It’s pretty clear to any parent that getting enough sleep is critical for children in terms of behavior. Delaying bedtime by an hour can have some major league consequences: tantrums, acting out, etc. What is becoming more and more clear is that not getting enough sleep on a regular basis has been associated with obesity. More importantly, early childhood sleep reduction is associated with obesity years later.
This is especially troubling as children are become more obese and sleeping less than they used to. When you think about it, it’s not surprising that there might be a relationship. What is especially remarkable is that of the 20 or so studies published, all of them demonstrate an association between short sleep and obesity. Let’s look at an example.
This study, by Elsie Taveras MD/MPH and colleagues, looked at the relationship between short sleep in infancy and weight at age three years. They asked mothers how long their children slept at ages 6 months, 12 months, and 2 years, then looked at a measure of weight called the body mass index which is a measure of height and weight, and a good way to estimate whether weight is happy or not. They found that short sleep (<12 hours/day) in the first two years of life doubled the risk of obesity at age 3. They performed some statistical manipulation to exclude other factors such as gender, race, and ethnicity. The also found that television viewing over 2 hours per day drastically increased this effect.
What I find so compelling about this study is the fact that sleep in early childhood has a direct effect later on weight. Parents can control the sleep patterns of children in that age group in a way which is more challenging in, say , teenagers.
Many other studies have found similar relationships between shortened sleep and obesity from infancy through adulthood. The amount of sleep which can be a problem depends on age.
- In school age kids (ages 5-10) less than 10 hours of sleep per night has been consistently associated with obesity.
- In teenagers sleep less than 8-9 hours correlates with increased weight.
- One study in teenagers showed a five fold increase in obesity risk for each hour in sleep reduction.
The take home message is that ensuring an appropriate night’s sleep for your child has an added dimension of urgency: doing so may help them maintain a healthy weight. It is not clear if increasing sleep reduces weight; to my knowledge, there are no trials yet of showing that improving sleep reduces weight, but it can’t hurt.
Why does short sleep cause increased weight? In a nutshell, there are two likely causes:
- Increased calorie intake: The longer you are awake, the more opportunities you have to eat. Interestingly, short sleep also seems to lead to hormonal changes which increase hunger as well.
- Decreased energy usage: Obviously, people who are tired are less likely to be active. Short sleep also seems to be associated with lower body temperature and metabolism. Your body is like a furnace: if it runs cooler, it uses less fuel.
If you are so inclined, there is a good review article from 2008 summarizing much of this research by Sanjay Patel and Frank Hu. For extra credit points, I’ve made a video reviewing the mechanism between short sleep and obesity. [youtube=http://www.youtube.com/watch?v=7JgPdzH3b08&feature=youtu.be]