挪威1975年对25,000人进行随机试验研究,五年后发现摄入维生素A少的人肺癌增高4.6倍。英国牛津大学Wald博士在1975～78年采集了16,000人的血清样品,采样前都进行了广泛的检查。到1980年4月取出已发现患癌症的86名男子的贮藏血清,并与172名情况相似的对照血清进行比较,结果表明血维生素 Norway conducted a randomized study of 25,000 people in 1975 and five years later found a 4.6-fold increase in lung cancer among those who consumed less vitamin A. Dr. Wald from the University of Oxford, UK, collected 16,000 human serum samples from 1975 to 1978 and conducted extensive tests prior to sampling. By April 1980, stored serum was collected from 86 men who had been found to have cancer and compared with 172 control sera that were in similar circumstances. The results showed that serum vitamin