Vitamin A

Today's lesson is the eye saving Vitamin A! Vitamin A has many important roles besides the well known vision function. So, let's get started!

Vitamin A is fat-soluble, which means it needs fat to be absorbed by the body. Insufficient fat intake can lead to a secondary Vitamin A deficiency. Fat soluble vitamins are stored in the body for longer periods of time than water soluble vitamins.

Vitamin A, aka the retinoids, consist of 3 preformed compounds: retinol (an alcohol), retinal (an aldehyde), and retinoic acid (an acid). These active forms of Vitamin A can only be found in animal products (liver, fat of eggs and milk).

The liver plays a major role in the transport and storage of Vitamin A. Liver disease can cause secondary Vitamin A deficiencies. Fun fact: 50-80% of the Vitamin A in your body is stored in your liver!

Carotenoids, found in dark green leafy, yellow-orange vegetables (carrots, sweet potatoes, kale, spinach), can yield retinoids when metabolized in the body. Fun fact: the deeper the color of the vegetable, the higher the levels of carotenoids. The amount of Vitamin A available from dietary carotenoids depends on how well they are absorbed and converted to retinol in the body. Beta carotene, a subgroup of the carotenoids, is well known for its antioxidant capacities.

Vitamin A plays essential roles in vision, cell differentiation, recognition, and growth, bone development, immune functions, and reproduction.  Retinal is a structural component of visual pigments of the rod and cone cells of the retina. Retinoic acid acts as a hormone to affect gene expression.

Vitamin A deficiencies can be very serious. The most significant cause of blindness is due to Vitamin A deficiency.
-->Xerophthalmia: clinical eye disease consisting of atrophy of the periocular glands
-->Nyctalopia: night blindness, failure of retina to regenerate rhodopsin, cannot adjust from bright light to darkness
-->Spontaneous abortions
-->Impaired spermatogenesis
-->Phrynoderma: blockage of hair follicles with plugs of keratin, which causes "toad skin" (rough, scaly, dry skin).

RDA for Vitamin A
-adult females: 700ug
-adult males: 900ug

Toxicity of Vitamin A occurs when persistent large doses (more than 100 times the required amounts) are consumed. Toxicity can eventually lead to liver disease. The most common side effect of excessive carotene intake is hypercarotenodermia, which causes an orange tint to the skin. This is reversible by decreasing carotenoid intake.

UL for Vitamin A
-adult females: 3000mg
-adult males: 3000mg