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Understanding salt

Why does one person love the taste of salty snacks, and another dislike it? An Israeli researcher has discovered that babies born with low sodium levels in their blood, have a particular fondness for salt that lasts throughout their lives.

Salt, according to researcher Dr. Micah Leshem, is the essence of life. Without salt in our bodies, we would suffer a range of symptoms from nausea, vomiting, headaches and weariness, to convulsions, coma, and eventually death. That's why we all eat salt. But why do some people have such a strong desire for salty foods, while others prefer to give them a miss? That's a question that Leshem, a professor of psychology at the University of Haifa, believes he has now found the answer to.

In a study of 41 children and teenagers born prematurely at two neonatal units at Ha'emek Medical Centre in Afula and the Galilee Medical Centre in Nahariya, Leshem and his colleagues found that those with low sodium levels in their blood at birth had a particular fondness for salty food.

In tests, the boys and girls, now aged between eight and 15, were offered a choice of either salty or sweet snacks. Those born with low sodium levels (hyponatremia) reached more frequently for the salty snack. They also consumed substantially more sodium each day, based on interviews with children and their parents.

The study also found that children with the most severe sodium deficiency at birth weighed 30 percent more, on average, than their peers born with the highest sodium levels.

Leshem has been studying sodium intake in animals and humans for many years. Previous research carried out by Leshem and other researchers in this field suggests that sodium loss in early infancy, through dehydration, vomiting, diarrhea and electrolyte deficient feeding, can affect salt preferences into adulthood, even once the sodium deficit is repaired. This research, however, relies heavily on recall, and remains to be proven.

In Leshem's current research he turned to the neonatal medical records of premature infants to see if there was a link between sodium loss and an increased desire for sodium later in life.

Though sodium deficiency can be found in full-term infants, particularly in babies whose mothers vomit excessively through pregnancy, or in babies with kidney dysfunction, premature infants have an increased risk of low blood sodium levels because their kidneys are underdeveloped.

Using these records the researchers recorded the lowest blood sodium levels a baby experienced in the few weeks after its birth. They discovered that these levels correlated with the amount of sodium the growing children looked for in their diets. The lower their blood sodium level at birth, the more sodium the children ate in their diet.

"It is now clear that perinatal sodium loss, from a variety of causes, is a consistent and significant contributor to long-term sodium intake," according to the report, published in the American Journal of Physiology - Regulatory, Integrative, and Comparative Physiology.

Leshem believes this research has many implications. Today, high salt intake is considered unhealthy. It is thought to be a risk factor for cardiovascular disease, high blood pressure, and hypertension, and a marker for the risk of obesity, possibly because it signifies a person's consumption of calorie-dense processed foods.

This is still a matter of controversy, however. Some experts suggest that high doses of salt are not unhealthy for everyone, but only those with an increased sensitivity towards it. Leshem believes it is too soon to say whether sodium deficiency early in life is a risk factor for obesity, but he does suggest that the study highlights the importance of monitoring and balancing sodium levels in premature babies.

In addition he hopes it will help pediatricians and parents direct children towards a healthy diet. "Once you are aware that low sodium levels in infancy lead to an increased appetite for salt, you can understand and explain what is happening to the child. Having knowledge is being forearmed," he says.

"Clinicians might want to tell families of neonates with low blood sodium of the risks for early increased sodium intake and corpulence," it states in the report. The research also hints at the mechanisms that influence people's salt intake. "Once we understand these mechanisms, intervention is possible," Leshem predicts.

Leshem is now involved in research on adults who experience regular dehydration, like soldiers, blood donors, or athletes. His aim is to discover if they, like infants, develop an increased desire for sodium in their diet after such events, and whether this is a permanent change.

While the results are so far from conclusive, Leshem says that initial findings suggest that some adults are more likely to become dehydrated than others, and that these people are constitutionally weak at monitoring the sodium balance in their bodies. "I suspect these are people who may be eating more salt than others," says Leshem. He now plans to study this phenomenon.

Reproduced with permission: Bicom


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