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:
"DRUG FACTS AND COMPARISONS"
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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.
Comparisons of Daily Amount Taken
1 serving is 300 mg daily, 4 servings is 1,200 mg daily. 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, just remember moderation, so if using milk to take the vitamins try to avoid additional excessive dairy products.
1 serving is 3,750 IU daily, and 4 servings is 15,000 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, occurs in the liver of cod, halibut, tuna and shark, also prepared synthetically. Absorption is greater in aqueous solution than in oily solution. Vitamin A deficiencies may cause Biliary tract or pancreatic disease, sprue, colitis, hepatic cirrhosis, celiac disease.
1 serving is 405 IU daily, and 4 servings is 1,620 IU daily. 60,000 units daily is considered toxic influence.