Low urinary sodium is associated with greater risk of myocardial infarction among treated hypertensive men

Dietary sodium intake and cardiovascular mortality: controversy resolved?

Universal reduction in sodium intake has long been recommended, largely because of its proven ability to lower blood pressure for some. However, multiple randomized trials have also demonstrated that similar reductions in sodium increase plasma renin activity and aldosterone secretion, insulin resistance, sympathetic nerve activity, serum cholesterol, and triglyceride levels. Thus, the health consequences of reducing sodium cannot be predicted by its impact on any single physiologic characteristic but will reflect the net of conflicting effects. Some 23 observational studies (>360,000 subjects and >26,000 end points) linking sodium intake to cardiovascular outcomes have yielded conflicting results. In subjects with average sodium intakes of less than 4.5 g/day, most have found an inverse association of intake with outcome; in subjects with average intakes greater than 4.5 g/day, most reported direct associations. Finally, in two, a "J-shaped" relation was detected. In addition, three randomized trials have found that heart failure subjects allocated to 1.8 g of sodium have significantly increased morbidity and mortality compared with those at 2.8 g. At the same time, a randomized study in retired Taiwanese men found that allocation to an average intake of 3.8 g improved survival compared with 5.3 g. Taken together, these data provide strong support for a "J-shaped" relation of sodium to cardiovascular outcomes. Sodium intakes above and below the range of 2.5-6.0 g/day are associated with increased cardiovascular risk. This robust body of evidence does not support universal reduction of sodium intake.

Habitual dietary sodium intake is inversely associated with coronary flow reserve in middle-aged male twins

BACKGROUND

Evidence links dietary sodium to hypertension and cardiovascular disease (CVD), but investigation of its influence on cardiovascular function is limited.

OBJECTIVE

We examined the relation between habitual dietary sodium and coronary flow reserve (CFR), which is a measure of overall coronary vasodilator capacity and microvascular function. We hypothesized that increased sodium consumption is associated with lower CFR.

DESIGN

Habitual daily sodium intake for the previous 12 mo was measured in 286 male middle-aged twins (133 monozygotic and dizygotic pairs and 20 unpaired twins) by using the Willett food-frequency questionnaire. CFR was measured by positron emission tomography [N(13)]-ammonia, with quantitation of myocardial blood flow at rest and after adenosine stress. Mixed-effects regression analysis was used to assess the association between dietary sodium and CFR.

RESULTS

An increase in dietary sodium of 1000 mg/d was associated with a 10.0% lower CFR (95% CI: -17.0%, -2.5%) after adjustment for demographic, lifestyle, nutritional, and CVD risk factors (P = 0.01). Across quintiles of sodium consumption, dietary sodium was inversely associated with CFR (P-trend = 0.03), with the top quintile (>1456 mg/d) having a 20% lower CFR than the bottom quintile (<732 mg /d). This association also persisted within pairs: a 1000-mg/d difference in dietary sodium between brothers was associated with a 10.3% difference in CFR after adjustment for potential confounders (P = 0.02).

CONCLUSIONS

Habitual dietary sodium is inversely associated with CFR independent of CVD risk factors and shared familial and genetic factors. Our study suggests a potential novel mechanism for the adverse effects of dietary sodium on the cardiovascular system. This trial was registered at clinicaltrials.gov as NCT00017836.

Salt consumption and cardiovascular, renal, and hypertensive diseases: clinical and mechanistic aspects

PURPOSE OF REVIEW

This review will discuss some relevant and novel studies on the relationship between sodium intake and cardiovascular structure and function, focusing on blood pressure independent effects of salt on the heart, arteries, and kidneys.

RECENT FINDINGS

Several new reports clearly demonstrate the role of high dietary salt in mediating cardiovascular and renal morbidity and mortality including stroke, myocardial infarction, arterial stiffening, heart failure, and renal insufficiency. A number of recent studies also indicate that in addition to increased sodium intake, simultaneous decrease in potassium intake may aggravate adverse cardiovascular and renal manifestations.

SUMMARY

It is now generally accepted that there is a direct positive correlation between dietary salt and arterial pressure. Thus, the beneficial effects of dietary salt reduction are, at least in part, due to a decrease in arterial pressure. Furthermore, the beneficial, pressure-independent effects of sodium restriction on the heart, blood vessels, and kidneys are being increasingly recognized, but not generally appreciated.

Dialysate sodium concentration and the association with interdialytic weight gain, hospitalization, and mortality

BACKGROUND AND OBJECTIVES

Recommendations to decrease the dialysate sodium (DNa) prescription demand analyses of patient outcomes. We analyzed morbidity and mortality at various levels of DNa, simultaneously accounting for interdialytic weight gain (IDWG) and for the mortality risk associated with lower predialysis serum sodium (SNa) levels.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We used multiply-adjusted linear mixed models to evaluate the magnitude of IDWG and Cox proportional hazards models to assess hospitalizations and deaths in 29,593 patients from the Dialysis Outcomes and Practice Patterns Study with baseline DNa and SNa as predictors, categorized according to lowest to highest levels.

