Victoria Adele Tobolsky

VICTORIA A. TOBOLSKY, then a graduate student at Harvard University, Cambridge, Massachusetts, received funding in April 2019 to aid research on ‘Investigating Energetic Contributions to Adolescent Growth Among Kalenjin Children,’ supervised by Dr. Daniel Lieberman. Insulin may regulate energetic trade-offs during life history. The adolescent growth spurt precedes the onset of menstruation and is accompanied by a period of insulin resistance that may help divert energy towards skeletal growth. We compared adolescent girls who had not yet menstruated in a rural community in western Kenya (n = 40) with girls from the same population in an urban context (n = 44; total, n = 84) to test four broad hypotheses: 1) rural and urban children occupy different energetic niches, 2) a urinarily-excreted proxy of insulin, c-peptide, predicts biomarkers of bone growth, 3) insulin, as measured by c-peptide, predicts hormonal biomarkers of gonadal maturation, and 4) insulin, as measured by c-peptide, mediates a trade-off between bone growth and remodeling and reproductive maturation. We collected urine samples, dried blood spots, body composition, 24-hour dietary recalls, and used the doubly labelled water method to calculate total energy expenditure (TEE) in a subset of children (n = 24). Average c-peptide was significantly different between communities (Rural: 11.62 ‘ 5.43, Urban: 20.91 ‘ 7.90, p < 0.001), suggesting energy constraints in the rural area. Results from the DLW tentatively support this insight, finding that children in the rural area have higher TEEs but spend fewer kilocalories per kilogram of fat free mass daily. C-peptide moderately predicts one biomarker of bone growth, NTX-1 (' = 0.05, p = 0.008) when controlling for age, tri-ponderal index (TPI), IGF-1, GH, and estradiol. C-peptide also predicts estradiol when controlling for age, TPI, IGF-1 and GH (' = 0.12, p < 0.001), but this relationship merits further scrutiny. This study provides evidence that c-peptide is responsive to the local environment, and that it supports skeletal growth. We do not find conclusive evidence of energetic trade-offs during adolescence in pre-menarcheal children, but future studies should explore the potential role of insulin in mediating trade-offs in the peri/post-menarcheal period.