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Effects of sodium restriction on blood pressure, renin, aldosterone, catecholamines, cholesterols, and triglyceride:
N A Graudal1, A M Galløe, P Garred
1Department of Medicine, Gentofte Hospital, University of Copenhagen, Denmark.
Insights
Reducing sodium intake lowers blood pressure in hypertensive individuals but not significantly in normotensive ones. This dietary change may have adverse effects on weight and certain hormones, questioning general recommendations.
Area of Science:
- Preventive Medicine
- Cardiovascular Health
- Nutritional Science
Background:
- Controversy exists regarding the benefits of general sodium intake reduction for preventing strokes and myocardial infarctions.
- Emerging studies suggest potential adverse effects of reduced sodium intake.
Purpose of the Study:
- To quantify the impact of reduced sodium intake on blood pressure (BP), body weight, and key hormones.
- To assess the long-term stability of BP effects from sodium reduction.
Main Methods:
- Systematic review of randomized controlled trials (RCTs) identified via MEDLINE search (1966-1997).
- Inclusion criteria: studies comparing high-sodium and low-sodium diets with measured effect parameters.
- Data extraction performed independently by two authors.
Main Results:
- In hypertensive participants, reduced sodium intake significantly lowered systolic BP by 3.9 mm Hg and diastolic BP by 1.9 mm Hg.
- In normotensive participants, the BP reduction was minimal and not statistically significant.
- Significant increases in renin and aldosterone levels were observed, proportional to sodium reduction.
- Body weight decreased, while noradrenaline and LDL cholesterol increased; no effect on triglycerides or HDL cholesterol.
Conclusions:
- Current evidence does not support a universal recommendation for sodium reduction.
- Sodium restriction may serve as an adjunct therapy for hypertension.
- Further long-term studies, particularly those with hard clinical endpoints (morbidity, survival), are needed to resolve controversies surrounding sodium intake.
Context:
One of the controversies in preventive medicine is whether a general reduction in sodium intake can decrease the blood pressure of a population and thereby reduce the number of strokes and myocardial infarctions. In recent years the debate has been extended by studies indicating that reduced sodium intake has adverse effects.
Objective:
To estimate the effects of reduced sodium intake on systolic and diastolic blood pressure (SBP and DBP), body weight, and plasma or serum levels of renin, aldosterone, catecholamines, cholesterols, and triglyceride, and to evaluate the stability of the blood pressure effect in relation to additional trials.
Data Sources:
MEDLINE search from 1966 through December 1997 and reference lists of relevant articles.
Study Selection:
Studies randomizing persons to high-sodium and low-sodium diets were included if they evaluated at least one of the effect parameters.
Data Extraction:
Two authors independently recorded data.
Data Synthesis:
In 58 trials of hypertensive persons, the effect of reduced sodium intake as measured by urinary sodium excretion (mean, 118 mmol/24 h) on SBP was 3.9 mm Hg (95% confidence interval [CI], 3.0-4.8 mm Hg) (P<.001) and on DBP was 1.9 mm Hg (95% CI, 1.3-2.5 mm Hg) (P<.001). In 56 trials of normotensive persons, the effect of reduced sodium intake (mean, 160 mmol/24 h) on SBP was 1.2 mm Hg (95% CI, 0.6-1.8 mm Hg) (P<.001) and on DBP was 0.26 mm Hg (95% CI, -0.3-0.9 mm Hg) (P=.12). The cumulative analysis showed that this effect size has been stable since 1985. In plasma, the renin level increased 3.6-fold (P<.001), and the aldosterone level increased 3.2-fold (P<.001); the increases were proportional to the degree of sodium reduction for both renin (r=0.66; P<.001) and aldosterone (r=0.64; P<.001). Body weight decreased significantly, and noradrenaline, cholesterol, and low-density lipoprotein cholesterol levels increased. There was no effect on adrenaline, triglyceride, and high-density lipoprotein cholesterol.
Conclusion:
These results do not support a general recommendation to reduce sodium intake. Reduced sodium intake may be used as a supplementary treatment in hypertension. Further long-term studies of the effects of high reduction of sodium intake on blood pressure and metabolic variables may clarify the disagreements as to the role of reduced sodium intake, but ideally trials with hard end points such as morbidity and survival should end the controversy.
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