Using lactase to lower the lactose content of breast milk or formula may be of some benefit if the lactase is given time to incubate in the milk before the feed is given.

• In one double-blind crossover study, 12 breastfed infants were given either lactase or placebo within 5 minutes of starting the feed [Miller et al, 1990]. There was no significant difference in total daily crying time between treatments.
• Another crossover study gave 10 bottle-fed infants cow's milk formula or pooled breast milk that had been pre-treated (and then frozen) with lactase or placebo [Stahlberg and Savilahti, 1986]. There was no significant difference between lactase and placebo in the number of days when colic was present. The duration of each colic episode was not reported.
• One randomized double-blind crossover study (funded by industry) of 13 bottle-fed infants found that lactase (added to the feed 24 hours before it was given) reduced daily crying time by about 1 hour compared with placebo [Kearney et al, 1998].
• A further randomized double-blind crossover study (funded and co-authored by industry) enrolled 53 infants [Kanabar et al, 2001]. For bottle-fed babies, two drops of lactase (or placebo) were added to bottle feed 4 hours before it was given. For breastfed babies, mothers were instructed to express a small amount of milk into a sterile container before starting a feed. Four drops of lactase (or placebo) were added to the expressed milk, the baby was breastfed as usual, and the treated milk was given to the baby at the end of the feed. Intention-to-treat analysis of the 46 infants with available data did not show a significant difference in crying time between babies given lactase or placebo. However, a significant difference was found when the 14 babies whose mothers were non-compliant were excluded from the analysis.