"The history of the Americas is one of constant warfare over salt." -- Mark Kurlansky,
Salt: A World History (Penguin Group, 2003)
Battles for the control of salt once pitted country against country, Cape Cod militiamen against British regulars, even the Union against the Confederacy. Although the physical fights are history, the salt wars still rage in the pages of medical journals and government recommendations.
The controversy boils down to one question: Should we all eat less salt?
Experts have been arguing about this for decades. It's been a bitter and passionate fight, with little middle ground. One side says everyone needs to cut back on salt and that doing so would substantially reduce heart disease. The other side says universal salt reduction would have little effect on public health and would be a needless deprivation for most people.
Is salt a crystalline demon? A harmless treat for the taste buds? Or something in between? As we're learning about so many things in medicine, there isn't a simple right answer. How salt affects your blood pressure and health depends on your genes, your age and your medical conditions.
Salt in Circulation
To a chemist, salt is what you get when positive and negative ions enter each other's orbit. To most everyone else, salt is sodium chloride, the white crystals left over when seawater evaporates. It's the sodium in salt that causes most of the problems. One teaspoon of sodium chloride -- table salt -- contains 2,300 milligrams of sodium.
The human body can't live without some sodium. It's needed to transmit nerve impulses, contract and relax muscle fibers (including those in the heart and blood vessels), and maintain a proper fluid balance. It doesn't take much to do this. The Yanomamo people of the Amazon rainforest get by on just 200 milligrams of sodium a day (about the amount found in one-tenth teaspoon of salt). By comparison, the average American gets 3,400 milligrams (about 11/2 teaspoons of salt), while in northern Japan the daily intake is a whopping 26,000 milligrams (more than 11 teaspoons of salt).When sodium is in short supply, a host of chemical and hormonal messages signal the kidneys and sweat glands to hold onto water and conserve sodium. When you get more sodium than you need, the kidneys flush out the excess by making more, or saltier, urine. If they can't get rid of enough sodium, though, it accumulates in the fluid between cells. Water inevitably follows sodium, and as the volume of this fluid increases, so does the volume of blood. This means more work for the heart and more pressure on blood vessels. Over time, this can stiffen blood vessels, leading to high blood pressure, heart attack or stroke. It can also lead to heart failure.There is also some evidence that salt can directly affect the heart, aorta and kidneys without necessarily increasing blood pressure.
Some people are exquisitely sensitive to salt -- their blood pressure rises and falls as a direct result of how much salt they get. Others don't seem to be affected at all. Unfortunately, there isn't an easy test to determine who is salt-sensitive.A Dash of EvidenceHundreds of studies have looked at the connections between salt intake and blood pressure, heart disease, stroke and mortality. In general, they show that cutting back on salt lowers blood pressure and reduces the chances of having a heart attack or stroke. The trouble with these studies is that virtually every one has flaws, which are pointed out immediately by those who disagree with the study's conclusions. They are too short, too small, not like the real world or influenced by factors other than sodium.Some of the most compelling evidence that eating less salt can lower blood pressure comes from the Dietary Approaches to Stop Hypertension (DASH) trials. The first DASH trial showed that a diet rich in fruits, vegetables, low-fat dairy products, whole grains, beans, nuts, fish and poultry lowered blood pressure in people with normal and high blood pressure. A follow-up trial added salt into the mix. It compared a DASH diet with a control diet that was much like the average American diet. Both also had three levels of sodium: high sodium, at 3,500 milligrams of sodium a day; moderate sodium, 2,300 milligrams; and low sodium, 1,100 milligrams. More than 400 volunteers followed their assigned diets for a month.
The DASH diet again proved better for blood pressure than the control diet. And across the board, the less sodium, the lower the systolic (the top number of a blood pressure reading) and diastolic (the bottom number) pressures. Lower sodium had the greatest effect in people with high blood pressure on the control diet, blacks on the control diet, and women on the DASH diet.The low-sodium DASH diet worked best of all. Among volunteers assigned to this combination, systolic blood pressure was 8.9 mm Hg lower than it was among those on the high-sodium control diet, while diastolic pressure was 4.5 mm Hg lower. In an individual, that's the equivalent of taking a medication to lower blood pressure. The study didn't last long enough to see if this translated into less heart disease. Similar reductions, though, have been shown to reduce the risk of heart disease by 20 percent and stroke by 35 percent.Next: We're all different >
Source: Health & Wellness
