Relationship between ambulatory and resting blood pressure responses to dietary salt restriction in normotensive men

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.

Association of 24-Hour Blood Pressure With Urinary Sodium Excretion in Healthy Adults

BACKGROUND

While the positive relationship between urinary sodium excretion and blood pressure (BP) is well established for middle-aged to elderly individuals using office BP, data are limited for younger individuals and ambulatory BP measurements.

METHODS

Our analysis included 2,899 individuals aged 18 to 90 years from 2 population-based studies (GAPP, Swiss Kidney Project on Genes in Hypertension [SKIPOGH]). Participants with prevalent cardiovascular disease, diabetes, or on BP-lowering treatment were excluded. In SKIPOGH, 24-hour urinary sodium excretion was used as a measure of sodium intake, while in GAPP it was calculated from fasting morning urinary samples using the Kawasaki formula. Multivariable linear regression models were used to assess the relationships of 24-hour urinary salt excretion with office and ambulatory BP measurements.

RESULTS

Mean age, ambulatory BP, sodium excretion, and estimated glomerular filtration rate in GAPP and SKIPOGH were 35 and 44 years, 123/78 and 118/77 mm Hg, 4.2 and 3.3 g/d, and 110 and 99 ml/min/1.73 m2, respectively. A weak linear association was observed between 24-hour ambulatory systolic BP and urinary sodium excretion (β (95% confidence interval [CI]) per 1 g increase in sodium excretion (0.33 % (0.09; 0.57); P = 0.008). No significant relationships were observed for 24-hour ambulatory diastolic BP (β (95% CI) (0.13 % (-0.15; 0.40) P = 0.37). When repeating the analyses in different age groups, all BP indices appeared to have stronger relationships in the older age groups (>40 years).

CONCLUSIONS

In these large cohorts of healthy adults, urinary sodium excretion was only weakly associated with systolic 24-hour ambulatory BP.

Role of dietary salt and potassium intake in cardiovascular health and disease: a review of the evidence

The objective of this review was to provide a synthesis of the evidence on the effect of dietary salt and potassium intake on population blood pressure, cardiovascular disease, and mortality. Dietary guidelines and recommendations are outlined, current controversies regarding the evidence are discussed, and recommendations are made on the basis of the evidence. Designed search strategies were used to search various databases for available studies. Randomized trials of the effect of dietary salt intake reduction or increased potassium intake on blood pressure, target organ damage, cardiovascular disease, and mortality were included. Fifty-two publications from January 1, 1990, to January 31, 2013, were identified for inclusion. Consideration was given to variations in the search terms used and the spelling of terms so that studies were not overlooked, and search terms took the following general form: (dietary salt or dietary sodium or [synonyms]) and (dietary potassium or [synonyms]) and (blood pressure or hypertension or vascular disease or heart disease or chronic kidney disease or stroke or mortality or [synonyms]). Evidence from these studies demonstrates that high salt intake not only increases blood pressure but also plays a role in endothelial dysfunction, cardiovascular structure and function, albuminuria and kidney disease progression, and cardiovascular morbidity and mortality in the general population. Conversely, dietary potassium intake attenuates these effects, showing a linkage to reduction in stroke rates and cardiovascular disease risk. Various subpopulations, such as overweight and obese individuals and aging adults, exhibit greater sensitivity to the effects of reduced salt intake and may gain the most benefits. A diet that includes modest salt restriction while increasing potassium intake serves as a strategy to prevent or control hypertension and decrease cardiovascular morbidity and mortality. Thus, the body of evidence supports population-wide sodium intake reduction and recommended increases in dietary potassium intake as outlined by current guidelines as an essential public health effort to prevent kidney disease, stroke, and cardiovascular disease.

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.

[Short-term effect of dietary-sodium intake on arterial blood pressure of patients treated with systemic corticosteroids: a prospective, randomised, crossover study]

INTRODUCTION

It is unknown if the level of dietary-sodium intake influences blood pressure in patients receiving systemic corticosteroids.

METHODS

Randomized, single centre, crossover trial involving patients starting systemic corticosteroid therapy and having initial blood pressure less or equals to 159/99 mm Hg. The first period of sodium regimen was randomized (<3 g/j versus >6 g/j) and each period of sodium regimen lasted 3 weeks. No washout period was performed. Blood pressure was recorded for each patient at inclusion and after 3 weeks and 6 weeks. Moreover, all patients were asked to record on a standardized questionnaire everything they ate during 1 week of each period regimen. Questionnaires were analysed by a dietician for mean daily energy and sodium intakes during each period. Mixed models were used to estimate the relationship between sodium intake and blood pressure variations.

