Insulin resistance in young salt-sensitive normotensive subjects

The impact of baseline potassium intake on the dose-response relation between sodium reduction and blood pressure change: systematic review and meta-analysis of randomized trials

Sodium and potassium appear to interact with each other in their effects on blood pressure with potassium supplementation having a greater blood pressure lowering-effect when sodium intake is high. Whether the effect of sodium reduction on blood pressure varies according to potassium intake levels is unclear. We carried out a systematic review and meta-analysis to examine the impact of baseline potassium intake on blood pressure response to sodium reduction in randomized trials in adult populations, with sodium and potassium intake estimated from 24-h urine samples. We included 68 studies involving 5708 participants and conducted univariable and multivariable meta-regression. The median intake of baseline potassium was 67.7 mmol (Interquartile range: 54.6-76.4 mmol), and the mean reduction in sodium intake was 128 mmol (95% CI: 107-148). Multivariable meta-regression that included baseline 24-h urinary potassium excretion, age, ethnicity, baseline blood pressure, change in 24-h urinary sodium excretion, as well as the interaction between baseline 24-h urinary potassium excretion and change in 24-h urinary sodium excretion did not identify a significant association of baseline potassium intake levels with the blood pressure reduction achieved with a 50 mmol lowering of sodium intake (p > 0.05 for both systolic and diastolic blood pressure). A higher starting level of blood pressure was consistently associated with a greater blood pressure reduction from reduced sodium consumption. However, the nonsignificant findings may subject to the limitations of the data available. Additional studies with more varied potassium intake levels would allow a more confident exclusion of an interaction.

Association study of fasting blood glucose and salt sensitivity of blood pressure in community population: The EpiSS study

BACKGROUND AND AIMS

To evaluate the association between fasting blood glucose (FBG) and salt sensitivity of blood pressure (SSBP).

METHODS AND RESULTS

This study is based on the baseline survey of systemic epidemiology of salt sensitivity study. Subjects were classified into salt sensitive (SS) and salt resistant groups according to blood pressure (BP) changes during the modified Sullivan's acute oral saline load and diuresis shrinkage test. Multivariate logistic and linear regression were used to evaluate associations between FBG with SS or BP changes. A total of 2051 participants were included in the analyses with 581 (28.33%) for SS. Multiple analysis showed that for every interquartile range increase in FBG, the OR (95%CI) for SS was 1.140 (1.069, 1.215), β (95%CI) for mean arterial pressure change (ΔMAP₁), systolic and diastolic BP changes during saline load were 0.421 (0.221, 0.622), 0.589 (0.263, 0.914) and 0.340 (0.149, 0.531), respectively. Compared to the lowest FBG quartile (Q₁), the OR (95%CI) for SS in Q₃ and Q₄ were 1.342 (1.014, 1.776) and 1.577 (1.194, 2.084), respectively. Compared to subjects with normal FBG, the β (95%CI) for ΔMAP₁ was 0.973 (0.055, 1.891) in subjects with impaired FBG, and was 1.449 (0.602, 2.296) in patients with diabetes mellitus. Stratified analyses showed significant and stronger associations between FBG with SSBP in youngers, females, hypertensives, non-diabetics, non-current smokers and non-current drinkers.

CONCLUSION

Our findings suggest FBG is an independent, dose-dependent associated factor for SSBP, and prevention of SS focusing on controlling FBG elevation in the early stage is important.

Effects of low sodium diet versus high sodium diet on blood pressure, renin, aldosterone, catecholamines, cholesterol, and triglyceride

BACKGROUND

Recent cohort studies show that salt intake below 6 g is associated with increased mortality. These findings have not changed public recommendations to lower salt intake below 6 g, which are based on assumed blood pressure (BP) effects and no side-effects.

OBJECTIVES

To assess the effects of sodium reduction on BP, and on potential side-effects (hormones and lipids) SEARCH METHODS: The Cochrane Hypertension Information Specialist searched the following databases for randomized controlled trials up to April 2018 and a top-up search in March 2020: the Cochrane Hypertension Specialised Register, the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE (from 1946), Embase (from 1974), the World Health Organization International Clinical Trials Registry Platform, and ClinicalTrials.gov. We also contacted authors of relevant papers regarding further published and unpublished work. The searches had no language restrictions. The top-up search articles are recorded under "awaiting assessment."

SELECTION CRITERIA

Studies randomizing persons to low-sodium and high-sodium diets were included if they evaluated at least one of the outcome parameters (BP, renin, aldosterone, noradrenalin, adrenalin, cholesterol, high-density lipoprotein, low-density lipoprotein and triglyceride,.

DATA COLLECTION AND ANALYSIS

Two review authors independently collected data, which were analysed with Review Manager 5.3. Certainty of evidence was assessed using GRADE.

MAIN RESULTS

Since the first review in 2003 the number of included references has increased from 96 to 195 (174 were in white participants). As a previous study found different BP outcomes in black and white study populations, we stratified the BP outcomes by race. The effect of sodium reduction (from 203 to 65 mmol/day) on BP in white participants was as follows: Normal blood pressure: SBP: mean difference (MD) -1.14 mmHg (95% confidence interval (CI): -1.65 to -0.63), 5982 participants, 95 trials; DBP: MD + 0.01 mmHg (95% CI: -0.37 to 0.39), 6276 participants, 96 trials. Hypertension: SBP: MD -5.71 mmHg (95% CI: -6.67 to -4.74), 3998 participants,88 trials; DBP: MD -2.87 mmHg (95% CI: -3.41 to -2.32), 4032 participants, 89 trials (all high-quality evidence). The largest bias contrast across studies was recorded for the detection bias element. A comparison of detection bias low-risk studies versus high/unclear risk studies showed no differences. The effect of sodium reduction (from 195 to 66 mmol/day) on BP in black participants was as follows: Normal blood pressure: SBP: mean difference (MD) -4.02 mmHg (95% CI:-7.37 to -0.68); DBP: MD -2.01 mmHg (95% CI:-4.37, 0.35), 253 participants, 7 trials. Hypertension: SBP: MD -6.64 mmHg (95% CI:-9.00, -4.27); DBP: MD -2.91 mmHg (95% CI:-4.52, -1.30), 398 participants, 8 trials (low-quality evidence). The effect of sodium reduction (from 217 to 103 mmol/day) on BP in Asian participants was as follows: Normal blood pressure: SBP: mean difference (MD) -1.50 mmHg (95% CI: -3.09, 0.10); DBP: MD -1.06 mmHg (95% CI:-2.53 to 0.41), 950 participants, 5 trials. Hypertension: SBP: MD -7.75 mmHg (95% CI:-11.44, -4.07); DBP: MD -2.68 mmHg (95% CI: -4.21 to -1.15), 254 participants, 8 trials (moderate-low-quality evidence).   During sodium reduction renin increased 1.56 ng/mL/hour (95%CI:1.39, 1.73) in 2904 participants (82 trials); aldosterone increased 104 pg/mL (95%CI:88.4,119.7) in 2506 participants (66 trials); noradrenalin increased 62.3 pg/mL: (95%CI: 41.9, 82.8) in 878 participants (35 trials); adrenalin increased 7.55 pg/mL (95%CI: 0.85, 14.26) in 331 participants (15 trials); cholesterol increased 5.19 mg/dL (95%CI:2.1, 8.3) in 917 participants (27 trials); triglyceride increased 7.10 mg/dL (95%CI: 3.1,11.1) in 712 participants (20 trials); LDL tended to increase 2.46 mg/dl (95%CI: -1, 5.9) in 696 participants (18 trials); HDL was unchanged -0.3 mg/dl (95%CI: -1.66,1.05) in 738 participants (20 trials) (All high-quality evidence except the evidence for adrenalin).

AUTHORS' CONCLUSIONS

In white participants, sodium reduction in accordance with the public recommendations resulted in mean arterial pressure (MAP) decrease of about 0.4 mmHg in participants with normal blood pressure and a MAP decrease of about 4 mmHg in participants with hypertension. Weak evidence indicated that these effects may be a little greater in black and Asian participants. The effects of sodium reduction on potential side effects (hormones and lipids) were more consistent than the effect on BP, especially in people with normal BP.

Effect of dose and duration of reduction in dietary sodium on blood pressure levels: systematic review and meta-analysis of randomised trials

OBJECTIVE

To examine the dose-response relation between reduction in dietary sodium and blood pressure change and to explore the impact of intervention duration.

DESIGN

Systematic review and meta-analysis following PRISMA guidelines.

DATA SOURCES

Ovid MEDLINE(R), EMBASE, and Cochrane Central Register of Controlled Trials (Wiley) and reference lists of relevant articles up to 21 January 2019.

