MONDAY, Dec. 28, 2015 (HealthDay News) -- For decades, doctors have urged heart failure patients to slash their salt intake as a way to preserve their health.

But a new study suggests -- but doesn't prove -- that that advice may be harmful, potentially increasing a heart failure patient's risk of death or hospitalization.

Patients with moderate heart failure who stuck to a low-sodium diet were 85 percent more likely to die or require hospitalization for heart disease, when compared to similarly ill patients who didn't restrict their salt intake, the researchers found.

"The conventional wisdom has been that salt is bad for you," said lead researcher Dr. Rami Doukky, a cardiologist and associate professor at Rush University Medical Center in Chicago. "This study says, not so fast. Maybe we should take that, no pun intended, with a grain of salt."

However, Doukky and other cardiologists warned that the study findings are very preliminary and should not be interpreted by heart failure patients to mean that it's OK to reach for the salt shaker. Rigorous clinical trials are needed to further test the safety of this hypothesis, the experts said.

"The study is meant to be an eye-opener, that we need to investigate this matter more. We used to take it [salt consumption] for granted, and now it is time to address it with more definitive trials," Doukky said.

Physicians have long assumed that salt is bad for heart failure patients because the mineral causes the body to retain water and pull additional fluid into the blood vessels, Doukky explained.

Physiologically, the assumption makes sense, said Dr. Clyde Yancy, chief of cardiology at Northwestern University's Feinberg School of Medicine in Chicago.

Heart failure patients struggle with fluid retention because their heart beats too weakly to fight the force of gravity, allowing blood and water to build up in their lungs, feet, ankles and legs, according to the U.S. National Institutes of Health.

Salt also increases blood pressure by drawing water into the arteries and veins, according to the American Heart Association, and high blood pressure is a long-known risk factor for heart disease.