RESULTS

Between June 2006 and June 2008, 49 patients were randomized, 24 in group 1 (first period regimen=salt<3g/day; women: 63%; mean age: 56+/-21 years; baseline prednisone dosage: 54+/-19 mg/day) and 25 in group 2 (first period regimen=salt>6g/day; women: 56%; mean age: 60+/-19 years; baseline prednisone dosage: 56+/-16 mg/day). Mean daily salt intakes were 2.5+/-1.8 and 9.3+/-1.9 g/day during the first period and 7.8+/-3.2 and 3.8+/-2.9 g/day during the second period, respectively for group 1 and group 2. Blood pressure variations were not significantly associated with daily salt intakes or with randomisation group. No order effect was evidenced. By comparison with baseline, systolic blood pressure increased by greater than 20 mm Hg at week 6 in five patients (2 in group 1 and 3 in group 2).

CONCLUSION

At short-term, sodium intake does not seem to influence blood pressure variations in patients starting systemic corticosteroids therapy.

Update on G-protein polymorphisms in hypertension

The classic candidate gene approach continues to be the most prevalent tool in the search for the genetic basis of essential hypertension. With the list of candidate genes for this disorder steadily increasing, the pertussis toxin-sensitive inhibitory G protein (Gi) protein beta3 subunit (GNB3) gene has remained "sizzling," challenging the domination of the renin-angiotensin system. Is the genetic variability of GNB3 a causative factor underlying the pathogenesis of essential hypertension? Is the "functional" polymorphism, C825T, only "another" of the countless single nucleotide polymorphisms (SNP) for this disorder after all? As such, does its presence merely reinforce our confidence that essential hypertension is indeed polygenic? Should the C825T polymorphism be used in clinical practice and individualized antihypertensive treatment? Currently, there are still more questions than answers. In this review, in conjunction with our own research, we bring readers up to date on the latest developments of GNB3 polymorphisms in the field of hypertension.

Aldosterone synthase gene (CYP11B2) C-344T polymorphism in Caucasians from the Berlin Salt-Sensitivity Trial (BeSST)

OBJECTIVE

Aldosterone synthase (CYP11B2) is a key enzyme in the biosynthesis of aldosterone. Recently, the T allele of a polymorphism in the 5'-flanking region of the CYP11B2 gene (C-344T) has been reported to be more frequent in hypertensives than in normotensives, and has also been associated with increased plasma aldosterone levels. We therefore hypothesized that this variant may be related to increased blood-pressure response to dietary salt intake.

SUBJECTS AND METHODS

We genotyped 1 63 young normotensive men recruited within the framework of the Berlin Salt-Sensitivity Trial (BeSST) for the CYP11B2 C-344T polymorphism. Subjects were characterized for family history of hypertension, plasma parameters of the renin-angiotensin-aldosterone system and blood-pressure response to a high (220 mmol/day) and low (20 mmol/day) salt diet

RESULTS

The frequency of the -344T allele (0.45) was similar to that reported previously and genotype distribution was in Hardy-Weinberg equilibrium (CC, n = 55; CT, n = 71; TT, n = 37). There was a trend towards a higher frequency of the T allele in subjects with a positive family history of hypertension (0.48 versus 0.42), but the C-344T genotype was not related to blood pressure under either diet Furthermore, when subjects were classified into salt-sensitive and salt-resistant groups, allelic distribution did not differ between the two groups (qT = 0.43 versus qT = 0.45). While renin activity and plasma aldosterone levels were not related to genotype, plasma angiotensinogen was significantly higher in T-allele carriers under both the high (P = 0.02) and low (P = 0.008) salt diet.

CONCLUSION

Our findings do not support the hypothesis that the C-344T polymorphism of the CYP11B2 gene is associated with salt sensitivity or increased activity of the renin-angiotensin system in young normotensive subjects. It is, therefore, unlikely that the C-344T polymorphism is a genetic marker for salt sensitivity in young normotensive Caucasian men.

