If you have not already done so, please read Blog Posts 1 through 5 that describe how sleep is important and beneficial. I will post specific information for parents and children based on my book, “Healthy Sleep Habits, Happy Child.” Please do not be put off by my book’s length. This is a reference book. Read only the topic of interest to you.
The exact same 60 infants that I examined at 4 months of age were restudied at 3 years. Again, at age 3 years, temperamentally easy children had longer total sleep durations compared with children with more difficult temperaments (12.5 versus 11.2 hours). However, there was no individual stability of temperament traits (except for adaptability) and no individual stability of sleep durations between the ages of 4 months and 3 years. Thus, except for adaptability, temperament ratings and associated sleep patterns at age 4 months do not predict temperament or sleep patterns at 3 years.
At 4 months of age, infants with an Easy temperament had a total sleep duration of 15.6 hours.
At 4 months of age, infants with a Difficult temperament had a total sleep duration of 12.3 hours.
Between 4 months of age and 3 years of age, some parents put forth a great effort to help their child sleep well and other parents put forth less effort to help their child sleep well. Some children developed easier temperaments and some children developed more difficult temperaments.
Temperament Temperament Total Sleep Duration
At 4 months At 3 years at 3 years (hours)
Easy Remained Easy 12.4
Difficult Became Easy 12.0
Easy Became Difficult 11.8
Difficult Remained Difficult 11.4
Comparing my data between 4 months and 3 years, individual infants who were ranked as having brief sleep periods (12.3 hours) and difficult temperaments at 4-5 months and who were ranked as sleeping longer at 3 years (12.0 hours) had easier temperaments. But for 4-5-month-olds with brief sleep durations (12.3 hours) and difficult temperaments who also had brief sleep durations at age 3 years (11.4 hours), the difficult temperament persisted.
Similarly, individual infants who were ranked as having long sleep periods (15.6 hours) and easy temperaments at 4 months and later, at 3 years, were ranked as sleeping for shorter durations (11.8 hours) had more difficult temperaments, but for those 4-month-olds with long sleep durations (15.6 hours) and easy temperaments who also had long sleep durations at age 3 years (12.4 hours), the easy temperament persisted.
So, from 4 months to 3 years, longer sleep durations by age 3 years are associated with a trend towards easier temperaments, independent of sleep durations at 4 months. The opposite also occurs. Sleep modulates temperament! Remember, small increases in sleep durations can produce big benefits (Blog Post 6)!
Dr. John Bates agrees with my hypothesis that sleep modulates temperament and told me that “parenting responses to [sleep] issues would be involved in the continuity/discontinuity of temperament. If parents make the effort to manage their kids’ sleep schedules consistently, I would think that over the years they are going to see less difficult and unmanageable behavior.”.
A 2021 study described the benefits of giving parents a mobile app offering tailored sleep strategies to improve sleep. Over 7-14 days, ratings of difficult temperament decreased from 51% to 36%. “At follow up, care givers reported fewer moderate/severe sleep problems, improved child sleep patterns, better temperament and improved care giver mental health. Again, the percentage of care givers rating their child as ‘more difficult than average’ decreased from 51 to 36%.”
It appears that both nature and nurture contribute to sleep, temperament, and fussing/crying. I believe that how babies sleep does influence the development of temperament at 4-5 months of age. And how babies sleep during the first few months is a combination of factors within the child and the parents’ ability and skill at soothing and sleeping the infant. I also believe that at 4-5 months of age, the difficult temperament represents a post-colic or an overtired baby and the easy temperament represents a well-rested baby. However, temperament at 4-5 months of age is not like a fingerprint; it is not a permanent marker of your baby’s personality. Going forward, practicing healthy sleep habits will tend to make your child temperamentally easier:
You can ask yourself, what is the magical power of a nap that turns a raving, ranting, manic, and out-of-control toddler into a sweet Prince Charming?