Ok, this may or may not be a bad question, but I just came up with this: Vitamin A is good for eyesight, per say. If someone were to have bad eyesight, could you inject their body and immune system with a large amount of Vitamin A to give them good or better eyesight? On the other hand, could you just give someone lots of Vitamin A and give them AMAZING eyesight? That being applied to Vitamins for strength or healing, could you technically create (I hesitate to say this, but...) a super soldier, basically breed someone or enhance some one to be a warrior? Another bad example but the only one i can think of being close to describing it, but same concept of Captain America, but more realistic. Thanks for listening to my bad examples! ;)

You have misunderstood. Whilst Vit A deficiency causes night blindness (see URL below), there is absolutely no evidence that raised level improves sight. In fact high levels of Vit A are toxic and can cause serious illness or even death!

https://en.wikipedia.org/wiki/Vitamin_A_deficiency