Seasonal pattern of phototherapy: a study in the Sardinian population

The relationship between season of birth and human diseases is well known and it has been suggested that such a relationship could be mediated by seasonal and environmental effects on early events of extrauterine life. In this context the physiological increase of bilirubin occurring in all infants during the neonatal period may be of paramount importance. Indeed, recent studies suggest a beneficial action of bilirubin in the early stages of extrauterine life due to its protective action against secondary oxidants. The newborn infant is particularly sensible to oxidative damage, thus seasonal variation of bilirubin level in the first few days of life could influence further development and susceptibility to pathological manifestations. In the present paper we have analysed the seasonal effect on the level of the serum bilirubin during the neonatal period by an analysis of the incidence of phototherapy in a sample of 5540 infants born consecutively in the population of Sassari during the years 1993-96. The proportion of infants undergoing phototherapy for neonatal hyperbilirubinemia is lower in those without glucose-6-phosphate-dehydrogenaser (G-6-PD) deficiency than in those with G-6-PD deficiency and in both categories the proportion is lower in females than in males. A highly significant association between the date of birth and the proportion of infants undergoing phototherapy has been observed in males without G-6-PD deficiency. The maximum incidence of phototherapy has been observed in the period May-August. A Fourier analysis carried out on these infants has shown the presence of two main components (harmonics) contributing to the seasonal cycle and corresponding respectively to a one year and to a two years period.