Dietary sodium reduction for hypertension prevention and treatment

The role of dietary salt and alcohol use reduction in the management of hypertension

Introduction: Despite the improved treatment protocol of hypertension, the magnitude of the disease and its related burden remains raised. Hypertension makes up the leading cause of stroke, kidney disease, arterial disease, eye disease, and cardiovascular disease (CVD) growth. Areas covered: This review provides the overview of the role of dietary salt and alcohol use reduction in the management of hypertension, a brief history of alcohol, the vascular endothelium functions, the effects of alcohol use on blood pressure (BP), the mechanisms of alcohol, brief history of salt, the effects of dietary salt intake on BP, and the mechanisms of salt. Expert opinion: Studies found that high dietary salt intake and heavy alcohol consumption have a major and huge impact on BP while both of them have been identified to increase BP. Also, they raise the risk of hypertension-related morbidity and mortality in advance. On the other way, the dietary salt and alcohol use reduction in the management of hypertension are significant in the control of BP and its related morbidity and mortality. Further, studies suggested that the dietary salt and alcohol use reductions are the cornerstone in the management of hypertension due to their significance as part of comprehensive lifestyle modifications.

Salt intake, asthma, and exercise-induced bronchoconstriction: a review

Despite the heterogeneous treatment options for patients with asthma, there remains a substantial burden of unaddressed disease, even with optimal treatment. Epidemiological studies indicate that patients frequently resort to complimentary and alternative therapies when being treated for asthma and other chronic health conditions. Changes in diet associated with the development of a more affluent lifestyle is one of the environmental factors considered to contribute to the increased prevalence of asthma in the past few decades. Dietary sodium in particular has been considered to be a dietary constituent implicated in this phenomenon. This article reviews the studies conducted that have questioned whether reducing dietary salt intake potentially improves pulmonary function and airway hyper-responsiveness in asthmatics, as well as studies evaluating dietary salt intake on the severity of exercise-induced bronchoconstriction (EIB). The data presented supporting dietary salt restriction for reducing airway hyper-responsiveness in asthmatics is encouraging, though not clinically convincing. Studies conducted previously have been limited for a variety of reasons, including limitations related to the experiment and populations studied. However, in studies that evaluated the severity of EIB in asthmatic individuals and involved altered dietary salt intake, data have been more convincing. A low-sodium diet maintained for 1 to 2 weeks decreases bronchoconstriction in response to exercise in individuals with asthma. There are no data regarding the longer-term effects of a low-sodium diet on either the prevalence or severity of asthma or on EIB. As a low-sodium diet has other beneficial health effects, it can be considered a therapeutic option for adults with asthma, although it should be considered as an adjunctive intervention to supplement optimal pharmacotherapy, and not as an alternative.

Dietary salt intake as a potential modifier of airway responsiveness in bronchial asthma

While pharmacologic treatment of chronic asthma is usually highly effective, medications often have significant side-effects or exhibit tachyphylaxis. Alternative and/or complementary treatments that reduce dependence on pharmacologic medications are of interest in reducing the severity of asthma. This review analyzes the literature that has evaluated dietary salt intake as a potential modifier of the severity of asthma and airway responsiveness. High dietary intakes of salt, greater than 9 g/d, are common in Western civilizations, as is asthma. The question is whether reducing dietary salt intake potentially would improve pulmonary function and airway responsiveness in individuals with asthma. This review details the existing studies in this regard and includes the studies that have evaluated dietary salt on the severity of exercise-induced asthma (exercise-induced bronchoconstriction [E1B]). From a critical analysis of the existing literature, the data that support a role for dietary salt reduction for reducing severity of asthma and airway responsiveness in individuals with asthma is considered encouraging but not clinically convincing. The existing studies have suffered from a variety of experimental and population limitations. In contrast, the data from studies that have altered dietary salt and evaluated severity of EIB in nonatopic individuals is much more convincing. In each study so far, lowering dietary salt has reduced the severity of EIB to subclinical levels. Correspondingly, the supplementing of diets to higher than normal salt intake increased EIB significantly. This review concludes that the data are sufficient to warrant a clinical trial that is properly controlled and randomized to further investigate the influence of dietary salt intake on pulmonary function, airway responsiveness, symptoms, quality of life, and medication requirements in asthma and EIB.

