Data from O’Donnell et al.
Low Sodium Intake Is a Risk Factor for Mortality
Cross-sectional and epidemiologic data has repeatedly shown low-sodium diets to be associated with worse outcomes This was made clear when O’Donnell et al looked at sodium intake and adverse outcomes in the ONTARGET and TRANSCEND trials. Both of these trials looked at high-risk patients over the age of 55 with either established CV disease or high risk diabetes.
Average 24-hour sodium excretion was 4.8 grams (208 mmol) or roughly double the recommended sodium intake for individuals. Expectedly morbidity and mortality rose as sodium excretion went up, but surprisingly, morbidity and mortality also rose as sodium excretion went down from the average. The mortality was lowest at precisely the average sodium intake.
The Belgians did a comprehensive evaluation of Flemish sodium habits and followed them for 8 years. Unlike just about any other study on sodium excretion, the Flemish Study on Genes, Environment, and Health Outcomes (1985-2004) and the European Project on Genes in Hypertension used honest-to-goodness 24-hour urine collections for all 3,681 participants. CV mortality was increased in the lowest tertile of sodium intake.
During the follow-up, over 500 previously normotensive people developed benign hypertension. The incidence of hypertension was not influenced by baseline sodium excretion. Though interestingly, the cross-sectional analysis showed exactly what the large epidemiologic studies have shown, that increased sodium excretion was associated with increased blood pressure.
This curious association of increased CV mortality with low sodium excretion has also been found in the analysis of the NHANES 1, 2, and 3. Low sodium diets increase renin, aldosterone, and the sympathetic nervous system activity, possibly driving the increased adverse outcomes.
High Sodium Intake Is a Risk Factor for Hypertension
He et al performed a Cochrane Systematic Review to determine the effect a reduction in dietary sodium (or more often urinary excretion of sodium) has on blood pressure and consistently found that even modest reductions of sodium for a month reduce blood pressure. In 22 trials of 1,990 people with hypertension, a reduction of salt excretion of 75 mmol (4.4 g) reduced blood pressure 5.39/2.82 mm Hg. A larger, 100 mmol (6 g) reduction in salt excretion lowered systolic blood pressure 10.8 mm Hg.
The meta-analysis examined 2,240 normotensive individuals from 12 trials. A reduction in salt excretion of 75 mmol (4.4 g) reduced blood pressure 2.4/1.0. A larger, 100 mmol (6 g) reduction in salt excretion lowered systolic blood pressure 4.4 mm Hg.
Translating these reductions in blood pressure to lives saved gives dramatic results. In the 2010 report of the Dietary Advisory Committee on the Dietary Guidelines for Americans, the authors estimated that a reduction in sodium intake of 400 mg/d would:
● Reduce heart attacks by 20,000 to 32,000 per year
● Reduce strokes by 13,000 to 20,000 per year
● Save between 17,000 and 28,000 lives every year