We’ve been bombarded for more than two decades with scientists and doctors telling us to eat less salt. Statistics show that those eating excessive salt in their diets are far more likely to suffer from cardiovascular problems, but as with any nutritional or diet information, moderation and balance is the key. Everyone is familiar with the active salt intake in hot countries like Mexico and Spain, where more salt is lost through perspiration, so it should come as no surprise that too little salt can also be a problem.

A study in the November 23 issue of JAMA shows that too high or too low sodium levels in urine carries a far higher risk for cardiovascular events (for higher levels), or cardiovascular death and hospitalization for congestive heart failure for lower levels.

Researchers also found higher estimated urinary potassium excretion was associated with a reduced risk of stroke.

The exact daily recommended salt intake is still not precisely clear, and would be an academic number, since it would be fairly difficult for the average person to accurately measure how much salt they eat on a day to day basis. A lot would also depend on the climate they live in and how active they are.

Researchers say that :

“Clarifying the optimal daily intake of sodium is particularly important in patients with established Cardiovascular (CV) disease, where it has been inadequately studied. Patients with CV disease may be especially vulnerable to the CV effects of high and low sodium intake and are most likely to receive recommendations on restricting sodium intake.”

The authors also note that the optimal level of daily potassium intake, a proposed modifier of the association between sodium intake and CV disease, has not been established.

Martin J. O’Donnell, M.B., Ph.D., and Salim Yusuf, D.Phil., F.R.C.P.C., F.R.S.C., of McMaster University, Hamilton, Ontario, Canada, and colleagues examined the association between sodium and potassium excretion (markers of intake) and CV events and mortality.

The study consisted of an observational analyses of 2 cohorts (n = 28,880) included in the ONTARGET and TRANSCEND trials (November 2001-March 2008 from initial recruitment to final follow-up). The researchers estimated 24-hour urinary sodium and potassium excretion from a morning fasting urine sample. Multivariable models were used to determine the association of urinary sodium and potassium with CV events (myocardial infarction [MI; heart attack], stroke, and hospitalization for congestive heart failure (CHF) and mortality.

At study entry, the average estimated 24-hour excretion for sodium was 4.77 g and 2.19 g for potassium. After a median (midpoint) follow-up of 56 months, the composite outcome occurred in 4,729 (16.4 percent) participants. The researchers found that after multivariable analysis, compared with baseline sodium excretion of 4 to 5.99 g per day (n = 14,156 [15.2 percent with the composite outcome]), higher baseline sodium excretion (18.4 percent for 7-8 g/d and 24.1 percent for greater than 8 g/d) and lower sodium excretion (18.2 percent for 2-2.99 g/d and 20.2 percent for less than 2g/d) were associated with an increased risk of the composite of CV death, heart attack, stroke, and hospitalization for CHF.

Compared with the reference group, higher baseline sodium excretion was associated with an increased risk of CV death (9.7 percent for 7-8 g/day; and 11.2 percent for greater than 8 g/day), MI (6.8 percent for greater than 8 g/day), stroke (6.6 percent for greater than 8 g/day), and hospitalization for CHF (6.5 percent for greater than 8 g/day). Lower sodium excretion was associated with an increased risk of CV death (8.6 percent for 2-2.99 g/day; 10.6 percent for less than 2 g/day), and hospitalization for CHF (5.2 percent for 2-2.99 g/day) on multivariable analysis. Compared with an estimated potassium excretion of less than 1.5 g per day, higher potassium excretion was associated with a reduced risk of stroke on multivariable analysis.

The researchers conclude that :

“Discrepant findings of previous studies are likely due to differences in ranges of sodium intake, study populations, methods of measurement, and failure to explore a nonlinear association … Compared with moderate sodium excretion, we found an association between high sodium excretion and CV events and low sodium excretion and CV death and hospitalization for CHF, which emphasizes the urgent need to establish a safe range for sodium intake in randomized controlled trials.

Higher urinary potassium excretion was associated with lower stroke risk and is a potential intervention that merits further evaluation for stroke prevention.”

They also mention that previous individual prospective cohort studies have either reported a positive association, no association, or an inverse relationship between sodium intake and CV mortality, and that this area clearly needs further investigation.

Written by Rupert Shepherd