Mar. 1, 1999
Volume 51, No. 22
Science catches up to age-old beliefs about children's growth
You're buying a second pair of shoes for your youngest child in as many months. At the school year's beginning her pants are dusting the ground; by its end they're hovering right above her ankles. But your 10-year-old hasn't grown out of any clothes in two years. As any parent could tell you, "Children Do Grow in Spurts"--the title of the Great Teachers Lecture given by anthropology Assistant Professor Michelle Lampl on Feb. 18.
Was there ever any doubt? Well, the way scientists have traditionally measured growth--in annual increments much like that yearly visit to the pediatrician's office--failed to account for how growth had occurred in the interim. Based on these types of measurements, researchers believed children's growth never exceeded 1 millimeter a day.
But Lampl found that growth sneaks up on children in a kind of stealth process, erupting into spurts of a half-inch or more in a single day and occurring while they sleep. Then they have little measurable growth, or none at all, until the next episode-an effect Lampl termed "saltation-stasis" (sudden growth-rest). What's more, the body doesn't grow as a unit but in "body-segmented" spurts, with arms, legs, feet or hands growing at their own pace.
Other mechanisms such as illness may factor into growth as well. Conventional medical wisdom once held that children do not grow when they are sick, although "mother" wisdom certainly disputed that fact. ("When a child stands up after a fever they stand taller," went one old saying.)
Children often get sick when they grow, "although we don't understand the underlying mechanisms," Lampl said. One theory is that "the chemical cascade that controls growth at the cellular level also suppresses the immune system," she said. And continual ear infections in children have been found to be "coincident with growth spurts," she added.
"On the one hand [this knowledge is] a little disturbing," Lampl said. "Then on the other hand it makes perfect sense if you watch children." But "it helps to understand the variability that we know occurs in children," she said, showing a slide of a boy and a girl of the same age--the boy significantly taller than the girl. In measuring the girl's growth, Lampl said, researchers found she underwent more growing episodes. While the boy had fewer growing episodes, he grew more when growth occurred. Lampl also measured a set of twins and found they each had 14 to 15 occurrences of growth at the same intervals. "That tells us there is a biological basis to the timing of growth," she said.
Here in America and elsewhere, where the practice of feeding babies bottled formula and nutritional supplements may have skewered the norm in terms of growth, researchers are taking another look at these "norms." "Our notion of what's normal and standard is biased," Lampl said. "The data will be recollated on normal growing by using only breastfed babies to establish the normality."
Assuming mothers eat a healthy diet, their breastfeeding babies should grow well. As for children, Lampl said, "kids tell you what they need to grow. Their appetite registers very clearly." Before and after growth spurts children usually increase their caloric intake anywhere from 20 percent to 100 percent a day, she added.
But that doesn't mean parents should try to impose their own dietary restrictions on their children, Lampl stressed. "Babies need dietary fat to grow," she said. "This notion that children need what we [adults] need is a problem."