Is it true that you harm yourself by having too much vitamin a?

Vitamin A: Rda for vit a varies according to age, gender, pregnancy, & lactation. See http://ods.Od.Nih.Gov/factsheets/vitamina/ [table 3] for specific numbers. Possible side effects of hypervitaminosis a are listed at http://www.Ncbi.Nlm.Nih.Gov/pubmedhealth/pmh0001390/. Generally, stopping/lowering supplemental doses reverses the symptoms.

Yes: If you are old enough to remember the big scares about Accutane and Retin-A treatments, you already have an idea. Those are essentially powerful relatives of vitamin a. Vit a is stored so is not easily excreted in urine like vits b and c. Usually od is from supplements, though have been very rare processing errors from supplemented milk.