Study: Salt Intake Controlled by Brain, Not Diet

30 Aug 2013 --- Reducing salt consumption has been recommended to help manage cardiovascular disease and high blood pressure, based on the idea that our sodium intake exceeds the needs of our body. But a study led by scientists at UC-Davis lends credence to a recent finding that sodium intake is controlled by networks in the brain, not by the salt we consume.

The current US sodium guidelines for healthy individuals are no more than 2,300 mg per day, while for those at risk of heart disease, the recommended level is no more than 1,500 mg per day.

But a study led by David McCarron and published in the American Journal of Hypertension found that humans have a specific range of sodium intake each day, which lies between 2,600 and 4,800 mg. This range, say the authors, has stayed constant during 50 years and across 45 countries.

David McCarron says: "Our data clearly demonstrate that humans' sodium (salt) intake is regulated within a relatively narrow 'normal' range that is defined by the body's physiology and biological need rather than by the food supply."

He adds that the future health policies and guidelines for sodium intake in the US should "be developed based on that biologically determined range."

Measuring sodium excretions

The study from McCarron and colleagues used data from 45 countries with research participants in 190 government-sponsored studies during the past 50 years, representing more than 69,000 research participants.

Salt intake from the participants was observed by measuring sodium excreted in urine over 24 hours.

Results show that the average intake of sodium per day was around 3,640 mg, with the normal range showing at 2,600 to 4,800 mg.

The findings from the team were recently presented to the Institute of Medicine, which prepared a report about sodium intake. The report states:"Sodium Intake in Populations recognizes the limitations of the available evidence, and explains that there is no consistent evidence to support an association between sodium intake and either a beneficial or adverse effect on most direct health outcomes other than some cardiovascular disease outcomes and all-cause mortality."

The study also draws attention to concerns that low sodium intake could negatively affect certain risk factors, such as blood lipids and insulin resistance, even potentially increasing the risk of heart disease and stroke.

Future sodium guidelines

McCarron says that in the report, the Institute of Medicine acknowledged that it did not previously weigh in on what the "normal range" of sodium intake should be, but he says the organization clearly states that the current US sodium guidelines for healthy people have been unsupported by medical data.

He notes that his team's new study now defines the normal range of salt intake for humans, showing that the past guidelines have been "well below human needs."

"If future nutritional guidelines are to be effective," he says, "they must be based on the scientific reality reflected in these data, which have documented that a normal range for human sodium intake exists."

He concludes:"Sodium intake will not be changed by altering the salt content of food products or other public-policy attempts to limit sodium consumption."