Circadian Rhythms in Infants

Objectives

After completing this article, readers should be able to:

1. Describe how circadian rhythms are generated.

2. Describe how lighting influences the circadian system.

3. Delineate the period during which the origin of circadian rhythms develops.

4. Describe the relationship between maternal circadian rhythms and the development of circadian rhythms in infants.

5. Characterize the potential sequelae of impaired fetal and early neonatal circadian rhythms related to sleep patterns.

6. Describe beneficial lighting patterns for preterm infants in the neonatal intensive care nursery.

Biology of Circadian Rhythmicity in Infants

Circadian rhythms are endogenously generated rhythms that have a period length of about 24 hours. Evidence gathered over the past decade indicates that the circadian timing system develops prenatally, with the suprachiasmatic nuclei (SCN) in the anterior hypothalamus, the site of a circadian clock, present by mid-gestation in primates. Recent evidence also shows that the circadian system of primate infants is responsive to light at very early stages (as early as 25 to 28 weeks’ gestation in humans) and that low-intensity lighting can regulate the developing clock. After birth, circadian system outputs mature progressively, with rhythms in sleep-wake cycles, body temperature, and hormone production generally developing between 1 and 3 months of age. The importance of light in regulation of circadian rhythm in infants is highlighted by the early establishment of rest-activity patterns that are in phase with the 24-hour light-dark cycle in preterm infants exposed to low-intensity cycled lighting. With the continued elucidation of circadian system development and influences on human physiology and illness, it is anticipated that consideration of circadian biology will become an increasingly important component of neonatal care.