It remains uncertain as to whether nutrient supplementation for the general population considered healthy could be useful in the prevention of RTIs, such as COVID-19. In this systematic review and meta-analysis, the evidence was evaluated for primary prevention of any viral respiratory tract infection (RTI) such as SARS-CoV-2, through supplementation of nutrients with a recognized role in immune function: multiple micronutrients, vitamin A, folic acid, vitamin B12, C, D, E, beta-carotene, zinc, iron and long-chain polyunsaturated fatty acids. The search produced 15,163 records of which 93 papers (based on 115 studies) met the inclusion criteria, resulting in 199,055 subjects (191,636 children and 7,419 adults) from 37 countries. Sixty-three studies were included in the meta-analyses, which was performed for children and adults separately. By stratifying the meta-analysis by world regions, only studies performed in Asia showed a significant but heterogeneous protective effect of zinc supplementation on RTIs (RR 0.86, 95% CI 0.7–0.96, I² = 79.1%, p = .000). Vitamin D supplementation in adults significantly decreased the incidence of RTI (RR 0.89, 95% CI 0.79–0.99, p = .272), particularly in North America (RR 0.82 95% CI 0.68–0.97), but not in Europe or Oceania. Supplementation of nutrients in the general population has either no or at most a very limited effect on prevention of RTIs. Zinc supplementation appears protective for children in Asia, whilst vitamin D may protect adults in the USA and Canada. In 10/115 (8.7%) studies post-hoc analyses based on stratification for nutritional status was performed. In only one study zinc supplementation was found to be more effective in children with low zinc serum as compared to children with normal zinc serum levels.

中文翻译：

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预防健康受试者病毒性呼吸道感染的营养补充剂：系统评价和荟萃分析

对于被认为是健康的普通人群补充营养是否有助于预防 RTIs，例如 COVID-19，仍然不确定。在这项系统评价和荟萃分析中，通过补充在免疫功能中具有公认作用的营养素：多种微量营养素、维生素 A 、叶酸、维生素B12、C、D、E、β-胡萝卜素、锌、铁和长链多不饱和脂肪酸。搜索产生了 15,163 条记录，其中 93 篇论文（基于 115 项研究）符合纳入标准，共有来自 37 个国家的 199,055 名受试者（191,636 名儿童和 7,419 名成人）。荟萃分析包括 63 项研究，分别针对儿童和成人进行。²  = 79.1%，p  = .000）。成人补充维生素 D 可显着降低 RTI 的发病率（RR 0.89, 95% CI 0.79–0.99, p  = .272），尤其是在北美（RR 0.82 95% CI 0.68–0.97），但在欧洲或大洋洲没有。在普通人群中补充营养对预防 RTIs 没有影响或至多影响非常有限。在亚洲，锌补充剂似乎对儿童具有保护作用，而在美国和加拿大，维生素 D 可能对成年人具有保护作用。在 10/115 (8.7%) 研究中，进行了基于营养状况分层的事后分析。只有一项研究发现，与血清锌水平正常的儿童相比，锌补充剂对血清锌水平低的儿童更有效。