purplepixie
It depends on the type of Vitamin A taken aswell as assessment of a person's individual deficiency status.
The Upper Intake Level is 10,000IU for male and female adults.
This page is excellent source for dosage and types of vit A:
http://ods.od.nih.gov/factsheets/VitaminA-HealthProfessional/
It's important to not think that it's best to buy the highest IU you can find as in retinol form (fat soluble) gets stored in the liver and toxicity can result...as the link above talks about.
Hency why knowing your Vit A nutritional status will better help determine the dosage.
Symptoms of deficiency affecting body function are hypothyroidism, keratin 'spots' (white small hard lumps on the skin), night blindness, acne..aswell as other symptoms.
It was 3 years ago that i developed night blindness, after years of having acne, keratin spots.
Co-factors of Vit E and zinc are needed for Vit A utilisation in the body.
I don't think it's wise to take the Vit A and E together at the same time though as research a while back on them suggests they both compete for the same receptors so taking them together is a waste of the supplement.
I stopped all supplements for a good 10 weeks to do some tests, and the keratin spots and hypothyroid symptoms have returned so i think it's a really valuable vitamin to consider in hormone health, and is mostly over-looked.