Vitamin A:The Forgotten Bodybuilding Nutrient:
Vitamin-A is essential to muscle-building. It is necessary for the utilization of protein and the production of testosterone and other growth factors.
"...one human study, discussed below, found the administration of vitamin A and iron to have results equivalent to the administration of testosterone itself."
Natural vitamin-A can be found in foods such as liver and food-based supplements such as cod liver oil.