Sodium reduction for hypertension prevention in overweight adults: further results from the Trials of Hypertension Prevention Phase II

Sodium reduction is efficacious for primary prevention of hypertension, but the feasibility of achieving this effect is unclear. The objective of the paper is detailed analyses of adherence to and effects of the sodium reduction intervention among overweight adults in the Trials of Hypertension Prevention, Phase II. Sodium reduction (comprehensive education and counselling about how to reduce sodium intake) was tested vs no dietary intervention (usual care) for 36-48 months. A total of 956 white and 203 black adults, ages 30-54 years, with diastolic blood pressure 83-89 mmHg, systolic blood pressure (SBP) <140 mmHg, and body weight 110-165% of gender-specific standard weight were included in the study. At 36 months, urinary sodium excretion was 40.4 mmol/24 h (24.4%) lower in sodium reduction compared to usual care participants (P<0.0001), but only 21% of sodium reduction participants achieved the targeted level of sodium excretion below 80 mmol/24 h. Adherence was positively related to attendance at face-to-face contacts. Net decreases in SBP at 6, 18, and 36 months of 2.9 (P<0.001), 2.0 (P<0.001), and 1.3 (P=0.02) mmHg in sodium reduction vs usual care were associated with an overall 18% lower incidence of hypertension (P=0.048); were relatively unchanged by adjustment for ethnicity, gender, age, and baseline blood pressure, BMI, and sodium excretion; and were observed in both black and white men and women. From these beneficial but modest results with highly motivated and extensively counselled individuals, sodium reduction sufficient to favourably influence the population blood pressure distribution will be difficult to achieve without food supply changes.

Dose–response of sodium excretion and blood pressure change among overweight, nonhypertensive adults in a 3-year dietary intervention study

A cross-sectional dose-response relationship between sodium intake and blood pressure (BP) has been demonstrated, but evidence for a graded longitudinal effect is limited. Evaluation of BP response to sodium reduction was assessed in a 3-year lifestyle dietary intervention trial. BP changes at 18 and 36 months after enrollment were analysed according to concurrent quantitative changes in sodium excretion and by categories of success in sodium reduction among 1157 men and women, ages 30-54 years, with a diastolic BP (DBP) 83-89 mmHg, systolic BP (SBP) <140 mmHg, body weight 110-165% of sex-specific standard weight, and valid baseline urinary sodium excretion. Participants were randomized to a Sodium Reduction intervention (n=581) or Usual Care (n=576). From a 187 mmol/24 h baseline mean sodium excretion, net decreases were 44 mmol/24 h at 18 months and 38 mmol/24 h at 36 months in Sodium Reduction vs Usual Care. Corresponding net decreases in SBP/DBP were 2.0/1.4 mmHg at 18 months, and 1.7/0.9 mmHg at 36 months. Significant dose-response trends in BP change over quintiles of achieved sodium excretion were seen at both 18 (SBP and DBP) and 36 (SBP only) months; effects appeared stronger among those maintaining sodium reduction. Estimated SBP decreases per 100 mmol/24 h reduction in sodium excretion at 18 and 36 months were 2.2 and 1.3 mmHg before and 7.0 and 3.6 mmHg after correction for measurement error, respectively. DBP changes were smaller and nonsignificant at 36 months. In conclusion, incremental decreases in BP with lower sodium excretion were observed in these overweight nonhypertensive individuals.

Hypertension therapy: mixing, matching, and meeting targets

The inappropriate control of hypertension is a public health problem worldwide. It is notable that although there are several causes for this situation, lack of effective pharmacotherapy is not among them. It has long been known that combinations of antihypertensive drugs are highly effective in most patients; the problem is implementing treatment recommendation guidelines into clinical practice with the most effective and best tolerated therapies. The latest guidelines on therapies for hypertension from the World Health Organization/International Society of Hypertension, the Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure (US), and the European Societies of Hypertension and Cardiology consistently emphasize this need of combination treatments in a large part of the hypertensive patient population. This review focuses on the combination of one of the oldest drugs, thiazide diuretics, with one of the youngest, angiotensin-receptor blockers, and analyzes the available literature regarding potential applications in specific populations. This represents one of the most widely used, rational and effective combination therapies, combining excellent control of blood pressure with unequalled tolerability. In addition, angiotensin-receptor blocker/diuretic combinations may have cardiovascular benefits beyond those from blood pressure lowering itself.

