Sleep is often a major factor in the decision between formula feeding and breastfeeding. Many believe that formula takes longer to digest, and therefore allows babies to sleep longer. However, a new study from the University of West Virginia has found that there is in fact no difference. These findings debunk the myth that breast-fed babies do not sleep well.

The study, which was led by Hawley E. Montgomery-Downs, PhD, studied mothers who were exclusively breastfeeding, exclusively formula feeding or combined both methods. Researchers found that the average new mother will get approximately 7.2 hours of regularly interrupted sleep per night, regardless of what methods she uses to feed her baby.

Ms. Montgomery-Downs explained that the findings could be due to a number of things. The unexpected finding that both methods produce similar outcomes could be due to the fact that earlier studies showing that formula-fed babies slept longer were simply wrong. Another possibility comes from the hormone prolactin, which is released during breastfeeding.

Prolactin has a sleep-inducing effect, such that even if a mother is woken up she will sink quickly back into sleep afterwards. It is also possible that even if bottle-feeding does make babies sleep longer, the effort of preparing it is more disruptive to sleep, thus compensating for the additional time in which the baby is not awake.

Ms. Montgomery-Downs said that the findings present “good information not be able to tell women [that] not breastfeeding is not going to help you get better sleep”.