Vit(A)min

What do you have to know about Vitamin A?

Let's start with some basics.

Vitamins fall under two categories-- fat soluble or water soluble. Vitamin A is fat soluble, which means that they are absorbed in the body by way of lipids. Due to its ability to be absorbed by fat cells, excess Vitamin A is accumulated in the body in adipose/fatty tissue. 

The compound can be further categorized as either pre-formed vitamin A or pro-vitamin A. 

Pre-formed vs. Pro-vitamin A:

Pre-formed vitamin A means that the body readily converts this into the active form of the vitamin once it enters your system. If you wish to get pre-formed vitamin A from whole foods, animal products such as liver, fish oil, milk, and eggs, have shown to have the highest concentration of pre-formed vitamin A [1].

The second category, pro-vitamin A, is NOT readily converted into the active form and is primarily used on an as-need basis. So, your body will not use these up until it is absolutely necessary. The majority of pro-vitamin A is derived from plant-based food, the most popular being carrots. Foods rich in pro-vitamin A tend to be more vibrant in color. The greener, redder, yellower, and orang-er the vegetables are, the more pro-vitamins it contains. 

One thing to note is that BOTH pre-formed and pro-vitamin A must be converted by the body to retinal, the active form of vitamin A, to aid in the biological function of the vitamin. The only difference between the two is when they are converted into the active form. 

So, now that the basics are out of the way-- What are some health benefits of Vitamin A?

• it plays a big role in vision, especially under low-light conditions (Although, it certainly won't make you have night-vision!) [2]
• vitamin A, in the form of beta-carotene, may have some anti-oxidant properties by eliminating free radicals that accumulate in the body. 
• the body requires vitamin A for cell growth and differentiation, [3]
• studies have shown that individuals that obtain vitamin A from food products show that there is a lower risk of certain cancers such as prostate or lung cancer. [4]

What about the side effects? Well, this is where things get a bit serious. 

Recall that vitamin A is a fat-soluble vitamin. This means that if you take too much pre-formed vitamin A, any excess will be stored in your body and cause what is known as "Hypervitaminosis A." Side effects of excess vitamin A intake can range from nausea, headache, and blurred vision to something more severe like hypercalcemia or in some cases, even death. 

However, there lies some exceptions. In the form of pro-vitamin (beta-carotene), it has not been shown to cause any toxicity or death in individuals that take too much of it. One sure way of knowing that an individual is taking too much pro-vitamin A is when their skin their orange, a condition called Carotenosis. 

Of course, the toxic effects of vitamin A may not always be immediate and is most probably the cause of long-term ingestion of pre-formed vitamin A. 

If there are serious side effects to taking vitamin A supplements, why should I take it then? 

In most individuals, vitamin A supplementation is not necessary-- especially in individuals with a diet rich in animal products such as meat and dairy. 

Some vegans and vegetarians might need to supplement their diet with Vitamin A as the levels of vitamin A in certain fruits and vegetables may not be sufficient. 

To summarize, vitamin A should be ingested via whole foods as part of a balanced, healthy diet. If an individual is not taking in enough vitamin A, a multivitamin that contains a low-moderate dose of pro-vitamins or a mixture of pre-formed and pro-vitamin A may suffice. 

1. Ross CA. Vitamin A. In: Coates PM, Betz JM, Blackman MR, et al., eds. Encyclopedia of Dietary Supplements. 2nd ed. London and New York: Informa Healthcare; 2010:778-91.
2. http://ods.od.nih.gov/factsheets/VitaminA-HealthProfessional/
3. http://www.ncbi.nlm.nih.gov/pubmed/7832047
4. http://www.ncbi.nlm.nih.gov/pubmed/2196482