Our tongue and palate taste foods that are sweet, salty, sour, bitter and savory (umami). Salt is essential for us, as it is found in our blood, cells, bones, and the fluid between cells. Salt is necessary for the function of our nerves and muscles. The digestion of food in our stomachs by hydrogen chloride also comes from salt. When humans were hunter-gatherers, we got salt from eating animals; they got theirs from finding salt in rocks, brackish water and brine springs. (The city of Buffalo is named for the buffalo who made a wide path to a salt lick near Lake Erie!) When we became farmers, we needed to find sources of salt for our diets; the story of how humans have found, prepared and traded salt is a fascinating one of early commerce. You can find it in "Salt - A World History" by Mark Kurlansky.
How much salt to we need? The answer varies – depending on our body size, the amount we sweat, and problems such as serious diarrhea or kidney disease. The present consensus is that adults need 1000 - 1500 mg of sodium a day, and should not get more than 2400 mg. However, we are now averaging 3436 mg a day. Sodium is present in all animal food we eat, in small amounts in vegetables, but in large amounts in bread and prepared foods, which make up 70-80% of our daily salt intake.
Why does excess salt in our diet matter? You know the answer – it has to do with high blood pressure (hypertension). Increased salt causes more fluid to be retained in the blood vessels, so the heart must work harder to pump blood through the body. Salt may also act on arterioles - blood vessels that dilate and constrict to regulate blood pressure and blood flow. By contracting under the influence of sodium, arterioles increase resistance to the movement of blood and thereby increase blood pressure. Genetics play a role in our sensitivity to salt – some people are more susceptible to high blood pressure, and sodium sensitivity appears to increase with age. African Americans tend to be more salt sensitive than others and should be especially careful to eat less salt. A national study showed that 29% of US adults have hypertension (systolic pressure consistently over 140, diastolic over 90 on multiple readings), and another 28% have prehypertension. (systolic pressure of 120-139, diastolic of 80-89 on multiple readings). An increased risk for heart disease and stroke is the reason for concern about blood pressure.
Since most of the salt in our diets comes from prepared food – be prepared to find it! Carefully read the labels on canned and dried soups, sauces, vegetable juices, salad dressing, lunch meats, bacon, bread, popcorn, crackers and chips. Most of us don’t have the time or desire to make everything at home, but we can all be detectives. Making more foods from scratch saves money as well as health. Your taste for lots of salt is reversible; decrease your use gradually and your taste buds will adjust. As you eat more fruits and vegetables you will be increasing the potassium in your diet. A potassium-rich diet blunts the effects of salt on blood pressure, may reduce the risk of developing kidney stones, and possibly decrease bone loss with age.
When you are on the go, pack fresh and dried fruit in your bag, along with carrots, celery and unsalted nuts. Try low sodium V-8, or Knudsen’s plain or organic low sodium Very Veggie.
Next week I’ll describe the DASH diet, and other ways to lower blood pressure, including the right kind of exercise, and gradual weight loss.
Sadja Greenwood, MD, MPH