The marketing of bacteria known as probiotics has done for the prokaryotic kingdom what Casper the Friendly Ghost once did for the underworld, convincing many Americans of the helpful benefits of forces unseen and mysterious.

Probiotics from the genus bifidobacterium are found in products such as yogurt and Gouda cheese, and are added to infant formula for myriad health benefits, including treatment for dyspepsia and — in the case of babies — colic and excessive crying. However, researchers from Australia now question the benefit of probiotics commonly added to infant formulas, saying that little evidence exists to support using probiotics, such as Lactobacillus reuteri, to manage colic in infants, particularly in those fed by formula.

Researcher Valerie Sung and her colleagues reviewed a dozen studies in the area involving more than 1,800 infants 3 months or younger, comparing probiotics with placebo. Five of the studies had examined the efficacy of probiotics in treating infant colic, while seven looked into prevention of the condition.

“There still appears to be insufficient evidence to support using probiotics [such as lactobacillus reuteri] to manage colic or to prevent crying in infants, especially in formula-fed babies, but it may be an effective treatment for crying infants who are breastfed exclusively and have colic,” Sung wrote.

In the review, half of the studies supported the efficacy of probiotics while half did not. However, three of the five trials supported the effectiveness of probiotics in treating breastfed infants, with one suggesting possible benefits to formula-fed infants with colic. One other study suggested that probiotics did not help breastfed babies with colic.

“Larger and more rigorously designed randomized clinical trials are needed to examine the efficacy of the probiotic l. reuteri in the management of breastfed and particularly formula-fed infants with colic and in the prevention of colic in healthy term infants,” Sung wrote.

Although most babies experience mild acid reflux, known to any parent as “spitting up,” researchers say such gastroesophageal reflux rarely causes a baby to cry. Fewer than five percent of infants crying excessively suffer from an underlying organic disease, such as gastroesophageal reflux disease or lactose intolerance, for example. Other conditions, such as anal fissures, subdural hematomas, and infantile migraine, also are unconnected to excessive crying, and the cause of colic remains unknown by medical researchers.

Source: Sung V, Collett S, De Gooyer T, et al. Probiotics To Prevent Or Treat Excessive Infant Crying: Systematic Review And Meta-Analysis. JAMA. 2013.