RESULTS

IDWG increased with higher DNa across all SNa categories, by 0.17% of body weight per 2 mEq/L higher DNa; however, higher DNa was not associated with higher mortality in a fully adjusted model (also adjusted for SNa; hazard ratio [HR]=0.98 per 2 mEq/L higher DNa, 95% confidence interval [CI] 0.95-1.02). Instead, higher DNa was associated with lower hospitalization risk (HR=0.97 per 2 mEq/L higher DNa, 95% CI 0.95-1.00, P=0.04). Additional adjustments for IDWG did not change these results. In sensitivity analyses restricted to study facilities, in which 90%-100% of patients have the same DNa (56%), the adjusted HR for mortality was 0.88 per 2 mEq/L higher DNa (95% CI 0.83-0.94). These analyses represented a pseudo-randomized experiment in which the association between DNa and mortality is unlikely to have been confounded by indication.

CONCLUSIONS

In the absence of randomized prospective studies, the benefit of reducing IDWG by decreasing DNa prescriptions should be carefully weighed against an increased risk for adverse outcomes.

Enduring direct association of baseline plasma renin activity with all-cause and cardiovascular mortality in hypertensive patients

BACKGROUND

Plasma renin activity (PRA) has been associated with cardiovascular disease mortality (CVD) events among hypertensive patients. We now report a long-term follow-up to assess the enduring association of PRA to CVD and all-cause mortality.

METHODS

Participants (3,791) in a systematic hypertension treatment study had entry systolic blood pressure (BP) ≥140 mm Hg and mean age 52. CVD and all-cause mortality was ascertained for mean of 16 years. Pretreatment PRA was analyzed as a continuous variable, and by tertiles. The 10-year Framingham score was similarly examined. Hazard ratios (HRs) were estimated from multivariate Cox proportional hazard models.

RESULTS

There were 804 deaths, and 360 (45%) were CVD. PRA was associated with all-cause mortality and CVD, but not cancer or non-CVD. Although T3 had lower mean baseline and follow-up systolic BP than T1, (146 vs. 152 mm Hg (P < 0.001) and 135 vs. 139 mm Hg (P < 0.001), respectively), T3 had 37% higher all-cause mortality (HR: 1.37, 95% confidence interval (CI): 1.15-1.63, P < 0.001) and 70% higher CVD mortality (HR: 1.70, 95% CI: 1.29-2.23, P < 0.001) after adjustment. The difference between T3 and T1 in mortality from coronary artery disease and myocardial infarction was more pronounced than for all CVD. PRA also significantly improved CVD risk estimation provided by Framingham.

CONCLUSIONS

These findings extend and reinforce previous evidence that pretreatment PRA has a significant, independent, specific, and direct long-term association with CVD mortality. Moreover, PRA adds significantly to risk identified by the Framingham score.

The association between dietary sodium intake, ESRD, and all-cause mortality in patients with type 1 diabetes

OBJECTIVE

Many guidelines recommend reduced consumption of salt in patients with type 1 diabetes, but it is unclear whether dietary sodium intake is associated with mortality and end-stage renal disease (ESRD).

RESEARCH DESIGN AND METHODS

In a nationwide multicenter study (the FinnDiane Study) between 1998 and 2002, 2,807 enrolled adults with type 1 diabetes without ESRD were prospectively followed. Baseline urinary sodium excretion was estimated on a 24-h urine collection. The predictors of all-cause mortality and ESRD were determined by Cox regression and competing risk modeling, respectively.

RESULTS

The median follow-up for survival analyses was 10 years, during which 217 deaths were recorded (7.7%). Urinary sodium excretion was nonlinearly associated with all-cause mortality, such that individuals with the highest daily urinary sodium excretion, as well as the lowest excretion, had reduced survival. This association was independent age, sex, duration of diabetes, the presence and severity of chronic kidney disease (CKD) (estimated glomerular filtration rate [eGFR] and log albumin excretion rate), the presence of established cardiovascular disease, and systolic blood pressure. During follow-up, 126 patients developed ESRD (4.5%). Urinary sodium excretion was inversely associated with the cumulative incidence of ESRD, such that individuals with the lowest sodium excretion had the highest cumulative incidence of ESRD.

CONCLUSIONS

In patients with type 1 diabetes, sodium was independently associated with all-cause mortality and ESRD. Although we have not demonstrated causality, these findings support the calls for caution before applying salt restriction universally. Clinical trials must be performed in diabetic patients to formally test the utility/risk of sodium restriction in this setting.

Dietary salt intake and mortality in patients with type 2 diabetes

OBJECTIVE

Many guidelines recommend that patients with type 2 diabetes should aim to reduce their intake of salt. However, the precise relationship between dietary salt intake and mortality in patients with type 2 diabetes has not been previously explored.

RESEARCH DESIGN AND METHODS

Six hundred and thirty-eight patients attending a single diabetes clinic were followed in a prospective cohort study. Baseline sodium excretion was estimated from 24-h urinary collections (24hU(Na)). The predictors of all-cause and cardiovascular mortality were determined by Cox regression and competing risk modeling, respectively.

