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、葡萄和其他含維生素C的食物對健康有很多益處。但是不斷地研究表明，維生素對于感冒幾乎沒有治療、預防作用，甚至也不能縮短感冒持續的時間。

    今年春季發表在“庫切拉內系統評審數據庫”的維生素C研究方面的最新摘要評估了幾十年來的研究，包括11000名每天食用維生素C 200毫克或以上的實驗對象。(政府建議每天定量60毫克。)研究發現，維生素C在普通人群中對于縮短感冒的時間或者降低感冒的嚴重程度幾乎沒有作用。然而研究發現，對于身體承受高強度體力消耗的人如馬拉松運動員和在亞北極地區訓練的士兵來說，服用維生素C可能降低得感冒的風險。如果這些人每天食用一定劑量的維生素，他們得感冒的幾率會降低50%。