Study shows daycare may protect kids from leukemia

LONDON (Reuters) - Sending children to day-care at an early age could protect them against leukemia, perhaps by exposing them to certain infections, U.S. researchers said on Tuesday.

Their analysis presented at a conference in London showed that children who attended daycare or playgroups have a 30 percent lower risk of developing the most common form of childhood leukemia compared to those who do not.

And the earlier the social interaction the better because the review of 14 studies showed children who started daycare at age 1 or 2 had the most protection, said Patricia Buffler, a cancer epidemiologist at the University of California, Berkeley.

"What we found was for across all the studies there was a level of protection in 12 of them and no protection seen in two," she said in a telephone interview. "No study showed an increased risk. They either showed protection or no effect."

The study did not identify how social contact may guard against leukemia but it adds to evidence that children exposed to infections early in life somehow gain protection against the rare disease, Buffler said.

Scientists believe two things must happen for most types of childhood cancer. The first is some kind of genetic mutation that a child is born with followed by a trigger in childhood such as an infection that results in the disease, she added.

"This is just more evidence pointing to the role that some type of infection early in life could stimulate the immune system," said Buffler, who led the research.

The researchers reviewed 14 published studies of nearly 20,000 children worldwide, about a third of whom had acute lymphoblastic leukemia. This is the most common form of the disease and accounts for about 80 percent of all childhood leukemias.

It affects about 20 to 30 children out of every million, Buffler added.

The studies -- in which parents were asked about day care and playgroup attendance -- varied when it came to the timing, duration and extent of social interaction with other children, the researchers.

But the overall results are clear and could help other researchers gain a better understand of the disease that typically strikes children before age 5, Buffler said.

"These are more clues to pursue to understand how to prevent childhood leukemia," she said. "Nobody before had pulled together all the work reported to date."

(Reporting by Michael Kahn; Editing by Maggie Fox and )