RESULTS

The mean baseline 24hU(Na) was 184 ± 73 mmol/24 h, which remained consistent throughout the follow-up (intraindividual coefficient of variation [CV] 23 ± 11%). Over a median of 9.9 years, there were 175 deaths, 75 (43%) of which were secondary to cardiovascular events. All-cause mortality was inversely associated with 24hU(Na), after adjusting for other baseline risk factors (P < 0.001). For every 100 mmol rise in 24hU(Na), all-cause mortality was 28% lower (95% CI 6-45%, P = 0.02). After adjusting for the competing risk of noncardiovascular death and other predictors, 24hU(Na) was also significantly associated with cardiovascular mortality (sub-hazard ratio 0.65 [95% CI 0.44-0.95]; P = 0.03).

CONCLUSIONS

In patients with type 2 diabetes, lower 24-h urinary sodium excretion was paradoxically associated with increased all-cause and cardiovascular mortality. Interventional studies are necessary to determine if dietary salt has a causative role in determining adverse outcomes in patients with type 2 diabetes and the appropriateness of guidelines advocating salt restriction in this setting.

Trends in 24-h urinary sodium excretion in the United States, 1957-2003: a systematic review

BACKGROUND

Few studies have examined temporal trends in sodium intake in the US population. Collections of 24-h urine sodium excretions are reliable markers for dietary sodium intake.

OBJECTIVE

We examined temporal trends in 24-h urine sodium excretions to estimate temporal trends in sodium intake in the US population.

DESIGN

We performed a systematic search of English-language articles in MEDLINE for studies that reported collections of 24-h urine sodium excretions in the United States. We estimated mean urine sodium excretions over time for all studies and demographic subgroups.

RESULTS

We analyzed 38 studies, which dated from 1957 to 2003, and estimated a mean (± SE) 24-h urine sodium excretion per person of 3526 ± 75 mg Na. In a multivariate random-effects model with study year, sex, age, and race, the study year was not associated with any significant change in sodium excretions (coefficient = 154 mg Na · 24 h⁻¹ · 10 y⁻¹; 95% CI: -140, 448 mg Na · 24 h⁻¹ · 10 y⁻¹). In subgroup analyses, there was no significant temporal trend seen in male, female, black, or white study participants.

CONCLUSION

Sodium intake in the US adult population appears to be well above current guidelines and does not appear to have decreased with time.

WASH-world action on salt and health

There is overwhelming evidence that our current high-salt intake is the major factor increasing blood pressure (BP) and, thereby, a major cause of cardiovascular disease and kidney disease worldwide. A reduction in salt intake to the recommended level of <5-6 g/day is very beneficial, and could prevent millions of deaths each year and make major savings for healthcare services. Several countries, e.g., Finland and the UK, have already reduced the amount of salt being consumed by a combined policy of getting the food industry to decrease the amount of salt added to foods, clear labelling on food products, and increasing public awareness of the harmful effects of salt on health. Many other developed countries, e.g., Australia, Canada, and the US, are also stepping up their activities. The major challenge now is to spread this out worldwide, particularly to developing countries where ≈80% of global BP-related disease burden occurs. In many developing countries, most of the salt consumed comes from salt added during cooking or from sauces; therefore, public health campaigns are needed to encourage consumers to use less salt. A modest reduction in salt intake across the whole population will result in major improvements in public health and have huge economic benefits in all countries around the world. World Action on Salt and Health (WASH) is a coalition of health professionals from different countries who know very well the harm of high BP and has a major role in implementing changes in their own countries. We welcome nephrologists to join (http://www.worldactiononsalt.com).

Nutritional profiles in a public health perspective: a critical review

Nutritional profiling is defined as 'the science of categorizing foods according to their nutritional composition' and it is useful for food labelling and regulation of health claims. The evidence for the link between nutrients and health outcomes was reviewed. A reduced salt intake reduces blood pressure, but only a few randomized controlled trials have verified the effect of salt on overall and cardiovascular mortality. Evidence linking a reduced fat intake with cardiovascular mortality and obesity is generally non-significant. Studies that have examined the relationship between obesity and diet have produced contrasting results. A simulation exercise that demonstrated that the impact of a reduced salt and fat intake on overall mortality would be negligible in the European population was carried out. Consideration of the literature and the results of this simulation exercise suggest that the introduction of nutritional profiles in Europe would be expected to have a very limited impact on health outcomes.

Reducing population salt intake worldwide: from evidence to implementation

Raised blood pressure is a major cause of cardiovascular disease, responsible for 62% of stroke and 49% of coronary heart disease. There is overwhelming evidence that dietary salt is the major cause of raised blood pressure and that a reduction in salt intake lowers blood pressure, thereby, reducing blood pressure-related diseases. Several lines of evidence including ecological, population, and prospective cohort studies, as well as outcome trials, demonstrate that a reduction in salt intake is related to a lower risk of cardiovascular disease. Increasing evidence also suggests that a high salt intake may directly increase the risk of stroke, left ventricular hypertrophy, and renal disease; is associated with obesity through soft drink consumption; is related to renal stones and osteoporosis; is linked to the severity of asthma; 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 foods 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. The challenge now 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.

