Can a Little Extra Salt Help Premature Babies Grow? Two New Studies Weigh In

What the 2025–2026 sodium-supplementation trials from India and Indianapolis mean for families of premature babies

Premature babies often struggle to grow as quickly as they would have inside the womb, and doctors have long searched for safe ways to help. Two new clinical trials tested a simple, inexpensive idea: giving tiny babies a measured amount of extra salt (sodium). One trial found that extra salt helped babies gain weight faster; the other found that, by the time babies reached the equivalent of about eight months of pregnancy, the salted and unsalted groups had ended up about the same. Read together, the studies tell a reassuring and useful story about what salt can and cannot do.

Two recent clinical trials — one from South India [1] and one from Indianapolis [2] — put this salt idea to the test, which is what this article walks through.

Why growth is such a big deal for premature babies

When a baby is born many weeks early, the hospital's job is partly to recreate what the womb would have provided — including nourishment for fast growth. Yet even with modern nutrition, many premature babies grow more slowly than expected and leave the hospital smaller than doctors would like [3]. This is not just about size. How well a premature baby grows in the first weeks is connected to how the brain develops later: babies who get enough nourishment early tend to do better on developmental tests as toddlers [4], and growth in length in particular seems especially tied to two-year brain development [5]. So anything that safely improves early growth is worth studying carefully.

For a long time, doctors focused mainly on protein and calories. Salt was often something they tried to limit, worried it might cause fluid buildup or strain on the lungs. But there is a catch rooted in how a premature baby's body works. The kidneys, which control how much salt the body keeps, are not finished developing until around 34 to 36 weeks of pregnancy. Until then, a premature baby's kidneys leak sodium into the urine, sometimes losing more than the baby takes in [6]. When the body runs low on sodium, growth can stall — sodium turns out to be one of the building blocks cells need to multiply and grow [7]. In other words, a premature baby can be eating enough calories and still be held back by a quiet salt shortage.

The problem families and doctors faced before these studies

For decades, this left neonatal teams in an awkward spot. The biology suggested that many premature babies were probably short on sodium, and a handful of small studies going back years hinted that adding salt might help them grow [8]. But the evidence was thin and inconsistent, so official guidelines could only offer a wide range — roughly 3 to 8 units of sodium per kilogram of body weight per day — without saying confidently who needed extra or how much [9]. Complicating matters, the milk premature babies drink, including fortified breast milk, often does not contain enough sodium for their needs [10]. Families rarely heard about any of this, because it played out in the fine print of feeding decisions. Two carefully designed trials set out to give clearer answers.

The two studies

The first study was done at a hospital in southern India and was a "double-blind" trial — the gold standard in which neither the parents nor the bedside nurses and doctors knew which babies were getting extra salt and which were getting a look-alike placebo [1]. It enrolled babies born between 25 and nearly 31 weeks of pregnancy once they were tolerating enough milk feeds, and gave the treatment group a fixed daily dose of extra sodium mixed into their feeds until they reached about 34 weeks' corrected age. The main thing the researchers measured was how fast the babies gained weight.

The second study was done across four neonatal units in Indianapolis, in the United States [2]. Instead of giving every baby extra salt, it tested a smarter, more targeted plan: doctors measured the amount of sodium in each baby's urine every two weeks, and only added salt to the babies whose results showed they were running low. The researchers tracked growth in weight, length, and head size all the way to about 36 weeks' corrected age, and even used a special "labeled water" technique to measure body composition. In this study, the parents and staff knew which plan each baby was on.

What the studies found

The Indian trial found a clear benefit. Babies who got the extra salt gained weight noticeably faster and also grew longer faster than the placebo group, with the difference showing up from about the third week onward [1]. They were also only half as likely to develop low blood sodium levels that needed emergency correction. Just as importantly, the extra salt caused no apparent harm — no extra problems with feeding, the intestines, or dangerously high sodium levels.

The Indianapolis trial found something more nuanced. Its targeted plan did successfully get more sodium into the babies who needed it — and it confirmed the underlying problem, since nearly 9 out of 10 babies in the monitored group turned out to be low on sodium at some point [2]. At first, the extra-salt babies did gain weight faster, just as in the Indian study. But over the following weeks the comparison babies caught up, so that by 36 weeks' corrected age the two groups were about the same size, with no lasting difference in weight, length, head size, or body composition. Reassuringly, this study also found no extra health problems from the added salt.

Making sense of two "different" answers

At first glance the studies seem to disagree, but they actually agree on the important things. Both confirmed that premature babies are frequently short on sodium. Both found that extra salt speeds up early weight gain. And both found that the doses used were safe. The real difference is about the finish line each study chose. The Indian study measured how fast babies grew over the whole period and stopped its clock at 34 weeks, when the salt group was still pulling ahead. The Indianapolis study waited until 36 weeks to compare final sizes, by which point the slower-starting babies had caught up. So the same underlying effect — a real but temporary early boost — looked like a "win" measured one way and a "tie" measured the other. The Indianapolis researchers also noticed that week-to-week weight gain lined up more closely with calories than with salt, a helpful reminder that salt is a supporting player, not a replacement for good overall nutrition.

