Peto R, Doll R, Buckley J D, Sporn M B
Nature. 1981 Mar 19;290(5803):201-8. doi: 10.1038/290201a0.
Human cancer risks are inversely correlated with (a) blood retinol and (b) dietary beta-carotene. Although retinol in the blood might well be truly protective, this would be of little immediate value without discovery of the important external determinants of blood retinol which (in developed countries) do not include dietary retinol or beta-carotene. If dietary beta-carotene is truly protective--which could be tested by controlled trials--there are a number of theoretical mechanisms whereby it might act, some of which do not directly involve its 'provitamin A' activity.
人类患癌风险与（a）血液视黄醇和（b）膳食β-胡萝卜素呈负相关。尽管血液中的视黄醇很可能具有真正的保护作用，但如果没有发现血液视黄醇的重要外部决定因素（在发达国家，这些因素不包括膳食视黄醇或β-胡萝卜素），这在当下几乎没有什么实际价值。如果膳食β-胡萝卜素确实具有保护作用（这可通过对照试验来检验），那么有多种理论机制表明它可能发挥作用，其中一些机制并不直接涉及其“维生素A原”活性。
