In a study of 41 children and teenagers who had been born prematurely, researchers found that those who'd had low sodium levels in their blood at birth had a particular fondness for salty food.
In tests where the children could choose from salty or sweet snacks, those born with low sodium levels reached for a salty snack more often. 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.
High salt intake is considered a marker for the risk of obesity, possibly because it signifies a person's consumption of calorie-dense processed foods.
It's too soon, however, to say that sodium deficiency early in life is a risk factor for obesity, according to study co-author Dr. Micah Leshem of the University of Haifa in Israel.
"There is insufficient evidence for parents to take a preference for salty food resulting from early sodium loss, of itself, as a predictor of weight gain in their children," Leshem told Reuters Health.
All of the children in the study had been born prematurely, which increases the chances that a newborn will have low blood sodium levels. Low birth weight itself is thought to promote excessive weight gain later in life, Leshem pointed out, offering a "better explanation" for the link between early sodium deficiency and childhood weight.
He and his colleagues report their findings in the American Journal of Physiology – Regulatory, Integrative, and Comparative Physiology.
Premature newborns are at greatest risk of sodium deficiency at birth and soon after, although it's also sometimes seen in full-term infants – particularly those with risk factors such as kidney dysfunction.
A number of factors, both before and after birth, can contribute to early sodium loss, Leshem noted.
Before birth, severe maternal vomiting can deplete fetal sodium, for example; after birth, infant vomiting or diarrhea, and infant formulas lacking electrolytes are among the potential causes.
This is not the first study to link low sodium levels in early life to a bigger "salt appetite" down the road, Leshem said. Other research suggests early sodium loss can affect salt preferences even into adulthood.
The current findings, Leshem's team writes, "accentuate the importance of monitoring and balancing sodium levels in premature babies."
But they also hint at the mechanisms that influence people's salt intake, pointing to a direction for future research, Leshem noted. "And that," he said, "is relevant to all of us, not just premature babies."
Source: American Journal of Physiology – Regulatory, Integrative, and Comparative Physiology.