Dietary sodium intake and mortality: the National Health and Nutrition Examination Survey (NHANES I).

BACKGROUND

Population-wide restriction of dietary sodium has been recommended. However, little evidence directly links sodium intake to morbidity and mortality. The aim of this study was to assess the relation of sodium intake to subsequent all-cause and cardiovascular-disease (CVD) mortality in a general population.

METHODS

The first National Health and Nutrition Examination Survey established baseline information during 1971-75 in a representative sample of 20729 US adults (aged 25-75). 11348 underwent medical examination and nutritional examination based on 24 h recall. Two had no data on sodium intake available. Vital status at June 30, 1992, was obtained for the 11346 participants through interview, tracing, and searches of the national death index. Mortality was examined in sex-specific quartiles of sodium intake, calorie intake, and sodium/calorie ratio. Multiple regression analyses were done to assess the relations with mortality.

FINDINGS

There were 3923 deaths, of which 1970 were due to CVD. All-cause mortality (per 1000 person-years; adjusted for age and sex) was inversely associated with sex-specific quartiles of sodium intake (lowest to highest quartile 23.18 to 19.01, p<0.0001) and total calorie intake (25.03 to 18.40, p<0.0001) and showed a weak positive association with quartiles of sodium/calorie ratio (20.27 to 21.71, p=0.14). The pattern for CVD mortality was similar (sodium 11.80 to 9.60, p<0.0019; calories 12.80 to 8.94, p<0.0002; sodium/calorie ratio 9.73 to 11.35, p=0.017). In Cox multiple regression analysis, sodium intake was inversely associated with all-cause (p=0.0069) and CVD mortality (p=0.086) and sodium/calorie ratio was directly associated with all-cause (p=0.0004) and CVD mortality (p=0.0056). By contrast, calorie intake in the presence of the two measures of sodium intake was not independently associated with mortality (all-cause p=0.86; CVD p=0.74). Analysis restricted to participants with no history of CVD at baseline gave similar results.

INTERPRETATION

This observational study does not justify any particular dietary recommendation. Specifically, these results do not support current recommendations for routine reduction of sodium consumption, nor do they justify advice to increase salt intake or to decrease its concentration in the diet.