Diagnostic and prognostic utility of electrocardiography for left ventricular hypertrophy defined by magnetic resonance imaging in relationship to ethnicity: the Multi-Ethnic Study of Atherosclerosis (MESA)

BACKGROUND

Left ventricular mass is a strong predictor of cardiovascular disease (CVD), and magnetic resonance imaging (MRI) of the heart is a standard of reference for left ventricular mass measurement. Ethnicity is believed to affect electrocardiographic (ECG) performance. We evaluated the diagnostic and prognostic performance of ECG for left ventricular hypertrophy (LVH) as defined by MRI in relationship to ethnicity.

METHODS

Data were analyzed from 4,967 participants (48% men, mean age 62 +/- 10 years; 39% white, 13% Chinese, 26% African American, 22% Hispanic) enrolled in the Multi-Ethic Study of Atherosclerosis (MESA) who were followed for a median of 4.8 years for incident CVD.

RESULTS

Thirteen traditional ECG-LVH criteria were assessed, and showed overall and ethnicity-specific low sensitivity (10%-26%) and high specificity (88%-99%) in diagnosing MRI-defined LVH. Ten of 13 ECG-LVH criteria showed superior sensitivity and diagnostic performance in African Americans as compared with whites (P = .02-.001). The sum of amplitudes of S wave in V(1), S wave in V(2), and R wave in V(5) (a MESA-specific ECG-LVH criterion) offered higher sensitivity (40.4%) compared with prior ECG-LVH criteria while maintaining good specificity (90%) and diagnostic performance (receiver operating characteristic area = 0.65). In fully adjusted models, only the MESA-specific ECG-LVH criterion, Romhilt-Estes score, Framingham score, Cornell voltage, Cornell duration product, and Framingham-adjusted Cornell voltage predicted increased CVD risk (P < .05).

CONCLUSIONS

Electrocardiography has low sensitivity but high specificity for detecting MRI-defined LVH. The performance of ECG for LVH detection varies by ethnicity, with African Americans showing higher sensitivity and overall performance compared with other ethnic groups.

Potential mechanisms of low-sodium diet-induced cardiac disease: superoxide-NO in the heart

RATIONALE

Patients on a low salt (LS) diet have increased mortality.

OBJECTIVE

To determine whether reduction in NO bioactivity may contribute to the LS-induced cardiac dysfunction and mortality.

METHODS AND RESULTS

Adult male mongrel dogs were placed on LS (0.05% sodium chloride) for 2 weeks. Body weight (25.4 + or - 0.4 to 23.6 + or - 0.4 kg), left ventricular systolic pressure (137.0 + or - 3.4 to 124.0 + or - 6.7 mm Hg), and mean aortic pressure (111 + or - 3.1 to 98 + or - 4.3 mm Hg) decreased. Plasma angiotensin II concentration increased (4.4 + or - 0.7 to 14.8 + or - 3.7 pg/mL). Veratrine-induced (5 microg/kg) NO-mediated vasodilation was inhibited by 44% in LS; however, the simultaneous intravenous infusion of ascorbic acid or apocynin acutely and completely reversed this inhibition. In LS heart tissues, lucigenin chemiluminescence was increased 2.3-fold to angiotensin II (10(-8) mol/L), and bradykinin (10(-4) mol/L) induced reduction of myocardial oxygen consumption in vitro was decreased (40 + or - 1.3% to 16 + or - 6.3%) and completely restored by coincubation with tiron, tempol or apocynin. Switching of substrate uptake from free fatty acid to glucose by the heart was observed (free fatty acid: 8.97 + or - 1.39 to 4.53 + or - 1.12 micromol/min; glucose: 1.31 + or - 0.52 to 6.86 + or - 1.78 micromol/min). Western blotting indicated an increase in both p47(phox) (121%) and gp91(phox) (44%) as did RNA microarray analysis (433 genes changed) showed an increase in p47(phox) (1.6-fold) and gp91(phox) (2.0 fold) in the LS heart tissue.

CONCLUSIONS

LS diet induces the activation of the renin-angiotensin system, which increases oxidative stress via the NADPH oxidase and attenuates NO bioavailability in the heart.

Low dietary sodium intake increases the death risk in peritoneal dialysis

BACKGROUND AND OBJECTIVES

To explore the correlation between dietary sodium intake and cardiovascular and overall mortality, and then determine whether this correlation can be explained by protein and energy intake paralleled with sodium intake in dialysis patients.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

This single-center retrospective cohort study enrolled 305 incident patients who started peritoneal dialysis in our unit from July 2002 to February 2007. All patients were followed until death or until being censored in February 2008. Demographic data were collected at baseline. Biochemical, dietary, and nutrition data were examined at baseline and thereafter at regular intervals to calculate the average values throughout the study.

RESULTS

Participants with the highest average sodium intake were more likely to be younger, male, and overweight. Patients in the high tertile of average sodium intake had higher albumin, prealbumin, and lean body mass levels, and more nutrient intakes paralleling with sodium intake. Low average sodium intake independently predicted the increased risk for overall and cardiovascular death after adjusting for recognized confounders. Further adjustment for dietary protein, energy, and other nutrient intakes individually had minimal impact on the association between average sodium intake and overall death, with hazard ratios varying between 0.35 and 0.44, and cardiovascular death, with hazard ratios varying between 0.06 and 0.11.

