Feeding young babies solid foods such as crackers, cereals and bread, which tend to be high in salt, may set them up for a lifelong preference for salt, researchers reported Tuesday.
The study, published in the American Journal of Clinical Nutrition, suggests that efforts to reduce salt intake among Americans should begin early in life.
It is even possible, the authors said, that infancy contains a "sensitivity window" in which exposure to certain foods and tastes programs the brain to desire them in the future.
Americans' fondness for salt, a source of dismay for health experts, is well known. A 2010 report from the Institute of Medicine concluded that the average intake of 3,436 milligrams a day for Americans over age 2 is more than double what is recommended, and that new government standards are needed to reduce the salt content in processed and restaurant food.
But little is known about the biology behind our love affair with salt. Researchers don't even know what receptors are involved in tasting it. And though babies are born with a clear preference for sweet foods and an absolute distaste for bitter foods, they appear indifferent to salt in the first few months of life, said Leslie Stein, the lead author of the study and a senior research associate at the Monell Chemical Senses Center in Philadelphia.
"When you give 2-month-old babies salt water, they have no facial expression," Stein said. "This could mean that the baby doesn't detect the salt or just doesn't give a hoot about it."
To get at the issue, Stein and her colleagues first gave 61 healthy 2-month-old infants a mild solution of salt water: Based on facial expressions and how much they drank, the authors concluded the infants indeed were indifferent to the taste.
When the babies were 6 months old, they were brought back to the Monell clinic by their parents. They were presented with three bottles containing water, a mild salt solution or a slightly saltier solution. Researchers recorded how much fluid they drank from each bottle during a one-minute period — an indication of how much they preferred each solution.
Parents were also asked what, if any, baby food and table foods the children received. Table food is considered regular food that other members of the family might eat.
Almost half of the infants — 26 — had been exposed to starchy foods such as crackers, soft bread or cereal, which are often high in salt. During the bottle test, those babies consumed 55% more salt compared with babies who had not yet been exposed to these kinds of foods.
The scientists also reexamined 26 of the children at preschool age and surveyed their mothers about the children's salt preferences, such as whether they licked salt from foods, ate plain table salt or added salt to food before eating it. Children who had been exposed early to the starchy, salt-rich foods clearly had a greater liking for salt, they found.
"It's absolutely possible that exposure early on in life could change the way the salt taste signal is transmitted to the brain," said Dr. James F. Battey Jr., director of the National Institute on Deafness and Other Communication Disorders, which funded the study. "The brain is very plastic at that time of life."
The study doesn't prove this, however — it merely shows a correlation between early exposure and a taste for salt later on, Battey added. But if it turns out to be true, "then parents have a way of reducing the risk," he said.
Research on infant feeding practices has shown that babies will learn to like a food if exposed to it at least 10 times. But that doesn't mean they prefer a food, Stein said; they just learn to tolerate it.
And, Stein said, studies have also shown that babies are learning about the flavors in Mom's diet even before birth, in the uterus, as well as afterward through the taste of their mother's breast milk.
"This very early exposure helps them learn to like those flavors as well," Stein said.
The American Academy of Pediatrics recommends mothers breast-feed exclusively for the first six months and continue to breast-feed even after introducing solid foods. Doctors usually recommend introducing solid foods to babies about 6 months of age, but there are few rules over which foods to introduce first and which to offer later.
A 1990 Dutch study showed persistently higher blood pressure for children whose early sodium consumption was highest, said Dr. Stephen R. Daniels, chief of pediatrics at Children's Hospital Colorado, who was not involved in the new study.
"We don't have as much science as we want or need about the best way to introduce babies to solid food," Daniels said. "There's a tremendous opportunity to think of the period during which a baby is being introduced to solid foods as a time to get babies and toddlers on the road to the most healthful diet."
Times staff writer Melissa Healy contributed to this report.