dietary sodium and disease

 somewhat striking report by the Institute of Medicine on the health effects of limiting sodium consumption  (See sodium and disease IOM report 2013 for the summary, or the 170 page full report as sodium and disease IOM full report 2013 in dropbox).  Current guidelines are overall lowering sodium intake to 2300mg/d for those over 14yo,  with target of 1500 mg/d in higher risk people (African-Americans, those with diabetes/hypertension/chronic kidney dz, and those over 51 yo – ie, a majority of the population). The concern is that lowering sodium intake may not be entirely positive.  For example, low sodium intake is assoc with high plasma renin activity (PRA), which in some studies is assoc with increased CVD risk.  In one study of high risk pts with atherosclerosis or diabetes, PRA was independently assoc with hypertension, left ventricular hypertrophy, abnormal lipids, and insulin resistance.  The detailed review suggested:

-- there are significant methodologic issues with the studies overall (quantitation of sodium intake, most studies are observational, many done in countries with very different diets, hard to disentangle sodium consumption from consumption of other nutrients)

-- no consistent evidence of relationship between sodium intake and noncardiovasc outcomes. Some data from outside US where very high sodium intake that there may be more gastric cancer

-- In terms of blood pressure, there seems to be quite large variability, with some patients more salt sensitive than others. In the aggregate, there is a positive relationship between sodium intake and blood pressure, esp down to 2300 mg/d. not enough evidence to conclude lowering sodium below 2300 mg/d is beneficial. 

--for prehypertensive people, some data that decreasing sodium to 2300 mg/d is beneficial, but no benefit and maybe harm in the 1500-2300mg/d range, esp in those with diabetes, chronic kidney disease or pre-existing CVD. No relevant data for the other “high-risk” groups of African-Americans or those >51yo.

--for CHF, some data it might be harmful to lower sodium too much: one study achieving 1840 mg/d assoc in pts with mod to severe CHF with low EF on aggressive med regimen found worse outcomes (though using different regimen than we use in US, so needs more studies)

--for CKD progression, data inconsistent that lowering Na helps

--for DM or metabolic syndrome, studies inadequate to draw conclusions

Turns out that we are not in serious danger of too little sodium – since the guidelines were published to decrease sodium intake with the 2300mg and 1500 mg targets, the MMWR found that sodium intake was actually increasing, with minimal difference between those who should be taking 2300 vs 1500 mg/d….   so, good that there are no consistent data supporting decreasing the level to below 2300mg for anyone, even high risk.