CONCLUSIONS

This study revealed that low dietary sodium intake independently predicts the high overall and cardiovascular mortality in dialysis patients. This correlation could not be entirely explained by deficient protein and energy intake.

Salt intake, stroke, and cardiovascular disease: meta-analysis of prospective studies

OBJECTIVE

To assess the relation between the level of habitual salt intake and stroke or total cardiovascular disease outcome.

DESIGN

Systematic review and meta-analysis of prospective studies published 1966-2008.

DATA SOURCES

Medline (1966-2008), Embase (from 1988), AMED (from 1985), CINAHL (from 1982), Psychinfo (from 1985), and the Cochrane Library. Review methods For each study, relative risks and 95% confidence intervals were extracted and pooled with a random effect model, weighting for the inverse of the variance. Heterogeneity, publication bias, subgroup, and meta-regression analyses were performed. Criteria for inclusion were prospective adult population study, assessment of salt intake as baseline exposure, assessment of either stroke or total cardiovascular disease as outcome, follow-up of at least three years, indication of number of participants exposed and number of events across different salt intake categories.

RESULTS

There were 19 independent cohort samples from 13 studies, with 177 025 participants (follow-up 3.5-19 years) and over 11 000 vascular events. Higher salt intake was associated with greater risk of stroke (pooled relative risk 1.23, 95% confidence interval 1.06 to 1.43; P=0.007) and cardiovascular disease (1.14, 0.99 to 1.32; P=0.07), with no significant evidence of publication bias. For cardiovascular disease, sensitivity analysis showed that the exclusion of a single study led to a pooled estimate of 1.17 (1.02 to 1.34; P=0.02). The associations observed were greater the larger the difference in sodium intake and the longer the follow-up.

CONCLUSIONS

High salt intake is associated with significantly increased risk of stroke and total cardiovascular disease. Because of imprecision in measurement of salt intake, these effect sizes are likely to be underestimated. These results support the role of a substantial population reduction in salt intake for the prevention of cardiovascular disease.

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.

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.

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.

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.

Reducing dietary sodium and decreases in cardiovascular disease in Canada

BACKGROUND

Increases in dietary sodium increase blood pressure, whereas emerging evidence confirms that the reduction in dietary sodium results in reduced cardiovascular events.

OBJECTIVES

To estimate the effect that reducing dietary sodium can have on cardiovascular events in Canada.

METHODS

Based on published meta-analyses of randomized controlled trials, blood pressure reductions associated with different levels of reduction in dietary sodium were used in the model. The RR for cardiovascular events associated with the blood pressure reduction was modelled based on a meta-analysis of diuretic trials. Assumptions were made that controlled hypertensive patients would or would not have similar reduction in blood pressure as the normotensive population. Cardiovascular events in Canada for 2002 were used to estimate the decrease in cardiovascular events.

RESULTS

A reduction in daily sodium intake of 1840 mg/day was estimated to prevent 11,550 cardiovascular disease events per year. This varied from about 7300 to 10,700 events per year when hypertension control rates were varied from 13% to 66%. Reduction in cardiovascular events ranged from 8300 to 16,800 per year for a reduction in dietary sodium from 1200 mg/day to 2400 mg/day.

CONCLUSIONS

Reducing dietary sodium can substantially reduce cardiovascular disease events in Canada. This information can aid policy makers in assessing the importance of public health policy and to monitor the health impact of changes in dietary sodium in Canada.

Salt: its role in chronic kidney disease

Few controversies in medicine have such a long history as that of whether salt is identifiably dangerous or not dangerous. The most common reported association between excess dietary salt intake and clinical outcome has been in the field of hypertension, but dietary sodium intake mediates effects that go far beyond, and are independent of, extracellular fluid expansion and elevation in blood pressure. For nephrologists, clinical trials that demonstrate no negative outcome of a high salt diet in the general population are thus not particularly assuasive, because patients with chronic kidney disease (CKD) represent an entity that is by no means comparable to the general population. This review takes a look at the challenges associated with salt balance in CKD patients (particularly at K/DOQI stage 5), followed by a summary of current concepts believed to play a part in salt-mediated pathophysiology, and the conclusion, based on the present state of scientific knowledge, that it appears advisable to advocate low dietary salt intake in this patient population.

Sodium, blood pressure, and cardiovascular disease

PURPOSE OF REVIEW

Persistent recommendations for universal restriction of dietary sodium intake are based on associations of sodium intake with blood pressure. No clinical trial data support an association of sodium intake with mortality and morbidity outcomes, however, while results of observational studies appear heterogeneous. Can these contradictory data be reconciled to inform health policy regarding sodium intake recommendations?

RECENT FINDINGS

We reported (2006) a statistically significant (P = 0.03) association of sodium intake less than 2.3 g/day with increased cardiovascular disease mortality (hazard ratio 1.37) in a representative sample of the US adult population with an observed baseline mean sodium intake of 2.7 g/day. Others reported (2004) a significant (P < 0.01) higher stroke death among males and borderline significant (P = 0.07) for females, for highest compared with lowest sodium tertile in a community in Japan with mean intake of 5.4 g/day.