Postexercise alpha-adrenergic receptor hyporesponsiveness in hypertensive rats is due to nitric oxide

We tested the hypothesis that a single bout of dynamic exercise produces a postexercise hypotension (PEH) and alpha(1)-adrenergic receptor hyporesponsiveness in spontaneously hypertensive rats (SHR). The postexercise alpha(1)-adrenergic receptor hyporesponsiveness is due to an enhanced buffering of vasoconstriction by nitric oxide. Male (n = 8) and female (n = 5) SHR were instrumented with a Doppler ultrasonic flow probe around the femoral artery. Distal to the flow probe, a microrenathane catheter was inserted into a branch of the femoral artery for the infusion of the alpha(1)-adrenergic receptor agonist phenylephrine (PE). A microrenathane catheter was inserted into the descending aorta via the left common carotid artery for measurements of arterial pressure (AP) and heart rate. Dose-response curves to PE (3.8 x 10(-3) - 1.98 x 10(-2)microg/kHz) were generated before and after a single bout of dynamic exercise. Postexercise AP was reduced in male (13 +/- 3 mmHg) and female SHR (18 +/- 7 mmHg). Postexercise vasoconstrictor responses to PE were reduced in males due to an enhanced influence of nitric oxide. However, in females, postexercise vasoconstrictor responses to PE were not altered. Results suggest that nitric oxide- mediated alpha(1)-adrenergic receptor hyporesponsiveness contributes to PEH in male but not female SHR.

Ethnic comparison of weight loss in the Trial of Nonpharmacologic Interventions in the Elderly

OBJECTIVE

To compare weight loss in blacks and whites in the Trial of Nonpharmacologic Interventions in the Elderly (TONE).

RESEARCH METHODS AND PROCEDURES

TONE enrolled 421 overweight white and 164 overweight black adults, 60 to 79 years old, with blood pressure well-controlled on a single, antihypertensive drug. Drug therapy withdrawal was attempted 3 months after randomization to counseling for weight loss, sodium reduction, both weight loss and sodium reduction, or to usual care, with follow-up for 15 to 36 months after enrollment. Statistical procedures included repeated measures analysis of covariance and logistic and proportional hazards regression.

RESULTS

In the weight-loss condition, net weight change (in kilograms) was -2.7 in blacks and -5.9 in whites (p < 0.001; ethnic difference, p = 0.0002) at 6 months and -2.0 (p < 0.05) in blacks and -4.9 (p < 0.001) in whites at the end of follow-up (ethnic difference, p = 0.007). In weight/sodium, net weight change was -2.1 (p < 0.01) in blacks and -2.8 (p < 0.001) in whites at 6 months, and -1.9 in blacks and -1.7 in whites at the end of follow-up (p < 0.05; ethnic difference, p > 0.5). Exploratory analyses suggested a more favorable pattern of weight change in blacks than in whites from 6 months onward. There was no ethnic difference in blood pressure outcomes.

DISCUSSION

Whites lost more weight than blacks without, but not with, a concurrent focus on sodium reduction.

Salt sensitivity and hypertension in African Americans: implications for cardiovascular nurses

Hypertension is a major public health problem in the U.S. Salt sensitivity is an important factor associated with hypertension and its complications, yet it has not been addressed in the nursing literature. Salt sensitivity is a directionally appropriate rise or fall in blood pressure when salt is added or removed, respectively. The change in blood pressure in salt-sensitive subjects occurs to a degree exceeding random blood pressure fluctuations. Salt sensitivity is present in 30% of normotensive and over 50% of hypertensive persons. It is more prevalent among African Americans, older persons, and individuals with renal insufficiency or diabetes. This paper provides nurses with an overview of salt sensitivity and its significance in hypertension. It presents conceptual and operational definitions of salt sensitivity, identifies factors contributing to its development, and describes implications for nursing practice.

Effects of a salt-restricted diet on the intake of other nutrients

BACKGROUND

Salt restriction, recommended as the first-line treatment of hypertension, has been proposed to lead to deficiencies in intakes of some other nutrients.

OBJECTIVE

The aim of this study was to investigate the effects of salt restriction for 20 wk on the intake of other nutrients in free-living subjects with mildly elevated blood pressure.

DESIGN

Thirty-nine subjects (24 men, 15 women) aged 28-65 y with a mean daytime ambulatory diastolic blood pressure of 90-105 mm Hg and a diastolic blood pressure measured in a health care center of 95-115 mm Hg participated in the study. The subjects completed 4-d food records and their salt intake was measured by 24-h urinary sodium excretion. The subjects received both oral and written instructions from a clinical nutritionist on how to reduce their daily sodium chloride intake to <5 g/d but were instructed not to change their diet otherwise. The subjects were provided with low-salt bread during the salt-restriction period.

RESULTS

Few changes were found in nutrient intakes. In men, total energy intake decreased by 1059 kJ/d and alcohol, potassium, and vitamin D intakes decreased, but there were no significant changes in energy-adjusted potassium and vitamin D intakes. In women, total potassium intake increased, but the potassium density of the diet remained unchanged. Total selenium intake and energy-adjusted intake of selenium both decreased significantly in women.

