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

美国科学家最新公布的一项研究结果显示，抗氧化剂和维生素似乎并不能增强人体预防肺癌的能力，这一说法可能会让许多吸烟者们大失所望。

科学家们对之前的8项此类研究结果进行了分析，发现并无证据表明维生素A、C、E或叶酸等能降低一个人罹患肺癌的危险。上述这些研究的时间跨度长达16年，研究对象达数千成年人。最终的分析报告刊登在最新一期的《国际癌症杂志》上。

从最终结果来看，平时各种维生素摄入量最多的人患上肺癌的可能性并不比摄入量最低的那些人更小。研究负责人、美国哈佛大学的曹恩永（音译）博士说，有一种观点一向颇为流行，那就是只要补充维生素，即使烟民也可以避免患肺癌。曹恩永说：“这是不符合实际的，我们的研究已经证实了这一点。”

人体内有一种被称做自由基的物质可以使多种细胞受到破坏，而维生素C和维生素E均属于抗氧化剂，这也就意味着它们会在清除自由基方面起到一定的作用。维生素A和叶酸（B族维生素的一种）同样会有助于保护住人体内那些既正常又健康的细胞。按照曹恩永的说法，上面所提到的这几种维生素一直以来均被假设成可以降低患肺癌的危险，但有关研究结果却显得摇摆不定，缺乏前后一致的结论。

曹恩永还指出，事实上即使单独某种维生素无法在抵御肺癌方面起到什么作用，但那些营养丰富的水果和蔬菜仍然有可能在一定程度上帮助人们远离肺癌的“魔爪”。这些食物之所以有益于人体健康，可能是通过其体内含有的其它成分而非各种维生素，或者是因为它们自身所具有的独一无二的营养组合，在这方面还有很多课题等待着人们去做进一步的研究。