Vitamin A

[fireblaze]

how long does it take for vitamin A to significantly improve eye sight?

[SU_reptile]

I think it has individual effect. Nevertheless, I am sure one need to have permanent diet reach in vit A in order to improve it's sight. However It doesn't have effect if one has efe defect (for example astigmatism, which is the defect of defraction in cornea).
For further information try to find some everaged data in medical or biological tables.

[canalon]

lack of vitamin A is bad for eyesight, I don't know how long you need to be on a regular diet to improve things in case of avitaminosis.

In case of problem not related to that I am not sure that taking vitamin A could significantly improve your vision.

[xand_3r]

You should not take vitamin A if you don't have sight problems related to avitaminosis (lack of night vision or bad night vision). Hipervitaminosis A is related with increased cancer risks, with facial malformations of the embryo during pregnancy or even with skin disorders (if you eat too many carrots which are rich in B-caroten your skin will become orange-like). Unlike hidrosoluble vitamins, which can be easily removed from the organism (even in very large quantities) fat soluble vitamins require more time to be eliminated. Even if you take a certain vitamin in large doses, if you don't have a lack of that vitamin the result will be 0 because the organism tends to eliminate any excess vitamin.

[Condraz23]

Retinol is converted into retinal and transported to the retina, thus improving eyesight.