CONCLUSIONS

Salt restriction can be undertaken in free-living hypertensive subjects without any untoward changes in the intake of other nutrients.

Role of dietary salt in hypertension

Hypertension is the most common chronic disease in the United States and, untreated, results in disability or death due to stroke, heart failure or kidney failure. Fortunately the results of hypertension can be avoided to a large extent by proper treatment. One treatment which is effective in some cases is the restriction of dietary NaCl intake. This review considers the role of dietary NaCl in the genesis, therapy and prevention of hypertension. Most people can eat as much NaCl as they like; they have good kidneys which, within about 24 hours, excrete the NaCl as fast as it is taken in and nothing happens to blood pressure. A few, especially those with kidney disease, do not excrete it as fast as it is taken in and blood pressure rises. They are "salt sensitive". Once hypertension is established, the proportion who are "NaCl sensitive" is much higher. About 60% of people with hypertension respond to a high NaCl intake with a rise in pressure and to NaCl restriction with a fall in pressure and reduction in the need for antihypertensive medication. These are the same people that respond to diuretics with a fall in blood pressure. Many are black and elderly and have low plasma renin activity (low-renin hypertension) but some have normal or high plasma renin activity (normal or high-renin hypertension). Evidence suggests that very early they have a subtle kidney defect which causes them to excrete NaCl and water more slowly, e.g., even before they become hypertensive, black and elderly subjects excrete intravenously administered NaCl more slowly than white and young subjects. How does NaCl retention raise blood pressure? One possibility is that the NaCl retention causes water retention which releases a digitalis-like substance that increases the contractile activity of heart and blood vessels. Another is that the sodium itself penetrates the vascular smooth muscle cell, causing it to contract. "Salt sensitive" hypertension also responds to increased potassium and calcium intakes, perhaps in part because they increase NaCl urinary excretion.

Trial of Nonpharmacologic Intervention in the Elderly (TONE). Design and rationale of a blood pressure control trial

National and international policy-making organizations advocate nonpharmacologic therapies to reduce blood pressure (BP). However, data to support such recommendations in older persons are virtually nonexistent. The Trials of Nonpharmacologic Intervention in the Elderly (TONE) is a randomized, controlled trial that will test whether weight loss or a reduced sodium (Na) intake or both can maintain satisfactory BP control, without unacceptable side effects, after withdrawal of antihypertensive drug therapy. Medication-treated hypertensives (aged 60 to 80 years) with a systolic BP less than 145 mm Hg and a diastolic BP less than 85 mm Hg who are taking one antihypertensive medication are randomly assigned to one of four groups: (1) weight loss alone, (2) reduced Na intake alone, (3) combined weight loss and reduced Na intake, or (4) usual life-style (control group). Overweight participants are randomized to one of these four groups, while nonoverweight individuals are assigned to either the reduced Na intake or the usual life-style group. The interventions, tailored to the needs of older persons, use behavioral approaches to accomplish intervention-specific goals (weight loss > or = 10 lb, daily Na intake < or = 80 mEqa). Three months after the start of intervention, antihypertensive drug therapy is withdrawn. The primary trial end point is a BP of 150/90 mm Hg or higher, resumption of antihypertensive drug therapy, or the occurrence of a BP-related clinical complication during 2 to 3 years of follow-up. It is anticipated that TONE findings may identify an effective and acceptable nonpharmacologic approach to control hypertension in the increasingly large number of older persons treated with antihypertensive drug therapy.

Abnormal atrial natriuretic peptide and renal responses to saline infusion in nonmodulating essential hypertensive patients

BACKGROUND

Nonmodulation seems to represent an inheritable trait characterized by abnormal angiotensin-mediated control of aldosterone release and renal blood supply and salt-sensitive hypertension. Recently, we demonstrated that atrial natriuretic peptide (ANP) response to angiotensin II also is altered in nonmodulators. Moreover, an abnormal ANP response to acute volume expansion has been shown by others in hypertensive patients displaying some features of nonmodulators. These data induced us to hypothesize that nonmodulators. These data induced us to hypothesize that nonmodulation could be characterized by an abnormal ANP response to saline load.

