Cardiorespiratory fitness and metabolic parameters in youth

Nutrition Research Newsletter, Dec, 2006

The United States has seen an epidemic increase in childhood obesity and its adverse health outcomes in recent years. In adults, emerging evidence suggests that having a moderate to high cardiorespiratory fitness (CRF) is consistently associated with lower risks for many health outcomes such as the metabolic syndrome, cardiovascular disease, and all-cause mortality. Despite the overwhelming evidence in adults, little is known about the role of CRF on health risks in youth.

Researchers examined the independent relationships between CRF and adiposity on insulin sensitivity (IS) and beta-cell function using the gold standard methods and 3 h hyperinsulinemic-euglycemic and 2 h hyperglycemic clamp in healthy African American and white youth. Subjects consisted of healthy African American (n = 65) and white (n = 57) youth. The subjects varied in age (8 to 17 years) and in BMI (14 kg/[m.sup.2] to 50 kg/[m.sup.2]). Total body fat was assessed by dual X-ray absorptiometry (DXA). To evaluate beta-cell function and IS, all patients underwent a hyperglycemic and a hyperinsulinemic-euglycemic clamp experiment on two separate occasions. Peak volume of oxygen (V[O.sub.2] Peak) was measured using the Bruce multistage treadmill protocol using standard open-circuit spirometry.

Independent of race, CRF was inversely (p < 0.05) related to total and abdominal fat, fasting insulin and first phase insulin secretion and positively (p < 0.05) related to IS. When subjects were categorized into low (5 [less than or equal to] 50th) and high (> 50th) CRF groups, IS was significantly (p < 0.05) higher in the high compared with the low CRF group independently of race. Furthermore, first and second phase insulin secretion were lower (p < 0.05) in the high CRF group in comparison with the low CRF group in both races. However, in multiple regression analyses CRF was not (p < 0.05) an independent predictor of IS and acute insulin secretion after accounting for total adiposity.

These findings demonstrate that low CRF is associated with decreased IS compensated by higher insulin secretion in both African American and white youth. However, this relationship appears to disappear after adjusting for differences in adiposity, suggesting that the association between fitness and IS is partially mediated through fatness.

S. Lee, F. Bacha, N. Gungor, et al. Cardiorespiratory Fitness in Youth: Relationship to Insulin Sensitivity and Beta-Cell Function. Obesity; 14:1579-1585 (September, 2006). [Correspondence: Silva A. Arslanian, Children's Hospital of Pittsburgh, 3705 Fifth Avenue at DeSoto Street, Pittsburgh, PA 15213. E-mail: Silva.Arslanian@chp.edu.]