When it comes to soothing preterm newborns' pain during medical pokes and prods, sugar water seems at least as good as breast milk, according to two studies published Monday.
Right now, there are guidelines recommending sugar water or breast milk for relieving newborns' pain during minor, but painful, medical tests.
But researchers are still trying to figure out the best way to ease infants' pain -- especially for preemies, who generally undergo more medical tests in their first days of life.
In one of the new studies, reported in the journal Pediatrics, researchers found that sugar water and breast milk seemed to have similar effects on preemies' pain during heel sticks -- which are done to get blood samples for various newborn tests.
But in the other study, also appearing in Pediatrics, sugar water seemed more effective than breast milk.
The researchers on the second study say that doesn't necessarily mean breastfeeding offers preemies less comfort during heel sticks.
One issue is that the study tried to isolate the possible effects of the milk itself, explained lead researcher Mariana Bueno, of the University of Sao Paulo in Brazil.
So the infants received breast milk via drops onto the tongue, rather than actually nursing.
"Breastfeeding is an acknowledged intervention for (newborn) pain relief, and it combines the presence of the mother, skin-to-skin contact, diversion of attention and sweet taste," Bueno told Reuters Health in an email.
In contrast, infants in the other study actually breastfed or, in cases where they were already bottle-feeding, had breast milk dropped into the mouth. But they were still given something to suck on during the heel stick.
"It is very likely that the results were related to the combination of breast milk and sucking," Bueno said.
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In their study, Bueno and her colleagues randomly assigned 113 "late" preemies -- born between the 34th and 36th weeks of pregnancy -- to either have sugar water or breast milk right before a heel stick. The liquid was dropped onto the infants' tongues.
The babies' faces were filmed during the procedure, and the researchers used a standard scale to "score" each infant's pain reaction -- looking at things like grimacing, heart rate and blood oxygen levels.
Overall, the sugar solution appeared more effective than breast milk: 60 percent of preemies who got sugar had a score in the "minimal" pain range, versus one-quarter of babies given breast milk.
The second study used a similar approach. Dr. Eva Simonse and colleagues at Amphia Hospital in Breda, the Netherlands, randomly assigned 71 preemies to get breast milk or sugar water during a heel stick.
Infants who got breast milk either nursed or, if they were already being bottle-fed, had breast milk given through a needle-free syringe. And regardless of whether they got breast milk or sugar water, all of the infants had something to suck on during the heel stick.
In the end, the average pain score in both the breast-milk and sugar-water groups fell in the minimal range.
According to Bueno, the fact that babies in this study were allowed to suckle may explain why the results differed from her team's findings.
"It is well documented," she said, "that sucking provides analgesic effects in (newborns), especially when combined with sweet solutions or milk."
But breast milk itself may also have pain-soothing qualities. It's thought, Bueno noted, that some of the fats, proteins and sugars in breast milk influence newborns' "reactivity" to pain.
One of the main reasons her team was interested in the effects of expressed breast milk, rather than breastfeeding, is because some preemies are not yet able to breastfeed.
And it may just take a bigger dose of milk, or giving it in a different way, to get a greater pain-relieving effect.
"We recommend further research on the role of expressed breast milk," Bueno said, "especially exploring the combination of breast milk with other interventions -- such as skin-to-skin contact or sucking -- for newborns (preterm mainly) who may not be mature enough or clinically stable enough to benefit from breastfeeding's analgesic effect."