METHODS AND RESULTS

Forty-three essential hypertensive men were subdivided into low-renin patients (n = 12), nonmodulators (n = 15), and modulators (n = 16) according to their renin profile and ability to modulate aldosterone and p-aminohippurate clearance responses to a graded angiotensin II infusion (1.0 ng.kg-1.min-1 and 3.0 ng.kg-1.min-1 for 30 minutes each) on both a low- (10 mmol Na+ per day) and a high- (210 mmol Na+ per day) Na+ intake. The intravenous saline load (0.25 mL.kg-1.min-1 for 2 hours) performed on a low-Na+ diet increased plasma ANP levels in low-renin (from 14.30 +/- 4.68 to 23.30 +/- 7.52 fmol/mL at 120 minutes, P < .05) and modulating patients (from 10.95 +/- 3.55 to 18.21 +/- 5.42 fmol/mL at 120 minutes, P < .05), whereas it did not change the hormone levels in nonmodulators (from 10.77 +/- 3.25 to 13.83 +/- 5.70 fmol/mL at 120 minutes, P = NS). When patients switched from a low- to a high-NaCl diet, plasma ANP levels increased significantly in all groups. However, when the saline load was repeated on a high-NaCl intake, ANP levels increased in both low-renin and modulating patients (P < .05), whereas it failed to increase in nonmodulators.

CONCLUSIONS

Nonmodulating hypertensive patients showed a reduced ANP response to saline infusion in the presence of a normal increase of plasma ANP with dietary NaCl load. The impaired ANP response to saline infusion could be due to a different distribution of volume load and contribute to determining the reduced ability to excrete sodium that is commonly described in nonmodulators.

Feasibility and efficacy of sodium reduction in the Trials of Hypertension Prevention, phase I. Trials of Hypertension Prevention Collaborative Research Group

Phase I of the Trials of Hypertension Prevention was a multicenter, randomized trial of the feasibility and efficacy of seven nonpharmacologic interventions, including sodium reduction, in lowering blood pressure in 30- to 54-year-old individuals with a diastolic blood pressure of 80 to 89 mm Hg. Six centers tested an intervention designed to reduce dietary sodium to 80 mmol (1800 mg)/24 h with a total of 327 active intervention and 417 control subjects. The intervention consisted of eight group and two one-to-one meetings during the first 3 months, followed by less-intensive counseling and support for the duration of the study. The mean net decrease in sodium excretion was 43.9 mmol/24 h at 18 months. Women had lower sodium intake at baseline and were therefore more likely to decrease to less than 80 mmol/24 h. Black subjects were less likely to decrease to less than 80 mmol/d, independent of sex or baseline sodium excretion. The mean (95% confidence interval) net decrease associated with treatment was -2.1 (-3.3, -0.8) mm Hg for systolic blood pressure and -1.2 (-2.0, -0.3) mm Hg for diastolic blood pressure at 18 months (both P < .01). Multivariate analyses indicated a larger systolic blood pressure effect in women (-4.44 versus -1.23 mm Hg in men), adjusted for age, race, baseline blood pressure, and baseline 24-hour urinary sodium excretion (P = .02). Dose-response analyses indicated an adjusted decrease of -1.4 mm Hg for systolic blood pressure and -0.9 mm Hg for diastolic blood pressure for a decrease of 100 mmol/24 h in 18-month sodium excretion. These results support the utility of sodium reduction as a population strategy for hypertension prevention and raise questions about possible differences in dose response associated with gender and initial level of sodium intake.

Metabolic effects of strict salt restriction in essential hypertensive patients

OBJECTIVE

Some observations suggest that a strict low-salt diet may induce unfavourable metabolic side-effects. The main aim of this study was to analyse the possible consequences of severe salt restriction in mildly hypertensive patients.

DESIGN

The study was carried out through a randomized double-blind protocol.

SUBJECTS

Forty-seven ambulatory patients proceeding from the hypertension unit were initially admitted: 17 were lost, and 30 non-diabetic mildly hypertensives (DBP 90-104 mmHg) with normal renal function completed the protocol.

INTERVENTION

After a wash-out period, patients were maintained on a low-salt intake (2.8 +/- 1.0 g day-1 of NaCl) and placebo for 2 weeks, and the same diet and salt supplements (11.7 +/- 2.5 g day-1 of NaCl) for another 2 weeks, separated by a second wash-out period.

MEASURES

At the end of each dietary period, blood pressure (BP) and body weight were measured, and a blood sample was taken for determination of routine serum chemistries, plasma lipid and apolipoprotein concentrations, immunoreactive insulin (IRI), and plasma renin activity (PRA). Urinary 24 h excretion of sodium and potassium were measured.

RESULTS

During the salt restriction period BP did not change, weight lowered, and PRA raised. There was a significant increase in serum level of creatinine, uric acid, IRI, total cholesterol and apo B, and a decrease in HDL cholesterol and apo A-I.

CONCLUSION

As previously suggested, these observations seem to indicate that strict salt restriction may cause, at least in the short-term, adverse metabolic changes in hypertensive patients.