Vitamin A and its antioxidant precursor, Beta-Carotene

A lesson from my nutrition class...

Food Sources:

Picture credit to: Ramzi Hashisho

Vitamin A is a fat-soluble nutrient that is found pre-formed (as retinyl esters) in many animal-sourced foods such as liver, milk & milk products, and egg yolk. It has many functions within the body, BUT it is not an antioxidant itself.

Beta-carotene, converted by the body into Vitamin A, is found in brightly coloured (especially orange) fruits and vegetables such as: papayas, yams*, tomatoes, spinach, pumpkin, carrots*, and broccoli. Beta-carotene and other related carotenoids are antioxidants.
(* = a single 125 ml serving meets or exceeds the RDA for women.)

Retinoids

There are 3 different forms of active Vitamin A in the body (retinoids), all with different uses: retinol, retinal, and retinoic acid. The body readily converts retinyl esters from animal food sources, and beta-carotene from plant sources into the retinoid form it requires. However, the conversion to retinoic acid is irreversible.
Retinol:
Retinol supports reproduction and growth. This translates to sperm development and normal fetal development in men and women, respectively. In children, vitamin A (retinol) helps remodel bone to allow for growth by supporting osteoclasts (cells that eat away at the bone to allow for growth & overall remodeling by osteoblasts).
Retinal:
Retinal is the form of vitamin A that everyone is well aware of - it supports vision. Specifically, it maintains a clear cornea (the clear front "window" of the eye), and helps covert the light energy arriving at the back of the eye (retina) into nerve impulses that allow us see.
Retinoic acid:
Retinoic acid regulates growth, thus helps maintain our constantly renewing barriers such as skin and mucous membranes within the body. Importantly, vitamin A (in the form of retinoic acid) helps protect our skin against sun damage. By maintaining our barriers, this form of vitamin A is also essential for our immune system.

Beta-carotene as an Antioxidant

Not all beta-carotene is converted to retinoids in the body. Some of it is used to quench free radicals, preventing disease, cancers, and promoting overall health. Without antioxidants to halt damage, free radicals are capable of altering DNA & RNA (thus changing proteins), causing overall cell damage, diseases and aging. For this reason, try to incorporate both dark green and bright orange vegetables and fruits in your daily diet. Adults should be consuming 7-10 servings of both raw and cooked fruits and vegetables every day (the majority should be vegetables) .

Recommended Intakes

Adult men: 700µg RAE/day
Adult men: 900µg RAE/day
Upper level/limit = 3000µg / day

RAE = Retinol activity equivalents
1 µg retinol = 1 RAE
12 µg beta-carotene = 1 RAE (due to inefficient conversion within the body)


Should you supplement with beta-carotene?
Research tends to show that supplementation with beta-carotene have either no effect or even increased mortality in smokers. (This must be taken with a grain of salt since there are usually many experimental design flaws in bio-availability of supplementation, diet, and lifestyles...)
Studies found that smokers have an increased risk of CHD and lung cancer when supplementing with beta-carotene.
However... increased food-sourced beta-carotene, decreases risk of both coronary heart disease (CHD) and colorectal cancer.
So eat up your veggies and toast to your health!

<3 Jessica


Reference:
Whitney, E., Rolfes, S., Hammond, G., & Piche, L. (2013). The Antioxidant Nutrients. In Understanding Nutrition (1st Canadian ed.). Toronto: Nelson Education.