Salt Risk Is Real

High sodium intake was associated with an increased risk of all-cause mortality, researchers reported.

On the other hand, in a large population-based study, an increase in potassium intake was linked to a reduced risk of all-cause mortality, according to Quanhe Yang, PhD, of the CDC, and colleagues.

And a high sodium-potassium ratio was linked with increased all-cause, cardiovascular, and ischemic heart disease mortality, Yang and colleagues reported in the July 11 issue of the Archives of Internal Medicine.

The findings come from an analysis of 12,267 adults who took part in the third National Health and Nutrition Examination Survey (NHANES), starting in 1988.

An earlier analysis of the data had found only an insignificant association between sodium intake and cardiovascular mortality, the researchers noted.

But that analysis had a shorter follow-up than the current median of 14.8 years, as well as some methodological differences.

Participants had an interview and a physical examination, as part of which they provided a 24-hour dietary recall; a subset of participants also provided a second 24-hour dietary recall.

Over the 170,110 person-years of follow-up, 2,270 participants died, including 825 who died of cardiovascular disease and 433 who died of ischemic heart disease.

On average, men had an estimated daily sodium intake of 4,323 mg a day and a potassium intake of 3,373 mg day; women had intakes of 2,918 and 2,433 mg daily of sodium and potassium, respectively.

Regardless of sex, sodium intakes on average were higher than the recommended 1,500 mg a day and potassium intakes were lower than the recommended 4,700 mg daily.

The sodium-potassium ratios for men and women were 1.31 and 1.23, respectively, the researchers found.

In multivariate analysis, Yang and colleagues found:

• Each 1,000-mg-a-day increase in sodium intake was associated with a 20% increase in the risk of all-cause mortality (HR 1.20, 95% CI 1.03 to 1.41).
• Each 1,000-mg-a-day increase in potassium was associated with a 20% lower mortality risk (HR 0.80, 95% CI 0.67 to 0.94).
• Sodium was not significantly associated with either cardiovascular or ischemic heart disease mortality.
• However, potassium was significantly and inversely associated with the incidence of both cardiovascular and ischemic heart disease death. Comparing the highest quartile with the lowest yielded a hazard ratio for cardiovascular disease mortality of 0.39 (95% CI 0.19 to 0.80) and for ischemic heart disease mortality of 0.26 (95% CI 0.10 to 0.71).
• For the sodium-potassium ratio, comparing the highest quartile with the lowest quartile yielded hazard ratios for all-cause, cardiovascular, and ischemic heart disease mortality of 1.46, 1.46, and 2.15, respectively. The 95% confidence intervals in each case did not cross unity.

The researchers cautioned that sodium and potassium intakes were not updated over time, so that changes in diet were not captured. Also, the intakes were estimates based on self-report, rather than on measurement of sodium excretion in urine.

Thus, the results should be interpreted carefully, they said.

Nevertheless, the study "strengthens the already compelling evidence of the relationship between sodium intake and mortality," argued Lynn Silver, MD, and Thomas Farley, MD, both of the New York City Department of Health and Mental Hygiene.

In an accompanying editorial, they said the findings have important public health implications, including continued efforts to reduce sodium artificially added to the food supply during processing.

Such efforts "have positive impacts on absolute sodium intake and the sodium-potassium ratio and thus should reduce mortality," they argued.

Also, they argued, policies to promote plant-based sources of dietary potassium are needed, and food makers should be required to display potassium content on packaging.