Why are you most likely to overdose on vitamin a than vitamin c?

Vitamin A comes in two forms: Retinol/Retinaldehyde and Beta-Carotene. Retinol/Retinaldehyde comes from animal sources while Beta-Carotene comes from plant sources. Only Vitamin A in the form of Retinol can be toxic or "over-dosed". This is because Vitamin A in this form is fat-soluble. Thus, when you consume over 100% of the recommended daily value, the rest is stored in your fat and organs, and thus can build up in your body and cause Vitamin A toxicity. Vitamins A,D,E, and K are the fat soluble vitamins and can all cause toxicity. However, Vitamin C and the B-vitamins (folate/folic acid, thiamin, riboflavin, niacin, cyanocobalamin etc) are the water soluble vitamins. Thus, when you consume over 100% of the recommended daily value, you excrete the rest in your urine and feces. It is EXTREMELY difficult and rare to find a toxicity of the water-soluble vitamins for this reason. Remember though, Vitamin A in the form of Beta-Carotene can not cause Toxicity because it is not fat soluble. Generally, the nutrition community will refer to Vitamin A in the Retinol/Retinaldehyde form in current texts and Beta-Carotene as its own entity.

Please visit www.eatright.org the website of the American Dietetic Association for more information or related questions.

PS. I'm a dietitian :)