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Disputed meta-analysis finds low sodium intake may increase CV risk, mortality
A low-sodium diet may increase the risk for CV events and mortality in adults with and without hypertension, researchers reported in The Lancet.
The systematic review and meta-analysis has come under fire from the American Heart Association and others.
Andrew Mente, PhD, from the department of clinical epidemiology and biostatistics at McMaster University in Hamilton, Ontario, Canada, and colleagues analyzed data from 133,118 individuals (63,559 with hypertension, 69,559 without hypertension) from four large prospective studies to determine the association between sodium intake and CVD events and all-cause mortality in adults with and without hypertension. BP measurement and 24-hour urinary excretion estimates were taken for each participant. The primary endpoint was a composite of death, MI, stroke and HF.
Salt and CVD
According to the results, the relationship between sodium excretion and CVD and all-cause mortality varied by hypertension status (P for heterogeneity = .0342).
A U-shaped association was observed in participants with hypertension: Both sodium excretion of 7 g/day or more (HR = 1.23; P < .0001) and sodium excretion of less than 3 g/day (HR = 1.34; P < .0001) were linked to increased risk for the composite outcome compared with sodium excretion of 4 g/day to 5 g/day. Adjusting for BP did not alter the associations.
In participants without hypertension, a sodium excretion of 7 g/day or more was not associated with risk for primary endpoint (HR = 0.9; 95% CI, 0.76-1.08), but an excretion of less than 3 g/day was linked to an increased risk (HR = 1.26; 95% CI, 1.1-1.45). In this cohort, BP also had no effect on the association between low sodium excretion and the composite outcome.
In addition, sodium excretion’s relationship to increased systolic BP was stronger in those with hypertension (2.08 mm Hg increment in systolic pressure per gram; 95% CI, 1.96-2.21) than in participants without hypertension (1.22 mm Hg increment in systolic pressure per gram; 95% CI, 1.13-1.3; P for interaction < .0001).
“The results showed that [CVD] and death are increased with low sodium intake (compared with moderate intake) irrespective of hypertension status, whereas there is a higher risk of CVD and death only in individuals with hypertension consuming more than 6 g of sodium per day (representing only 10% of the population studied),” Mente and colleagues wrote.
The researchers cautioned against making broad public health recommendations and suggested that “until new robust data emerge from large trials, it might be prudent to recommend reduction in sodium intake only in those with high sodium intake and with hypertension.”
The salt controversy
The findings by Mente and colleagues have drawn strong reactions by members of the medical community, particularly the AHA.
In a press release, Mark A. Creager, MD, president of the AHA and director of the Heart and Vascular Center at Dartmouth-Hitchcock Medical Center in Lebanon, New Hampshire, said: “This is a flawed study and you shouldn’t use it to inform yourself about how you’re going to eat. The large body of science clearly shows how excessive amounts of sodium in the American diet can cause high [BP], which can lead to disease and even death.”
Mark A. Creager
Creager said the methodology is poor because “low sodium excretion, based on spot urine collections, is a misleading measure of usual dietary intake over a lifetime. Other factors, beyond dietary sodium intake, are present and probably are responsible for the association of lower sodium excretion with [CVD] — factors such as reduced calorie intake, low physical activity, or a concurrent illness.”
In a related editorial, Eoin O’Brien, MD, of the molecular pharmacology department, Conway Institute, University College Dublin, wrote that the findings are “provocative” and that they “will be challenged,” particularly the method used to estimate urinary sodium excretion.
“We must acknowledge that given the dependency of so many physiological systems on the sodium cation, it should come as no surprise that a low-salt-for-all policy would benefit some and disadvantage others. So rather than allowing contrary evidence to dispel the positive efforts that have been made to reduce the salt content of foods, we must now direct our efforts to formulating a policy that will benefit the majority in society without [compromising] the minority,” O’Brien wrote. – by Tracey Romero
Disclosure: The researchers, Creager and O’Brien report no relevant financial disclosures.