Research carried out by scientists in the US has found that young children who are exposed to infection early and often may have a reduced risk of developing acute lymphoblastic leukaemia (ALL).

Previous studies have suggested that this form of leukaemia is caused by a rare immune response to common infections.

Scientists believe that this causes the child's body to produce cancerous cells in response to the barrage of infections the child faces later in life.

Researchers from the Northern California Childhood Leukaemia Study analysed 140 children between the ages of one and 14 years who had been diagnosed with ALL between 1995 and 1995.

These were compared to a group of children randomly selected from the California birth registry. Detailed data on nursery attendance was collected through questionnaires and interviews with the child's guardian.

Risks reduced

They found that extensive contact with other children in a nursery setting is associated with a reduced risk of ALL.

According to their findings, starting nursery at a younger age, attending for a longer duration and having contact with a high number of children all reduce the risks of developing the disease.

Writing in the latest issue of the British Journal of Cancer, Prof Patricia Buffler who heads the California study, said the findings backed up previous studies.

"As well as attending nursery, there are many ways in which the immune system can receive developmental stimulation, such as vaccination and exposure to siblings and friends.

"Our study contributes to the idea that isolation from common infections can increase the risk of childhood leukaemia."

Further research

Dr Xiamei Ma, author of the study, said further work is needed to determine if specific infections could trigger the disease.

"The results are from the first phase of an ongoing study. We anticipate that later studies will confirm the association between delayed exposure to infection and childhood leukaemia and eventually lead to effective prevention strategies."

Sir Paul Nurse, interim chief executive of Cancer Research UK, welcomed the study.

He said further research is needed to enable doctors to draw up preventative measures for children.

"This research adds to the increasing evidence that infections play a role in some cancers, the nature of which is still unknown.

"Further investigation into exposure to infection with larger numbers of children should help us to identify the role of the immune system in childhood leukaemia and may lead to new ways to prevent the disease."