Ah, salt. It gives personality to chips, balance to bread and flavor to just about everything else that comes in a can, jar or squeeze bottle. Salt is such a mealtime staple it can be hard to imagine life without a shaker on the table. But as far back as the 1960s, physicians linked salt to high blood pressure, a major risk factor for heart disease and stroke.
Today, more than 65 million Americans have hypertension - repeatedly high blood pressure - according to the National Heart, Lung, and Blood Institute, and 59 million more have pre-hypertension, a level higher than normal that can also lead to health problems.
These entreaties - which have taken on renewed vigor of late - have so far fallen on deaf ears. The average American adult consumes twice the 2,300 milligrams (about a teaspoon's worth) recommended for most adults by the Institute of Medicine and the Department of Health and Human Services' Dietary Guidelines for Americans.
To help people do what they can't seem to do on their own, in the last few years a consumer advocacy group and several medical organizations and health experts have been pushing for legislation that would regulate sodium content in the foods we buy.
They say that more than 75% of the salt we get comes from processed foods and restaurant dishes, making it easy to blow a day's allotment in a single meal without even picking up the saltshaker.
A McDonald's bacon, egg, and cheese biscuit contains 1,250 milligrams of sodium. Frozen entrees in grocery stores can easily top 5,000 milligrams. A typical serving of jarred tomato sauce packs more than 700 milligrams - even bread often has a couple of hundred milligrams per slice.
A few researchers studying the link between salt and health say salt has been unfairly villainized. They argue that only a fraction of the population is sensitive to salt's blood-pressure-raising effects, that our fixation on salt distracts us from focusing on what's really responsible for our nation's epidemic of heart disease, namely, obesity. They say for some people, lowering sodium intake might be harmful.
But the vast majority of such researchers believes the science indicting salt overconsumption is clear. "There's very broad consensus on this," says Dr. Darwin Labarthe, director of the Division for Heart Disease and Stroke Prevention at the Centers for Disease Control and Prevention in Atlanta. "Excess salt is clearly bad for us."
Effects of diet
Strong evidence of this comes from a series of studies called DASH, for "Dietary Approaches to Stop Hypertension." Funded by the National Heart, Lung, and Blood Institute, a division of the National Institutes of Health, the studies set out in the 1990s to discover how diets affect blood pressure.
Blood pressure measurements use two numbers to indicate how hard it is for the blood to get through the arteries, veins and smaller blood vessels. A reading of 120/80 or less is ideal. Hypertension is defined as blood pressure that is consistently higher than 140/90. Pre-hypertension lies between.
In the first DASH study, for two months, researchers carefully controlled what went into the mouths of more than 450 people. One group ate a normal American diet, that is, one with typical amounts of fat and cholesterol. Some ate the same diet with extra fruits and vegetables. And a third group ate what became the recommended DASH diet: full of fruits, vegetables, whole grains and low-fat dairy foods, and low on red meat, sweets and saturated fats. All diets contained about 3,000 milligrams of sodium.
Within two weeks, researchers measured a reduction in blood pressure among the second group, but the third group experienced a drop that was twice as big - a decrease of 5/3 mm Hg - suggesting that a healthful diet can have a large effect on heart health.
Statistics zero in
Armed with that information, the researchers embarked on a second version of the study that aimed to quantify what salt contributes to the blood pressure equation. More than 400 participants ate either a regular American or a DASH diet for three months. For a month each, every participant's food contained either 3,300, 2,300 or 1,500 milligrams of sodium.
(A limit of 1,500 milligrams is recommended for African Americans, anyone middle-aged or older and those with high blood pressure and other health problems - groups particularly sensitive to salt's influence on blood pressure.)
Results of the study, published in the New England Journal of Medicine in 2001, were dramatic, says Eva Obarzanek, a registered dietitian and research nutritionist with the National Heart, Lung, and Blood Institute and a coauthor of the study.
"It showed in a stepwise fashion that if you reduce sodium, you reduce blood pressure," she says.