Abnormal gut bacteria could play a role in why some babies cry excessively and others don't, a new study has found.
Researchers have identified a distinct bacterial "signature" in the guts of infants with colic, a term that describes babies who cry for more than three hours a day without a medical reason.
In the first few weeks of life, colicky babies had higher numbers of bacteria from a group called Proteobacteria in their guts compared to babies without colic, website MyHealthNewsDaily reported.
"Proteobacteria include bacteria known to produce gas, which may cause pain in infants and lead to crying," said study researcher Carolina de Weerth, a developmental psychologist at Radboud University Nijmegen in the Netherlands.
Colicky babies also had lower numbers of bacteria from other groups, called bifidobacteria and lactobacilli.
"The members of these groups can have anti-inflammatory effects, which may reduce gut inflammation and pain," de Weerth said.
"For a long time, many researchers and professionals have believed that colic could just be one extreme of the normal crying curve in young infants," de Weerth told the website.
"This study shows how, at least in some cases of colic, abnormalities in early colonisation of the infant intestines may lead to colic behaviour," de Weerth said.
The abnormalities in gut bacteria appear to disappear after the first few months of life, suggesting they are temporary.
Previous studies had suggested differences in gut bacteria may be involved in colic, but these studies had typically included infants who were more than 6 weeks old, past the peak time for colic.
The new study examined 12 colicky infants and 12 normal infants, periodically looking at stool samples from birth until the babies were 100 days old.
Researchers chose these 24 subjects from a larger group because, at age 6 weeks, they displayed the highest or lowest levels of daily crying.
They analysed stool samples for the presence of more than 1,000 different kinds of bacteria.
The results also showed bacteria were slower to colonise the guts of colicky babies compared to normal babies.
Dr William Muinos, co-director of the gastroenterology department at Miami Children's Hospital, said the findings made sense because the type of bacteria in the gut are known to affect gas production and bowel movements, which could cause crying.
However, Muinos said more things likely contribute to colic, with gut bacteria just one factor among many.
The study was published in the journal Pediatrics.
