The Carotenoids that Aid Vision


image of the macula with ocular coherence tomography

There are 4 known carotenoids essential for the eye health and functioning. Those are bera-carotene, vitamin A (retinol), 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. 

The Main Functions of Carotenoids for Eye Health

  • 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, especially the macular area.

Beta-Carotene and Vitamin A     

Beta carotene serves more than one purpose.  It acts as a free radical scavenger and an anti-oxidant.  Beta-carotene is also 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.

Clinical Studies on Vitamin A

Vitamin A and beta-carotene have been studied as supplements beneficial for ARMD, cataracts, retinitis pigmentosa, dry eyes, and thyroid eye disease.

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)

Dietary Sources of Vitamin A

Vitamin A, which is formed in the body from beta-carotene by a biochemical process, can be found as preformed vitamin A from animal sources: chicken, fish oils, egg yolks, and beef products of cows which are grass-feed: liver, butter, whole milk, cheese, and cream.

The recommended daily dietary intake of Vitamin A for men is 900 micro-grams and 700 mcg for women.  Taking large doses of Vitamin A does not insure healthy eyes.  Vitamin A is a fat soluble nutrient that is stored in the body.  Those who supplement excess Vitamin A, greater than 3000 mcg per day, may experience Vitamin A toxicity. There are many side effects associated with hypervitaminosis A including visual disturbances, headache, hair loss, dry skin, jaundice, and sunlight sensitivity.  Avoid high dose Vitamin A supplements.

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 Vitamin A, the absorption and use by the body is determined by existing levels of Vitamin A already present in the body.

How Lutein and Zeaxanthin Protect Macular Health

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.  The free radical formation  by blue light energy is one of the underlying causes of degenerative macular disease.

How Lutein and Zeaxanthin effect MPD (macular pigment density) and Why It is Important

Macular Pigment Optical Density (MPOD) is a technique of measuring the concentration of these pigmented carotenoids in the macula area.  This can indicate the level of protection to the macula and the risk for developing AMD.  Patients with lower levels of macular pigment are exposed to more harmful blue light, increasing their risk of developing AMD. These patients are at greatest need of nutritional supplementation.

MPOD is measured using a specialized instrument that presents the patient with flickering lights of blue and green. The blue wavelength is absorbed by the macular pigment, the green wavelength of light is not absorbed by the macular pigment.  The person being tested is told to click the button when they detect flicker, as the radiance of the blue light is adjusted.   This test is can be done in the doctor’s office. It is quick and easy. 

Studies have shown that the higher concentration of macular pigment, formed by the accumulation of lutein and zeaxanthin, the lower the risk for developing macular degeneration.  Another study suggested that supplementing with lutein and zeaxanthin partially reversed vison loss due to macular degeneration. (Ref: Effect of lutein and zeaxanthin on macular pigment…).

Clinical Studies

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 decreased 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

The best sources for lutein and zeaxanthin are green leafy vegetables.
The NIH National Eye Institute did a study called the ARED Study. They looked at the effect of supplementation on the progression of macular degeneration.  In the second study, AREDS 2, they added lutein and zeaxanthin. They found that these two carotenoids reduce the risk for developing advanced age-related macular degeneration.  The AREDS 2 recommendation is lutein 10 mg and zeaxanthin 2 mg.

The AREDS 2 document:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4096000/#!po=17.5000

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 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:

The AREDS 2 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.

By the way…The AREDS 2 study found that the beta-carotene had the capability of competing with, and therefore decreasing, the absorption of lutein, zeaxanthin, and meso-zeaxanthin.  So do not take them together. (i.e. Do not supplement beta-carotene with the other macular pigment carotenoids.)

Other Eye Vitamin related articles:

Astaxanthin and Vision Benefits

Saffron and Eye Health

Meso-zeaxanthin, The Third Carotenoid for Macular Health

3 Most Commonly Recommended Supplements for Prevention of Macular Degeneration

Brain Health: Another Good Reason to Supplement with the Carotenoids

Carotenoids and the Brain

Researchers have found that the lutein and zeaxanthin levels in the brain correlate with the levels in the macula.  Studies have shown that the carotenoids are beneficial to visual performance. So the question is; Do the Carotenoids benefit brain performance?

There have been several studies looking at this question. Thus far, the indication is that levels of lutein and zeaxanthin as measured by MPOD relate to cognitive function in older adults. (Age and Aging,Opens in a new tab. Neurol AgingOpens in a new tab. )

Cognitive functions are skills like learning, remembering, problem-solving, and attention. Cognitive skills are not knowledge but our capability to process and speed with which we are able to carry out tasks. There seems to be a close correlation of the concentration of lutein and zeaxanthin between the retina and the brain. It was found that when measuring the level of macular pigment, that those individuals with low amcular pigment also demonstrated low cognitive function.
Carotenoid supplementation has been found to be beneficial not only for older adults but are also beneficial for younger and healthier individuals.(NutrientsOpens in a new tab.)
Researchers are also looking at the benefits of the macular carotenoids and their role in possibly reducing the progression of Alzheimer’s disease. ( J Alzheimers Dis.Opens in a new tab.)

In the end…

The carotenoids are a vast group of nutrients found in both plant and animal sources. They are vital for their anti-oxidant, anti-inflammatory and protective functions. Diseases such as cataract, age-related macular degeneration (AMD), glaucoma, and diabetic retinopathy progress by pro-oxidant and inflammatory processes. Ongoing studies have linked carotenoids to therapeutic benefits for these degenerative eye diseases.

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