Vitamin A

Vitamin A

Vitamin A is a group of compounds that includes retinol, retinal, and retinoic acid. In addition, certain carotenoids (beta-carotene, alpha-carotene, and beta-cryptoxanthin). Another carotenoid, lycopene is not itself a precursor to vitamin A, but it is a precursor to beta-carotene.

Retinol is essential for cell growth and differentiation. It plays a major role in vision, immune system and brain functioning, metabolism and tissue regeneration. Vitamin A deficiency exacerbates thyroid dysfunction due to iodine deficiency and may play a role in metabolic syndrome.1 It is important for the reproductive system and bone growth.

Retinoic acid apparently plays a role in structuring the fovea area of the eye.2 The fovea is a tiny dip in the center of the macula which is responsible for high-sharpness vision. The photoreceptor cones are highly concentrated in that area.

Vision Health. Vitamin A is essential for vision health. As a powerful antioxidant it is one of the keystones of protection against oxidative damage caused by exposure to blue, violet and ultra violet light.

Cataract. Researchers noted as early as 1944, after reviewing data from the Nutrition and Eye Disease Study, that moderate levels of Vitamin A in patients' diets were connected to a 40% lower risk of opaque lenses, or cataracts. The researchers adjusted the risk for age, sex, smoking, and heavy drinking and found that for those who were smokers, the cataract risk was reduced by 50%.3

The Nurses Health Study was a nearly-20-year study which tracked the health of more than 50,000 female registered nurses along with their diet and levels of nutrients. Similarly, they found a 39% less risk of developing cataract with greater consumption of vitamin A in the diet (top 1/5th in levels of vitamin A consumed). Consumption of spinach was most closely tied to lowered risk. In addition, the risk of cataract in women taking vitamin C was lowered by 45%. The researchers did not evaluate consumption of multi-vitamins.4 A later meta-analysis again found significant connections between vitamin A consumption and lower cataract incidence.5

More recently researchers looked to patterns of nutrients with respect to cataract. That is, rather than looking at vitamin A (and other nutrients) in isolation, they looked at reasonably groups. Two groups that decreased cataract risk significantly were an antioxidant group (carotenes, vitamins A and C) and an omega-3 group.6

Glaucoma. IOP tends to increase slightly after the eyelids have been closed. For this reason one test used in evaluating therapies for glaucoma is the closed-eyelid test. Researchers found that giving patients vitamin A was somewhat effective in lowering IOP.7

Night blindness. Early research demonstrated that vitamin A supplementation can reverse the effects of night blindness. Even a small increase in vitamin A levels is helpful. Nepali women receiving various forms of vitamin A (vitamin A-fortified rice, retinyl palmitate, amaranth leaves, goat liver, or carrots) were evaluated weekly by standard methods, compared to healthy vision women. The researchers concluded that all of the methods decreased night blindness, and each the methods with better results were not significantly so. Both dietary vitamin A and vitamin A supplementation were effective.8

Similarly, pregnant women with varying degrees of night blindness were tested in a placebo-controlled study examining the benefits of supplementation with vitamin A and beta-carotene. Almost half of them were also tested three months after they gave birth. The degree of night blindness was evaluated by looking at the amount of light needed for the pupils of the eyes to constrict after suddenly being exposed to light. The effectiveness was also evaluated by measuring before and after blood retinol concentrations. The women who were give vitamin A performed significantly better than those receiving a placebo.

The researchers concluded that successful adaption to changes in light were closely tied to serum (blood) retinol levels and markedly improved with vitamin A supplementation.9

Retinitis pigmentosa. The retinal dystrophies such as retinitis pigmentosa (RP) lack standard treatments or widely accepted nutritional therapies and recommendations. Researchers reviewed the literature and found that a daily 15,000 IU daily dose of vitamin A had a small protective effect in slowing RP progression. In addition, lutein and beta-carotene (a vitamin A precursor) also showed some benefit.10

Stargardt's disease. Stargardt's is a type of macular dystrophy similar to AMD which forms in young children. In the case of Stargardt's, vitamin A supplementation is not recommended. Similarly, supplementation with vitamin A precursors (alpha- and beta-carotene, and beta-cryptoxanthin) is not recommended as it can be toxic to the photoreceptor cells in the retina. Patients with lower vitamin A intake experience better visual acuity.11

As part of the natural biological processes in the eye, vitamin A transforms chemically. Molecules of vitamin A sometimes bond to other vitamin A molecules and create clumps or deposits called “dimers." These dimers are found both in the elderly with AMD and in young children with Stargardt's.12

Researchers are now working on the structure of vitamin A itself. If it is possible to reduce the vitamin A’s tendency to clump within the eye, scientists might be able to create a new therapy for Stargardt's.13, 14

Source. The top source of vitamin A is beef liver. Since many people are vegetarians or don't eat beef, then the top vegetable sources are carrots and sweet potato, followed by kale, spinach, seaweed, apricots, broccoli, butter, eggs, and winter squash.

