ReviewSalt and Hypertension: Is Salt Dietary Reduction Worth the Effort?
Section snippets
Salt
For most of our evolution, humans consumed less than 0.25 g of salt per day. Today, salt intake remains high because of its use in food seasoning, but especially because of highly salted processed foods. In 2005, only 9.6% of adults met recommended guidelines for sodium intake (<1.5 g/d for persons with hypertension, middle-aged and older adults, and blacks, and < 2.3 g/d for all other adults).2
Mechanism of Action: How Salt is Related to Blood Pressure
“Salt” and “sodium” are used synonymously. In fact, salt is only 40% sodium; 1 g of salt has 400 mg sodium. The remaining 60% of salt—chloride—is an often forgotten but likely important part of the link between salt and blood pressure. Replacing sodium chloride with sodium citrate abolished the increase in plasma volume and blood pressure induced by sodium chloride.3 Similar effects have been observed when sodium chloride was replaced by sodium phosphate or sodium bicarbonate. Therefore, with
Age: Salt Intake Reduction on Blood Pressure in the Young Versus Old(er)
Salt intake first increases at 6 to 9 months of age when solid foods are introduced. Almost all 12- to 24-month-old toddlers have salt intake exceeding “adequate levels.”12 Salt intake in children and adolescents remains high because of increasing consumption of processed foods.
In children aged 8 to 16 years, sodium intake reduction of 42% yielded a reduction in blood pressure of 1.17/1.29 mm Hg. In infants, salt intake reduction of 54% yielded a systolic blood pressure reduction of 2.47 mm Hg.
Correlation of Salt Intake to Blood Pressure
The relationship of salt intake and blood pressure is direct and progressive. There is a consistent dose-response relation between salt intake and blood pressure within the range of 3 to 12 g of salt per day.18 A reduction of only 3 g/d predicts a decrease in blood pressure of 3.6 to 5.6/1.9 to 3.2 mm Hg in hypertensive subjects and 1.8 to 3.5/0.8 to 1.8 mm Hg in normotensive subjects. A modest reduction of 6 g in salt intake for 4 or more weeks predicted a decrease in blood pressure of
Non-Blood Pressure-Related Effects of Dietary Salt
Increasing evidence suggests that a high salt intake may directly (ie, beyond the effect of salt intake on blood pressure) increase the risk of stroke, left ventricular hypertrophy, and proteinuric renal disease; is related to renal stones and osteoporosis and to the severity of asthma; and is probably a major cause of stomach cancer (Table).
Salt and Heart Failure
Any physician who cares for patients with heart failure knows how salt intake can tip the balance between compensated and decompensated heart failure; the increase in cardiogenic pulmonary edema admissions after holiday seasons among patients with heart failure is empirically ascribed to excessive salt intake and treated (with good effect) accordingly. However, there is a paucity of evidence clearly delineating the relationship between salt intake and heart failure incidence or progression, or
Are There Adverse Effects of Salt Reduction?
There is still insufficient power to exclude clinically important effects of reduced dietary salt intake on mortality or cardiovascular morbidity.31 Nonetheless, for modest salt reduction, there was no detectable change in plasma renin activity or in total cholesterol, triglycerides, and low- or high-density lipoprotein cholesterol.18 Reduced sodium intake was not associated with adverse effects but rather with fewer instances of angina and significantly fewer reports of headache.17
The argument
Salt Intake and Cardiovascular Prognosis
It has been estimated that reducing salt intake by 9 g/d (eg, from 12 to 3 g/d) would reduce strokes by approximately one third and ischemic heart disease by one quarter, and this would prevent 20,500 stroke deaths and 31,400 ischemic heart disease deaths per year in the United Kingdom.37 Salt intake reduction of 5 g was related to a 23% reduction in stroke and a 17% reduction in the rate of cardiovascular disease.38 Among overweight individuals, a higher salt intake was associated with a
Is Accomplishing Population-Wide Salt Intake Reduction Realistic?
It is difficult to reduce salt intake at the community level.44 The challenge must be approached at the level of the consumers and the producers; a strategy to change the salt contents of foods will require the cooperation of the food industry. More than 80% of excess salt intake, especially in developed countries, comes from salt added to processed foods (eg, sandwiches, pizza, soups) by producers and not from salt added by the consumer during cooking.45 A strategy of 10% to 20% yearly or
Comparing and Combining Modalities
The optimal effect on blood pressure is achieved with correction not just of salt intake but of multiple contributors to hypertension. It seems that the blood pressure effects of weight loss and sodium intake reduction, for example, are partly additive in that patients who lost weight and reduced sodium intake delayed onset of hypertension more than those who only lost weight or reduced sodium intake.49 Combining low salt intake with the Dietary Approaches to Stop Hypertension is another
Conclusions
Physicians influence patients through simple assessments and basic advice. However, because most dietary salt comes from processed food, an effective public health strategy must complement this patient/physician-based approach. Salt intake reduction can delay or prevent incidence of or treatment for hypertension in non-hypertensive subjects and contribute to blood pressure reduction in hypertensive subjects already receiving medical therapy. There is a growing body of evidence that salt intake
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Funding: None.
Conflict of Interest: None.
Authorship: All authors had access to the data and played a role in writing this manuscript.