We hope to learn the clinical and functional signs of sub-clinical vitamin B12 deficiency and its response to supplementation in non-anemic, non-pregnant, and non-lactating women in Rural Mexico. Vitamin B12 is important in hematopoiesis, neuro-cognitive functions and genetic integrity. However vitamin B12 is only found in animal source foods therefore a large segment of the population in developing countries and those practicing vegetarianism are at risk of deficiency of the vitamin. This information will help decide weather supplementation with vitamin B12 is necessary in such populations for public health reasons.