Allen Lindsay H
USDA, ARS Western Human Nutrition Research Center, University of California, Davis, CA 95616, USA.
Food Nutr Bull. 2008 Jun;29(2 Suppl):S20-34; discussion S35-7. doi: 10.1177/15648265080292S105.
This review describes current knowledge of the main causes of vitamin B12 and folate deficiency. The most common explanations for poor vitamin B12 status are a low dietary intake of the vitamin (i.e., a low intake of animal-source foods) and malabsorption. Although it has long been known that strict vegetarians (vegans) are at risk for vitamin B12 deficiency, evidence now indicates that low intakes of animal-source foods, such as occur in some lacto-ovo vegetarians and many less-industrialized countries, cause vitamin B12 depletion. Malabsorption of the vitamin is most commonly observed as food-bound cobalamin malabsorption due to gastric atrophy in the elderly, and probably as a result of Helicobacter pylori infection. There is growing evidence that gene polymorphisms in transcobalamins affect plasma vitamin B12 concentrations. The primary cause of folate deficiency is low intake of sources rich in the vitamin, such as legumes and green leafy vegetables, and the consumption of these foods may explain why folate status can be adequate in relatively poor populations. Other situations in which the risk of folate deficiency increases include lactation and alcoholism.
本综述阐述了目前关于维生素B12和叶酸缺乏主要原因的知识。维生素B12水平低下最常见的原因是维生素的膳食摄入量低（即动物源性食物摄入量低）和吸收不良。尽管长期以来人们都知道严格的素食者（纯素食者）有维生素B12缺乏的风险，但现在有证据表明，动物源性食物摄入量低，如一些蛋奶素食者和许多工业化程度较低的国家的情况，会导致维生素B12耗竭。维生素吸收不良最常见的表现是由于老年人胃萎缩导致的食物结合钴胺素吸收不良，可能也是幽门螺杆菌感染的结果。越来越多的证据表明，转钴胺素中的基因多态性会影响血浆维生素B12浓度。叶酸缺乏的主要原因是富含该维生素的食物来源（如豆类和绿叶蔬菜）摄入量低，而食用这些食物可能解释了为什么在相对贫困的人群中叶酸水平也可能充足。叶酸缺乏风险增加的其他情况包括哺乳期和酗酒。
