreased by 6 +/- 12/3 +/- 3 mm Hg (p <or=0.001), with 952 subjects (38.4%) normalizing their BP (p <or=0.001). In subjects with a baseline systolic BP of 120 to 139 mm Hg (n = 2,082), systolic BP decreased by 7 +/- 12 mm Hg (p <or=0.001). In subjects with a baseline diastolic BP of 80 to 89 mm Hg (n = 1,504), diastolic BP decreased by 6 +/- 3 mm Hg (p <or=0.001). There were no racial differences in the magnitude of reduction in BP; however, women had greater BP reductions than men (p <or=0.001). Also, subjects with a baseline body mass index (BMI) <30 kg/m(2) had a greater reduction in BP than those with a BMI >or=30 kg/m(2). In conclusion, the present study adds to previous research by reporting on the effectiveness, rather than the efficacy, of TLC when administered in a real-world, community-based setting.

Does a low sodium diet modify heart rate variability? A randomised placebo-controlled double-blind trial

BACKGROUND

Increased heart rate variability (HRV) is associated with a low risk of mortality, as is consuming a low sodium diet. As the survival benefits of a low sodium diet may be mediated partly by an increase in HRV, we have tested the hypothesis that adopting a low sodium diet increases HRV.

METHODS

We used a randomised double-blind placebo-controlled trial design. Participants were aged 18-65 years old, had a physician diagnosis of asthma. All adopted a low sodium diet and they were randomised to receive either 80 mmol/day of oral sodium supplements (normal sodium intake - NSI) or matched placebo (low sodium intake-LSI) for 6 weeks. The primary outcome was change in SDNN (standard deviation of the N-N intervals); secondary outcomes were changes in other time domain and frequency domain measures of HRV.

RESULTS

In those allocated to the LSI, mean daily urinary sodium excretion decreased by 22 mmol; and in those allocated to the NSI mean daily urinary sodium excretion increased by 31 mmol. There were no differences between the two groups for either the primary or secondary outcome measures. The mean difference in change in SDNN between those who received the LSI compared to the NSI was -2.7 ms (95% Confidence Intervals CI; -18.0 to +12.6).

CONCLUSIONS

Adopting a low sodium diet does not have an impact on SDNN over a 6 weeks period. Future studies should aim to achieve a larger change in dietary sodium intake for a longer duration than 6 weeks.

Measuring Salt Consumption to Guide Behavior Change in Applied Settings: A Critical Review

Objective.

A critical review of the accuracy of salt consumption measurement can enhance future dietary sodium interventions.

Data Source.

A review of the measures of salt consumption was conducted with a focus on the measurement that may facilitate behavior modification. Measures were critiqued for factors known to threaten the validity of behavioral measurement in applied settings.

Study Inclusion and Exclusion Criteria.

The review included observational, interventional, and measurement studies that used at least one measure of behavior indicative of salt consumption.

Data Extraction.

Eighteen articles were retrieved by examining their definitions of salt consumption to ensure a measurement of behavior and a discussion of factors known to influence behavior and its measurement.

Data Synthesis.

Articles meeting the above criteria were critically reviewed for factors related to a valid measurement of behavior: participant and setting characteristics, measurement definitions, and measurement procedures.

Results.

The results indicate that imprecise definitions of salt consumption and insensitive measurement tools limit valid measurement of salt-eating behaviors.

Conclusions.

Further research is needed to improve the specificity of measures of behaviors that are indicative of salt consumption and to produce tools that clinicians and patients may use for more accurate, and possibly real-time, salt consumption measurement. The increasing burden of cardiovascular disease in the aging U.S. population demands better methods to assess and subsequently control salt consumption in applied settings.

Effect of low vs. high dietary sodium on blood pressure levels in a normotensive Indo-Asian population

BACKGROUND

Hypertension is a major modifiable risk factor, and while sodium restriction in hypertensive patients appears effective, its role in normotensive individuals remains unclear. We assessed the effect of a low vs. high-sodium diet on blood pressure in normotensive Indo-Asian adults.

