Living at high altitude and risk of sudden infant death syndrome.

OBJECTIVE To investigate the association between altitude of residence and risk of sudden infant death syndrome (SIDS). METHODS A retrospective, case control study in the Tyrol, Austria enrolled 99 infants with SIDS occurring between 1984 and 1994, and 136 randomly selected control cases. Data on pregnancy, delivery, child care practice, and socio-demographic characteristics including altitude of residence were collected with a standardised questionnaire. RESULTS The risk of SIDS increased gradually with increasing altitude of residence. This relation remained independently significant when the analysis was adjusted for gestational age, birth weight, prenatal care, mother's age at delivery, educational level of parents, and cigarette smoking during pregnancy. The prone sleeping position emerged as an obligatory cofactor in this association. In the whole of Austria, a similar trend of association emerged between the average altitudes in the 99 political counties and the rates of SIDS. CONCLUSIONS This study identified altitude of residence as a significant risk predictor of SIDS, primarily in combination with the prone sleeping position. Respiratory disturbances, reduced oxygen saturation, and lower temperatures at high altitude might explain this association.