世界衛生組織 (WHO) 近日的數據顯示，全球新增新型冠狀病毒肺炎 (COVID-19)感染和死亡個案從三月高鋒期（全球每週超過一千萬宗感染，超過四萬五千宗死亡）跌至本週的最低水平（全球每週三百多萬宗感染，九千多宗死亡）。雖然疫情大流行結束有望，但新冠病毒帶來的後遺症亦不可忽視。
2019冠狀病毒長期綜合症或長新冠 (long COVID)，是指新冠病人在痊癒後（病毒檢測陰性/超低病毒量）出現持續至少兩個月的多種 (multifarious) 症狀，包括疲倦、腦霧、失眠、咳嗽等。不論輕症或重症的新冠患者都有機會出現長新冠症狀。
有研究推算全球有近五成新冠患者，在痊癒後持續出現長新冠症狀至少4個月。而疲倦是最常見的症狀，大概在兩成長新冠患者中出現。香港有研究調查106名新冠患者，有八成出現長新冠症狀，當中超過三成在半年後亦有持續性疲倦的問題。英國亦有研究追蹤八百多名新冠曾住院、其後出現長新冠症狀的患者一年，發現當中只有約四分一患者在五個月後長新冠症狀消失；而一年後亦再只有三成左右患者完全痊癒，還有一半的患者繼續受長新冠症狀影響。可見新冠病毒的後遺症對日常生活及工作或會帶來一定的影響。
長新冠腸道菌失衡 或缺丁酸/L-異亮氨酸
科學家對長新冠的成因只有初步的認識。有研究指出免疫系統紊亂造成炎症、肌肉病變 (myopathy)，導致肌肉無力及疲乏等，都可能是促成長新冠的原因。前文曾提及本港一項研究發現，腸道菌失衡與長新冠症狀有重要的關聯。其中長新冠患者的腸道比沒有感染過新冠病毒的人，缺少了不少益菌，例如有調節免疫系統及抗炎作用的普拉梭菌 (Faecalibacterium prausnitzii)。研究指出，缺少普拉梭菌與長新冠症狀如疲乏、脫髮、呼吸道症狀、腸道症狀等有關。
除了長新冠患者，另一項本地研究分析了66名新冠感染者，亦發現感染者的腸道也比沒有感染的人明顯地缺少了普拉梭菌。普拉梭菌佔健康成年人的腸道菌約5%，能促進有益化合物如短鏈脂肪酸(short chain fatty acid) 丁酸 (butyric acid) 和支鏈氨基酸 (branched chain amino acid) L-異亮氨酸 (L-isoleucine) 的產生。亦有研究發現新冠感染者在感染期間，甚至在痊癒後30天，糞便中的L-異亮氨酸和丁酸水平都比正常健康人士少。長新冠患者可能因缺少普拉梭菌而缺少丁酸和L-異亮氨酸。
腸道益菌產有益代謝物 抗炎解乏調免疫
丹麥有研究邀請16名長期持續感到疲倦乏力的長新冠患者，進行各種肌肉檢測。結果發現有五成受試者肌肉乏力、75%在肌電圖 (Electromyography)中發現肌肉病變、38%有肌肉萎縮的現象。L-異亮氨酸能幫助修復和重建肌肉組織、調節免疫等作用。最近有研究發現被餵食L-異亮氨酸的高脂飲食小鼠，五週後它們的肌肉量及肌肉纖維密度明顯比沒有吃L-異亮氨酸的多，可見L-異亮氨酸有幫助修復和重建肌肉組織。
巴西研究指出長新冠患者與沒有後遺症的新冠康復者有不同的細胞因子譜 (cytokine profile)，例如長新冠患者有較少能抑制發炎的IL-10 (interleukin-10)，可能因此令炎症反應維持，並引起多種長新冠症狀。中國有研究給受輪狀病毒感染的小豬服用L-異亮氨酸，發現L-異亮氨酸亦可透過調節細胞因子 (cytokine) 以提升IL-10水平，來增強先天 (innate) 和後天 (adaptive) 免疫能力。而丁酸具有抗炎及維持腸道健康的作用。有研究指出服用丁酸的小鼠體內有更多IL-10；而另一項研究也發現餵食普拉梭菌的小鼠體內有更高的IL-10基因表達。長新冠患者可透過增加腸道中的普拉梭菌，或它的代謝物丁酸和L-異亮氨酸，調節免疫系統和減少炎症。
L-異亮氨酸亦與情緒及腦部運作有關。墨西哥有研究分析90多名有抑鬱症狀的年長婦女，發現她們血液中的支鏈氨基酸，包括L-異亮氨酸水平，與抑鬱症狀有反向關聯。抑鬱症狀越明顯的患者，其血液中的L-異亮氨酸水平就越低。美國亦有研究發現腦部被注入丁酸鈉 (sodium butyrate) 的小鼠有更好的學習能力和記憶力。總括而言，普拉梭菌和它的代謝物丁酸和L-異亮氨酸，對減輕長新冠症狀或有效用。
