A recent study from La Trobe University suggests a surprising link between a mother’s shift work and the hormones present in her breast milk.

The research, led by Dr Lauren Booker, found that mothers who worked multiple night shifts in a row had lower levels of melatonin in their breast milk compared to days they weren’t working.

Breast milk naturally follows a 24-hour cycle, with melatonin levels peaking at night and remaining low during the day. Melatonin is a hormone known to regulate sleep-wake cycles.

Newborn babies haven’t yet developed their own circadian rhythm, and researchers believe the melatonin in breast milk may play a role in helping them establish healthy sleep patterns.

“If the timing of these hormones in breast milk is disrupted,” Dr Booker said, “it could potentially have a negative impact on an infant’s sleep, digestion, and development.”

The findings from this study add to previous research suggesting that feeding a baby breast milk expressed at the wrong time of day can disrupt their sleep. Dr Booker emphasised the importance of this research as more mothers return to work early after childbirth, particularly in healthcare fields with high shift work demands.

“This is an important first step. It shows there’s a good chance that a mother’s circadian rhythm being disrupted by shift work can affect the hormones in her breast milk,” Dr Booker said.

The study involved 11 mothers who were shift workers. Participants collected breast milk and saliva samples throughout the day for five days.