Measurement of Mediators
Spirometry was performed as per a previously standardized
protocol.16 In our previous study, the ratio of forced
expiratory volume in 1 second (FEV1) to forced vital capacity (FVC)
showed the strongest association with body mass index
(BMI).17 Hence, FEV1/FVC was used as a surrogate for
pulmonary function performance.
FeNO, a marker of airway inflammation, was measured
using a portable NO analyzer NIOX MINO® Airway Inflammation Monitor
(Aerocrine AB, Solna, Sweden) according to standardized
protocols.18
Physical fitness was assessed based on a combination of all physical
fitness tests (800 m sprint, jump and reach, sit-ups, and sit-and-reach)
administered during school visits using a standardized
protocol.19 Physical fitness parameters included
cardiorespiratory endurance, muscular strength, endurance, and
flexibility. We added them up to formulate a physical fitness index and
transformed them into z-scores using age- sex- specific reference. A
higher physical fitness index indicates better physical fitness.
Sleep behaviors were assessed using a parent-administrated
questionnaire—the Children’s Sleep Habit Questionnaire (CSHQ). The
CSHQ was designed and developed to assess the sleep behaviors of
school-aged children.20 It was proven to be a valid
tool for detecting the presence of SDB by comparing it with objective
polysomnography-defined obstructive sleep apnea.21
A validated Chinese version of the Tanner-derived composite stage
(TDCS)22 was used to evaluate the Tanner stage.
Children with early puberty were defined as those reaching a certain
pubertal stage earlier than the median age for that
stage23 based on large-scale population-based Chinese
studies.24,25