CHILDREN who attend day-care centres or playgroups have a 30 per cent less chance of developing a life-threatening cancer, a study has found.

Researchers found that children who had regular contact with their peers and were exposed to a multitude of infections were more likely to develop a stronger immune system, helping them fight the development of the most common form of childhood cancer, acute lymphoblastic leukaemia.

The research, which looked at 14 studies involving more than 20,000 children, is the first of its kind to make a direct link between social contact and leukaemia, which affects about one in 2000 youngsters aged between two and five.

The author of the study and a professor of epidemiology at the University of California, Patricia Buffler, said the analysis bolstered the theory that children exposed to common infections early in life gained protection from the disease.

"It is known that environments such as day-care centres increase the chance of infections spreading," Professor Buffler said.

"Some proponents of the theory believe that if the immune system is not challenged early in life and does not develop normally, it may mount an inappropriate response to infections encountered later in childhood and that this could provoke the development of leukaemia."

Scientists believe that for most types of childhood leukaemia to develop, there first must be a genetic mutation in the foetus, followed by a second trigger during childhood that results in 1 per cent of those children developing the disease. Infection is one of the suspected triggers.

"There is definitely a link between cancer and infection," the chief executive of the NSW Cancer Council, Andrew Penman, said yesterday. "We have seen that recently with cervical cancer, and we know that the age at which infection occurs can determine the outcome, but this research raises a lot of questions without answering any of them."

The president of Childcare Associations Australia, Amanda Morphett, said the findings indicated that "well regulated, quality assured care has a positive impact on children's growth and development".

"If there is an upper respiratory, viral or gastro type of infection to be caught, children who are new to care tend to be the first to catch it, [but] anecdotal evidence suggests that those who have participated in high social contact situations are better able to manage exposure to both viral and bacterial infection," she said.

But parents should not to rush to send their child to a day-care centre on the basis on the study, warned David Ziegler, a pediatric oncologist at the Sydney Children's Hospital.

"We're happy to look closely at anything which can help us work out what causes leukaemia, but we are talking about something that is already very, very rare, so the change for a child going to child care would be tiny. I'd urge parents to be cautious."

研究发现，参加日托或者进幼儿园的儿童可能减少 30 ％ 发生威胁生命的癌症的机会。

研究人员发现，经常与他们的小朋友接触的以及暴露于感染群体的儿童更有可能获得一个强大的免疫系统，帮助他们抗击最常见的儿童癌症形式——急性淋巴细胞白血病的发展。

这项调查，查看了 14 项涉及 20,000 以上儿童的研究，是第一次这类在社会接触和白血病之间建立直接联系的调查。白血病，大约影响两岁到五岁之间幼童的 2,000 分之一。

该研究报告的作者，加州大学的流行病学教授帕特里夏 比夫莱说，结果分析支持了这样的理论，即儿童在生活的早期暴露于常见的感染能够增进对疾病防护。

教授比夫莱说：“这是众所周知的，例如日托中心那样的环境，会增加感染蔓延的机会。”

“一些支持这种理论的人认为，如果免疫系统没有在生活早期遇到挑战并且未能正常发展，它可能对幼童后来遇到的感染挂载一个不恰当的回应，而这可能挑起白血病的发展。” 

科学家们认为，大多数类型儿童白血病的发生，首先必定是在胎儿期的基因变异，然后是在童年期的第二次触发，结果是这些儿童的 1％ 发生疾病。感染是怀疑的诱因之一。

“在癌症和感染之间肯定有联系，”新南威尔士州癌症理事会的行政主管安德鲁 彭曼昨天表示。“我们最近对于子宫颈癌已经看到，而且我们知道感染发生的年龄可能决定未来的结果，但是这项研究提出了很多没能回答的问题。”

澳大利亚托儿协会的主席阿曼达 莫费特说，调查结果显示，“良好的管理、有质量保证的照料对儿童的成长与发展产生了积极的影响。” 

“如果赶上上呼吸道，病毒或肠道类型的感染，那些新照看的孩子趋向于首先被感染，[但是]传闻证据表明，那些参与高社会接触情况的孩子能够较好地抗御对于病毒和细菌两者感染的暴露，”她说。

但是，父母们不应该基于这项研究急于将他们的孩子送往日托中心，悉尼儿童医院的儿科肿瘤学家戴维 齐格勒警告说。

“我们很高兴能够仔细研究可以帮助我们找出白血病病因的任何事情，但是我们所谈论的事情已经是非常、非常罕见的了，所以孩子去往幼托的改变可能是极微小的。我呼吁家长们要慎重。”