18 February 2011

Doubt cast on salt guidelines for diabetics

In a study that seems to turn conventional wisdom on its head, researchers found that patients with the highest urinary sodium levels had the smallest risk of dying.


Australian researchers are challenging guidelines that urge diabetics to cut back on salt intake.

In a study that seems to turn conventional wisdom on its head, they found that patients with the highest urinary sodium levels had the smallest risk of dying over a 10-year period.

"Such data call into question universal recommendations that all adults should endeavor to reduce their salt intake," Dr Elif I. Ekinci of the University of Melbourne in Victoria and colleagues wrote in the online paper Diabetes Care.

But don't reach for pretzels just yet

Although it isn't the first time findings like these have surfaced, this study, like others before, was just observational.

The research team followed 638 people with longstanding type 2 diabetes, often accompanied by heart disease and high blood pressure. At the outset of the study, all patients were in their 60s on average, and nearly half were obese.

"These are precisely the patients in whom more aggressive lifestyle interventions are often applied," the researchers note.

The study

All the patients were treated at a single diabetes clinic, and doctors collected several 24-hour urine samples from each patient when the study began.

The average urinary sodium, 4.2 g/day, was in line with earlier global surveys, the researchers say.

Over ten years of follow-up, 175 patients died, mostly due to heart disease.

For every extra 2.3 g of urinary sodium above the mean, the risk of dying during the study dropped by 28%, even after accounting for kidney disease, age and other factors likely to be important.

"This is unexpected," Dr Ekinci and Dr George Jerums, who also worked on the study, said. "It raises the possibility that in people with type 2 diabetes, low salt intake is not always beneficial."

The main problem is that the patients who had lower sodium levels in their urine were sicker and older, said Dr Paul Elliott, who studies the link between diet and high blood pressure at Imperial College London.

Although the authors tried to correct for these imbalances, it remains likely that the results are still confounded by them, he said.

That reasoning seems to be bolstered by the finding that higher blood pressure was tied to longer survival in the study, "which just isn't plausible," Dr Elliott said.

The bad effects

But another expert said the Australian researchers might be onto something.

"The reality is that reducing sodium has many effects, some good like reducing average blood pressure, and others bad," said Dr Michael H. Alderman of the Albert Einstein College of Medicine in New York.

For instance, he said, reducing sodium increases insulin resistance. It also ramps up production of other hormones that have been linked to heart disease.

"The impact of reducing sodium must be the sum total of all these physiological effects," Dr Alderman said.

To get to the bottom of the issue, a clinical trial comparing people told to eat less sodium to those who maintain their usual intake is necessary.

"It is surely safer, and probably cheaper than to ask 300 million Americans to reduce their sodium intake because of the hope that it will actually extend or improve life," Dr Alderman said.

(Reuters health, Frederik Joelving, February 2011)

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