I recently posted on a study demonstrating a correlation between short sleep duration and attention deficit and hyperactivity disorder (ADHD). Momofcutie wrote in response:
The question about causation is interesting. I remember when the studies about the relationship between ADHD and sleep deprivation came out and my consequential anxiety about my toddler not getting enough sleep. Currently my almost 2 year old gets about 11 hours of sleep per day (anywhere between 9-10 per night and 1-2 hours for nap). She is constantly below the 12-14 hours of sleep recommended for her age. But where do these sleep recommendations come from? My child is very active and rambunctious but also in good spirits and rarely irritable. But could she be doing better if she was getting more sleep?
BTW, I tried the sleep training and she ended up climbing out of her crib and falling on the floor. I think I will need to wait to start the sleep training until she is transitioned to her toddler bed.
The question of how much sleep a child needs at a given age is a very good one, and the answer is not as straightforward as one might imagine. Many people have tried to look at this so as to be able to come up with age appropriate recommendations, but most have examined relatively small groups of children, which meant that they were either looking at certain, specific age groups of children, not at the entire spectrum between birth and adulthood (and we know there are huge differences seen in both sleep needs and patterns when comparing 2 week old infants with 16 year old teenagers), or were unable to control for individual variability within the age groups (and we also know that some people just naturally need more sleep than others).
In the February 2003 issue of Pediatrics, a Swiss group published its findings from a longitudinal study they had conducted looking at the sleep patterns of 493 children from Zurich, Switzerland, born between the years 1974-1978, and regularly followed from birth through the age of 16. Structured interviews were conducted every 3 months in the first year of life, every 6 months in the second year of life, and yearly thereon, through the age of 16. the children's parents were asked about nighttime bed and wake times, and about naps. The results were summarized both in chart form and graphically. The researchers found, for example, that 2 year olds were in bed on average 13.2 hours/24 hour day, with a range of between 10.8-15.6 hours/24 hour day (between the 2nd and 98th percentiles).
When looking at these data, however, it is important to remember that they reflect the amount of time the child is in bed, not asleep. There is also no mention of the correlation between time in bed and number of awakenings at night. Beyond a certain point, the more time one spends in bed, the more likely it is that one will wake up at night, and this is one of the principals utilized to help children to sleep through the night: the stronger the sleep pressure is, the more likely a child is to stay asleep. It is akin to what would happen to you, dear reader, if you were put in a bedroom for 16 hours and asked to lie down and go to sleep. Unless you were severely sleep deprived, you would sleep 8, 9, 10 hours, and then wake up and start to look for something to do (read a book, watch TV, exercise), because you simply would not be able to sleep any longer. So it may be that some of the children whose parents reported were in bed for longer periods across the day were waking up more, and not actually sleeping for their entirety. Nonetheless, their findings give a good starting point to get a rough sense of what a child's sleep needs are at any given day.
In order to assess what a specific child's sleep needs are, I ask parents to keep detailed sleep diaries for 4-6 weeks, recording when the child's "lights out" time is, when s/he actually falls asleep, the number of awakenings at night, the child's "wake up" time, the time the child actually gets out of bed, naps, other sleep (such as dozing in the car), and whether the child arouses spontaneously or needs to be awakened in the morning and/or at the end of naps. When there is concern about a child needing too much or getting too little sleep, I usually recommend starting off with the average sleep needs and breakdown (nighttime sleep versus naps) for the "average child" that age, and instruct the parents on how to make adjustments based upon the patterns that unfold. When I sit down with them after the diaries are completed and review them, it usually turns out that the parents had either been underestimating their child's sleep patterns (not counting car sleep, for example, or naps in daycare), or overestimating them, assuming for example that their child was falling asleep immediately after being put to bed instead of playing quietly by herself, simply because she was not crying out for them.
I'll discuss the jumping out of the crib in my next posting.
The reference for the study cited above is as follows:
Ivo Iglowstein, Oskar G. Jenni, Luciano Molinari, and Remo H. Largo
Sleep Duration From Infancy to Adolescence: Reference Values and Generational Trends
Pediatrics, Feb 2003; 111: 302 - 307.