SUMMARY

These results are consistent with earlier studies suggesting that the association of sodium with morbidity and mortality in industrial societies follows a 'J shape' with a direct association at high levels of average intake (over 4 g), an inverse association at lower levels (less than 2 g) and no measurable effect for the widely prevalent intakes in between.

Salt substitution: a low-cost strategy for blood pressure control among rural Chinese. A randomized, controlled trial

OBJECTIVE

Dietary sodium and potassium consumption is associated with blood pressure levels. The objective of this study was to define a practical and low-cost method for the control of blood pressure by modification of these dietary cations in rural Chinese.

METHODS

This study was a double-blind, randomized, controlled trial designed to establish the long-term effects of a reduced-sodium, high-potassium salt substitute (65% sodium chloride, 25% potassium chloride, 10% magnesium sulphate) compared to normal salt (100% sodium chloride) on blood pressure among high-risk individuals. Following a 4-week run-in period on salt substitute, participants were randomly assigned to replace their household salt with either the study salt substitute or normal salt for a 12-month period.

RESULTS

The mean age of the 608 randomized participants was 60 years and 56% of them were female. Sixty-four percent had a history of vascular disease and 61% were taking one or more blood pressure-lowering drugs at entry. Mean baseline blood pressure was 159/93 mmHg (SD 26/14). The mean overall difference in systolic blood pressure between randomized groups was 3.7 mmHg (95% confidence interval 1.6-5.9, P < 0.001). There was strong evidence that the magnitude of this reduction increased over time (P = 0.001) with the maximum net reduction of 5.4 mmHg (2.3-8.5) achieved at 12 months. There were no detectable effects on diastolic blood pressure.

CONCLUSION

Salt substitution produced a substantial and sustained systolic blood pressure reduction in this population, and should be actively promoted as a low-cost alternate or adjunct to drug therapy for people consuming significant quantities of salt.

Sodium and potassium intake and risk of cardiovascular events and all-cause mortality: the Rotterdam Study

BACKGROUND

Dietary electrolytes influence blood pressure, but their effect on clinical outcomes remains to be established. We examined sodium and potassium intake in relation to cardiovascular disease (CVD) and mortality in an unselected older population.

METHODS

A case-cohort analysis was performed in the Rotterdam Study among subjects aged 55 years and over, who were followed for 5 years. Baseline urinary samples were analyzed for sodium and potassium in 795 subjects who died, 206 with an incident myocardial infarction and 181 subjects with an incident stroke, and in 1,448 randomly selected subjects. For potassium, dietary data were additionally obtained by food-frequency questionnaire for 78% of the cohort.

RESULTS

There was no consistent association of urinary sodium, potassium, or sodium/potassium ratio with CVD and all-cause mortality over the range of intakes observed in this population. Dietary potassium estimated by food frequency questionnaire, however, was associated with a lower risk of all-cause mortality in subjects initially free of CVD and hypertension (RR = 0.71 per standard deviation increase; 95% confidence interval: 0.51-1.00). We observed a significant positive association between urinary sodium/potassium ratio and all-cause mortality, but only in overweight subjects who were initially free of CVD and hypertension (RR = 1.19 (1.02-1.39) per unit).

CONCLUSION

The effect of sodium and potassium intake on CVD morbidity and mortality in Western societies remains to be established.

Serum sodium concentration is significantly associated with the angiographic characteristics of coronary atherosclerosis

AIM

To explore the relationship between serum sodium concentration and coronary atherosclerosis.

METHODS

The study population consisted of 896 consecutive patients (684 males and 212 females) who underwent coronary angiography for suspected or known coronary atherosclerosis. Smoking and drinking were investigated. The anthropometric measurements, including body mass index, systolic blood pressure and diastolic blood pressure, and the serum measurements, including sodium, potassium, chlorine, lipids, blood glucose, urea, creatinine, and uric acid for every patient were conducted. The severity of coronary atherosclerosis was defined by the Gensini score system. The statistical methods, including one-way ANOVA, Kruskal-Wallis test, Spearman correlation analysis, partial correlation analysis, multivariate stepwise linear regression analysis, and multinomial logistic regression analysis were employed to explore the relationship between serum sodium concentration and the Gensini score.

RESULTS

The analysis of the Kruskal-Wallis test indicated that the distribution of the Gensini score (P=0.000) differed among the groups according to serum sodium concentration, quartile values of which were used as cut-off points. The Spearman correlation and partial correlation analysis controlling for gender, smoking status, and drinking status indicated that the Gensini score significantly correlated with the sodium concentration (r=-0.241, P=0.000 for the Spearman correlation, r=-0.114, P=0.000 for the partial correlation). The results from the multivariate stepwise linear regression analysis showed that the left ventricular ejection fraction (beta=-0.228, P=0.000), age (beta=0.137, P=0.010), glucose level (beta=0.129, P=0.000), and sodium level (beta=-0.106, P=0.004) were significantly and independently associated with the Gensini score. The results of the multinomial logistic regression analysis suggested that the hyponatremia was the risk factor for the higher Gensini score.