METHODS

A randomized, controlled, crossover trial was conducted on 200 normotensive subjects randomly selected from the general population in Karachi, Pakistan. Participants were randomized to either a low (20 mEq/day) or a high-sodium diet (220 mEq/day) for 1 week, followed by 1 week of washout, then the alternate diet for 1 week. The primary outcome was difference in systolic blood pressure (SBP) measured at the end of each phase in the overall population.

RESULTS

Mean (95% confidence interval) decline in 24-h urinary sodium excretion was 81.0 (69.6-92.4) mEq/day (P < 0.001), and in SBP was 1 (0-3)mm Hg (P = 0.17) between high and low-sodium phase. A significant interaction was detected (P = 0.001) between dietary sodium and baseline SBP with a greater adjusted mean (95% confidence interval) decline in SBP (6 (2-9)mm Hg) among participants with high-normal SBP (130-139 mm Hg) and no significant change (-1(-2 to 1)) in those with normal baseline SBP (<130 mm Hg), respectively.

CONCLUSIONS

Reducing sodium intake has a beneficial effect on blood pressure in Indo-Asians with high-normal SBP, at least in the short term. Given the ubiquity of high-normal blood pressure (BP), and frank hypertension in this population, we argue that primary prevention strategies, targeted at use of discretionary sodium, should now be designed and evaluated.

Nut consumption and risk of hypertension in US male physicians

BACKGROUND & AIMS

Hypertension is a risk factor for cardiovascular disease and dietary factors may play an important role in its prevention. We sought to examine the association between nut consumption and incident hypertension.

METHODS

Prospective cohort of 15,966 participants from the Physicians' Health Study I who were free of hypertension at baseline. Nut consumption was assessed using a simple abbreviated food questionnaire and hypertension was self-reported. We used Cox regression to estimate relative risks of hypertension according to nut consumption.

RESULTS

During 237,585 person-years of follow up, 8,423 new cases of hypertension occurred. Compared to subjects who did not consume nuts, multivariable adjusted hazard ratios (95% CI) for hypertension were 0.97 (0.91-1.03), 0.98 (0.92-1.05), 0.96 (0.89-1.03), and 0.82 (0.71-0.94) for nut consumption of 1-2 times per month and 1, 2-6, and > or = 7 times/week, respectively. In a secondary analysis stratified by body mass index, there was an inverse relation between nut intake and hypertension in lean subjects (p for trend 0.0019) but not in overweight or obese subjects (p for interaction 0.0037).

CONCLUSION

Our data suggest that nut consumption is associated with a lower risk of hypertension in US male physicians and that such relation may be influenced by adiposity.

Sodium intake and mortality follow-up in the Third National Health and Nutrition Examination Survey (NHANES III)

BACKGROUND

Sodium restriction is commonly recommended as a measure to lower blood pressure and thus reduce cardiovascular disease (CVD) and all-cause mortality. However, some studies have observed higher mortality associated with lower sodium intake.

OBJECTIVE

To test the hypothesis that lower sodium is associated with subsequent higher cardiovascular disease (CVD) and all cause mortality in the Third National Health and Nutrition Examination Survey (NHANES III).

DESIGN

Observational cohort study of mortality subsequent to a baseline survey.

PARTICIPANTS

Representative sample (n = 8,699) of non-institutionalized US adults age > or = 30, without history of CVD events, recruited between 1988-1994.

MEASUREMENTS AND MAIN RESULTS

Dietary sodium and calorie intakes estimated from a single baseline 24-h dietary recall. Vital status and cause of death were obtained from the National Death Index through the year 2000. Hazard ratio (HR) for CVD mortality of lowest to highest quartile of sodium, adjusted for calories and other CVD risk factors, in a Cox model, was 1.80 (95% CI 1.05, 3.08, p = 0.03). Non-significant trends of an inverse association of continuous sodium (per 1,000 mg) intake with CVD and all-cause mortality were observed with a 99% CI of 0.73, 1.06 (p = 0.07) and 0.86, 1.04 (p = 0.11), respectively, while trends for a direct association were not observed.

CONCLUSION

Observed associations of lower sodium with higher mortality were modest and mostly not statistically significant. However, these findings also suggest that for the general US adult population, higher sodium is unlikely to be independently associated with higher CVD or all-cause mortality.