American Journal of Clinical Nutrition, Vol 5, 431-439, Copyright © 1957 by The American Society for Clinical Nutrition, Inc.

The Relationship of Vitamin B₁₂ to Carbohydrate Metabolism and Diabetes Mellitus

¹ From the Dept. of Biochemistry, School of Hygiene and Public Health of the Johns Hopkins University, and the Wilmer Ophthalmological Institute of the Johns Hopkins University and Hospital, Baltimore

This report consists of a brief summary of experimental studies which emphasize (a) the dominant role played by vitamin B₁₂ in the utilization of carbohydrates, (b) interrelationships between vitamin B₁₂ absorption and endocrine function, and (c) some relationships of vitamin B₁₂ to diabetes mellitus.

(1) Weanling rats fed a diet, rich in carbohydrate and low in fat require more vitamin B₁₂ for growth.

(2) The fat content of the carcass of vitamin B₁₂-deficient rats is abnormally low but can be elevated by injection of this vitamin.

(3) The administration of glucose to rats results in a decrease in the vitamin B₁₂ levels of plasma or liver.

(4) Deficiency of vitamin B₁₂ causes hyperglycemia correctable with vitamin B₁₂. In vitro experiments indicate that the red cells of vitamin B₁₂-deficient animals are low in glutathione content as well as enzyme activity essential for the degradation of glucose. Other enzyme systems involved in carbohydrate metabolism such as coenzyme A in liver or DPN in liver are also deranged due to this deficiency.

(5) The effect of cortisone and thyroid on absorption of orally administered vitamin B₁₂ and retention of injected vitamin B₁₂ was re-emphasized. It was found that corticotropin (ACTH) or cortisone causes hyperglycemia, destruction of vitamin B₁₂-binding substances in muscles as well as an elevation of the vitamin B₁₂ serum level. Thyroidectomy decreases absorption of vitamin B₁₂.

(6) Some evidence of adrenal hyperactivity in diabetic patients with diabetic retinopathy, (as gathered by other investigators), has been reviewed. We caution against a premature interpretation that adrenal hyperactivity is causally or pathogenetically related to diabetic retinopathy; it may turn out to be a mere associated phenomenon.

(7) Diabetic patients without retinopathy excrete in their urines a significantly smaller amount of an orally administered radioactive vitamin B₁₂-test dose than do non-diabetic subjects or diabetic patients with retinopathy. Fecal excretion tests confirm the above findings.