Infant daycare helps prevent childhood leukaemia


By Shaoni Bhattacharya Babies who attended daycare are much less likely to suffer childhood leukaemia when they grow older than those who did not mix with other infants, a new study suggests. The findings, from the largest-ever investigation into the causes of leukaemia, provide strong backing to a theory linking common infections to the childhood cancer. Leukaemia experts presented these and other results from the UK Childhood Cancer Study (UKCCS) in London on Friday. The 15-year-long study tracked 11,000 children, over 1700 of whom suffered with leukaemia. “Social contact with children outside the home may have a protective effect later in life,” said Eve Roman, director of the UK Leukaemia Research Fund’s epidemiology and genetics unit at the University of York. The expert panel say the general UKCCS results should reassure parents over “scares or anecdotal reports” about possible leukaemia risks. “It’s never easy to prove a negative, and once the spectre of risk is raised, getting rid of that is very difficult,” says Roman. She says the study found “absolutely no association” between electromagnetic fields and the risk of childhood leukaemia. And the findings also rule out a speculated association between vitamin K – injected into newborns to prevent haemorrhagic disease – and leukaemia. Leukaemia is the most common childhood cancer in the industrialised world. One in about 2000 children in the UK will suffer from the disease, says Mel Greaves, head of haemato-oncology at the Institute of Cancer Research in London, and co-author of the latest study on daycare published in the British Medical Journal. He says scientists believe leukaemia is caused by a “double whammy”. The first “hit” is a genetic one, where a chromosome breaks and exchanges a bit of its DNA with another chromosome. This is stitched back incorrectly to form a hybrid gene. But this abnormality, which he believes occurs in utero, is fairly common. Screening hundreds of samples of umbilical cord blood from newborns revealed that one in 20 has this fusion gene, he says. The fact that only 1 in 100 babies with the gene defect actually develops leukaemia suggests there is a second triggering event. This, he believes, is a low exposure to common infections during infancy which leads to an exaggerated immune response to the infections later in childhood. The latest study examined 6300 children without cancer and 3100 children with cancer, including the main type, acute lymphoblastic leukaemia (ALL). It found that increased levels of social activity outside the home reduced the risk of ALL. But this cut in risk was greatest in children who attended formal daycare during their first three months of life. This could be because being exposed to common bugs from other children at a young age helps to educate the immune system on how to respond effectively, says Greaves. Without that experience, the immune system might overreact when children get to school and are exposed to further infections. This could cause “a great deal of proliferative stress to the bone marrow” – where immune cells are produced – potentially triggering the leukaemia, he says. If this theory does prove correct, Greaves says it might be possible to develop a prophylactic vaccine to immunise children against leukaemia by giving them the early exposure to infections needed to educate their immune systems. Journal reference: British Medical Journal (DOI:
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