Studies have been done to determine the optimal dosage of vitamin E. Vitamin E is generally considered to be relatively nontoxic at high dosage in spite of the fact that it is a fat-soluble vitamin. From our experiments using mice, when various dosages of all-rac-alpha-tocopherol were injected into the intraperitoneal cavity every day, 1) the body weight decreased when the dose was more than 100 IU/kg per day, and all the mice died within 3 days at 400 IU/kg per day; 2) immune responses investigated by lymphoproliferative assays with phytohemagglutinin, concanavalin A and lipopolysaccharide were enhanced significantly between 5 and 20 IU/kg per day, but were inhibited by 80 IU/kg per day. When the immunopotentiation effect of vitamin E was discernible, serum tocopherol levels were about twice the control values. From our results, the optimal dosage of vitamin E was between 5 and 20 IU/kg per day, and dosages over 80 IU/kg per day were toxic to mice. We then experimented similarly with vitamin K, which is fat soluble and possesses a quinone structure resembling vitamin E. When doses between 12.5 and 150 mg/kg per day of vitamin K were injected into the intraperitoneal cavity daily fore 14 days, increase of body weight was generally inhibited. This did not depend on the dose, and there was no definite relationship between mitogen responses and vitamin K.

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