WEDNESDAY, March 6, 2002 (HealthDayNews) -- Infants born more than seven weeks premature need dietary salt supplements to avoid the risk of reduced cognitive and motor skills once they reach puberty.
That's the conclusion of a British pediatricians' report that found premature infants who received carefully controlled salt supplementation during the first two weeks of life had superior neurodevelopmental skills once they reached puberty. But, the researchers stress, extra salt isn't necessary for healthy, full-term children.
The research appears in the March 2002 issue of the journal Archives of Disease in Childhood: Fetal and Neonatal Edition.
Any child born before 37 weeks of gestational age is considered premature. And doctors have known since the early 1980s that premature infants often become salt-depleted during the first two or three weeks of life.
Dr. George Haycock, a professor of pediatrics at Guy's, King's and St. Thomas' Hospitals School of Medicine in London, was one of the first researchers to demonstrate that these infants were losing a lot of salt in their urine.
"Premature babies
are not designed for independent life out of the womb," Haycock says.
"The fetus in utero has a high urine output in the mid-trimester, and this is necessary to maintain amniotic fluid volume," he says. "Of course, in utero that's immediately replaced across the placenta by the mother," and because the fetus swallows amniotic fluid.
"As soon as the baby is born with the high urine sodium output, and he goes onto what is basically a very low sodium diet, then they get into a negative balance," Haycock says.
Dr. Michael Speer, a professor of pediatrics who specializes in newborns at Baylor College of Medicine in Houston, says, "The normal preterm kidney has difficulty retaining salt."
During its research, Haycock's team determined how much salt the premature infants were losing and showed that dietary salt supplements could make up for the loss.
"There's a lot of experimental evidence in animals that salt deficiency at periods of critical growth, particularly perhaps of the nervous system, can cause impairment of development," Haycock says.
Based on those animal studies, Haycock and his colleagues decided to look back at infants studied in the early 1980s to determine whether salt supplementation influenced developmental differences.
The researchers reviewed records of 46 infants who were born at a gestational age of 31 to 33 weeks. Twenty-four of the babies hadn't received salt supplementation and acted as a control group, while 22 of them did receive dietary salt supplements.
Although their salt levels were roughly the same at birth, by 14 to 25 days later, the infants who didn't receive salt supplements had significantly lower blood sodium levels. Thirty-eight percent were diagnosed with hyponatremia (low salt levels), compared to 18.2 percent of babies who received supplements.
The researchers followed up with 37 children from the low-salt group, 16 from the supplement group and 22 from the control group. The children, who were between the ages of 10 and 13 by the time of the follow-up, were tested during two 3½ hour sessions, using motor function exams that looked for balance and dexterity. The children also completed tests for language and cognitive function and behavior, as well as memory, learning and intelligence quotient (IQ).
Haycock found that children from the salt supplement group performed "significantly" better on tests of motor skills and intelligence. They also performed about 10 percent better on tests of memory and learning than the non-supplement group. And the children who didn't receive salt supplements were more likely to show signs of behavioral problems.
While the exact function of salt in neurodevelopment isn't clear, Haycock says there are several possibilities.
"In order to grow normally, you need sufficiency of all essential nutrients," he says. "If you're deficient in any one of these, that will not be compatible with normal growth."
But the researchers note that salt supplementation should not begin until roughly four to five days after birth, during which time newborns lose about 5 to 15 percent of their weight in fluids. Giving salt too early, the study says, could increase stress on heart and lung function and increase the risk of chronic lung disease.
Speer says current practices for preterm infants involve giving supplements that replace the salt loss, but stop short of giving extra salt.
And Haycock stresses that his group's findings don't suggest that healthy, full-term babies need extra salt in their diet. It wouldn't be beneficial for neurodevelopment, he says, and, in fact, could lead to an increased risk of high blood pressure in later life or even salt poisoning.
"This work that we've done applies only to very premature babies, and only for the first two weeks after birth," Haycock says.
He says that with improvements in modern medicine, infants born as early as 23 weeks into gestation can survive, although many have medical problems. He adds that future studies could look at salt and mineral balances in these children.
What To Do
Check out KidsHealth.org's primer on preemies, or read about the nutrient needs of premature infants at the Web site of the Nutrition Committee of the Canadian Paediatric Society.
Parents of a premature infant who need information or support can start their search using this list of Preemie Parent Support Groups.