INCLUSION CRITERIA

Randomised trials comparing different levels of sodium intake undertaken among adult populations with estimates of intake made using 24 hour urinary sodium excretion.

DATA EXTRACTION AND ANALYSIS

Two of three reviewers screened the records independently for eligibility. One reviewer extracted all data and the other two reviewed the data for accuracy. Reviewers performed random effects meta-analyses, subgroup analyses, and meta-regression.

RESULTS

133 studies with 12 197 participants were included. The mean reductions (reduced sodium v usual sodium) of 24 hour urinary sodium, systolic blood pressure (SBP), and diastolic blood pressure (DBP) were 130 mmol (95% confidence interval 115 to 145, P<0.001), 4.26 mm Hg (3.62 to 4.89, P<0.001), and 2.07 mm Hg (1.67 to 2.48, P<0.001), respectively. Each 50 mmol reduction in 24 hour sodium excretion was associated with a 1.10 mm Hg (0.66 to 1.54; P<0.001) reduction in SBP and a 0.33 mm Hg (0.04 to 0.63; P=0.03) reduction in DBP. Reductions in blood pressure were observed in diverse population subsets examined, including hypertensive and non-hypertensive individuals. For the same reduction in 24 hour urinary sodium there was greater SBP reduction in older people, non-white populations, and those with higher baseline SBP levels. In trials of less than 15 days' duration, each 50 mmol reduction in 24 hour urinary sodium excretion was associated with a 1.05 mm Hg (0.40 to 1.70; P=0.002) SBP fall, less than half the effect observed in studies of longer duration (2.13 mm Hg; 0.85 to 3.40; P=0.002). Otherwise, there was no association between trial duration and SBP reduction.

CONCLUSIONS

The magnitude of blood pressure lowering achieved with sodium reduction showed a dose-response relation and was greater for older populations, non-white populations, and those with higher blood pressure. Short term studies underestimate the effect of sodium reduction on blood pressure.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO CRD42019140812.

Dietary sodium and potassium and risk of diabetes: A prospective study using data from the China Health and Nutrition Survey

AIMS

Dietary sodium and potassium intakes are well-known risk factors for cardiovascular outcomes. However, the associations between dietary sodium and potassium and diabetes are still controversial. Our study aimed to examine whether dietary sodium, potassium and the sodium-potassium ratio are associated with the risk of diabetes, based on a large sample of Chinese adults.

METHODS

The study data were from the 2004-2009 China Health and Nutrition Survey (CHNS), and 5867 participants were eligible for analysis. Sodium and potassium intakes were estimated based on three consecutive 24-h recalls at an individual level combined with a food inventory at a household level performed over the same 3-day period. Diabetes was defined as fasting glucose ≥7.0mmol/L (≥126mg/dL), HbA_1c ≥6.5% or use of antidiabetic drugs.

RESULTS

Over a mean follow-up of 4.7 years, there were 611 (10.4%) incident cases of diabetes. Participants in the higher quartiles (Q3 and Q4) of sodium intake had significantly higher risks of diabetes than those with the lowest sodium intake [Q3, RR: 1.41, 95% CI: 1.06-1.86 and Q4, RR: 1.35, 95% CI: 1.02-1.80; P<0.001 for trend]. In addition, high sodium intakes were significantly associated with levels of fasting glucose and HbA_1c (P<0.05 for trend), with similar associations also found with sodium-potassium ratios (P<0.05 for trend), but not for potassium intakes.

CONCLUSION

This study found that higher sodium intakes and sodium-potassium ratios were significantly associated with a higher risk of diabetes. Further clinical research is now necessary to confirm these results.

Effects of low sodium diet versus high sodium diet on blood pressure, renin, aldosterone, catecholamines, cholesterol, and triglyceride

BACKGROUND

In spite of more than 100 years of investigations the question of whether a reduced sodium intake improves health is still unsolved.

OBJECTIVES

To estimate the effects of low sodium intake versus high sodium intake on systolic and diastolic blood pressure (SBP and DBP), plasma or serum levels of renin, aldosterone, catecholamines, cholesterol, high-density lipoprotein (HDL), low-density lipoprotein (LDL) and triglycerides.

SEARCH METHODS

The Cochrane Hypertension Information Specialist searched the following databases for randomized controlled trials up to March 2016: the Cochrane Hypertension Specialised Register, the Cochrane Central Register of Controlled Trials (CENTRAL) (2016, Issue 3), MEDLINE (from 1946), Embase (from 1974), the World Health Organization International Clinical Trials Registry Platform, and ClinicalTrials.gov. We also searched the reference lists of relevant articles.

SELECTION CRITERIA

Studies randomising persons to low-sodium and high-sodium diets were included if they evaluated at least one of the above outcome parameters.

DATA COLLECTION AND ANALYSIS

Two review authors independently collected data, which were analysed with Review Manager 5.3.

MAIN RESULTS

A total of 185 studies were included. The average sodium intake was reduced from 201 mmol/day (corresponding to high usual level) to 66 mmol/day (corresponding to the recommended level).The effect of sodium reduction on blood pressure (BP) was as follows: white people with normotension: SBP: mean difference (MD) -1.09 mmHg (95% confidence interval (CI): -1.63 to -0.56; P = 0.0001); 89 studies, 8569 participants; DBP: + 0.03 mmHg (MD 95% CI: -0.37 to 0.43; P = 0.89); 90 studies, 8833 participants. High-quality evidence. Black people with normotension: SBP: MD -4.02 mmHg (95% CI:-7.37 to -0.68; P = 0.002); seven studies, 506 participants; DBP: MD -2.01 mmHg (95% CI:-4.37 to 0.35; P = 0.09); seven studies, 506 participants. Moderate-quality evidence. Asian people with normotension: SBP: MD -0.72 mmHg (95% CI: -3.86 to 2.41; P = 0.65); DBP: MD -1.63 mmHg (95% CI:-3.35 to 0.08; P =0.06); three studies, 393 participants. Moderate-quality evidence.White people with hypertension: SBP: MD -5.51 mmHg (95% CI: -6.45 to -4.57; P < 0.00001); 84 studies, 5925 participants; DBP: MD -2.88 mmHg (95% CI: -3.44 to -2.32; P < 0.00001); 85 studies, 6001 participants. High-quality evidence. Black people with hypertension: SBP MD -6.64 mmHg (95% CI:-9.00 to -4.27; P = 0.00001); eight studies, 619 participants; DBP -2.91 mmHg (95% CI:-4.52, -1.30; P = 0.0004); eight studies, 619 participants. Moderate-quality evidence. Asian people with hypertension: SBP: MD -7.75 mmHg (95% CI:-11,44 to -4.07; P < 0.0001) nine studies, 501 participants; DBP: MD -2.68 mmHg (95% CI: -4.21 to -1.15; P = 0.0006). Moderate-quality evidence.In plasma or serum, there was a significant increase in renin (P < 0.00001), aldosterone (P < 0.00001), noradrenaline (P < 0.00001), adrenaline (P < 0.03), cholesterol (P < 0.0005) and triglyceride (P < 0.0006) with low sodium intake as compared with high sodium intake. All effects were stable in 125 study populations with a sodium intake below 250 mmol/day and a sodium reduction intervention of at least one week.

AUTHORS' CONCLUSIONS

Sodium reduction from an average high usual sodium intake level (201 mmol/day) to an average level of 66 mmol/day, which is below the recommended upper level of 100 mmol/day (5.8 g salt), resulted in a decrease in SBP/DBP of 1/0 mmHg in white participants with normotension and a decrease in SBP/DBP of 5.5/2.9 mmHg in white participants with hypertension. A few studies showed that these effects in black and Asian populations were greater. The effects on hormones and lipids were similar in people with normotension and hypertension. Renin increased 1.60 ng/mL/hour (55%); aldosterone increased 97.81 pg/mL (127%); adrenalin increased 7.55 pg/mL (14%); noradrenalin increased 63.56 pg/mL: (27%); cholesterol increased 5.59 mg/dL (2.9%); triglyceride increased 7.04 mg/dL (6.3%).

