Pernicious anemia is a common cause of megaloblastic anemia throughout the world and especially in persons of European or African descent. Dietary deficiency of vitamin B12 due to vegetarianism is increasing and causes hyperhomocysteinemia. The breast-fed infant of a vitamin B12-deficient mother is at risk for severe developmental abnormalities, growth failure, and anemia. Elevated methylmalonic acid and/or total homocysteine are sensitive indicators of vitamin B12-deficient diets and correlate with clinical abnormalities. Dietary vitamin B12 deficiency is a severe problem in the Indian subcontinent, Mexico, Central and South America, and selected areas in Africa. Dietary vitamin B12 deficiency is not prevalent in Asia, except in vegetarians. Areas for research include intermittent vitamin B12 supplement dosing and better measurements of the bioavailability of B12 in fermented vegetarian foods and algae.

中文翻译：

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维生素B12缺乏症是一个全球性的问题。

恶性贫血是导致全世界巨幼细胞性贫血的常见原因，尤其是在欧洲或非洲血统的人中。由于素食导致的饮食中维生素B12的缺乏正在增加，并引起高同型半胱氨酸血症。缺乏维生素B12的母亲的母乳喂养的婴儿有发生严重发育异常，生长衰竭和贫血的风险。甲基丙二酸和/或总高半胱氨酸水平升高是维生素B12缺乏饮食的敏感指标，并且与临床异常相关。在印度次大陆，墨西哥，中美洲和南美洲以及非洲的某些地区，饮食中维生素B12缺乏症是一个严重的问题。饮食中维生素B12缺乏症在亚洲并不普遍，素食主义者除外。