Seasonal relationship of sudden infant death syndrome and environmental pollutants.

Evidence that chronic hypoxia precedes death from sudden infant death syndrome (SIDS) is mounting. Prolonged exposure to moderate levels of pollutants could be a contributing factor to hypoxia. Levels of carbon monoxide (CO), sulphur dioxide (SO2), nitrogen dioxide (NO2) and hydrocarbons (HC) are highest in the winter when incidence of SIDS is increased. SIDS cases in Los Angeles County were correlated with daily mean levels of these pollutants, temperature, barometric pressure and monthly lead levels with the aid of time series analyses. Peaks in CO, SO2, NO2, HC and lead preceded the seasonal increase in SIDS by seven weeks. Theoretical considerations, such as the hypoxia-inducing effects of CO, support the hypothesis that this temporal relation has functional significance. Three additional findings provided evidence for this hypothesis: 1) SIDS infants born during months of low pollution lived longer than those born during months of high pollution. 2) SIDS infants born in a district with low pollution lived longer than those born in a district with high pollution. 3) The bimonthly rate of SIDS was directly proportional to the level of CO pollution to which the infants had been exposed between conception and two months of age. The role of pollution levels as a predisposing factor in risk for SIDS cannot be summarily dismissed.