The role of breast milk in the formation of the newborn’s circadian rhythm

Circadian rhythm, also called the biological rhythm, refers to the repetition of an individual's 24-hour biochemical, physiological, and behavioral cycles. The sleep wake cycle is the most basic circadian rhythm. The hormones that play a key role in regulating it are cortisol and melatonin. In the first years of life, breast milk plays an important role in the formation of the circadian rhythm and helps the newborn adapt to its new environment outside the womb. The composition of breast milk is quite variable, and this variability provides the baby with clues about the outside world. Breast milk secreted during the day has a high lactose content, which provides energy for the baby, improves learning ability, and quenches thirst. Breast milk secreted at night has a lower lactose concentration but higher fat and melatonin concentrations. In the case of feeding with expressed milk, the time of expression and the time of feeding should align to maintain the sleep-wake cycle.