For people who have chronic kidney disease (CKD), which is characterized by the slow loss of kidney function over time, reducing salt intake may be the best way to prolong life, lower the risk for heart disease, and fend off the progression of CKD, a new study found.  

Sodium plays a large part in kidney function. According to Mayo Clinic, the kidneys regulate the amount of sodium in the body — if there’s too much, the kidneys release it through urine. The kidneys are unable, however, to deal with abnormally high sodium levels, and usually deal with this by releasing it into the bloodstream. In turn, the sodium captures water, and increases blood volume, forcing the heart to work harder and increasing pressure in the arteries. This can lead to a number of heart problems as well as kidney failure.

Researchers found that reducing salt consumption resulted in a lower volume of extracellular body fluid (an average of one liter) among patients with CKD. This meant that the blood was able to retain its fluid, subsequently maintaining regular blood flow. Reduced salt also led to lower blood pressure and 50 percent less protein excretion in the participants’ urine — good news, because the kidney’s nephrons are supposed to hold back proteins when filtering contaminants from the blood.

“These are clinically significant findings, with this magnitude of blood pressure reduction being comparable to that expected with the addition of a [blood-pressure lowering] medication, and larger than effects usually seen with sodium restriction in people without chronic kidney disease,” Emma McMahon, of the University of Queensland, said in a statement, according to HealthDay.

She also said that if maintaining the reduction in protein excretion is possible, it “could reduce risk of progression to end-stage kidney disease, where dialysis or transplant is required to survive, by 30 percent.”

The study involved 20 patients with CKD who were told to eat a low-sodium diet of 1,080 to 1,440 mg/day for one week. At the end of the week, some patients were told to eat a high-sodium diet consisting of the aforementioned amount plus a 2,160 mg tablet each day. Other patients were told to continue eating the same amount of sodium, but instead of adding a sodium pill to their diet, they were given a placebo, Medscape reports.

The average American consumes about 3,400 mg of sodium per day, much more than the recommended 2,300 mg/day — about a teaspoon of salt. For people who are ages 51 and older, that amount should be reduced to 1,500 mg/day, according to the Dietary Guidelines for Americans.  

Source: McMahon E, Bauer J, Hawley C, et al. A Randomized Trial of Dietary Sodium Restriction in CKD. Journal of the American Society of Nephrology. 2013.