It also helps to picture what "running low on sodium" actually looks like day to day. A premature baby whose kidneys are leaking salt may keep drinking normal amounts of milk and taking in plenty of calories, yet the scale barely moves — because without enough sodium, the body cannot build new tissue efficiently. Correcting the shortage does not add water weight (the Indianapolis team confirmed this using their body-composition measurements, which showed no extra fluid), so the early weight gain reflects real growth rather than puffiness. That distinction matters to parents who worry that "more salt" means their baby is retaining fluid; the evidence says it does not.

What this means for families and their baby's care

If your premature baby is receiving extra sodium, these studies offer reassurance on two fronts: it is a low-cost, well-tolerated addition, and it helps prevent the low-sodium levels that can otherwise require more aggressive treatment. The doses studied fit comfortably within existing nutrition guidelines [9], and follow-up research has not linked this kind of supplementation to later high blood pressure [11]. At the same time, families should keep expectations realistic. The clearest, most consistent benefit is faster early growth and fewer low-sodium episodes — not a proven improvement in long-term brain development. The only long-term hint comes from an older study that followed salt-supplemented premature babies to ages 10 to 13 and found somewhat better developmental scores [12], but that single study is not enough to promise anything. These are questions worth asking your baby's care team, who can explain how your unit approaches sodium and why.

What researchers are working on next

The most important next step is a larger, blinded study that follows children for two years or more to see whether correcting sodium shortages early actually helps the brain and body over the long run — not just in the first weeks. Researchers also want to agree on a single, fair way to measure "growth" so that future studies do not end up talking past each other the way these two nearly did, and to study the very smallest babies (born before 25 weeks), who lose sodium for the longest time. For now, the takeaway is encouraging: making sure premature babies are not quietly running low on salt is safe, helps them grow sooner, and is an easy, inexpensive part of good neonatal nutrition.

References

  1. Amiti A, Balakrishnan U, Devi U, Amboiram P, Salahudeen AG. Effect of early sodium supplementation on weight gain of very preterm infants: a randomised controlled trial. BMJ Paediatr Open. 2025;9(1):e003444. doi:10.1136/bmjpo-2025-003444 ↩
  2. Liberio BM, Sokol GM, Rakow M, et al; Segar JL. Sodium supplementation algorithm to promote growth in infants who are preterm: randomized clinical trial. Pediatrics Open Science. 2026;2(1):1. doi:10.1542/pedsos.2025-001089 ↩
  3. Horbar JD, Ehrenkranz RA, Badger GJ, et al. Weight growth velocity and postnatal growth failure in infants 501 to 1500 grams: 2000–2013. Pediatrics. 2015;136(1):e84–e92. doi:10.1542/peds.2015-0129 ↩
  4. Stephens BE, Walden RV, Gargus RA, et al. First-week protein and energy intakes are associated with 18-month developmental outcomes in extremely low birth weight infants. Pediatrics. 2009;123(5):1337–1343. doi:10.1542/peds.2008-0211 ↩
  5. Ramel SE, Demerath EW, Gray HL, et al. The relationship of poor linear growth velocity with neonatal illness and two-year neurodevelopment in preterm infants. Neonatology. 2012;102(1):19–24. doi:10.1159/000336127 ↩
  6. Segar JL. Renal adaptive changes and sodium handling in the fetal-to-newborn transition. Semin Fetal Neonatal Med. 2017;22(2):76–82. doi:10.1016/j.siny.2016.11.002 ↩
  7. Haycock GB. The influence of sodium on growth in infancy. Pediatr Nephrol. 1993;7(6):871–875. doi:10.1007/BF01213376 ↩
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  9. Embleton ND, Moltu SJ, Lapillonne A, et al. Enteral nutrition in preterm infants (2022): a position paper from the ESPGHAN Committee on Nutrition and Invited Experts. J Pediatr Gastroenterol Nutr. 2023;76(2):248–268. doi:10.1097/MPG.0000000000003642 ↩
  10. Perrin MT, Friend LL, Sisk PM. Fortified donor human milk frequently does not meet sodium recommendations for the preterm infant. J Pediatr. 2022;244:219–223. doi:10.1016/j.jpeds.2022.01.029 ↩
  11. Petersen RY, Clermont D, Williams HL, Buchanan P, Hillman NH. Oral sodium supplementation on growth and hypertension in preterm infants: an observational cohort study. J Perinatol. 2024;44(10):1515–1522. doi:10.1038/s41372-024-02088-x ↩
  12. Al-Dahhan J, Jannoun L, Haycock GB. Effect of salt supplementation of newborn premature infants on neurodevelopmental outcome at 10–13 years of age. Arch Dis Child Fetal Neonatal Ed. 2002;86(2):F120–F123. doi:10.1136/fn.86.2.f120 ↩