Although urban legend claims formula fed babies sleep longer, there is no scientific evidence to support this. The few studies that have been done to compare the sleep of breastfed and formula fed babies do not show a statistically significant difference. Anecdotal evidence from parents around us also gives varying reports. Many formula feeding parents are equally sleep deprived and exhausted. Some do testify to longer stretches of sleep. However, there are several other parenting practices that are not accounted in these cases and so it is difficult to draw any solid conclusions.

Formula is heavier than breastmilk and takes longer to digest. While this can lead to some longer stretches of sleep in the newborn stage when baby tummies are really very small, the heaviness of formula can also cause stomach troubles like gas which can disturb sleep. Furthermore, the link between a full stomach and long hours of sleep is not strong. If it was, the introduction of solids would ensure breastfed babies too slept longer hours, which doesn’t happen.

In fact, breastmilk contains the sleep hormone melatonin, which induces sleep.

Breastfed babies wake more easily from active sleep, perhaps due to the sleep hormones. And while this makes them more prone to nightwakings, it is also probably what contributes to the lower risk of SIDS recorded amongst breastfed babies.

Studies show that, while breastfed babies may be waking more, breastfeeding mums report more sleep. Nursing mothers benefit from high levels of sleep-inducing hormones like prolactin, experience more than double the normal duration of nocturnal slow wave sleep, and may be able to sleep during night-time feeds, if they bedshare and nurse lying down.

Babies sleep longer hours/ sleep through the night when they are developmentally ready for it. They wake for several reasons at night – at the end of sleep cycles or due to some internal or external factor that they are incapable of regulating on their own. No single factor, like milk source, can override this developmental trajectory.