It has long been known that regular, moderate exercise is one of the best things you can do for your health, with studies showing that trained athletes have increased levels of natural killer cells that fight infection. But as anyone who practises endurance sports probably knows, hard training for an event like a cycle race or a marathon run can leave you with a dandy head cold or other upper respiratory tract infection (URTI).
人们很早以前就知道，定期而适度的锻炼是对健康最有益的事情之一。研究表明，受过训练的运动员体内抗感染的“自然杀伤细胞”水平升高。不过，练习耐力运动的人也许都知道，为参加自行车比赛或马拉松长跑这样的赛事而开展的艰苦训练，可能会让你患上头伤风或其他上呼吸道感染(URTI)。
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