In regard to acceptable levels determined by authorities as to whether there is a potential toxicity level relative to the amount a person can take of any given drug, vitamin, mineral, or any type of nutritional supplement:
The following is per the pharmacology reference:
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The following is not guaranteed by anybody, as information or opinions can change without notification. This information is provided as an intended guideline. The reader is responsible for its own verification and is advised to discuss this information with their doctor or assume their own responsibility of verification.
One serving is 30 mg daily. Zinc must be taken with food, no exceptions. Although bran and dairy products will reduce zinc absorption, it is fine when used in a shake to mix with the vitamins because it helps to get the vitamins into the body. Remember moderation. If using milk to take the vitamins then avoid additional excessive dairy products.
One serving is 3,750 IU daily. FDA guidelines indicate a maximum of: 25,000 in a single serving, 1 million daily for 3 days, or 50,000 daily for 18 months, when no deficiency is evident. If deficiency is evident, then treatment can be as high as 500,000 for 3 days followed by 50,000 for 2 weeks.
Only found in animal sources. It occurs in the liver of cod, halibut, tuna and shark. Also is prepared synthetically. Absorption is greater in aqueous solution than in oily solution.
One serving is 405 IU daily. 60,000 units daily is considered toxic influence.