Vitamin B12 metabolism in the fruit bat (Rousettus aegyptiacus). The induction of vitamin B12 deficiency and its effect on folate levels

1. Vitamin B 12 metabolism was studied in bats of the species Rousettus aegyptiacus , which live on an all-fruit diet in the wild. 2. There was a wide range in values for the serum vitamin B 12 concentration of newly captured bats, but bats captured in the early spring had significantly higher mean serum vitamin B 12 levels than bats captured in the early autumn. 3. There was an exponential decrease in serum vitamin B 12 concentration with time in captivity for bats fed on a vitamin B 12 -deficient, all-fruit diet; the biological half-life was 80 d in serum, 109 d in liver and 164 d in kidney. 4. The main storage organ for vitamin B 12 in the bat was the liver, mean content 1067 ng vitamin B 12 . After 50 d, injected [ 57 Co]cyanocobalamin had equilibrated with body vitamin B 12 stores, and 17% of the retained radioactivity was present in the liver. From these results it was calculated that the total body vitamin B 12 content of the bat was c. 6500 ng. 5. The biological half-life of injected [ 57 Co]cyanocobalamin was 70–88 d and the calculated daily requirement was 50–60 ng (0.2 μg/kg body-weight per d). 6. As serum vitamin B 12 levels decreased, serum folate levels increased. The erythrocyte folate concentration increased significantly after 130 d on the all-fruit diet and then decreased to the initial values after 190 d. 7. Vitamin B 12 metabolism in the fruit bat is similar in many respects to that of man, but on a ‘weight-for-weight’ basis the bat has a 5- to 15-fold greater requirement for this vitamin. 8. Vitamin B 12 deficiency may be induced fairly rapidly in fruit bats fed on an all-fruit diet.