Molecular basis of human salt sensitivity: the role of the 11beta-hydroxysteroid dehydrogenase type 2

Salt-sensitive subjects (SS) increase their blood pressure with increasing salt intake. Because steroid hormones modulate renal sodium retention, we hypothesize that the activity of the 11beta-hydroxysteroid dehydrogenase type 2 (11betaHSD2) enzyme is impaired in SS subjects as compared with salt-resistant (SR) subjects. The 11betaHSD2 enzyme inactivates 11-hydroxy steroids in the kidney, thus protecting the nonselective mineralocorticoid receptor from occupation by glucocorticoids. We performed an association study using a recently identified single AluI polymorphism in exon 3 and a polymorphic microsatellite marker of the HSD11B2 gene in 149 normotensive white males (37 SS and 112 SR). The activity of the enzyme 11betaHSD2 was assessed by determining the urinary ratio of cortisol (THF+5alphaTHF) to cortisone (THE) metabolites by gas chromatography in all the 37 SS subjects and in 37 age- and body habitus-matched SR volunteers. Mean (THF+5alphaTHF)/THE ratio was markedly elevated in SS subjects compared with SR subjects (1.51 +/- 0.34 vs. 1.08 +/- 0.26, P < 0.00001), indicating enhanced access of glucocorticoids to the mineralocorticoid receptor in SS subjects. In 58% of SS subjects this ratio was higher than the maximum levels in SR subjects. The salt-induced elevation in arterial pressure increased with increasing (THF+5alphaTHF)/THE ratio (r2 = 0.51, P < 0.0001). A total of 12 alleles of the polymorphic microsatellite marker were detected. Homozygosity for the allele A7 was higher in SS subjects than in SR subjects (41 vs. 28%, P < 0.005), whereas the occurrence of the allele A7 with allele A8 was lower in SS subjects than in SR subjects (8 vs. 15%, P < 0.03). The prevalence of salt sensitivity was 35% in subjects with allele A7/A7, whereas salt sensitivity was present in only 9% of the subjects with allele A7/A8. The (THF+5alphaTHF)/THE ratio was higher in subjects homozygous for the A7 microsatellite allele as compared with the corresponding control subjects. The prevalence of the AluI allele was 8.0% in SR subjects and 5.4% in SS subjects and did not correlate with blood pressure. The decreased activity of the 11betaHSD2 in SS subjects indicates that this enzyme is involved in salt-sensitive blood pressure response in humans. The association of a polymorphic microsatellite marker of the gene with a reduced 11betaHSD2 activity suggests that variants of the HSD 11B2 gene contribute to enhanced blood pressure response to salt in humans.

Effect of dietary patterns on ambulatory blood pressure : results from the Dietary Approaches to Stop Hypertension (DASH) Trial. DASH Collaborative Research Group

We measured ambulatory blood pressure (ABP) in 354 participants in the Dietary Approaches to Stop Hypertension (DASH) Trial to determine the effect of dietary treatment on ABP (24-hour, day and night) and to assess participants' acceptance of and compliance with the ABP monitoring (ABPM) technique. After a 3-week run-in period on a control "typical" American diet, subjects (diastolic blood pressure [BP], 80 to 95 mm Hg; systolic BP, <160 mm Hg; mean age, 45 years) were randomly assigned to 1 of 3 diets for an 8-week intervention period: a continuation of the control diet; a diet rich in fruits and vegetables; and a "combination" diet that emphasized fruits, vegetables, and low-fat dairy products. We measured ABP at the end of the run-in and intervention periods. Both the fruit/vegetable and combination diets lowered 24-hour ABP significantly compared with the control diet (P<0. 0001 for systolic and diastolic pressures on both diets: control diet, -0.2/+0.1 mm Hg; fruit/vegetable diet, -3.2/-1.9 mm Hg; combination diet, -4.6/-2. 6 mm Hg). The combination diet lowered pressure during both day and night. Hypertensive subjects had a significantly greater response than normotensives to the combination diet (24-hour ABP, -10.1/-5.5 versus -2.3/-1.6 mm Hg, respectively). After correction for the control diet responses, the magnitude of BP lowering was not significantly different whether measured by ABPM or random-zero sphygmomanometry. Participant acceptance of ABPM was excellent: only 1 participant refused to wear the ABP monitor, and 7 subjects (2%) provided incomplete recordings. These results demonstrate that the DASH combination diet provides significant round-the-clock reduction in BP, especially in hypertensive participants.

Angiotensinogen M235T variant and salt sensitivity in young normotensive Caucasians

BACKGROUND AND AIMS

A single-nucleotide variant of the angiotensinogen gene (AGT 235T) has been associated with essential hypertension and increased plasma levels of angiotensinogen. This variant may also serve as a genetic marker for the increased blood pressure response to dietary salt intake, but the relationship between AGT genotype and salt sensitivity has not been studied until now. We therefore examined the relationship between the AGT 235T genotype and the blood pressure response to short-term dietary salt restriction in young normotensive men.

