Kids Can Grow Overnight

Parents have always talked about “growth spurts,” though many scientists believed them to be an old wives’ tale. But old wives can sometimes be right, and about ten years ago scientists confirmed this traditional belief. Kids literally do have brief periods of very rapid growth.

A mother in my son’s kindergarten class admitted to me that her daughter had suddenly been eating so much that she actually considered restricting her diet. But then suddenly, about a week later, Kara woke up in the morning and her pants were all too short, and her appetite went back to normal.

Growth spurts are real. It’s amazing that kids really can literally grow overnight. But what’s even more strange is that most of the time kids don’t grow at all. In fact, current research has shown that 90 to 95 percent of normal development is growth-free! Research in endocrinology, the study of hormones, and molecular biology shows that specific growth-related chemical messengers in the body—as well as the receptors on cells that they trigger—are produced and function in sporadic spurts. Previously, it was believed that they were created by a constant, unwavering molecular assembly-line. Further there is no regular cycle between the spurts, so it is impossible to predict when a child is going to have a growth spurt.

We do know that sleep is very much related to growth and can predict when a young infant will have a growth spurt. Researchers have long known that growth hormone is released after we fall asleep. So they explored whether periods of increased sleep in babies are associated with these growth spurts.⁠1 Indeed, they found a strong correlation between increased slow-wave sleep, growth hormone release, and subsequent long-bone growth. In one study, babies actually grew in length directly following periods of increased napping and increased nighttime sleep. We can’t directly observe the effects of sleep on the bones in humans, of course. But, in a study of lambs, measuring devices were actually implanted in their growth plates and growth was observed in the bones following periods of increased sleep.

So babies’ growth is not only far more complex than scientists believed a decade ago, but the complex relationship between sleep and growth has more far-reaching implications than one could have guessed. In fact, the amount of sleep a baby gets during infancy may have profound effects later in childhood. Researchers in Massachusetts have found that chronic sleep deprivation in early childhood, as early as 6 months of age, is a risk factor for obesity.⁠2 They followed more than 1000 children from 6 months to 7 years of age and found that reduced sleep in infancy was directly linked to obesity and increased abdominal fat at school age. The CDC recommends about 14 hours/day of total sleep for infants under age 1. And we are beginning to see that this is not just a pleasant suggestion, but critically important for normal growth and health.

  1. Infant Growth in Length Follows Prolonged Sleep and Increased Naps. Sleep. 2011 May 1; 34(5): 641–650.
  2. Chronic Sleep Curtailment and Adiposity. Pediatrics. Vol. 133 No. 6 June 1, 2014 Parenting Team Contributor

Author: Wendy Hunter, MD

Pediatrician at Children's Primary Care Medical Group, La Jolla, CA

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