Hemoglobin-to-platelet-count ratio is an independent predictor of cardiovascular fitness in children: Does residential air quality provide the mechanism?

Abstract

Cardiorespiratory fitness (CRF) is a well-known and robust indicator of health in childhood, as well as a valuable predictor of all-cause mortality in adulthood. Understanding the associations and possible mechanisms between CRF and residential location is an important focus for public health research. A cross-sectional sample of 2250 children and adolescents, aged 6 to 17 years, were recruited from public and private schools in Santa Cruz do Sul, Rio Grande do Sul, Brazil. In addition to age, sex, and body size measurements, we also recorded hemoglobin and platelet count measurements using venous blood samples (10ml). CRF was predicted using the 6-minute run/walk test. The association between CRF and a range of possible predictors was explored using allometry. Results identified a novel and independent association between the hemoglobin-to-platelet count ratio and children’s CRF, having controlled for the usual confounding variables of age, sex, and body size. We also provide evidence of a possible mechanism for this association, having identified reduced measures of hemoglobin and increased platelet counts observed in children living in urban (vs rural) areas. These results suggest the need for more effective public health practices and policies related to the health effects of the built environment for children and adults in Brazil. We can also speculate that similar changes in health policy are necessary in congested cities worldwide, such as the introduction of ultra-low emission zones in London (introduced in April 2019).