Hydroxyproline excretion in schoolchildren and its relationship to measures of indoor air pollution

The urinary hydroxyproline excretion was investigated in a population of 6- to 9-year-old schoolchildren living in the Netherlands. Early morning samples of urine were collected at the end of a week in which personal and home monitoring for nitrogen dioxide (NO2) was carried out, and in which detailed information on gas appliances and on parental smoking habits was gathered. In addition, the pulmonary function of the children was measured, and their respiratory symptoms were collected using a standardized questionnaire which was completed by the parents. The hydroxyproline concentrations were standardized for urinary creatinine content. The hydroxyproline/creatinine ratio (HOP/C ratio) was found to be unrelated to NO2 exposure. The presence of major NO2-sources in the kitchen, vented and unvented gas-fired waterheaters, was significantly associated with elevated HOP/C ratios, due to a negative relationship with the creatinine concentration. There was a tendency for HOP/C to increase with the amount of tobacco smoked in the presence of a child. Respiratory symptoms and pulmonary function were unrelated to HOP/C. In this population, the urinary HOP/C ratio was not found to be a close correlate of exposure to NO2 or tobacco smoke, and of respiratory symptoms and pulmonary function.