Cancer study: Children who attend daycare centres on a regular basis are less likely to develop leukaemia than children who do not, a UK study has found.
The results of the research support the theory that reduced exposure to common infections in the first year of life increases risk of developing acute lymphoblastic leukaemia (ALL).
This form of leukaemia can occur in people of all ages but is the most common cancer in children. It accounts for 25 per cent of all cancers in children younger than 15 years of age - leukaemias are cancers of white blood cells.
The study of more than 3,000 children with cancer of whom 1,286 had ALL, was carried out as part of the UK Childhood Cancer Study. The study was designed to test a number of hypotheses, one of which was that leukaemia may be caused by abnormal responses to common infectious agents. Parents were interviewed about daycare and social activity of children outside the family during the first year of life.
Published on the British Medical Journal website, Online First, the results show a direct link between increasing levels of social activity outside the home and a consistent reduction in the risk of ALL. The greatest reduction in risk of ALL was seen in children who attended formal daycare during the first three months of life. This was defined as attendance at a day nursery at least once a week, or at least two half day sessions a week at a playgroup, mother and toddler group or at a child minder with a minimum of four children attending.
"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," the authors said. They believe the most plausible interpretation is that this protection comes from exposure to common infections. A similar protective mechanism has been reported for allergies in children and type 1 diabetes mellitus.
The idea that infections are implicated in the development of childhood leukaemia dates back to the 1940s. One theory suggests a deficit of exposure to infectious agents in infancy and the resulting delayed challenge to the immune system, is a key factor in the development of a sub group of ALL. This B cell form of ALL is responsible for the childhood peak of acute leukaemia between the ages of two and five.
"We conclude that some degree of early exposure to infection seems to be important to child health," the authors said.