Vitamin A, Beta-carotene, Lutein, and Zeaxanthin
The category of vitamin carotenoids is a vast group of biochemicals essential for biological function of immunity, cardiovascular health, cancer prevention, and vision. We are concerned here only with the 4 known to be vital for the eye health and functioning. Those are bera-carotene, vitamin A (retinol), lutein, and zeaxanthin.
- Beta-carotene and vitamin A are responsible for retinal function in the eye, and
- lutein and zeaxanthin are important for protection of the retina of the eye.
Beta-Carotene and Vitamin A
Beta-carotene is a provitamin, meaning it is a precursor to vitamin A (retinol). Vitamin A is made in the body from the beta-carotene molecule:
Beta-carotene >> Vit. A (retinol) >> Retinal (retinaldehyde)
The retinal is processed in the retina into a light sensitive molecule which becomes a part of the visual cycle of the photoreceptors called rods. This retinal-based molecule is important for detecting light. A deficiency in Vitamin A is responsible for night blindness.
Vitamin A and beta-carotene have been studied as supplements beneficial for ARMD, cataracts, retinitis pigmentosa, dry eyes, and thyroid eye disease.
A 1993 study found that a regiment of Vitamin A, 15,000 IU per day, slowed the progression of typical retinitis pigmentosa. More recent studies have focused on vitamin A in combination with omega-3 fatty acids (DHA), (Read more).
Vitamin A has not been recommended as a supplement for those with inherited macular dystrophies, such as Stargardt’s disease (ABC A-4 mutation), Best’s disease, and cone-rod dystrophies. It is thought to cause an increase in deposits resulting in toxicity and death to the cells of the retina. (Read more.) Clinical trials are now underway for a modified form of Vitamin A which is safer for those with the ABC A-4 mutation. (Read more.) (clinicaltrials.gov)
Supplementation of beta-carotene for smokers and former smokers has not been recommended because of a possible risk of developing lung cancer. (See safety concerns,Medline)
Signs and symptoms of Vitamin A toxicity include blurred vision, bone pain, headaches, liver damage, and yellowing of the skin.
Dietary Sources of Vitamin A
Vitamin A, which is formed in the body from beta-carotene by a biochemical process, can be found as vitamin A from animal sources: fish oils, egg yolks, and beef products of cows which are grass-feed: liver, butter, whole milk, and cream.
Dietary Sources of Beta-carotene
Beta-carotene, which is the provitamin of Vitamin A is from plant sources. The carotenoids, as a group are the pigment of plants. It is easy to remember, because the carotenoid-rich plants are the ones which are highly pigmented such as orange foods: carrots, sweet potatoes, apricots, yellow foods like squash and mangos, and green leafy vegetables like spinach and kale, and peppers which come in all 3 colors.
Since beta-carotene is a provitamin to Viamin A, the absorption and use by the body is determined by existing levels of Vitamin A already in the body.
Lutein and Zeaxanthin
Lutein and zeaxanthin are carotenoids found in the retina and lens. They tend to be concentrated in the very sensitive macula. These carotenoids have the capability to absorb blue light. This protects the light sensitive layers of the eye from the high-energy wavelengths of light that can damage the retina and supporting tissues.
Lutein and zeaxanthin are a part of the Age-Related Macular Degeneration Study 2 (AREDS 2). It is part of a supplement formula which can reduce the risk of advanced ARMD by 25%. Many studies have been done which hypothesize a decrease risk for the development of ARMD for those with higher levels of macular lutein and zeaxanthin. It is also being studied for its role in decreasing the progression of cataracts. There is a study of lutein and zeaxanthin as a supplement for those with albinism. (clinicaltrials.gov)
Dietary Sources of Lutein and Zeaxanthin
There was a study reported in the British Journal of Ophthalmology which found that egg yolks and corn had the highest levels of lutein and zeaxanthin, but could be found in most green leafy vegetables and colored fruits and vegetables. Lutein enriched egg yolks can be found that were naturally formed by feeding the chickens pigment -rich feed.
Eye Vitamins and the Carotenoids
There are many eye vitamins out there. It can be difficult to determine which is best.
Those that claim to be an AREDS formula, which you will recall studied those with intermediate or advanced ARMD, will have 15 mg of beta-carotene. A vitamin that claims AREDS 2 formula, will substitute 10 mg lutein and 2 mg of zeaxanthin for the beta-carotene. This formula may also be called an aging eye formula or macular formula:
Vitamin C 500mg / per day
Vitamin E 400 IU / per day
zinc 80 mg / per day
copper 2 mg / per day
lutein 10 mg /per day
zeaxanthin 2 mg / per day
Vitamins that are called an eye multi-vitamin formula, may include vitamin A. If it is described as a formula which supports eye health, it may not be a multi-vitamin but it may include other supplements that have been determined to be eye healthful, such as fish oils (DHA), selenium, and vitamin D to name a few.
In future blogs I will be covering other supplements considered eye healthful.