With data from over 1000 infants, we are excited to share with you some updated results from the NYU Baby Sleep Study. So far, parents and caregivers have logged a total of 6.1 million entries, including 1.4 million sleep events, 2.3 million eating events, and 1.4 million diaper changes. We’ve started by looking at how sleep, eating, and digestion change with age from newborn to 12 months.
The first four charts below show the proportion of sleep and eating events logged throughout the 24-hour period at months 1, 4, 8 and 12. In other words, at which points in the day or night are sleep and eating events logged? Each chart corresponds to a different age and shows results for sleeping (blue) and eating (red). The x (horizontal)-axis is time of day/night (24-hour clock). The y (vertical)-axis is the proportion of sleeping or eating events logged during each 1-hour period. For example, if sleeping events were logged at random times, then we would see a flat blue line meaning that the same number of events (proportion = 0.04) were logged each hour.
1 month old: Eating and sleeping is logged uniformly throughout the 24 hours with no indication of circadian rhythm. There’s no pattern discerning day and night for infants at this age.
4 months old: More sleeping and eating events are logged during the daytime (8am to 9pm) than at nighttime (e.g., midnight). But we cannot tell (yet) whether this is because of the emergence of a circadian rhythm in the infants. It might instead reflect behavior of the parents and caregivers. Parents and caregivers might be more likely to log a sleep or eating event during the daytime. We’ll be working toward teasing these two things apart.
8 months old: A pattern begins to emerge. There are 3 peaks in sleep at 3 points in the day: 9:00 (9am), 13:00 (1pm) and 20:00 (8pm). There are 2 peaks in eating at 2 points in the day: 7:00-8:00 (7-8 am) and 19:00 (7pm). The peaks in eating precede the peaks in sleeping. This means that 8 month old infants are beginning to show a typical schedule for their day. They eat at around 8:00 followed by a nap. Eating is logged uniformly during the day between the first and last meals. In other words, 8 month olds are eating at random times between their first and last meal of the day. There is a dip in the blue curve at about 18:00 (6 pm) indicating that infants sleep less at that time, followed by dinner at about 19:00 (7 pm), and bedtime at about 20:00 (8 pm). There are consistently fewer events logged overnight from midnight to 6 am.
12 months old: The pattern that began to emerge at 8 months becomes more evident. The 3 peaks in sleep are more pronounced, as are the 2 peaks in eating. There is an eating peak beginning to emerge at 12:00 (noon), prior to the second sleeping peak at 13:00(1pm). It is more evident that the eating peaks precede the sleeping peaks. The eating peaks occur at 7:00-8:00, 12:00, and 19:00-20:00 (7-8 pm). The sleeping peaks occur at 10:00, 15:00 (3 pm), and 20:00 (8 pm). And there are very few events logged from midnight to 6 am.
The chart (below) shows how long an infant is sleeping each time he or she falls asleep as the first year of life progresses. The x-axis is age in months. The y-axis is sleep bout duration in minutes. The red curve is nighttime sleep (8 pm to 8 am). The blue curve is daytime sleep (8 am to 8 pm). The shading surrounding each curve is the variability, or range, of reported sleep bout durations across infants in the study.
Nighttime hours (in red) steadily increase from 2 hours to a little under 8 hours by the end of the first year. The variability across infants for nighttime sleep bout duration is greater than that of daytime.
Daytime hours (in blue) slightly decrease from the first to the fifth month then remain relatively constant with infants napping, typically, for one hour at a time during the day.
The chart (below) shows the total amount of sleep per day, and how it changes with age. The x-axis is again age in months. The y-axis is the total amount of sleep during each 24-hour period in minutes. The red curve is nighttime sleep (8 pm to 8am). The blue curve is daytime sleep (8:00 to 20:00). The grey curve is all sleep (nighttime plus daytime). The grey curve increases until three months and remains pretty flat after three months, meaning that the total amount of sleep during a 24-hour period remains relatively constant over the year. But the red curve increases while the blue curve decreases, meaning that infants sleep increasingly more during the night and less during the day. In other words, a circadian rhythm develops as the first year of life progresses.
The chart (below) shows the proportion of diaper changes logged during a 24-hour period. The x-axis is time of day (24-hour clock). The y-axis is proportion of diaper changes. The different colors correspond to different ages from 1 month (dark red) to 12 months (yellow).
1 month old: Diaper changes are logged almost equally throughout the 24 hour day. There are more diaper changes during the daytime (8 am to 8 pm) than at nighttime (midnight to 6 am) but this difference between daytime and nighttime is small.
4 months old: The difference between daytime and nighttime becomes more evident with a much higher proportion of diaper changes during the daytime then at nighttime. This pattern may have more to do with parent and caregiver schedules than infant digestion. Parents and caregivers might be more likely to change a diaper during the daytime and/or they might be more likely to log a diaper change during the daytime.
8 months old – 12 months old: Two peaks emerge, one at about 8:00 (8 am) and the other at about 20:00 (8 pm). Parents and caregivers are logging the greatest proportion of diaper changes in the morning when their infant wakes up and, in the evening, just before bedtime. This coincides with the morning feedings as well as evening feedings and bedtime shown in the first set of charts above. But again, this reflects both infant digestion and the behavior of parents and caregivers. We’ll be working toward teasing these two things apart.