Salt is bad for blood pressure but good for brain development, researchers say
By Jeanie Lerche Davis
WebMD Weight Loss Clinic - Feature
Reviewed By Brunilda Nazario
Pass the salt: Who hears that anymore? Salt's been nearly banished, and rightly so. Too much salt affects blood pressure -- and not in a good way. But for some people, cutting back has a downside.
Take stock of the facts.
Too little salt -- iodized salt, that is -- is dangerous, too. It's the iodine in iodized salt that helps the body make thyroid hormone, which is critical to an infant's brain development.
A little salt is essential to good health. Healthy adults should consume salt and water to replace the amount lost daily through sweat and to achieve a diet that provides sufficient amounts of other essential nutrients.
The American Heart Association and NIH advise adults to get no more than 2,400 milligrams of sodium daily. That's about 1 teaspoon of salt. Just think how salty your favorite snacks taste. Eat too many salty foods (even soft drinks have sodium), and you easily go overboard.
Truth About Iodized Salt
Is the salt in your kitchen salt iodized? Most people don't know. "Most people buy just whatever one their hand grabs... and until about five years ago, it didn't really matter," says Glen Maberly, MBBS, MD, an endocrinologist and professor of international health in the Rollins School of Public Health at Emory University School of Medicine in Atlanta.
Yet getting too little iodine -- called iodine deficiency -- is a serious issue. Iodine is an essential mineral for the production of thyroid hormones. Too little iodine in a pregnant women's diet can affect the development of the fetus' brain and can cause cretinism, an irreversible form of physical and mental retardation. Iodine deficiency during infancy can also result in abnormal brain development and impaired intellectual development.
"The developing brain is the most sensitive organ. Iodine deficiency doesn't make people idiots, but it does make them less smart," says Maberly.
In the U.S., iodine deficiency is more common in women than men. It's also common in pregnant women and adolescents, he tells WebMD.
Iodine deficiency is thought to be rare in the U.S. It's considered a problem of third-world countries, but Maberly disagrees. "Iodine nutrition in the U.S. is borderline," he tells WebMD. "A pregnant woman may not be protected. Even if she eats a normal diet, her intake is probably inadequate. Only 70% of table salt is iodine-fortified."
Until nearly five years ago, Americans who got dairy, bread, and meat in their diets got plenty of iodine, he explains. Machines used in production were cleaned with an iodine disinfecting solution, so some iodine ended up in dairy, bread, meat products. That ended when companies quit using iodine disinfectant.
Iodized salt is rarely found in canned, frozen, or boxed food, says Maberly. French fries and other snack foods mostly contain regular salt -- not iodized salt.
In fact, Americans now get one-third less iodine than they once did, he notes.
Both newborns and toddlers are affected by iodine deficiency. A recent study showed lower IQ scores among children with mild iodine deficiency -- proof that the problem exists in developed countries, writes researcher Piedad Santiago-Fernandez, MD, an endocrinologist at the Complejo Hospitalario Carlos Haya in Malaga, Spain.
It's true, says Michael Karl, MD, an endocrinologist with the University of Miami School of Medicine. "You can certainly see even subtle changes in iodine can affect IQ," Karl tells WebMD. "Iodine is critical in the first years of life, extraordinarily important up to 3 or 5 years of age."
Children in financially stressed families are likely at highest risk. They rarely take multivitamins, he tells WebMD. "Iodine deficiency is not an epidemic yet, but it's serious enough that it should be watched."
Sea salt and most salt substitutes are not iodized. Unless fruits and vegetables are grown in iodine-rich soil, they will not contain iodine. Restaurants usually order salt in bulk, and often it's not iodized salt.
However, anything from the sea - such as seaweed (kelp) or fish -- can be a good source of iodine, says Maberly. A cup of cow's milk contains nearly 100 micrograms of iodine. Some breads contain iodine, but not all.
The normal requirement for iodine, according to World Health Organization standards: Adults need 150 micrograms a day. Women trying to get pregnant should increase their intake to 200 to 300 micrograms a day.
"We certainly should make pregnant and lactating women aware of this deficiency," says Karl. "I don't think most primary care doctors are aware of it."
Salt and Your Blood Pressure
The link between sodium and blood pressure has been rocky in recent years. Two decades ago, the landmark study known as Dietary Approaches to Stop Hypertension (DASH) showed that a low-sodium, low-fat diet -- high in calcium, fruits, and vegetables -- had a direct impact on lowering blood pressure.
But a study last year challenged that dictum. It indicated that high-sodium intake is a marker for a poor-quality diet. It wasn't the sodium that affected blood pressure, but the lack of other important vitamins and minerals. That study was funded by the salt industry.
However, a new report from the DASH research group shows -- once again -- that cutting sodium improved blood pressure, especially as people hit their 40s and 50s.
"In general, people who are older benefit more from lowering their sodium. Around age 40, 50, we begin to see a real difference," says Daniel W. Jones, MD, a hypertension expert with the University of Mississippi, and spokesman for the American Heart Association.
Whether a person is salt-sensitive is at the heart of this issue. Everyone's response to sodium is different, Jones explains. Obese people and black people, seem to benefit more from sodium restriction than white people do, studies have shown.
But he says "that most people have some salt sensitivity," says Jones. "Some have more than others." Problem is, there is no easy test for determining salt sensitivity, he explains.
His personal philosophy: "Everyone hopes to become old, and as we get older, we become sensitive to salt. It makes sense to start early enough to affect your health. I think the direct health benefits from restricting sodium -- like the DASH study -- does call for restricting sodium," says Jones.
SOURCES: Glen Maberly, MBBS, MD, endocrinologist and professor, international health, Rollins School of Public Health at Emory University School of Medicine, Atlanta. Michael Karl, MD, endocrinologist, University of Miami School of Medicine. Daniel W. Jones, MD, hypertension expert, University of Mississippi; and spokesman, American Heart Association.
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