Researchers affiliated with the United Kingdom Childhood Cancer Study (UKCCS) have reported that day care in infancy decreases the risk of childhood acute lymphoblastic leukemia (ALL). The details of this report appeared as an early online publication in the British Medical Journal on April 22, 2005.

The cause of childhood ALL is unknown, but there is evidence that ALL is more common in developed as compared to undeveloped countries. There have been speculations that ALL is associated with abnormal immune responses. Previous studies have suggested that children exposed to a wide range of pathogens early in life have a decreased incidence of childhood ALL. The authors of the present study sought to determine if this hypothesis had merit. They used daycare attendance in the first year of life as a measure of exposure to a wide range of pathogens. These researchers found that any activity outside the home during the first year of life was associated with a decreased incidence of ALL. Formal day care attendance and especially attendance during the first three months of life was associated with the lowest risk of ALL. The magnitude of this risk reduction was in the 40-50% range. There was also a reduction in the incidence of all other childhood cancers, but the magnitude of this effect was less than for ALL. The authors of the report concluded that the most likely explanation of the results is a protective effect of exposure to common infections. They pointed out that similar observations have been made concerning type 1 diabetes and allergies. They suggest that these data support what is becoming a growing consensus that child health is improved with early infection exposure.

Comment: These data may also explain why the incidence of childhood ALL is lower in undeveloped countries.

Reference: Gilham C, Peto J, Simpson J, et al. Day care in infancy and risk of childhood acute lymphoblastic leukemia: findings from UK case-control study. British Medical Journal . Published online April 22, 2005.