The complexity and mystery of linear growth

Student Blogger for Global Nutrition Council at ASN’s Scientific Sessions and Annual Meeting at EB 2016

By: Sheela Sinharoy, MPH

A symposium called Biology of Linear Growth on Tuesday examined linear growth from the molecular to the population level, bringing perspectives from biology, physical anthropology, nutrition, and epidemiology

Are you familiar with the process of endochondral ossification? Julian Lui, MD PhD explained that this is the process that results in linear growth. It takes place in the growth plates, at the end of long bones such as the femur, and is subject to systemic regulation by endocrine, nutritional, and inflammatory cytokine factors as well as local regulation by paracrine factors and other cellular mechanisms. Malnourished children have lower levels of hormones like insulin-like growth factor 1 (IGF-1) and estrogen, as well as increased levels of glucocorticoids, leading to decreased linear growth. Dr. Liu explained that this allows the body to conserve resources and that, in situations of food insecurity, “Growth is something of a luxury that can be postponed until better times.”

Rather than growing continuously, children grow in saltations, meaning that – as many a parent has observed – a child may grow substantially overnight and then not at all for a number of days afterwards. Michelle Lampl, MD PhD stated that as children age, these saltations become less and less frequent, with older children growing much less often than infants. The amount and frequency of these growth saltations can be affected by environmental factors, which can interact with cellular effects. Maternal smoking, for example, has a well-documented inhibitory effect on growth, as does maternal alcohol consumption and stress.

Since linear growth happens most rapidly in early life, the first 1,000 days from conception to two years of age are considered a critical period. Parul Christian, DrPH presented results from a meta-analysis analyzing various maternal and child nutrition interventions targeting this 1,000-day window. Starting during pregnancy, balanced protein-energy, iron-folic acid, and multiple micronutrient supplementation were all found to increase birth weight. However, maternal supplementation during pregnancy was not associated with any long-term linear growth in children under five years old. For infants and young children, nutrition promotion and food supplementation showed promise as interventions with positive impacts on child height.

In the final talk of the symposium, Aryeh Stein, PhD addressed the question of linear catch-up growth: for those children whose growth has been suppressed by malnutrition, is it possible to catch up on missed growth, even after the first 1,000 days? A number of studies have provided different nutrients and foods to children ages two and older. Dr. Stein presented results from studies of protein, zinc, iron, iodine, calcium, multiple micronutrients, and food. Protein and some of the micronutrients may have promise, but several of the calcium studies reported negative effects, while food had no association with growth.

The symposium made it clear that nutrition has an important role to play in stimulating or inhibiting linear growth. However, a great deal remains to be learned about these complex biological processes and the most effective interventions to promote children’s optimal growth.

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