Higher sodium intake may be linked with increased mortality risk

An analysis of two randomized trials found that people who had a high sodium intake had an increased risk of mortality during a median follow-up period of 24 years.

The studies estimated sodium intake based on urinary sodium excretion and collected multiple 24-hour urine samples from adults between 30 and 54 years old.

Lead researcher Nancy R. Cook, ScD, of Brigham and Women’s Hospital and Harvard Medical School in Boston, and colleagues published their results online Oct. 3 in the Journal of the American College of Cardiology.

“New strategies are needed to reduce the amount of sodium in the food supply and to educate people about the importance of dietary sodium restriction,” they wrote.

Previous trials showed a direct relationship between dietary sodium intake and blood pressure, according to the researchers. They cited a meta-analysis of 35 trials that found a 100 mmol reduction in 24-hour urinary sodium led to a 5.4 mm Hg reduction in systolic blood pressure among people with hypertension and a 2.4 mm Hg reduction among people who did not have hypertension. There was also a 2.8 mm Hg and 1 mmg reduction in diastolic blood pressure, respectively.

However, they noted that there is controversy and mixed results on whether the blood pressure reduction associated with lower sodium intake has a beneficial effect on the incidence of cardiovascular disease and total mortality.

In this analysis, they evaluated 3,126 patients who participated in phase I and II of the TOHP (Trials of Hypertension Prevention). Phase I took place from September 1987 to January 1990 and phase II took place from December 1990 to March 1995.

The researchers collected three to seven 24-hour urine specimens during 18 months of follow-up in phase I and three to four years of follow-up in phase II.

Through 2013, there were 77 deaths in phase I participants and 174 deaths in phase II participants. The median follow-up among the survivors was 25.7 years in phase I and 22.4 years in phase II. Of the 2,974 participants who did not receive an active sodium intervention, there were 272 deaths.

The researchers said there was a direct linear association between average sodium intake and mortality. They added that there was also no evidence of a J-shaped or nonlinear relationship.

There was an estimated 15 percent reduced risk among patients who were assigned to the sodium reduction intervention compared with those assigned to the usual care group.

The researchers mentioned a few potential limitations of the study, including they did not know how well patients maintained the sodium intervention over time. They also did not have measurements of sodium intake during the follow-up period. In addition, they said that other dietary factors such as eating more fruits and vegetables and consuming less saturated fat could have played a role in the mortality risk reduction.

“Average levels of sodium intake in the United States remain too high (28) and even appear to be increasing,” the researchers wrote. “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.”