Daily need. 5,000 IU per day.

Caution. Stargardt's patients should not supplement with vitamin A.

1. Brossaud, J., Pallet, V., Corcuff, J.B., (2017). Vitamin A, endocrine tissues and hormones: interplay and interactions. Endocr Connect. Jul 18. pii: EC-17-0101.
2. da Silva, S., Cepko, C.L. (2017). Fgf8 Expression and Degradation of Retinoic Acid Are Required for Patterning a High-Acuity Area in the Retina. Dev Cell. Jul 10;42(1):68-81.e6.
3. Mares-Perelman, J.A., Klein, B.E.K., et al. (1944). Relationship Between Lens Opacities and Vitamin and Mineral Supplement Use, Ophthal.
4. Hankinson, S.E., Stampfer, M.J., Seddon, J.M., Colditz, G.A., Rosner, B., et al. (1992). Nutrient intake and cataract extraction in women: a prospective study, BMJ, Aug 8;305(6849):335-9.
5. Wang, A., Jiang, Y., Zhang, D., et al. (2014). Association of vitamin A and ß-carotene with risk for age-related cataract: a meta-analysis, Nutrition, Oct;30(10):1113-21
6. Sedaghat, F., Ghanavati, M., Nezhad, Hajian, P., Hajishirazi, S., Ehteshami, M., et al. (2017). Nutrient patterns and risk of cataract: a case-control study. Int J Ophthalmol. Apr 18;10(4):586-592.
7. Pescosolido, M., Malagola, R., Scarsella, G., Lenarduzzi, F., Dapoto, L., et al. (2012). Oxidative stress in the closed-eyelid test: management of glaucoma. Eur Rev Med Pharmacol Sci. Oct;16(10):1453-7.
8. Haskell, M.J., Pandey, P., Graham, J.M., Peerson, J.M., Shrestha, R.K., et al. (2005). Recovery from impaired dark adaptation in nightblind pregnant Nepali women who receive small daily doses of vitamin A as amaranth leaves, carrots, goat liver, vitamin A-fortified rice, or retinyl palmitate. American Journal of Clinical Nutrition. Feb;81(2):461-71.
9. Congdon, N., Dreyfuss, M., Christian, P., Navitsky, R.C., Sanchez, A.M., et al. (2000). Responsiveness of dark-adaptation threshold to vitamin A and beta-carotene supplementation in pregnant and lactating women in Nepal, Am J Clinical Nutr. Oct;72(4):1004-9.
10. Brit-Garcia, N., Del Pino-Sedeno, T., Trujillo-Martin, M.M., Coco, R.M., Rodriguez de al Rua, E., et al. (2017). Effectiveness and safety of nutritional supplements in the treatment of hereditary retinal dystrophies: a systematic review. Eye (Lond). Feb;31(2):273-285.
11. Sofi, F., Sodi, A., Franco, F., urro, V., Biagini, D., et al. (2016). Dietary profile of patients with Stargardt's disease and Retinitis Pigmentosa: is there a role for a nutritional approach? BMC Ophthalmol. Jan 22;16:13.
12. Kim, S.R., Jang, Y.P., Jockusch, S., Fishkin, N.,Turro, N., et al. (2007). The all-trans-retinal dimer series of lipofuscin pigments in retinal pigment epithelial cells in a recessive Stargardt disease model. PNAS. 104(49):19273-19278.
13. Ma, L., Kaufmann, Y., Zhang, J., Washington, I. (2010). C20-D3-vitamin A Slows Lipofuscin Accumulation and Electrophysiological Retinal Degeneration in a Mouse Model of Stargardt Disease. J. Biol. Chem. 285(10): 7966-7974.
14. Saad, L., Washington, I. (2016). Can Vitamin A be Improved to Prevent Blindness due to Age-Related Macular Degeneration, Stargardt Disease and Other Retinal Dystrophies? Adv Exp Med Biol. 854:355-61.