Dietary Vitamin E Supplementation Attenuates Hypertension in Dahl Salt-Sensitive Rats

There is strong evidence that excess dietary salt (NaCl) is a major factor contributing to the development of hypertension. Salt-sensitive humans and rats develop hypertension even on a normal-salt diet. Salt sensitivity is associated with glucose intolerance and insulin resistance in both humans and animal models, including Dahl salt-sensitive (DSS) rats. In insulin resistance, impaired glucose metabolism leads to elevated endogenous aldehydes that bind sulfhydryl groups of membrane proteins, altering calcium channels, and increasing cytosolic free calcium ([Ca2+] i) and blood pressure. Vitamin E lowers tissue aldehyde conjugates, cytosolic [Ca2+] i, and blood pressure in spontaneously hypertensive rats and fructose-induced hypertensive Wistar Kyoto rats, models of insulin resistance. This study investigated the effect of a normal-salt diet on tissue aldehyde conjugates, cytosolic [Ca2+] i, and blood pressure in DSS rats and the effect of vitamin E supplementation on blood pressure and associated biochemical changes in these animals. Seven-week-old DSS rats were divided into 3 groups of 6 animals each and treated for 6 weeks with diets as follows: low-salt (0.4% NaCl); normal-salt (0.7% NaCl) and normal salt (0.7% NaCl) plus vitamin E (34 mg/kg feed). At completion, animals in the normal-salt group had significantly elevated systolic blood pressure, cytosolic [Ca2+] i, and tissue aldehyde conjugates compared with the low-salt group. They also showed smooth muscle cell hyperplasia in small arteries and arterioles of the kidney. Dietary vitamin E supplementation significantly attenuated the increase in systolic blood pressure and associated biochemical and histopathologic changes.

Short-term effects of espresso coffee on heart rate variability and blood pressure in habitual and non-habitual coffee consumers--a randomized crossover study

OBJECTIVE

Coffee is one of the most widely consumed beverages worldwide. Aim of this study was to investigate short-term effects of espresso coffee on heart rate variability (HRV), a marker of vagal activity, in healthy habitual and non-habitual coffee consumers.

METHODS

Seventy-seven healthy subjects (38 habitual and 39 non-habitual coffee consumers, 74% women, mean age 26.97 ± 6.88 years) took part in three laboratory sessions in a randomized order. In condition 1, subjects consumed espresso; in condition 2, subjects consumed decaffeinated espresso; and in condition 3, subjects consumed warm water. HRV and blood pressure were assessed at rest before and after ingestion of the respective beverage.

RESULTS

HRV was significantly increased after consumption of caffeinated espresso, decaffeinated espresso, or water, indicating increased vagal activity in the course of the experiments. In the habitual coffee consumers, the increase in vagally mediated HRV was significantly lower after consumption of decaffeinated espresso compared to caffeinated espresso. Increases of systolic blood pressure were only found in the non-habitual consumers.

CONCLUSION

We found no evidence for specific short-term effects of caffeinated espresso on vagal activity in healthy subjects. Instead, consumption of decaffeinated espresso inhibited vagal activity in habitual consumers. This may be explained by an attempt of the organism to establish a sympathovagal equilibrium comparable to that after caffeine consumption. In the absence of caffeine-induced sympathetic activation, this may have been achieved by relative vagal withdrawal.

Low Salt Diet and Insulin Resistance

It is well known that high sodium intake is closely associated with the risk of cardiovascular disease, but the effect of low sodium intake on insulin resistance is not clear. In this article, we summarize findings from previous studies focusing on the association between low sodium intake and insulin resistance. While many investigations on this topic have been conducted actively, their major findings are inconsistent, partly due to different study designs. Thus, additional randomized controlled trials with an adequate study period and reasonable levels of low sodium intake are needed.

Effect of low salt diet on insulin resistance in salt-sensitive versus salt-resistant hypertension

Accumulating evidence shows an increase in insulin resistance on salt restriction. We compared the effect of low salt diet on insulin resistance in salt-sensitive versus salt-resistant hypertensive subjects. We also evaluated the relationship between salt sensitivity of blood pressure and salt sensitivity of insulin resistance in a multivariate regression model. Studies were conducted after 1 week of high salt (200 mmol per day sodium) and 1 week of low salt (10 mmol per day sodium) diet. Salt sensitivity was defined as the fall in systolic blood pressure>15 mm Hg on low salt diet. The study includes 389 subjects (44% women; 16% blacks; body mass index, 28.5±4.2 kg/m2). As expected, blood pressure was lower on low salt (129±16/78±9 mm Hg) as compared with high salt diet (145±18/86±10 mm Hg). Fasting plasma glucose, insulin, and homeostasis model assessment were higher on low salt diet (95.4±19.4 mg/dL; 10.8±7.3 mIU/L; 2.6±1.9) as compared with high salt diet (90.6±10.8 mg/dL; 9.4±5.8 mIU/L; 2.1±1.4; P<0.0001 for all). There was no difference in homeostasis model assessment between salt-sensitive (n=193) versus salt-resistant (n=196) subjects on either diet. Increase in homeostasis model assessment on low salt diet was 0.5±1.4 in salt-sensitive and 0.4±1.5 in salt-resistant subjects (P=NS). On multivariate regression analysis, change in systolic blood pressure was not associated with change in homeostasis model assessment after including age, body mass index, sex, change in serum and urine aldosterone, and cortisol into the model. We conclude that the increase in insulin resistance on low salt diet is not affected by salt sensitivity of blood pressure.

Effect of longer-term modest salt reduction on blood pressure

BACKGROUND

A reduction in salt intake lowers blood pressure (BP) and, thereby, reduces cardiovascular risk. A recent meta-analysis by Graudal implied that salt reduction had adverse effects on hormones and lipids which might mitigate any benefit that occurs with BP reduction. However, Graudal's meta-analysis included a large number of very short-term trials with a large change in salt intake, and such studies are irrelevant to the public health recommendations for a longer-term modest reduction in salt intake. We have updated our Cochrane meta-analysis.

OBJECTIVES

To assess (1) the effect of a longer-term modest reduction in salt intake (i.e. of public health relevance) on BP and whether there was a dose-response relationship; (2) the effect on BP by sex and ethnic group; (3) the effect on plasma renin activity, aldosterone, noradrenaline, adrenaline, cholesterol, low-density lipoprotein (LDL), high-density lipoprotein (HDL) and triglycerides.

SEARCH METHODS

We searched MEDLINE, EMBASE, Cochrane Hypertension Group Specialised Register, Cochrane Central Register of Controlled Trials, and reference list of relevant articles.

SELECTION CRITERIA

We included randomised trials with a modest reduction in salt intake and duration of at least 4 weeks.

DATA COLLECTION AND ANALYSIS

Data were extracted independently by two reviewers. Random effects meta-analyses, subgroup analyses and meta-regression were performed.

MAIN RESULTS

Thirty-four trials (3230 participants) were included. Meta-analysis showed that the mean change in urinary sodium (reduced salt vs usual salt) was -75 mmol/24-h (equivalent to a reduction of 4.4 g/d salt), the mean change in BP was -4.18 mmHg (95% CI: -5.18 to -3.18, I (2)=75%) for systolic and -2.06 mmHg (95% CI: -2.67 to -1.45, I (2)=68%) for diastolic BP. Meta-regression showed that age, ethnic group, BP status (hypertensive or normotensive) and the change in 24-h urinary sodium were all significantly associated with the fall in systolic BP, explaining 68% of the variance between studies. A 100 mmol reduction in 24 hour urinary sodium (6 g/day salt) was associated with a fall in systolic BP of 5.8 mmHg (95%CI: 2.5 to 9.2, P=0.001) after adjusting for age, ethnic group and BP status. For diastolic BP, age, ethnic group, BP status and the change in 24-h urinary sodium explained 41% of the variance between studies. Meta-analysis by subgroup showed that, in hypertensives, the mean effect was -5.39 mmHg (95% CI: -6.62 to -4.15, I (2)=61%) for systolic and -2.82 mmHg (95% CI: -3.54 to -2.11, I (2)=52%) for diastolic BP. In normotensives, the mean effect was -2.42 mmHg (95% CI: -3.56 to -1.29, I (2)=66%) for systolic and -1.00 mmHg (95% CI: -1.85 to -0.15, I (2)=66%) for diastolic BP. Further subgroup analysis showed that the decrease in systolic BP was significant in both whites and blacks, men and women. Meta-analysis of hormone and lipid data showed that the mean effect was 0.26 ng/ml/hr (95% CI: 0.17 to 0.36, I (2)=70%) for plasma renin activity, 73.20 pmol/l (95% CI: 44.92 to 101.48, I (2)=62%) for aldosterone, 31.67 pg/ml (95% CI: 6.57 to 56.77, I (2)=5%) for noradrenaline, 6.70 pg/ml (95% CI: -0.25 to 13.64, I (2)=12%) for adrenaline, 0.05 mmol/l (95% CI: -0.02 to 0.11, I (2)=0%) for cholesterol, 0.05 mmol/l (95% CI: -0.01 to 0.12, I (2)=0%) for LDL, -0.02 mmol/l (95% CI: -0.06 to 0.01, I (2)=16%) for HDL, and 0.04 mmol/l (95% CI: -0.02 to 0.09, I (2)=0%) for triglycerides.

