Calder Philip C, Kew Samantha
Institute of Human Nutrition, School of Medicine, University of Southampton, Bassett Crescent East, UK.
Br J Nutr. 2002 Nov;88 Suppl 2:S165-77. doi: 10.1079/BJN2002682.
The immune system acts to protect the host from infectious agents that exist in the environment (bacteria, viruses, fungi, parasites) and from other noxious insults. The immune system is constantly active, acting to discriminate 'non-self' from 'self'. The immune system has two functional divisions: the innate and the acquired. Both components involve various blood-borne factors (complement, antibodies, cytokines) and cells. A number of methodologies exist to assess aspects of immune function; many of these rely upon studying cells in culture ex vivo. There are large inter-individual variations in many immune functions even among the healthy. Genetics, age, gender, smoking habits, habitual levels of exercise, alcohol consumption, diet, stage in the female menstrual cycle, stress, history of infections and vaccinations, and early life experiences are likely to be important contributors to the observed variation. While it is clear that individuals with immune responses significantly below 'normal' are more susceptible to infectious agents and exhibit increased infectious morbidity and mortality, it is not clear how the variation in immune function among healthy individuals relates to variation in susceptibility to infection. Nutrient status is an important factor contributing to immune competence: undernutrition impairs the immune system, suppressing immune functions that are fundamental to host protection. Undernutrition leading to impairment of immune function can be due to insufficient intake of energy and macronutrients and/or due to deficiencies in specific micronutrients. Often these occur in combination. Nutrients that have been demonstrated (in either animal or human studies) to be required for the immune system to function efficiently include essential amino acids, the essential fatty acid linoleic acid, vitamin A, folic acid, vitamin B6, vitamin B12, vitamin C, vitamin E, Zn, Cu, Fe and Se. Practically all forms of immunity may be affected by deficiencies in one or more of these nutrients. Animal and human studies have demonstrated that adding the deficient nutrient back to the diet can restore immune function and resistance to infection. Among the nutrients studied most in this regard are vitamin E and Zn. Increasing intakes of some nutrients above habitual and recommended levels can enhance some aspects of immune function. However, excess amounts of some nutrients also impair immune function. There is increasing evidence that probiotic bacteria improve host immune function. The effect of enhancing immune function on host resistance to infection in healthy individuals is not clear.
免疫系统的作用是保护宿主免受环境中存在的感染因子（细菌、病毒、真菌、寄生虫）以及其他有害侵害。免疫系统持续活跃，致力于区分“非己”与“己”。免疫系统有两个功能分区：先天性免疫和获得性免疫。这两个组成部分都涉及多种血源性因子（补体、抗体、细胞因子）和细胞。存在多种评估免疫功能方面的方法；其中许多方法依赖于在体外培养中研究细胞。即使在健康人群中，许多免疫功能也存在很大的个体差异。遗传因素、年龄、性别、吸烟习惯、运动习惯水平、饮酒量、饮食、女性月经周期阶段、压力、感染和疫苗接种史以及早期生活经历可能是观察到的差异的重要影响因素。虽然很明显免疫反应明显低于“正常”水平的个体更容易受到感染因子的影响，并且感染发病率和死亡率会增加，但尚不清楚健康个体之间免疫功能的差异与感染易感性的差异之间有何关系。营养状况是影响免疫能力的一个重要因素：营养不良会损害免疫系统，抑制对宿主保护至关重要的免疫功能。导致免疫功能受损的营养不良可能是由于能量和大量营养素摄入不足和/或特定微量营养素缺乏所致。这些情况通常同时出现。（在动物或人体研究中）已证明免疫系统有效运作所需的营养素包括必需氨基酸、必需脂肪酸亚油酸、维生素A、叶酸、维生素B6、维生素B12、维生素C、维生素E、锌、铜、铁和硒。实际上，所有形式的免疫都可能受到这些营养素中一种或多种缺乏的影响。动物和人体研究表明，在饮食中补充缺乏的营养素可以恢复免疫功能和抗感染能力。在这方面研究最多的营养素是维生素E和锌。将某些营养素的摄入量增加到习惯水平和推荐水平以上可以增强免疫功能的某些方面。然而，某些营养素过量也会损害免疫功能。越来越多的证据表明益生菌可改善宿主免疫功能。在健康个体中，增强免疫功能对宿主抗感染能力的影响尚不清楚。
