A recent report shows that an infant who spends time outdoors in the early afternoon is more likely to sleep well at night than an infant who remains indoors. Noting that light is an important regulator of the circadian system, investigators examined the relationship among daytime exposure to light, developing sleep-wake patterns, and excessive crying in young infants. They monitored 56 babies across three consecutive days at 6, 9, and 12 weeks of age, using parents' diary of behavior, an ankle device to monitor activity, and a light monitor mounted near the baby at all times.
As babies grew older, they gradually slept less overall and shifted their sleeping toward night, spending more of the day awake. They also became more active during the day than at night. Babies cried more at 6 weeks of age than at 9 or 12 weeks of age; at all ages, crying tended to peak in early evening. Compared with infants who didn't cry much, babies who cried a lot in early evening at 6 weeks tended to sleep less at night (and throughout each 24-hour period). Light exposure was not associated with how much, or when, babies cried but had a significant effect on how well they slept at night. Good sleepers were exposed to significantly more light in the early afternoon than those who slept poorly (Harrison Y: J Sleep Res 2004;13:345).
Commentary: I wonder if a baby in a sunny city is a better night sleeper. Sleepless in Seattle?