AUTHORS' CONCLUSIONS

A modest reduction in salt intake for 4 or more weeks causes significant and, from a population viewpoint, important falls in BP in both hypertensive and normotensive individuals, irrespective of sex and ethnic group. With salt reduction, there is a small physiological increase in plasma renin activity, aldosterone and noradrenaline. There is no significant change in lipid levels. These results provide further strong support for a reduction in population salt intake. This will likely lower population BP and, thereby, reduce cardiovascular disease. Additionally, our analysis demonstrates a significant association between the reduction in 24-h urinary sodium and the fall in systolic BP, indicating the greater the reduction in salt intake, the greater the fall in systolic BP. The current recommendations to reduce salt intake from 9-12 to 5-6 g/d will have a major effect on BP, but are not ideal. A further reduction to 3 g/d will have a greater effect and should become the long term target for population salt intake.

Differential predictors of insulin resistance in nondiabetic salt-resistant and salt-sensitive subjects

We studied the characteristics of insulin resistance in 19 normotensive and 25 hypertensive subjects who underwent an acute protocol for determination of salt-sensitivity of blood pressure. Hypertensive subjects were older and more obese, with higher creatinine, lipids, and aldosterone than normotensive volunteers. They also had higher glucose and insulin levels with a marked decrease in insulin sensitivity (HOMA2-S index). Once all participants were classified into salt-sensitive (SS) and salt-resistant (SR) groups, most of these differences were no longer present. In contrast, SS had classical characteristics of this phenotype (higher percentage of blacks, suppressed plasma renin, increased aldosterone-to-renin ratio, and blunted renin and aldosterone responses to changes in salt balance). Despite similar insulin levels, HOMA2-S was significantly lower in SS than SR. Salt-loading did not change HOMA2-S in SS or SR. In contrast, salt-depletion, by significantly increasing glucose and insulin of SR, decreased their HOMA2-S to the levels observed in SS. Correlates of insulin resistance in SR included age, triglycerides, body mass index, mean arterial pressure, aldosterone, and epinephrine. However, only body mass index and aldosterone remained as significant predictors in multivariate analyses. Correlates of insulin resistance in SS were mean arterial pressure, epinephrine, and norepinephrine, all remaining as significant predictors in multivariate modeling. Our data confirm that salt-sensitivity of blood pressure is associated with insulin resistance, suggest that salt restriction may be beneficial in SS but perhaps detrimental in SR subjects, and uncover possible differences in mechanisms of insulin resistance between SS and SR, with implications for pharmacological therapy.

Increased daily sodium intake is an independent dietary indicator of the metabolic syndrome in middle-aged subjects

AIMS

We investigated the association between daily sodium intake and each individual component of the metabolic syndrome (MS) as well as the metabolic cluster per se and clarified which of the combinations of MS features is particularly associated with sodium intake.

METHODS

A total of 716 subjects from our OPERA (Oulu Project Elucidating Risk of Atherosclerosis) cohort were selected to fill in a food follow-up diary for a 1-week period. The MS was determined using the International Diabetes Federation (IDF) criteria.

RESULTS

Subjects with the MS used more sodium (P < 0.001), less carbohydrate (P < 0.001), less fibre (P = 0.031), and more alcohol (P < 0.001) than those without the MS. High sodium intake was strongly related to elevated BMI (P = 0.003), waist (P < 0.001), and higher fasting blood glucose (P < 0.001). The subjects with the highest sodium intake suffered more often from type 2 diabetes (P = 0.007). Sodium intake was highest in the group where all the MS criteria were present (P < 0.001). High sodium intake was a statistically significant predictor of the MS in logistic regression analysis (P = 0.009). The highest sodium intake was observed in the IDF criteria combination waist + glucose + blood pressure.

CONCLUSIONS

These findings suggest that a reduction in sodium intake may be especially beneficial in the treatment of individuals with the MS.

The antihypertensive effect of arginine

Hypertension is a leading cause of morbidity and mortality worldwide. Individuals with hypertension are at increased risk of stroke, heart disease and kidney failure. Although the etiology of essential hypertension has a genetic component, lifestyle factors such as diet play an important role. Reducing dietary salt is effective in lowering blood pressure in salt-sensitive individuals. Insulin resistance and altered glucose metabolism are common features of hypertension in humans and animal models, with or without salt sensitivity. Altered glucose metabolism leads to increased formation of advanced glycation end products. Insulin resistance is also linked to oxidative stress, and alterations in the nitric oxide pathway and renin angiotensin system. A diet rich in protein containing the semiessential amino acid, arginine, and arginine treatment, lowers blood pressure in humans and in animal models. This may be due to the ability of arginine to improve insulin resistance, decrease advanced glycation end products formation, increase nitric oxide, and decrease levels of angiotensin II and oxidative stress, with improved endothelial cell function and decreased peripheral vascular resistance. The Dietary Approaches to Stop Hypertension (DASH) study demonstrated that the DASH diet, rich in vegetables, fruits and low-fat dairy products; low in fat; and including whole grains, poultry, fish and nuts, lowered blood pressures even more than a typical North American diet with similar reduced sodium content. The DASH diet is rich in protein; the blood pressure-lowering effect of the DASH diet may be due to its higher arginine-containing protein, higher antioxidants and low salt content.

The antihypertensive effect of cysteine

Hypertension is a leading cause of morbidity and mortality worldwide. Individuals with hypertension are at an increased risk for stroke, heart disease and kidney failure. Essential hypertension results from a combination of genetic and lifestyle factors. One such lifestyle factor is diet, and its role in the control of blood pressure has come under much scrutiny. Just as increased salt and sugar are known to elevate blood pressure, other dietary factors may have antihypertensive effects. Studies including the Optimal Macronutrient Intake to Prevent Heart Disease (OmniHeart) study, Multiple Risk Factor Intervention Trial (MRFIT), International Study of Salt and Blood Pressure (INTERSALT) and Dietary Approaches to Stop Hypertension (DASH) study have demonstrated an inverse relationship between dietary protein and blood pressure. One component of dietary protein that may partially account for its antihypertensive effect is the nonessential amino acid cysteine. Studies in hypertensive humans and animal models of hypertension have shown that N-acetylcysteine, a stable cysteine analogue, lowers blood pressure, which substantiates this idea. Cysteine may exert its antihypertensive effects directly or through its storage form, glutathione, by decreasing oxidative stress, improving insulin resistance and glucose metabolism, lowering advanced glycation end products, and modulating levels of nitric oxide and other vasoactive molecules. Therefore, adopting a balanced diet containing cysteine-rich proteins may be a beneficial lifestyle choice for individuals with hypertension. An example of such a diet is the DASH diet, which is low in salt and saturated fat; includes whole grains, poultry, fish and nuts; and is rich in vegetables, fruits and low-fat dairy products.

Circulatory syndrome: an evolution of the metabolic syndrome concept!

The metabolic syndrome has been a useful, though controversial construct in clinical practice as well as a valuable model in order to understand the interactions of diverse cardiovascular risk factors. However the increasing importance of the circulatory system in particular the endothelium, in both connecting and controlling organ function has underlined the limitations of the metabolic syndrome definition. The proposed "Circulatory Syndrome" is an attempt to refine the metabolic syndrome concept by the addition of recently documented markers of cardiovascular disease including renal impairment, microalbuminuria, arterial stiffness, ventricular dysfunction and anaemia to more classic factors including hypertension, dyslipidemia and abnormal glucose metabolism; all of which easily measured in clinical practice. These markers interact with each other as well as with other factors such as aging, obesity, physical inactivity, diet and smoking. The final common pathways of inflammation, oxidative stress and hypercoagulability thereby lead to endothelial damage and eventually cardiovascular disease. Nevertheless, the Circulatory (MARC) Syndrome, like its predecessor the metabolic syndrome, is only a small step toward an understanding of these complex and as yet poorly understood markers of disease.

Altered dietary salt intake for preventing and treating diabetic kidney disease

BACKGROUND

There is strong evidence that our current consumption of salt is a major factor for increased blood pressure (BP) and a modest reduction in salt intake lowers BP whether BP levels are normal or raised. Tight control of BP in diabetics lowers the risk of strokes, heart attacks and heart failure and slows the progression of diabetic kidney disease (DKD). Currently there is no consensus in restricting salt intake in diabetic patients.

OBJECTIVES

To evaluate the effect of altered salt intake on BP and markers of cardiovascular disease and DKD.