CONCLUSION

The serum sodium concentration was significantly and negatively associated with the Gensini score; and the actual mechanism underlying the association needs further study.

Dietary sodium and cardiovascular outcomes: a rational approach

Hypertension, the leading risk factor for mortality in the world, affects nearly one in four Canadians. There is substantive evidence that high dietary sodium contributes to hypertension. Animal studies consistently demonstrate increased blood pressure and cardiovascular morbidity and mortality with high dietary sodium intake. Evidence of the adverse health effects in humans associated with increased sodium intake is accumulating rapidly. Previously, limitations on sodium consumption were recommended only for those identifiable groups of people shown to be at higher risk. With the lifetime risk of developing hypertension being more than 90% in an average lifespan, the need for a population-based approach to reducing hypertension is clear. The present paper reviews the evidence of sodium and cardiovascular disease, resulting in the 2007 Canadian Hypertension Education Program recommendation of daily intake of less than 100 mmol of sodium in both normotensive and hypertensive adults.

Salt, blood pressure and cardiovascular disease

PURPOSE OF REVIEW

To review the evidence that relates salt intake to blood pressure and cardiovascular disease.

RECENT FINDINGS

Raised blood pressure throughout the range seen in developed countries is the major cause of cardiovascular disease, responsible for 62% of strokes and 49% of coronary heart disease. There is overwhelming evidence that dietary salt is a major cause of raised blood pressure, and a modest reduction in salt intake lowers blood pressure, which is predicted to reduce cardiovascular disease. Several lines of evidence including ecological, population and prospective cohort studies, as well as follow-up studies of individuals who participated in short-term salt reduction trials, have consistently shown a direct relation between salt intake and cardiovascular risk, and a reduction in population salt intake is associated with a reduction in cardiovascular mortality in the population.

SUMMARY

The evidence for universal salt reduction is strong, and reducing salt from the current intake of 10-12 g/day to the recommended level of 5-6 g/day will have a major effect on blood pressure and cardiovascular mortality. Additionally, this will result in considerable savings on health expenditure as, not only is raised blood pressure the biggest cause of death, but the second biggest cause of disability worldwide.

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

OBJECTIVE

To examine the effects of reduction in dietary sodium intake on cardiovascular events using data from two completed randomised trials, TOHP I and TOHP II.

DESIGN

Long term follow-up assessed 10-15 years after the original trial.

SETTING

10 clinic sites in 1987-90 (TOHP I) and nine sites in 1990-5 (TOHP II). Central follow-up conducted by post and phone.

PARTICIPANTS

Adults aged 30-54 years with prehypertension.

INTERVENTION

Dietary sodium reduction, including comprehensive education and counselling on reducing intake, for 18 months (TOHP I) or 36-48 months (TOHP II).

MAIN OUTCOME MEASURE

Cardiovascular disease (myocardial infarction, stroke, coronary revascularisation, or cardiovascular death).

RESULTS

744 participants in TOHP I and 2382 in TOHP II were randomised to a sodium reduction intervention or control. Net sodium reductions in the intervention groups were 44 mmol/24 h and 33 mmol/24 h, respectively. Vital status was obtained for all participants and follow-up information on morbidity was obtained from 2415 (77%), with 200 reporting a cardiovascular event. Risk of a cardiovascular event was 25% lower among those in the intervention group (relative risk 0.75, 95% confidence interval 0.57 to 0.99, P=0.04), adjusted for trial, clinic, age, race, and sex, and 30% lower after further adjustment for baseline sodium excretion and weight (0.70, 0.53 to 0.94), with similar results in each trial. In secondary analyses, 67 participants died (0.80, 0.51 to 1.26, P=0.34).

CONCLUSION

Sodium reduction, previously shown to lower blood pressure, may also reduce long term risk of cardiovascular events.

Non-pressure-related effects of dietary sodium

After the demonstration of a positive correlation between sodium intake and arterial pressure in large population studies, the effect of short-term reduction in sodium intake demonstrated the efficacy of this nonpharmacological therapy. In addition, a positive relation between urinary sodium (the most reliable estimate of salt intake) and left ventricular hypertrophy was found; and in recent years it was shown that cardiovascular morbidity clearly progressed with increasing sodium intake, despite one contradictory study. The role of non-pressure-related effects of dietary sodium is discussed in order to bring more arguments for a large-scale attempt to reduce sodium intake by 30% to 50%.

Gender differences in adherence to the sodium-restricted diet in patients with heart failure

BACKGROUND

Despite the importance of the sodium-restricted diet (SRD) to heart failure (HF) management, patient adherence is poor. Little is known about gender differences in adherence or factors that affect patients' ability to follow SRD recommendations. The purposes of this study were to determine whether there were gender differences in (1) adherence to the SRD; (2) knowledge about SRD and HF self-care; and (3) perceived barriers to following the SRD.

METHODS AND RESULTS

Forty-one men and 27 women completed the Heart Failure Attitudes and Barriers questionnaire that measured HF self-care, knowledge, and perceived barriers to follow an SRD. Diet adherence was measured by 24-hour urinary sodium excretion (UNa). Women were more adherent to the SRD than men as reflected by 24-hour urine excretion (2713 versus 3859 mg UNa, P = .01). Women recognized signs of excess sodium intake such as fluid buildup (P = .001) and edema (P = .01) more often than men and had better understanding of appropriate actions to take related to following an SRD. There were no gender differences in perceived barriers to follow an SRD.