益生菌助增好菌 減輕長新冠症狀
雖然補充普拉梭菌有助舒緩長新冠症狀，但普拉梭菌是一種絕對厭氧微生物(obligate anaerobes)，對氧氣極度敏感。有研究指出，普拉梭菌在有氧環境下兩分鐘內便會死亡。雖現今技術上並未能將普拉梭菌穩定地製成方便服用的益生菌補充產品，但可以服用其他合適的益生菌來增加腸道普拉梭菌的水平。
印度有臨床研究顯示腸易激 (irritable bowel syndrome, IBS) 患者服用80天的芽孢乳酸桿菌 (Bacillus coagulans) 後，腸道內有更多普拉梭菌，以及與改善長新冠有關的腸道菌，如假鏈狀雙歧桿菌 (Bifidobacterium pseudocatenulatum)、腹真桿菌 (Eubacterium ventriosum) 等。除此之外，研究也發現凝結芽孢桿菌亦能增加與改善新冠重症有關的青春雙歧桿菌 (Bifidobacterium adolescentis) 水平。另一項英國臨床研究發現，服用了28天芽孢乳酸桿菌GBI-30, 6086（BC30）的長者，比服用安慰劑的長者，腸道內有更多普拉梭菌；而其免疫細胞在培植環境下，能製造更多抗炎細胞因子IL-10。印度亦有臨床研究發現長新冠患者服用含有芽孢乳酸桿菌的補充劑後，疲倦症狀有明顯改善。益纖蛋白及益纖朱古力富含能增加腸道普拉梭菌的芽孢乳酸桿菌BC30，對長新冠有關的腸道失衡或有幫助。
金裝益纖菌內的雙歧桿菌 HN019和嗜酸乳桿菌 NCFM，亦能調節腸道，補充丁酸和L-異亮氨酸。前文曾提及有研究將雙歧桿菌 HN019和嗜酸乳桿菌 NCFM分別以糞便和大腸模型培植，發現丁酸的濃度都有顯著增加。而嗜酸乳桿菌 NCFM亦有製造L-異亮氨酸的基因，有利增加體內L-異亮氨酸水平。
大家可食用金裝益纖菌、益纖蛋白及益纖朱古力來補充益生菌，增強免疫力、維持腸道健康及改善新冠後遺症，建立健康的體魄來迎接疫後新生活。
參考資料/延伸閱讀:
＜益生第一關＞2022/07/29--『益生菌增強免疫防感染緩長新冠』
https://hskgene.com/blogs/probiolife-first/probiotics_long_covid
＜益生第一關＞2022/04/01--『染疫後遺長新冠 [HN019] 益生菌恢復健康』
https://hskgene.com/blogs/probiolife-first/long_covid
＜益生第一關＞2022/03/11--『打3針增強免疫「HN019」益生菌添助力』
https://hskgene.com/blogs/probiolife-first/3rd-vaccination
＜益生第一關＞2021/12/10--『益生菌促進益菌適當補充保健康』
https://hskgene.com/blogs/probiolife-first/beneficial_bacteria
Easy Reading:
End of Covid pandemic in sight: WHO
https://news.rthk.hk/rthk/en/component/k2/1666828-20220915.htm
Coronavirus disease (COVID-19): Post COVID-19 condition
新冠後遺症（長新冠）是甚麼？
中大發現新冠患者的腸道內缺乏可調節免疫力的益菌八成新冠患者出現「長新冠」症狀腸道微生態失衡成關鍵
Beneficial Bacteria: A Focus on Faecalibacteriumprausnitzii
Google Images:
long COVID and gut dysbiosis 長新冠和腸道菌群失調
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