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The conclusion was based on a review of 14 studies involving 6 108 children with leukaemia - cancer of the blood - and 13 704 without the condition led by Dr Patricia Buffler, from the University of California, Berkeley.
"Overall, we are seeing a 30 percent reduction in leukaemia risk for the children who have been in playgroups, (and) have had the opportunity of the social experience of being around other children early in life compared to children who don't have those experiences," she told BBC television.
"That provides us with some firmer understanding of the potential role of infection or immune regulation in this process." The research was to be presented for the first time at the Children With Leukaemia conference in London Tuesday.
Scientists believe there are two "triggers" for childhood leukaemia, which is one of the commonest forms of cancer in young people in the industrialised world, with about one in 2 000 affected.
The first is thought to be a genetic mutation occurring in the womb.
The second is believed to be caused by infection in a child's early years, prompting an "inappropriate response" and making leukaemia more likely.
But it is believed that "priming" the immune system to the coughs, sneezes and other childhood ailments that spread at playgroups and crèches can switch off the second trigger.
Buffler said the exact mechanism of how childhood leukaemia develops was not fully understood, but none of the studies her team reviewed found that social contact increased the risk of a child developing leukaemia.
"It's believed that having that experience earlier in life does prepare the immune system better than if the child were isolated or doesn't have the experience of having a large number of siblings, or experience in play groups," she added.
Britain's Leukaemia Research Fund charity in 2005 published similar findings in the British Medical Journal after a 10-year study. – (Sapa-AFP)
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Leukaemia
April 2008