SEARCH STRATEGY

In January 2010, we searched the Cochrane Renal Group's Specialised Register, CENTRAL (in The Cochrane Library), MEDLINE (from 1966) and EMBASE (from 1980) to identify appropriate articles.

SELECTION CRITERIA

We included all randomised controlled trials of salt reduction in individuals with type 1 and type 2 diabetes.

DATA COLLECTION AND ANALYSIS

Two authors independently assessed studies and resolved differences by discussion with a third independent author. We calculated mean effect sizes using both the fixed-effect and random-effects models.

MAIN RESULTS

Thirteen studies (254 individuals) met our inclusion criteria. These included 75 individuals with type 1 diabetes and 158 individuals with type 2 diabetes. The median reduction in urinary sodium was 203 mmol/24 h (11.9 g/day) in type 1 diabetes and 125 mmol/24 h (7.3 g/day) in type 2 diabetes. The median duration of salt restriction was one week in both type 1 and type 2 diabetes. BP was reduced in both type 1 and type 2 diabetes. In type 1 diabetes (56 individuals), salt restriction reduced BP by -7.11/-3.13 mm Hg (systolic/diastolic); 95% CI: systolic BP (SBP) -9.13 to -5.10; diastolic BP (DBP) -4.28 to -1.98). In type 2 diabetes (56 individuals), salt restriction reduced BP by -6.90/-2.87 mm Hg (95% CI: SBP -9.84 to -3.95; DBP -4.39 to -1.35). There was a greater reduction in BP in normotensive patients, possibly due to a larger decrease in salt intake in this group.

AUTHORS' CONCLUSIONS

Although the studies are not extensive, this meta-analysis shows a large fall in BP with salt restriction, similar to that of single drug therapy. All diabetics should consider reducing salt intake at least to less than 5-6 g/day in keeping with current recommendations for the general population and may consider lowering salt intake to lower levels, although further studies are needed.

Salt sensitivity is associated with insulin resistance, sympathetic overactivity, and decreased suppression of circulating renin activity in lean patients with essential hypertension

BACKGROUND

The mechanisms by which a derangement of glucose metabolism causes high blood pressure are not fully understood.

OBJECTIVES

This study aimed to clarify the relation between salt sensitivity of blood pressure and insulin resistance, which are important subcharacteristics of hypertension and impaired glucose metabolism, respectively. Effects on the renin-angiotensin and sympathetic nervous systems were also studied.

DESIGN

The state of glucose metabolism was assessed by a hyperinsulinemic euglycemic glucose clamp technique and a 75-g oral-glucose-tolerance test in 24 essential hypertensive patients who were lean and without diabetes or chronic kidney disease. The subjects were classified as salt-sensitive or salt-resistant on the basis of the difference (Delta mean blood pressure > or =5%) between 24-h ambulatory blood pressure monitoring results on the seventh day of low-salt (34 mmol/d) and high-salt (252 mmol/d) diets. Urine and blood samples were collected for analyses.

RESULTS

There was a robust inverse relation between the glucose infusion rate (GIR) and the salt sensitivity index. The GIR correlated directly with the change in urinary sodium excretion and was inversely related to the change in hematocrit when the salt diet was changed from low to high, which is indicative of salt and fluid retention in salt-sensitive subjects. The GIR also showed an inverse correlation compared with the changes in urinary norepinephrine excretion, plasma renin activity, and plasma aldosterone concentration.

CONCLUSIONS

Salt sensitivity of blood pressure is strongly associated with insulin resistance in lean, essential hypertensive patients. Hyperinsulinemia, sympathetic overactivation, and reduced suppression of the renin-angiotensin system may play a role in this relation.

Salt sensitivity and circadian rhythm of blood pressure: the keys to connect CKD with cardiovascular events

In healthy subjects, blood pressure (BP) drops by 10-20% during the night. Conversely, in patients with the salt-sensitive type of hypertension or chronic kidney disease, nighttime BP does not fall, resulting in an atypical pattern of circadian BP rhythm that does not dip. This pattern is referred to as the 'non-dipper' pattern. Loss of renal functional reserve, due to either reduced ultrafiltration capacity or enhanced tubular sodium reabsorption, induces the salt-sensitive type of hypertension. When salt intake is excessive in patients with salt-sensitive hypertension, the defect in sodium excretory capability becomes evident, resulting in elevated BP during the night. This nocturnal hypertension compensates for diminished natriuresis during the daytime and enhances pressure natriuresis during the night. Nocturnal hypertension and the non-dipper pattern of circadian BP rhythm cause cardiovascular events. When excess salt intake is loaded in patients who are in a salt-sensitive state, glomerular capillary pressure is also elevated, resulting in glomerular sclerosis and eventual renal failure. In this way, salt sensitivity and excess salt intake contribute to both cardiovascular and renal damage at the same time. We propose that salt sensitivity of BP and excess salt intake have important roles in the genesis of the cardiorenal connection. Salt sensitivity and circadian rhythm of BP are the keys to understanding the connections between cardiovascular and renal complications.

Mineralocorticoid Receptors, Salt-Sensitive Hypertension, and Metabolic Syndrome

Obese persons with metabolic syndrome often have associated with salt-sensitive hypertension, microalbuminuria, and cardiac dysfunction, and the plasma aldosterone level in one-third of metabolic syndrome patients is clearly elevated. Hyperaldosteronism, which may be caused at least partially by certain adipocyte-derived factors, contributes to the development of proteinuria in obese hypertensive rats, and salt loading aggravates the proteinuria and induces cardiac diastolic dysfunction because of inadequate suppression of plasma aldosterone level. However, mineralocorticoid receptor (MR) antagonists prevent salt-induced renal and cardiac damage, suggesting that aldosterone excess and a high-salt diet exert an unfavorable synergistic action on the kidney and heart. In Dahl salt-sensitive rats, however, despite appropriate suppression of plasma aldosterone with a high-salt diet, salt loading paradoxically activated renal MR signaling, and the renal injury was markedly prevented by MR antagonists. Accordingly, we discovered an alternative pathway of MR activation in which Rac1, a small GTP-binding protein, activates MRs. Salt loading activates renal Rac1 in Dahl salt-sensitive rats, and Rac1 in turn induces MR activation, which results in renal injury, and the renal injury has been found to be prevented by Rac1 inhibitors. Moreover, several metabolic syndrome-related factors induce Rac1 activation, and one of them, hyperglycemia, activates MRs via Rac1 activation. Consistent with this, Rac1 inhibitors attenuated the proteinuria and renal injury in obese hypertensive animals. Thus, both salt and obesity activate Rac1 and cause MR activation. Abnormal activation of the aldosterone/MR pathway plays a key role in the development of salt-sensitive hypertension and renal injury in metabolic syndrome.

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.

Effect of insulin-unstimulated diabetic therapy with miglitol on serum cystatin C level and its clinical significance

The serum cystatin C level is thought to provide a more accurate estimate of renal function in diabetic subjects than creatinine-based methods. This study was designed to compare miglitol and miglitinide, on cystatin C levels. Forty patients with type 2 diabetes were randomly assigned to receive 150 mg/day miglitol or 30 mg/day mitiglinide. The serum cystatin C level was measured in 36 patients (19 in the miglitol group and 17 in the mitiglinide group) undergoing meal tolerance testing. High sensitivity C reactive protein (hsCRP) was also assessed. After 3 months of therapy, the cystatin C level did not change but the log-transformed hsCRP value decreased (3.03+/-0.32 to 2.83+/-0.34log[microg/L], P<0.05) in the miglitol group, whereas in the mitiglinide group the cystatin C level increased (0.75+/-0.18 to 0.78+/-0.20mg/L, P<0.05) but the hsCRP value did not change. After 3 months, the levels of cystatin C and hsCRP were each correlated with the postprandial insulin level in the meal tolerance test in all patients. These results suggest that postprandial insulin secretion might increase cystatin C and that insulin-unstimulated miglitol therapy might suppress an increase in cystatin C accompanied by an anti-inflammatory effect in diabetic patients.

Low anxiety males display higher degree of salt sensitivity, increased autonomic reactivity, and higher defensiveness

BACKGROUND

Psychological parameters such as heightened anxiety and defensiveness are associated with increased cardiovascular morbidity and mortality. Autonomic dysfunction is considered to be an important pathogenetic pathway. Little research has been done regarding potential links between emotional factors and salt sensitivity. The aim of the present study was to determine whether subjects with different levels of trait anxiety differ in the degree of salt sensitivity and autonomic reactivity to a mental stress task.

METHODS

Seventy-two young normotensive men were phenotyped for salt sensitivity and underwent a standardized mental stress test and psychological assessment. According to their trait anxiety test scores, they were classified as low-, moderate- or high-anxiety subjects. A measure of defensiveness was used to assess self-deceptive tendencies.

