Evidence regarding the minimal daily requirement of dietary vitamin B12

The minimal daily requirement of dietary vitamin B12 is defined as that amount which must be ingested in the diet to prevent the occurrence of megaloblastosis, anemia, or other manifestations of vitamin B12 deficiency. An attempt has been made to define this requirement by studying hematological responses to varying amounts of the vitamin in five south Indian subjects with vitamin B12 deficiency anemia (one due to gastric atrophy and four due to dietary deficiency). Amounts ranging from 0.07 to 0.25 micrograms of dietary vitamin B12 were shown to be inadequate but amounts ranging from 0.3 to 0.65 microgram were adequate or possibly more than adequate. It is concluded that the minimal daily requirement of dietary vitamin B12 for the average south Indian adult is in the region of 0.5 microgram/day and that an intake of 1.0 microgram/day would cover the needs of the vast majority of the population and allow a wide margin of safety.