Contrary to what some smokers may hope, antioxidants and other vitamins seem to offer no protection against lung cancer, new research suggests.

    In an analysis of eight previous studies, researchers found no evidence that vitamins A, C, E or folate lower a person's risk of lung cancer.

    Across the studies, which followed thousands of adults for up to 16 years, people with the highest intakes of the vitamins were no less likely to develop lung cancer than those with the lowest intakes.

    There has been a popular notion that even smokers can ward off lung cancer by taking vitamin supplements, Dr. Eunyoung Cho, the lead author of the new report, told Reuters Health.

    "This is not true, and our study confirmed that," said Cho, an assistant professor of medicine at Harvard Medical School and Brigham and Women's Hospital in Boston.

    She and her colleagues report the findings in the International Journal of Cancer.

    Vitamins C and E are antioxidants, which means they help neutralize cell-damaging substances in the body called free radicals. Vitamin A and folate, a B vitamin, also help maintain normal, healthy cells.

    All of these vitamins have been hypothesized to cut lung cancer risk, according to Cho's team, but the research evidence has been spotty. In particular, most prospective studies -- those that follow people over time -- have found no clear protective effect.

    But because these studies have included only a small number of lung cancer cases, their findings are less reliable. So Cho and her colleagues pooled data from eight prospective studies that followed a total of 430,281 adults in Europe and North America, including 3,206 who developed lung cancer.

    After the researchers factored in smoking habits and other variables, like overall diet, weight and education, there was no evidence that vitamins A, C, E or folate reduced lung cancer risk.

    There was initially some evidence that vitamin C from food, but not supplements, was protective. But that connection disappeared when the researchers accounted for beta-cryptoxanthin, a plant chemical that gives color to oranges, red peppers, carrots and other red-orange fruits and vegetables.

    Because many vitamin C-rich foods contain beta-cryptoxanthin, the latter nutrient may help explain the link some studies have found between vitamin C and lower lung cancer risk, the researchers speculate.

    In fact, it is still possible that nutrient-rich fruits and vegetables, if not individual vitamins, help protect against lung cancer, Cho said.

    These foods, she explained, might confer benefits through components other than vitamins, or through their unique combinations of nutrients -- though, she added, there is still much to be learned in this area

    美國科學家最新公布的一項研究結果顯示，抗氧化劑和維生素似乎并不能增強人體預防肺癌的能力，這一說法可能會讓許多吸煙者們大失所望。

    科學家們對之前的8項此類研究結果進行了分析，發現并無證據表明維生素A、C、E或葉酸等能降低一個人罹患肺癌的危險。上述這些研究的時間跨度長達16年，研究對象達數千成年人。最終的分析報告刊登在最新一期的《國際癌癥雜志》上。

    從最終結果來看，平時各種維生素攝入量最多的人患上肺癌的可能性并不比攝入量最低的那些人更小。研究負責人、美國哈佛大學的曹恩永（音譯）博士說，有一種觀點一向頗為流行，那就是只要補充維生素，即使煙民也可以避免患肺癌。曹恩永說：“這是不符合實際的，我們的研究已經證實了這一點。”

    人體內有一種被稱做自由基的物質可以使多種細胞受到破壞，而維生素C和維生素E均屬于抗氧化劑，這也就意味著它們會在清除自由基方面起到一定的作用。維生素A和葉酸（B族維生素的一種）同樣會有助于保護住人體內那些既正常又健康的細胞。按照曹恩永的說法，上面所提到的這幾種維生素一直以來均被假設成可以降低患肺癌的危險，但有關研究結果卻顯得搖擺不定，缺乏前后一致的結論。

    曹恩永還指出，事實上即使單獨某種維生素無法在抵御肺癌方面起到什么作用，但那些營養豐富的水果和蔬菜仍然有可能在一定程度上幫助人們遠離肺癌的“魔爪”。這些食物之所以有益于人體健康，可能是通過其體內含有的其它成分而非各種維生素，或者是因為它們自身所具有的獨一無二的營養組合，在這方面還有很多課題等待著人們去做進一步的研究。