RESULTS

Low-anxiety subjects displayed a higher degree of salt sensitivity compared to moderate- and high-anxiety subjects (P < 0.001), increased heart rate (HR) and electrodermal responses to the stressor compared to moderate-anxiety subjects (P < 0.01 and P < 0.05 respectively) and elevated levels of self-deception compared to moderate- and high-anxiety subjects (P < 0.001).

CONCLUSION

Low-anxiety subjects were characterized by a higher degree of salt sensitivity and increased autonomic responsiveness. Defensiveness was also shown to be elevated in this group and might be the underlying psychological trait explaining these findings. Future research on the associations of anxiety and cardiovascular risk should implement measurement of defensiveness in order to identify these subjects at potential risk for cardiovascular disease despite self-reports of low anxiety.

Salt-sensitive men show reduced heart rate variability, lower norepinephrine and enhanced cortisol during mental stress

Salt sensitivity (SS) represents a risk factor for essential hypertension, which has been related to enhanced cardiovascular stress reactivity possibly mediated by increased noradrenergic susceptibility. We investigated biophysiological responses to mental stress in salt-sensitive (ss) and salt-resistant (sr) subjects, hypothesizing lower heart rate variability (HRV) and higher cortisol in the ss. A total of 48 healthy normotensive Caucasian men (age 25.6+/-2.6, body mass index 22.9+/-2.3) were phenotyped for SS (defined as significant drop in mean arterial pressure>3 mm Hg under the low-salt diet) by a 2-week high- versus low-salt diet. Subjects underwent a standardized mental stress task with continuous cardiovascular monitoring before, during and after the test (Finapres; Ohmeda, Louisville, CO, USA). Blood samples were drawn to examine cortisol and catecholamines before, after and 20 min after stress. The task elicited significant increases of systolic blood pressure (SBP), diastolic BP (DBP) and heart rate (HR) and a significant decrease of HRV (all time effects P<0.0001). The ss subjects showed lower norepinephrine (NE) and higher cortisol, indicated by significant group effects (P=0.009 and 0.025, respectively). HR increased and HRV decreased more in the ss under the stress, shown by significant time by group interactions (P=0.045 and 0.003, respectively). The observation of a more pronounced HR rise coupled with a greater decrease of HRV in healthy ss men under the influence of brief mental stress confirms their enhanced physiological stress reactivity. The lower peripheral NE may represent an effort to compensate for increased noradrenergic receptor sensitivity. The enhanced cortisol levels are backed by recent genetic findings on HSD11B2 polymorphisms and may promote hypertension.

Pathophysiological Mechanisms of Salt-Dependent Hypertension

Changes in salt intake are associated in general with corresponding changes in arterial blood pressure. An exaggerated increment in blood pressure driven by a salt load is characteristic of salt-sensitive hypertension, a condition affecting more than two thirds of individuals with essential hypertension who are older than 60 years. In the last decade, significant insight was gained about the role of the kidney in the increment in blood pressure induced by sodium retention. The present review focuses on the pathophysiological characteristics of the blood pressure increase driven by expansion of extracellular fluid and the increment in plasma sodium concentration. In addition, we discuss systemic and renal conditions that result in decreased urinary sodium excretion and were implicated in the development of salt-sensitive hypertension.

Evaluation of Insulin Resistance and Sodium Sensitivity in Normotensive Offspring of Hypertensive Individuals

BACKGROUND

Sodium sensitivity (SS) and insulin resistance (IR) might be a common link in the pathogenesis of essential hypertension. The aim of the present study is to investigate the relationship, if any, between SS and IR in a population with a family predisposition to develop hypertension.

METHODS

Twenty normotensive subjects aged 20 to 40 years with a family history of hypertension (1 or both parents hypertensive) and no other risk factor (group A) and 10 normotensive subjects aged 20 to 40 years without a family history of hypertension (group B) were enrolled. SS and IR were estimated using the euglycemic clamp technique and correlated in both groups. Blood pressure, mean blood pressure (MAP), and biochemical control were recorded.

RESULTS

The frequency of SS was equal in offspring of hypertensive subjects and the control group. Individuals with a family history of hypertension had a tendency to develop IR (45%) compared with the control group (20%). This group had a greater MAP at both salt-loading and salt-deprivation periods. Increased IR was associated with increased MAP. No significant relationship was found between SS and IR in either the entire sample or the subgroup of individuals with a family history of hypertension. Serum urea and total cholesterol levels were significantly greater in group A. Age, sex, and body mass index were not related to the presence of IR or SS in either group.

CONCLUSION

SS and IR do not relate in young normotensive adults or offspring of hypertensive parents. However, the latter may comprise a high-risk group, currently normotensive, who have an increased possibility to present or develop IR in early adolescent life. Moreover, the increased IR is related to the greater MAP in group A. Thus, they are subject to increased cardiovascular risk because of the subsequent disturbed glucose and lipid metabolism.

The antinatriuretic effect of insulin: an unappreciated mechanism for hypertension associated with insulin resistance?

Insulin resistance is proposed to be causally related to the metabolic syndrome disorders, but a direct cause-and-effect relationship between insulin resistance and hypertension was not originally obvious. Previous data suggested that insulin promotes sodium retention from the kidney, and thus research efforts focused on this action among several other possible pathways connecting insulin resistance and hyperinsulinemia with hypertension. A review of numerous studies provides evidence that this antinatriuretic effect of insulin is preserved in states of metabolic insulin resistance, representing a major mechanism for blood pressure elevation. More recent experimental and clinical studies have added data about the exact tubular sites of this insulin action, its relation with the respective insulin action on potassium handling, its possible role in the development of salt sensitivity in essential hypertension, as well as the involvement of oxidant stress in these associations. This review summarizes the current state of knowledge in this area and attempts to highlight an important but rather overlooked pathway for hypertension development in the metabolic syndrome, the influence of high insulin levels leading to volume expansion.

Influence of salt intake on renin-angiotensin and natriuretic peptide system genes in human adipose tissue

We tested the hypothesis that changes in sodium intake modulate adipose-tissue renin-angiotensin and natriuretic peptide system gene expression in humans. We studied 9 healthy young men in a metabolic ward at constant room temperature, humidity, and water, potassium, and calcium intake. Subjects were submitted to 4 different periods of sodium intake, and blood samples, microdialysis samples (interstitial fluid), and biopsies from subcutaneous abdominal adipose tissue were obtained at the end of the low-sodium period (0.7 mmol Na/kg per day) and at the end of the high-sodium period (7.7 mmol Na/kg per day). Urinary sodium excretion was 64+/-4 mmol per day with the low-sodium diet and 521+/-8 mmol per day with the high-sodium diet. Systemic and microdialysate sodium concentrations were similar with both interventions. With high-sodium intake, systemic renin activity and aldosterone levels were suppressed, angiotensin-converting enzyme activity did not change, and systemic levels of the atrial natriuretic peptide increased. High-sodium diet increased angiotensin-converting enzyme and atrial natriuretic peptide gene expression in adipose tissue. None of the other genes tested were influenced by changes in dietary sodium intake. Our findings suggest that the adipose-tissue renin-angiotensin system is not part of a feedback mechanism regulating sodium homeostasis and blood pressure. Systemic and adipose-tissue renin-angiotensin systems are regulated at least in part independently from each other. In contrast, systemic atrial natriuretic peptide and adipose-tissue atrial natriuretic peptide respond similarly to changes in sodium intake.

Surgical Menopause Increases Salt Sensitivity of Blood Pressure

Salt sensitivity of blood pressure is associated with an elevated risk of developing hypertension (HTN) and is an independent risk factor for cardiovascular disease. The prevalence of HTN increases after menopause. The aim of this study was to investigate prospectively whether the loss of ovarian hormones increases the occurrence of salt sensitivity among healthy premenopausal women. We enrolled 40 normotensive, nondiabetic women (age 47.2+/-3.5), undergoing hysterectomy-oophorectomy for nonneoplastic processes and not on hormone replacement, to determine the effect of changes in sodium intake on blood pressure the day before and subsequently 4 months after surgical menopause. Salt loading was achieved using a 2-L normal saline infusion and salt depletion produced by 40 mg of intravenous furosemide. A decrease >10 mm Hg in systolic blood pressure between salt loading and salt depletion was used to define salt sensitivity. Before and after menopause, salt-sensitive women exhibited higher waist/hip and waist/thigh ratios (P<0.01). Although all of the women remained normotensive, the prevalence of salt sensitivity was significantly higher after surgical menopause (21 women; 52.5%) than before (9 women; 22.5%; P=0.01), because 12 (38.7%) salt-resistant women developed salt sensitivity after menopause. In summary, we demonstrated that the prevalence of salt sensitivity doubled as early as 4 months after surgical menopause, without an associated increase in blood pressure. Epidemiological studies indicate that development of HTN may not occur until 5 to 10 years after menopause. The loss of ovarian hormones may unmask a population of women prone to salt sensitivity who, with aging, would be at higher risk for the subsequent development of HTN and cardiovascular disease.

