Can preformed vitamin A (retinol) be toxic?
Vitamin A can be toxic in EXCESS, and so can iron, selenium, manganese, vitamin D and many other important nutrients. It is even possible to overdose on pure water. We no longer fear vitamin D toxicity, but for some reason the fear of vitamin A still persists. The fear is largely unfounded. Just because a toxicity of retinol is possible, does not mean that it is highly toxic or something to avoid. To put it into perspective, let’s use the most extreme precaution. It has long been suggested not to exceed 10,000 IU of pre-formed vitamin A during pregnancy due to an increased risk of birth defects. As a result, even health professionals have often treated this number as a “toxic” level, even advising women to avoid vitamin A altogether. But, that is not how safety levels are set, and it does not accurately represent the toxicity of vitamin A. There haven’t been any confirmed birth defects at levels less than 25,000 IU. The 10,000 IU level has a large safety margin built into it. Levels of 25,000-50,000 IU taken chronically over months or years have been problematic, but primarily in people with already compromised liver function. The level at which it becomes potentially toxic far exceeds what you would get from a diet (unless you eat large amounts of liver every day) or typical multivitamin supplements. Basically, you would have to be taking separate high dose vitamin A or over consuming cod liver oil consistently to have a concern over vitamin A toxicity.
Vitamin A as retinol, retinyl palmitate, or retinyl acetate is not something to fear or avoid. After all, it is an essential vitamin.