For years, hospitals have been giving sugar water to newborns about to undergo short, potentially painful procedures, on the assumption that the sweet drink would ease the little ones' pain.

A new study based on brain imaging of newborns casts doubt on that notion.

The sugar water may be only affecting babies' facial expressions, not dampening their pain, researchers from University College London say.

"All of us feel bad if we have to hurt a baby. The baby does, we do, the parents do. But if this is only masking what's going on, we need to think about it carefully," said Dr. Judith Meek, a neonatologist at the College Hospital who was a study researcher.

Sugar water has been given to babies all over the world since the early 1990s, Meek said, and is generally used when health care professionals need to lance a heel (to draw blood for testing), put in intravenous tubes or conduct a spinal tap on an infant less than 3 months old. The soothing effect is thought to last about two minutes, she said.

Many studies have found that infants given sugar water make faces indicating they're not feeling as much as pain as infants who are given regular water, Meek said, and the practice has been well accepted by those who work with babies.

The new finding may be most important for babies who are not well and need such procedures performed several times each day, Meek said.

"If you have painful procedures done repeatedly while the brain is developing, the brain will change," she told MyHealthNewsDaily. This could affect pain perception in the long term.

"If we think we're having an impact and we're not, that's worrying," she said.

In the study, 59 newborns received either sugar water or regular water prior to having a heel lanced. From electrodes placed on the babies' heads, the researchers measured the brainwaves of the lanced infants via electroencephalography (EEG). The researchers also used a standard test that rated babies' facial expressions, heart rates, breathing rates and cries.

According to the standard scoring system, the faces of the babies who received the sugar solution indicated that they were in less pain. However, the EEGs showed that the brain waves were no different between those babies and the ones given plain water.

"We measured what was actually going on in the brain's cortex – the actual processing of pain. We felt that was more objective than the standard scoring," Meek said. The findings appear in the current issue of the journal The Lancet.

Other researchers were less convinced. Robert Lasky, a researcher in pediatrics at the University of Texas Medical School at Houston, wrote in The Lancet that the trial was too small to draw definitive conclusions, and he pointed out the tests did not include sick newborns who may be subjected to multiple painful procedures.

Meek said that if she now had a baby undergoing a heel lance, she would hold or nurse it during the procedure rather than give it sugar water. The study was large enough, she said, to show that there was a significant difference in the babies' facial expressions, so if there was a meaningful difference in the babies' brainwaves, that too would have been shown.

This article was provided by MyHealthNewsDaily, a sister site to LiveScience.