CONCLUSIONS

Although men and women perceived similar barriers, women were more adherent to the SRD and had greater knowledge about following an SRD. Further investigation of this phenomenon is warranted to determine if better adherence contributes to improved outcomes in women.

Evidence relating dietary sodium to cardiovascular disease

The expectation that dietary sodium intake might influence cardiovascular disease occurrence has been based upon its impact on blood pressure (BP). Solid experimental data confirms the ability of large (75-100 mmols/24 hours) changes in dietary sodium to reduce pressure by, on average, mid-low single digits. However, there is substantial inter-individual variation in BP response. In addition, sodium restriction generates other, sometimes undesirable effects, including increased insulin resistance, activation of the renin-angiotensin system, and increased sympathetic nerve activity. The health effects of salt restriction are, therefore, the sum of these recognized, and probably other unrecognized, intermediate effects. Ideally, salt restriction would be tested in a randomized clinical trial. In its absence, there are 9 observational studies linking baseline sodium intake, estimated by either 24 hour urine or dietary intake, to morbidity and mortality. The results have been inconsistent. The only study in hypertensive patients, there was an inverse relation of sodium to cardiovascular outcome. In a Japanese study, stroke incidence was increased among males with the highest salt intake. Two studies found a direct relation of sodium intake to cardiovascular mortality in an obese minority of the group studied. Taken together, these results suggest, not surprisingly given the genetic, behavioral, and environmental variety of humankind, that heterogeneity best describes the relation of sodium intake to cardiovascular morbidity and mortality. In short, the available data provides no support for any universal recommendation of a particular level of dietary sodium.

Effect of Lifelong High- or Low-Salt Intake on Blood Pressure, Left Ventricular Mass and Plasma Insulin in Wistar Rats

BACKGROUND

Salt restriction is recommended for hypertension treatment to reduce blood pressure, but its effect on some risk factors is still a matter of discussion. The aim of this study was to observe the effect of a long period of salt restriction or overload on blood pressure, left ventricular mass (LVM), kidney mass (KM), glucose tolerance, and plasma insulin.

METHODS

Male Wistar rats were fed from weaning with a low-salt diet (LSD) or a high-salt diet (HSD) until 72 weeks of age. After 48 weeks, the diets were changed in half of the rats: HSD until 48 weeks and then LSD (LHSD) and LSD until 48 weeks and then HSD (HLSD). Body weight, blood pressure, electrolyte excretion, creatinine clearance, plasma renin activity, LVM, KM, and intravenous glucose tolerance test with insulin determinations were evaluated.

RESULTS

Blood pressure, LVM and KM were higher on the HSD than on the LSD. Blood pressure was lower on the LHSD than on the HLSD. There were no differences in LVM and KM on the LHSD compared with the HLSD. The relationship between area under the curve (AUC) of insulin and glucose during the intravenous glucose tolerance test was higher on the LSD. No differences were detected in AUC between the two groups of rats whose diet were inverted with 48 weeks of age.

CONCLUSIONS

A chronic HSD increases blood pressure, LVM, and KM and a chronic LSD increases plasma insulin in response to a glucose challenge in aging rats. The hypotensive effect of salt restriction is not modified by a previous long period on a HSD.

Sodium intake and mortality in the NHANES II follow-up study

PURPOSE

US Dietary Guidelines recommend a daily sodium intake <2300 mg, but evidence linking sodium intake to mortality outcomes is scant and inconsistent. To assess the association of sodium intake with cardiovascular disease (CVD) and all-cause mortality and the potential impact of dietary sodium intake <2300 mg, we examined data from the Second National Health and Nutrition Examination Survey (NHANES II).

METHODS

Observational cohort study linking sodium, estimated by single 24-hour dietary recall and adjusted for calorie intake, in a community sample (n = 7154) representing 78.9 million non-institutionalized US adults (ages 30-74). Hazard ratios (HR) for CVD and all-cause mortality were calculated from multivariable adjusted Cox models accounting for the sampling design.

RESULTS

Over mean 13.7 (range: 0.5-16.8) years follow-up, there were 1343 deaths (541 CVD). Sodium (adjusted for calories) and sodium/calorie ratio as continuous variables had independent inverse associations with CVD mortality (P = .03 and P = .008, respectively). Adjusted HR of CVD mortality for sodium <2300 mg was 1.37 (95% confidence interval [CI]: 1.03-1.81, P = .033), and 1.28 (95% CI: 1.10-1.50, P = .003) for all-cause mortality. Alternate sodium thresholds from 1900-2700 mg gave similar results. Results were consistent in the majority of subgroups examined, but no such associations were observed for those <55 years old, non-whites, or the obese.

CONCLUSION

The inverse association of sodium to CVD mortality seen here raises questions regarding the likelihood of a survival advantage accompanying a lower sodium diet. These findings highlight the need for further study of the relation of dietary sodium to mortality outcomes.