These results support the theory that reduced exposure to common infections in the first year of life increases the risk of developing acute lymphoblastic leukaemia (ALL).

The study involved 6305 children (aged 2-14 years) without cancer, 3140 children with cancer (diagnosed 1991-6), of whom 1286 had ALL. Parents were interviewed about day care and social activity with children outside the family during the first year of life.

Increasing levels of social activity outside the home were associated with consistent reductions in risk of ALL. However, the greatest reduction in risk of ALL was seen in children who attended formal day care during the first three months of life (defined as attendance at a day nursery or nursery school at least once a week, or at least two half day sessions a week at a playgroup, mother and toddler group, or at a childminder with a minimum of four children attending).

Results were similar for cases diagnosed between 2-14 years and for cases diagnosed between 2-5 years.

"Our results provide further support that social activity with other infants and children during the first few months of life protects against subsequent risk of ALL," say the authors.

The most plausible interpretation is that this protection comes from exposure to common infections. Similar associations have been reported for type 1 diabetes and allergies in children.

"Whether early exposure to one or more specific infections, or to a spectrum of non-specific agents, protects against each of these disparate diseases remains to be clarified. Nevertheless, we conclude that some degree of early exposure to infection seems to be important for child health."

Note: If no author is given, the source is cited instead.

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