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Long-term study highlights link between sodium intake, mortality
Risk for mortality appears increased in people who consume high amounts of sodium and lower in people with reduced sodium intake, according to 2 decades of follow-up data from the Trials of Hypertension Prevention.
“Numerous randomized trials and observational studies have demonstrated a direct relationship between dietary sodium intake and blood pressure,” Nancy R. Cook, ScD, associate biostatistician at Brigham and Women’s Hospital and professor of medicine at Harvard Medical School, and colleagues wrote in the Journal of the American College of Cardiology. “How well this blood pressure reduction translates into a beneficial effect on incidence of CVD and particularly on total mortality remains controversial.”
The researchers analyzed data on sodium reduction interventions from phase I (1987-1990) and phase II (1990-1995) of the Trials of Hypertension Prevention Follow-up Study. Participants were followed from baseline through 2013, for a total extended follow-up period of 23 to 26 years. In phase I, 2,182 participants (mean age, 43 years; 71% men; 20% black) with normal BP were randomly assigned to a sodium reduction intervention or usual care. In phase II, 2,382 participants (mean age, 44 years; 66% men; 18% black) with prehypertension were randomly assigned to a sodium reduction intervention or sodium control. Participants in the trials had 24-hour urine specimens collected three to seven times during 18 months of follow-up in phase I and 3 to 4 years of follow-up in phase II so researchers could measure usual intake of sodium or potassium or sodium-potassium ratio.
The current observational analysis included 1,844 participants from phase I and 1,167 from phase II.
Overall, 251 deaths occurred during follow-up among participants assigned to a sodium reduction intervention or sodium control. According to the researchers, this represents a nonsignificant 15% reduced risk for mortality in the active sodium intervention group (HR = 0.85; 95% CI, 0.66-1.09). The number of deaths was 272 among participants who were not assigned to an active sodium reduction intervention, according to the results.
Cook and colleagues reported observing a direct linear association between mortality and average sodium intake after adjustment (P trend = .3):
HR = 0.75 for sodium intake < 2,300 mg per 24 hours;
HR = 0.95 for sodium intake of 2,300 to < 3,600 mg per 24 hours;
HR = 1 (reference category) for sodium intake of 3,600 to < 4,800 mg per 24 hours; and
HR = 1.07 for sodium intake 4,800 mg per 24 hours
In another analysis that treated average urinary sodium excretion as a continuous term, the HR was 1.12 for 1,000 mg per 24 hours (P = .052), according to the findings.
“In contrast to some other studies, we found a direct linear relationship of an accurate measure of usual sodium intake to total mortality over a period of 23 to 26 years, with higher risk at high sodium intake and no evidence of a U- or J-shape, although, as in other studies, power is limited to estimate effects at the tails of the sodium distribution,” Cook and colleagues wrote.
When the researchers analyzed sodium-potassium ratio, the HR per unit increase was 1.13 (95% CI, 1.01-1.27), according to the findings.
“Average levels of sodium intake in the United States remain too high and even appear to be increasing. In 2010, the Institute of Medicine recommended a gradual reduction in sodium levels, which would be more palatable to consumers. Such reductions appear feasible and would serve to reduce the population level of blood pressure and incidence of hypertension and help prevent subsequent morbidity and mortality,” Cook and colleagues wrote.
Andrew Mente, PhD, from the Population Health Research Institute, Hamilton Health Sciences, Ontario, Canada, and colleagues discussed the findings in a related editorial.
“The latest analyses of the [Trials of Hypertension Prevention] and those of prospective cohort studies support modest reductions in sodium intake among persons consuming high-sodium diets, enveloped within the context of health dietary patterns,” Mente and colleagues wrote in the editorial. “However, the null effect of low sodium intake on mortality rates adds to the growing uncertainty about the health effects of low sodium intake and reinforces the need for large, definitive randomized controlled trials of low versus moderate sodium intake.” – by Cassie Homer
Disclosure: The researchers and editorial authors report no relevant financial disclosures.