Oranges, grapefruits and other vitamin C-loaded foods have many health benefits. But study after study has shown that the vitamin does little to cure, prevent or even shorten the duration of the common cold. 

    The most recent roundup of vitamin C research, published this spring in the Cochrane Database of Systematic Reviews, evaluated several decades of studies that included more than 11,000 subjects taking 200 or more milligrams of vitamin C each day. (The government's recommended daily allowance is 60 milligrams.) The research found that vitamin C did little to reduce either the length or severity of colds among the general population. However, studies have found that it may lower the risk of catching a cold among people whose bodies are under high physical stress—think marathon runners or soldiers on subarctic exercises. They were 50 percent less likely to catch a cold if they took a daily dose of vitamin C. 
 
    橙子、葡萄和其他含维生素C的食物对健康有很多益处。但是不断地研究表明，维生素对于感冒几乎没有治疗、预防作用，甚至也不能缩短感冒持续的时间。

    今年春季发表在“库切拉内系统评审数据库”的维生素C研究方面的最新摘要评估了几十年来的研究，包括11000名每天食用维生素C 200毫克或以上的实验对象。(政府建议每天定量60毫克。)研究发现，维生素C在普通人群中对于缩短感冒的时间或者降低感冒的严重程度几乎没有作用。然而研究发现，对于身体承受高强度体力消耗的人如马拉松运动员和在亚北极地区训练的士兵来说，服用维生素C可能降低得感冒的风险。如果这些人每天食用一定剂量的维生素，他们得感冒的几率会降低50%。