Pleiotropic Benefits of Moderate Salt Reduction
- blood pressure
- cardiovascular disease
- chronic kidney disease
The report by He and colleagues provides additional support for reducing daily salt intake from the ≈9 g/d typical of UK and US populations to <6 g recommended by health authorities in both countries.1,2 In their study, moderate sodium reduction lowered clinic blood pressure −4.8/−2.2 mm Hg and daytime ambulatory blood pressure a nearly identical −4.7/−2.2 mm Hg. The blood pressure benefits of moderate sodium restriction were clinically and statistically significant in middle-aged hypertensive adults with predominantly Stage 1 disease. And, the blood pressure changes were significant not only in self-identified blacks and whites, which is consistent with previous reports,2 but also Asians, which adds new information.
The mean sodium intake on slow sodium and placebo in this study were comparable to the high (target 150 mmol/d) and intermediate (100 mmol/d) intake in DASH sodium.2 Yet, the blood pressure reduction in the current study was roughly double the −2.1/−1.1 mm Hg change observed between the high and intermediate sodium control diets in the previous report. The greater blood pressure reduction with moderation of sodium intake in the present report may partially reflect the slightly higher mean age of volunteers, their ≈5 mm Hg higher baseline pressures, and their roughly 10 mmol/d higher baseline and greater change in sodium intake between the 2 study periods.1
Another potentially important and less well-recognized factor that impacts the blood pressure response to sodium reduction is diet quality. In the DASH Sodium study,2 for example, blood pressure fell −2.1/−1.1 and 6.9/−3.5 mm Hg between high and intermediate and between high- and low-sodium control diets, respectively. Comparable changes were −1.3/−0.6 and −3.0/−1.6 mm Hg on DASH high- and intermediate- and high- and low-sodium phases. Thus, the relatively large impact of moderate sodium reduction among UK residents in the current report may partially reflect low quality of the usual diets. These observations are of particular importance to the US population as dietary patterns in the United States have become less DASH-like, since publication of the original DASH report.3 Thus, the blood pressure benefits of isolated moderation of salt intake may be even greater now than previously, especially in view of the progressive increase in mean population age, another important factor related to salt sensitivity.
The study by He and colleagues also documents that moderate salt reduction decreases urinary albumin excretion, a marker of endothelial function,4 which is independently related to incident cardiovascular disease, even within the currently defined normal range.5 Moreover, the present study documents that moderate salt reduction lowers pulse-wave velocity in all subjects combined and self-identified blacks separately. Pulse-wave velocity, like urinary albumin excretion, is also independently predictive of cardiovascular events.6 Additionally, He and colleagues have confirmed that moderate salt reduction, similar to thiazide-type diuretic therapy, decreases the urine calcium leak in hypertensive patients, which is in turn associated with greater bone density and fewer fractures. Although osteoporosis is not commonly linked to adverse cardiovascular outcomes, available evidence suggests such a relationship may exist.7
We raised concerns that universal salt restriction may have unintended adverse consequences, especially among patients with a more robust counter-regulatory response.8 However, moderate long-term sodium reduction does not appear to induce a marked activation of the renin–angiotensin system, even among middle-aged whites, who are predominantly overweight men, the group for whom our concerns were greatest. In fact, >80% of the white group had plasma renin activity <1 ng/mL/h after 6 weeks of moderate sodium restriction. Moreover, the relationship observed between lower sodium intake and less risk for cardiovascular and total mortality appeared to be greatest in overweight white men.9
The beneficial effects of moderate sodium reduction on urinary albumin excretion and arterial pulse-wave velocity could not be separated from the blood pressure effects in the present study.1 Nevertheless, the pleiotropic benefits of moderate salt reduction, which include a decrease in blood pressure, urinary albumin and calcium excretion, and pulse-wave velocity, may help explain the reported relationships between salt intake and cardiovascular and all-cause mortality.9,10
The opinions expressed in this editorial are not necessarily those of the editors or of the American Heart Association.
He FJ, Visagie E, Markandu ND, Anan V, Dalton RN, MacGregor G. Effect of modest salt reduction on blood pressure, urinary albumin and pulse wave velocity in white, black, and Asian mild hypertensives. Hypertension. 2009; 54: 482–488.
Sacks FM, Svetkey LP, Vollmer WM, Appel LJ, Bray GA, Harsha D, Obarzanek E, Conlin PR, Miller ER III, Simons-Morton DG, Karanja N, Lin PH. Effects on blood pressure of reduced dietary sodium and the Dietary Approaches to Stop Hypertension (DASH) Diet. N Engl J Med. 2001; 344: 3–10.
Stehouwer CDA, Henry RMA, Dekker JM, Nijpels G, Heine RJ, Bouter LM. Microalbuminuria is associated with impaired brachial artery, flow-mediated vasodilation in elderly individuals without and with diabetes. Further evidence for a link between microalbuminura and endothelial dysfunction—The Hoorn Study. Kid Internat. 2004; 66: S42–S44.
Arnlov J, Evans JC, Meigs JB, Wang TJ, Fox CS, Levy D, Benjamin EJ, D'Agostino RB, Vasan RS. Low-grade albuminuria and incidence of cardiovascular disease events in nonhypertensive and nondiabetic individuals: the Framingham Heart Study. Circulation. 2005; 112: 969–975.
Hak AE, Pols HA, van Hemert AM, Hofman A, Witteman JC. Progression of aortic calcification is associated with metacarpal bone loss during menopause: a population-based longitudinal study. Arterioscler Thromb Vasc Biol. 2000; 20: 1926–1931.
Cook NR, Cutler JA, Obarzanek E, buring JE, Rexrode KM, Kumanyika S, Appel LJ, Whelton PK. Long-term effects of dietary sodium reduction on cardiovascular disease outcomes: Observational follow-up of the trials of preventing hypertension. BMJ. 2007; 334: 885.