Low ethanol intake prevents salt-induced hypertension in WKY rats

Low alcohol intake in humans lowers the risk of coronary heart disease and may lower blood pressure. In hypertension, insulin resistance with altered glucose metabolism leads to increased formation of aldehydes. We have shown that chronic low alcohol intake decreased systolic blood pressure (SBP) and tissue aldehyde conjugates in spontaneously hypertensive rats and demonstrated a strong link between elevated tissue aldehyde conjugates and hypertension in salt-induced hypertensive Wistar-Kyoto (WKY) rats. This study investigated the antihypertensive effect of chronic low alcohol consumption in high salt-treated WKY rats and its effect on tissue aldehyde conjugates, platelet cytosolic free calcium ([Ca2+]i, and renal vascular changes. Animals, aged 7 weeks, were divided into three groups of six animals each. The control group was given normal salt diet (0.7% NaCl) and regular drinking water; the high salt group was given a high salt diet (8% NaCl) and regular drinking water; the high salt + ethanol group was given a high salt diet and 0.25% ethanol in drinking water. After 10 weeks, SBP, platelet [Ca2+]i, and tissue aldehyde conjugates were significantly higher in rats in the high salt group as compared with controls. Animals on high salt diets also showed smooth muscle cell hyperplasia in the small arteries and arterioles of the kidney. Ethanol supplementation prevented the increase in SBP and platelet [Ca2+]i and aldehyde conjugates in liver and aorta. Kidney aldehyde conjugates and renal vascular changes were attenuated. These results suggest that chronic low ethanol intake prevents salt-induced hypertension and attenuates renal vascular changes in WKY rats by preventing an increase in tissue aldehyde conjugates and cytosolic [Ca2+]i.

Salt sensitivity and hypertension after menopause: role of nitric oxide and angiotensin II

Hypertension is a major risk factor for cardiovascular disease and renal disease. After menopause, the incidence of hypertension increases in women to levels that equal or exceed that in men, suggesting a protective role of female sex hormones. Salt sensitivity of blood pressure is associated with an increased risk for development of hypertension and cardiovascular disease. We and others have demonstrated that after menopause, the prevalence of salt sensitivity increases, suggesting that female sex hormones influence renal sodium handling and blood pressure regulation. A homeostatic balance between the counteracting effects of nitric oxide (NO) and angiotensin (Ang) II on pressure natriuresis, renal hemodynamics, tubular sodium reabsorption, and oxidative stress plays an important role in modulating salt sensitivity as well as hypertensive end-organ injury. Estrogens modulate the activity and expression of NO and Ang II. We infer that after menopause, estrogen deficiency promotes an unbalance between NO and Ang II, resulting in disturbed renal sodium handling, oxidative stress, and hypertension, particularly in genetically prone women. A better understanding of the mechanisms underlying the development of postmenopausal hypertension and associated cardiovascular and renal diseases should provide insights into preventive and therapeutic strategies.

PPARgamma agonists do not directly enhance basal or insulin-stimulated Na(+) transport via the epithelial Na(+) channel

Selective agonists of peroxisome proliferator-activated receptor gamma (PPARgamma) are anti-diabetic drugs that enhance cellular responsiveness to insulin. However, in some patients, fluid retention, plasma volume expansion, and edema have been observed. It is well established that insulin regulates Na(+) reabsorption via the epithelial sodium channel (ENaC) located in the distal tubule. Therefore, we hypothesized that these agonists may positively modulate insulin-stimulated ENaC activity leading to increased Na(+) reabsorption and fluid retention. Using electrophysiological techniques, dose-response curves for insulin-mediated Na(+) transport in the A6, M-1, and mpkCCD(cl4) cell lines were performed. Each line demonstrated hormone efficacy within physiological concentration ranges and, therefore, can be used to monitor clinically relevant effects of pharmacological agents which may affect electrolyte transport. Immunodetection and quantitative PCR analyses showed that each cell line expresses viable and functional PPARgamma receptors. Despite this finding, two PPARgamma agonists, pioglitazone and GW7845 did not directly enhance basal or insulin-stimulated Na(+) flux via ENaC, as shown by electrophysiological methodologies. These studies provide important results, which eliminate insulin-mediated ENaC activation as a candidate mechanism underlying the fluid retention observed with PPARgamma agonist use.

Urinary sodium and potassium excretion and the risk of type 2 diabetes: a prospective study in Finland

AIMS/HYPOTHESIS

No previous studies on the association between salt intake and the risk of type 2 diabetes have been reported. The aim of this study was to assess whether high salt intake, measured by 24-h urinary sodium excretion, is an independent risk factor for type 2 diabetes.

METHODS

We followed prospectively 932 Finnish men and 1,003 women aged 35-64 years with complete data on 24-h urinary sodium and potassium excretion and other study parameters. Hazard ratios for the incidence of type 2 diabetes were estimated for different levels of 24-h urinary sodium and potassium excretion.

RESULTS

During a mean follow-up of 18.1 years, there were 129 incident cases of type 2 diabetes. The multivariate-adjusted (age, sex, study year, body mass index, physical activity, systolic blood pressure, antihypertensive drug treatment, education, smoking and coffee, alcohol, fruit, vegetable, sausage, bread and saturated fat consumption) hazard ratio for diabetes for the highest vs combined lower quartiles of 24-h urinary sodium excretion was 2.05 (95% CI, 1.43-2.96). This positive association persisted in non-obese and obese subjects, in normotensive and hypertensive subjects, as well as in men and women. Potassium excretion was not associated with the risk of type 2 diabetes.

CONCLUSIONS/INTERPRETATION

High sodium intake predicted the risk of type 2 diabetes, independently of other risk factors including physical inactivity, obesity and hypertension. These results provide direct evidence of the harmful effects of high salt intake in the adult population, although the confounding effect of other dietary factors cannot be fully excluded.

Dietary lipoic acid supplementation attenuates hypertension in Dahl salt sensitive rats

There is strong evidence that excess dietary salt (NaCl) is a major factor contributing to the development of hypertension. Salt sensitive humans and rats develop hypertension even on a normal salt diet. Salt sensitivity is associated with glucose intolerance and insulin resistance in both humans and animal models, including Dahl salt sensitive (DSS) rats. In insulin resistance, impaired glucose metabolism leads to elevated endogenous aldehydes. These aldehydes bind sulfhydryl groups of membrane proteins, altering calcium channels, increasing cytosolic free calcium ([Ca2+]i) and blood pressure. Treatment with lipoic acid, an endogenous sulfur-containing fatty acid, normalizes insulin resistance and lowers tissue aldehyde conjugates, cytosolic [Ca2+]i, and blood pressure in spontaneously hypertensive rats (SHR). The objective of this study was to investigate the effects of a normal salt diet on tissue aldehyde conjugates, cytosolic [Ca2+]i and blood pressure in DSS rats and to determine whether lipoic acid supplementation prevents the increase in blood pressure and biochemical changes. Starting at 7 weeks of age, DSS rats were divided into three groups of six animals each and treated for 6 weeks with diets as follows: DSS-low salt, 0.4% NaCl; DSS-normal salt, 0.7% NaCl, and; DSS-normal salt + lipoic acid, 0.7% NaCl + lipoic acid 500 mg/kg feed. At completion, animals in the normal salt group had elevated systolic blood pressure, cytosolic [Ca2+]i and tissue aldehyde conjugates as compared to the low salt group. They also showed smooth muscle cell hyperplasia in small arteries and arterioles of the kidney. Dietary lipoic acid supplementation attenuated the increase in systolic blood pressure and associated biochemical and histopathological changes.

