Excess salt may stiffen heart vessels

Eating foods laced with too much salt may be as risky as smoking cigarettes, at least in terms of a risk factor for heart attacks called coronary flow reserve, a new study of middle-aged American men finds.

Coronary flow reserve, or CFR, offers a gauge of how well tiny blood vessels in the heart dilate or contract in response to hormonal commands. The lower the CFR, the stiffer the vessels — and the less responsive they become to the heart’s constantly changing workloads.

The new study examined CFR and salt intake among 143 pairs of male twins in their 50s or older. CFR declined by about 10 percent for each additional 1,000 milligrams of sodium that a man consumed per day compared with his brother.

“That’s huge,” says Viola Vaccarino of Emory University in Atlanta and coauthor of the study, which appears in the March American Journal of Clinical Nutrition. The difference in CFR for men with the highest sodium intake versus those with the lowest, she notes, was equivalent to changes other studies had linked to smoking.

The results imply that adults who routinely consume too much sodium might have trouble raising sufficient blood flow in the heart — which could lead to angina or disturbances of heart function, observes Bruce Van Vliet of Memorial University of Newfoundland in St. John’s, Canada.

CFR values among men with the highest salt intake fell within the range considered abnormal. So the heart risk in the study isn’t just a numerical difference that stands out above the noise, Vaccarino emphasizes, “but a change that is medically significant.” The same effect was seen in identical and nonidentical twins, she adds, strongly suggesting “that the effect is due to the diet — and is sodium-specific.”

Using twins in a sodium study to account for the potentially confounding effects of genetics and upbringing “is novel and quite interesting,” says epidemiologist Paul Whelton of the Tulane University School of Public Health and Tropical Medicine in New Orleans. Linking sodium to CFR is also novel, he says.

Most research has attributed sodium’s cardiovascular effects to its role in elevating blood pressure. But the new study identified sodium’s link to falling CFR even in men with normal blood pressure or whose hypertension was controlled with medicine.

Average sodium intake by Americans age 2 and older is about 3,400 milligrams per day. That’s well above the generally recommended cap of 2,300 milligrams per day, or 1,500 milligrams for people older than age 50 or who have high blood pressure, diabetes or chronic kidney disease. Vaccarino’s group recommends Americans work hard at diminishing their sodium intake.

“That’s a big challenge,” Whelton points out. ”About 80 percent comes from the processed foods that we eat,” not from the source people can most visibly control: the salt shaker.