SUBJECTS AND METHODS

A total of 187 young normotensive men were characterized for family history of hypertension, salt sensitivity, plasma parameters of the renin-angiotensin system under high- and low-salt diets, and the AGT 235T genotype.

RESULTS

While the T allele was significantly associated with a positive family history of hypertension (chi2 = 7.0; P< 0.03) and higher plasma angiotensinogen levels (P< 0.015) and renin activity (P < 0.037), blood pressure under both diets was not significantly affected by the AGT genotype. When the subjects were classified into salt-resistant and salt-sensitive groups, genotypic distribution was nearly identical between both groups (frequency of T allele: 0.45 versus 0.46).

CONCLUSION

Our findings demonstrate that the AGT 235T allele is significantly associated with a positive family history of hypertension, but is not an important determinant of the blood pressure response to dietary salt intake in young normotensive subjects. It is therefore unlikely that the AGT 235T genotype can serve as an early genetic marker of salt sensitivity.

Sodium sensitivity in young adults with high resting end-tidal CO2

BACKGROUND

Previous research with normotensive adults aged over 40 years ('older') found that sensitivity of blood pressure of subjects with high resting end-tidal partial pressures of CO2 to high sodium intake was greater than normal.

OBJECTIVE

To test the hypothesis that the lesser sensitivity of blood pressure of young normotensive adults to high sodium intake is also a function of resting end-tidal partial pressure of CO2.

DESIGN

Forty-eight Caucasian men and women (age 28.5 +/- 1.4 years) had a lower than normal dietary intake of sodium chloride for 4 days, and then ingested sodium chloride capsules for 7 days (an additional 190 mmol/day sodium chloride). Resting end-tidal partial pressure of CO2 and blood pressure, and 24 h ambulatory blood pressure, were measured before and after the high-sodium diet. Overnight urine samples were collected before and after the high-sodium diet to determine dietary compliance, and to assess changes in urinary excretion of endogenous digitalis-like factors (a ouabain-like factor, and a marinobufagenin-like factor) that covary with plasma volume.

RESULTS

Subjects with high end-tidal partial pressures of CO2 had lower resting heart rates and lower urinary excretion of ouabain-like factor before sodium loading. Sodium loading decreased mean partial pressure of CO2 (by 0.8 +/- 0.2 mmHg) and increased only ambulatory systolic blood pressure (by 2.1 +/- 0.8 mmHg) for the whole group. However, the changes in resting systolic (r = 0.32, P < 0.025) and diastolic (r = 0.36, P < 0.01) blood pressures and in 24 h systolic (r = 0.28, P < 0.05) blood pressure after sodium loading were all positive functions of individual resting end-tidal partial pressures of CO2. Sodium loading increased urinary excretion of marinobufagenin-like factor (by 1.78 +/- 0.88 nmol) and the magnitude of the individual increase was a function of end-tidal partial pressure of CO2.

CONCLUSIONS

The results indicate that a high resting partial pressure of CO2 augments the effects of high sodium intake on plasma volume, levels of endogenous digitalis-like factors, and blood pressure in young normotensive humans.

Importance of the blood pressure-heart rate relationship

In studies of the effects of salt intake on blood pressure (SBP, MBP, DBP), influences on heart rate (HR) are usually neglected even though the longterm load on both left ventricle (LV) and systemic arteries (SA) is better related to the product of HR x SBP (or MBP) than to pressure alone. After all, altered salt intakes often induce considerable volume-related changes in HR, and the heart operates more economically at low HR and high stroke volume (SV). Thus, about 3/4 of LV metabolism is used for the build-up of systolic tension, while the cost for SV expulsion, or for SV increases, is far lower. Moreover, low HR prolongs the diastolic period, so important for LV coronary supply. Against this background we have used results from studies in both rats and man, in which both BP and HR were followed during marked changes in salt intake, to explore how this affected the HR x SBP (or HR x MBP) product. Briefly, in ordinarily salt-resistant organisms, whether normo- or hypertensive, salt intake increases, which in man ranged from 10-20 to 250-300 mM (in rats over 100-fold), if anything reduced the computed longterm load (HR x SBP, or MBP) on LV and SA, as consequences of an efficient reflex volume control. By contrast, in salt-sensitive man, HR reflex reductions to increased salt intake were almost absent despite substantial SBP elevations, suggesting the influence of a CNS suppression of bulbar reflex centres combined with CNS neurohormonal interference with renal salt volume excretion, as in SHR.