Real-time three-dimensional imaging of lipid signal transduction: apical membrane insertion of epithelial Na(+) channels

In the distal tubule, Na(+) resorption is mediated by epithelial Na(+) channels (ENaC). Hormones such as aldosterone, vasopressin, and insulin modulate ENaC membrane targeting, assembly, and/or kinetic activity, thereby regulating salt and water homeostasis. Insulin binds to a receptor on the basal membrane to initiate a signal transduction cascade that rapidly results in an increase in apical membrane ENaC. Current models of this signaling pathway envision diffusion of signaling intermediates from the basal to the apical membrane. This necessitates diffusion of several high-molecular-weight signaling elements across a three-dimensional space. Transduction of the insulin signal involves the phosphoinositide pathway, but how and where this lipid-based signaling pathway controls ENaC activity is not known. We used tagged channels, biosensor lipid probes, and intravital imaging to investigate the role of lipids in insulin-stimulated Na(+) flux. Insulin-stimulated delivery of intracellular ENaC to apical membranes was concurrent with plasma membrane-limited changes in lipid composition. Notably, in response to insulin, phosphatidylinositol 3,4,5-trisphosphate (PIP(3)) formed in the basolateral membrane, rapidly diffused within the bilayer, and crossed the tight junction to enter the apical membrane. This novel signaling pathway takes advantage of the fact that the lipids of the plasma membrane's inner leaflet are not constrained by the tight junction. Therefore, diffusion of PIP(3) as a signal transduction intermediate occurs within a planar surface, thus facilitating swift responses and confining and controlling the signaling pathway.

The metabolic syndrome or the insulin resistance syndrome? Different names, different concepts, and different goals

The goal of this article is to differentiate the insulin resistance syndrome from the metabolic syndrome. In the case of the insulin resistance syndrome, the abnormalities and clinical syndromes that are increased in prevalence in insulin-resistant individuals have been summarized, with a brief discussion of the causal relationship between insulin resistance, compensatory hyperinsulinemia, and associated consequences. Discussion of the metabolic syndrome has focused on the five criteria chosen by the adult treatment panel III to diagnose the syndrome, evaluating them in terms of their relationship to insulin resistance and their role as cardiovascular disease risk factors.

Effect of longer-term modest salt reduction on blood pressure

BACKGROUND

Many randomised trials assessing the effect of salt reduction on blood pressure show reduction in blood pressure in individuals with high blood pressure. However, there is controversy about the magnitude and the clinical significance of the fall in blood pressure in individuals with normal blood pressure. Several meta-analyses of randomised salt reduction trials have been published in the last few years. However, most of these included trials of very short duration (e.g. 5 days) and included trials with salt loading followed by salt deprivation (e.g. from 20 to 1 g/day) over only a few days. These short-term experiments are not appropriate to inform public health policy which is for a modest reduction in salt intake over a prolonged period of time. A meta-analysis by Hooper et al is an important attempt to look at whether advice to achieve a long-term salt reduction (i.e. more than 6 months) in randomised trials causes a fall in blood pressure. However, most trials included in this meta-analysis achieved a small reduction in salt intake; on average, salt intake was reduced by 2 g/day. It is, therefore, not surprising that this analysis showed a small fall in blood pressure, and that a dose-response to salt reduction was not demonstrable.

OBJECTIVES

To assess the effect of the currently recommended modest reduction in salt intake (WHO 2003; SACN 2003; Whelton 2002), on blood pressure in individuals with normal and elevated blood pressure. To assess whether the magnitude of the reduction in blood pressure is dependent on the magnitude of the reduction in salt intake.

SEARCH STRATEGY

We searched MEDLINE, EMBASE, Cochrane library, CINAHL, and reference list of original and review articles.

SELECTION CRITERIA

We included randomised trials with a modest reduction in salt intake and a duration of 4 or more weeks.

DATA COLLECTION AND ANALYSIS

Data were extracted independently by two persons. Mean effect sizes were calculated using both fixed and random effect models using Review Manager 4.2.1 software. Weighted linear regression was used to examine the relationship between the change in urinary sodium and the change in blood pressure. We used funnel plots to detect publication and other biases in the meta-analysis.

MAIN RESULTS

Seventeen trials in individuals with elevated blood pressure (n=734) and 11 trials in individuals with normal blood pressure (n=2220) were included. In individuals with elevated blood pressure the median reduction in 24-h urinary sodium excretion was 78 mmol (4.6 g/day of salt), the mean reduction in systolic blood pressure was -4.97 mmHg (95%CI:-5.76 to -4.18), and the mean reduction in diastolic blood pressure was -2.74 mmHg (95% CI:-3.22 to -2.26). In individuals with normal blood pressure the median reduction in 24-h urinary sodium excretion was 74 mmol (4.4 g/day of salt), the mean reduction in systolic blood pressure was -2.03 mmHg (95% CI: -2.56 to -1.50) mmHg, and the mean reduction in diastolic blood pressure was -0.99 mmHg (-1.40 to -0.57). Weighted linear regression analyses showed a correlation between the reduction in urinary sodium and the reduction in blood pressure.

REVIEWERS' CONCLUSIONS

Our meta-analysis demonstrates that a modest reduction in salt intake for a duration of 4 or more weeks has a significant and, from a population viewpoint, important effect on blood pressure in both individuals with normal and elevated blood pressure. These results support other evidence suggesting that a modest and long-term reduction in population salt intake could reduce strokes, heart attacks, and heart failure. Furthermore, our meta-analysis demonstrates a correlation between the magnitude of salt reduction and the magnitude of blood pressure reduction. Within the daily intake range of 3 to 12 g/day, the lower the salt intake achieved, the lower the blood pressure.

A high-fat, refined-carbohydrate diet affects renal NO synthase protein expression and salt sensitivity

Chronic consumption of a high-fat, refined-carbohydrate (HFS) diet causes hypertension. In an earlier study, we found increased nitric oxide (NO) inactivation by reactive oxygen species (ROS) and functional NO deficiency in this model. Given the critical role of NO in renal sodium handling, we hypothesized that diet-induced hypertension may be associated with salt sensitivity. Female Fischer rats were fed an HFS or a standard low-fat, complex-carbohydrate (LFCC) rat chow diet starting at 2 mo of age for 2 yr. Arterial blood pressure, renal neuronal NO synthase (nNOS), endothelial NO synthase (eNOS), and inducible NO synthase (iNOS) protein and nitrotyrosine abundance (a marker of NO inactivation by ROS), and urinary NO metabolite excretion were measured. To assess salt sensitivity, the blood pressure response to a high-salt (4%) diet for 1 wk was determined. After 2 yr, renal nNOS and urinary NO metabolite excretion were significantly depressed, whereas arterial pressure, eNOS, iNOS, and nitrotyrosine were elevated in the HFS group but remained virtually unchanged in the LFCC group. Consumption of the high-salt diet resulted in a significant rise in arterial pressure in the HFS, but not in the LFCC, group. Thus chronic consumption of an HFS diet results in hypertension and salt sensitivity, which may be in part due to a combination of ROS-mediated NO inactivation and depressed renal nNOS protein expression.

Silent ischemia is more prevalent among hypertensive patients with microalbuminuria and salt sensitivity

Some patients with essential hypertension manifest greater than normal urinary albumin excretion (UAE). Salt-sensitive hypertensives also manifest greater UAE compared to salt-resistant individuals. Although the significance of these associations is not well established, several lines of evidence suggest that microalbuminuria and/or salt sensitivity may be associated with greater prevalence of cardiovascular risks and events. In this study, we have evaluated by ergometric exercise 42 subjects with microalbuminuria and 42 matched individuals with normal UAE. All these subjects also underwent a standardized protocol to determine blood pressure sensitivity to a high salt intake. Patients with microalbuminuria displayed greater levels of ambulatory blood pressure and a greater rise in systolic blood pressure during exercise compared to patients with normal UAE (33.1 +/- 1.56 vs 26.4 +/- 1.7 mmHg, P < 0.001). Seven hypertensive patients with microalbuminuria developed ST segment depression during exercise compared to only one subject with normal UAE. Salt-sensitive patients manifested greater UAE than salt-resistant subjects (58 and 14 mg, 24 h, P < 0.001) and greater prevalence of silent ischemia (6 vs 2) than salt-resistant individuals. In conclusion, these studies have shown that hypertensive individuals with microalbuminuria and/or salt sensitivity manifest an increased prevalence of silent ischemia.

Nonhypertensive cardiac effects of a high salt diet

Dietary salt intake plays a major role in variation of blood pressure levels and cardiovascular conditions. High salt intake is associated with the occurrence of hypertension. The evidence that high salt intake increases risk of cardiovascular disease is inconsistent. Some studies indicate a significant and positive association between salt intake and risk of cardiovascular disease, whereas several other studies report that such an association may not exist and that low sodium may even be harmful. It is clear that left ventricular hypertrophy is closely related to salt intake. There is evidence indicating that high salt intake increases renal glomerular filtration rate and glomerular filtration fraction in salt-sensitive patients. The association of high salt intake, insulin resistance, and salt sensitivity, and the interaction between high salt intake, heart rate, and blood pressure are debated.