呼吸道感染儿童补锌以改善治疗效果
生物学、行为学和背景依据
锌是维持肠道细胞、骨骼生长和免疫功能所必需的基本微量元素。生活在低收入地区的儿童常发生营养不良和缺锌1, 2. 严重缺锌可造成发育停滞、免疫受损、皮肤疾病、学习障碍和厌食3, 4. 导致缺锌的原因包括含锌食物摄入不足或锌吸收不足。多数含锌量高的食物是动物源性食物，如肉、鱼和乳制品。低收入人群很难获得此类食物。谷物、坚果和豆类等膳食中常见的膳食纤维和肌醇六磷酸类化合物可与锌结合，导致锌吸收不良5, 6. 频繁腹泻（常伴有慢性营养不良）也可进一步消耗机体锌储量7, 8.
缺锌儿童出现生长发育迟缓及发生腹泻病和呼吸道感染（如急性下呼吸道感染）的风险较高 9–11. 腹泻病和急性下呼吸道感染（尤其是肺炎）是导致低收入国家婴幼儿死亡最常见的两个病因12. 大约一半急性下呼吸道感染儿童死亡的原因是营养不良11. 每年有200多万名儿童死于肺炎，超过了艾滋病、疟疾和麻疹所致儿童死亡人数的总和13. 一些研究提示，儿童补锌可减少支气管炎和肺炎的发病次数，并降低其严重程度9,14–19 世界卫生组织/联合国儿童基金会已将补锌结合口服补液的方法，作为其提出的管理儿童腹泻病建议的基础20.
一般认为，锌可调节多项免疫功能（包括在肺部炎症或损伤期保护呼吸道细胞的健康与完整），从而降低儿童对急性下呼吸道感染的易感性21. 研究表明，补锌在治疗或改善急性下呼吸道感染方面的结果不一14, 22–27. 例如，最近有一篇综述对现有研究的荟萃分析发现，补锌的效果在南亚最为显著，那里的儿童每周至少补充70毫克锌19. 然而，该综述未能明确采用低剂量补锌是否会降低效果， 以及在其它地区补锌是否对急性下呼吸道感染发病率影响相对较小。此外，在资源有限地区很难确定儿童是否缺锌，因此，难于有效对最高危人群开展补锌10, 28, 29. 另一篇系统综述证实:补锌可显著降低肺炎发病率，并建议缺锌人群补锌18.
已针对多种补锌剂量方案开展了评估，从每周15毫克至140毫克不等，上限范围甚至超过了推荐的每日摄入量（RDI），即，1岁以下儿童每日2毫克，1至3岁儿童每日最高7毫克30. 有必要对最佳补充剂量有更深入的了解，因为有研究表明，大剂量补锌和长期补锌可能会抑制机体对其他营养物质（如铜和铁）的吸收14, 23, 31, 32 并可能导致艾滋病毒感染儿童的生存率下降33. 膳食因素对微量营养素吸收的影响也应加以考虑，有研究表明:较精细的城市饮食中锌的生物利用度更高27,34.此外，缺锌可使儿童更易罹患感染，但补锌并不是降低缺锌发生的唯一途径。应探寻其它可能的替代途径，如减少摄取抑制锌吸收的食物、采取饮食多样化和食品强化26.
大量研究证实，常规补锌3个月以上的确可有效缩短发展中国家儿童急性下呼吸道感染的持续时间11, 19, 35, 36. 鉴于每年都有大量儿童死于急性下呼吸道感染，这些补锌产生的效果可使儿童期发病率和死亡率绝对值大幅下降9. 仍然十分重要的是，进一步了解在与抗生素联合使用治疗重症急性下呼吸道感染儿童时，锌元素可能起的作用，以及如何降低儿童肺炎的死亡人数。
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