反转：咬指头竟然可以增加免疫力

　　

——新西兰完成的一项纵向研究结果支持一卫生假说

生物通报道：在我们小时候，常常父母亲会告诉我们不要吸手指或者咬手指，这会把细菌给吃下去的，但是这些“脏”习惯可能具有意料不到的好处：增加免疫，减少过敏。

近期来自新西兰奥塔哥大学等处的研究人员展开了一项包括1037位儿童的纵向研究，这些儿童出生在新西兰达尼丁，1972至1973年间成年。研究人员发现有吸手指或者咬手指习惯的孩子，在 13 岁时有39%会在一个常见的过敏原测试中出现阳性，而没有这些习惯的孩子，这一比率则为49%，而同时具有两种这样习惯的孩子则风险会降低大31%。这一研究公布在7月11日的 Pediatrics杂志上。

“这些研究发现支持‘卫生假说（hygiene hypothesis）’，也就是说接触细菌能减少儿童过敏的风险，”文章作者，奥塔哥大学呼吸流行病学教授Robert Hancox说。

1989年科学家们首次提出的卫生假说理论，认为孩子在成长早期如果接触多种病毒、细菌和寄生虫，将有利于其免疫系统的发展，似乎这样能促进大脑对其做出更好的防御准备。反之，如果缺乏这类早期接触，免疫系统就可能出现紊乱，做出过激反应，如对食物、花粉和宠物毛屑过敏等，或者引发人体机理问题，出现自身免疫失调。

参与这项研究的儿童的父母报告了是否孩子们在5岁，7岁，9岁和11岁时有吸手指或者咬手指的习惯，然后在13岁和32岁时，参与者就要接受特应性致敏作用 （皮肤点刺）检测。如果在13岁时，他们没有被强迫停止吸手指或者咬手指，并结合家族史、性别、宠物所有和母乳喂养等因素，研究人员发现这并不会影响其患哮喘、花粉等疾病的风险。

“我们当然不是建议吸手指或者咬手指，”Hancox说，“但是如果孩子有这样的习惯，也许很难制止，那么减少他们过敏的危险，也许能带来一些安慰。”

同时本月 Perspectives in Public Health杂志的一系列文章也在探讨现代卫生标准是否对我们的身体有害，这也许会增加我们人体抗击过敏和慢性炎症疾病的能力。

过敏是个令人头疼的问题，近年来，哮喘和过敏逐渐成为了全世界最常见的慢性疾病，在四岁以上的儿童中尤为普遍。越来越多的证据表明，这两种疾病与人类微生物组的组成和功能有关。

加州大学旧金山分校的Susan Lynch和Kei E. Fujimura介绍了相关研究的最新进展，探讨了呼吸道、肠道和环境微生物组在哮喘和过敏疾病中起到的作用。他们相信，将呼吸道和肠道微生物组作为靶标，可以有效预防或者管理哮喘、过敏和其他以适应性免疫紊乱为主要特征的疾病。断奶、抗生素都会影响孩子的微生物组

（生物通：万纹）

原文摘要：

Thumb-Sucking, Nail-Biting, and Atopic Sensitization, Asthma, and Hay Fever

BACKGROUND: The hygiene hypothesis suggests that early-life exposure to microbial organisms reduces the risk of developing allergies. Thumb-sucking and nail-biting are common childhood habits that may increase microbial exposures. We tested the hypothesis that children who suck their thumbs or bite their nails have a lower risk of developing atopy, asthma, and hay fever in a population-based birth cohort followed to adulthood.

METHODS: Parents reported children’s thumb-sucking and nail-biting habits when their children were ages 5, 7, 9, and 11 years. Atopic sensitization was defined as a positive skin-prick test (≥2-mm weal) to ≥1 common allergen at 13 and 32 years. Associations between thumb-sucking and nail-biting in childhood, and atopic sensitization, asthma, and hay fever at these ages were assessed by using logistic regression with adjustments for sex and other potential confounding factors: parental atopy, breastfeeding, pet ownership, household crowding, socioeconomic status, and parental smoking.

RESULTS: Thirty-one percent of children were frequent thumb-suckers or nail-biters at ≥1 of the ages. These children had a lower risk of atopic sensitization at age 13 years (odds ratio 0.67, 95% confidence interval 0.48–0.92, P = .013) and age 32 years (odds ratio 0.61, 95% confidence interval 0.46–0.81, P = .001). These associations persisted when adjusted for multiple confounding factors. Children who had both habits had a lower risk of atopic sensitization than those who had only 1. No associations were found for nail-biting, thumb-sucking, and asthma or hay fever at either age.

CONCLUSIONS: Children who suck their thumbs or bite their nails are less likely to have atopic sensitization in childhood and adulthood.