By: Skyra
Diet has long been established to play an essential role in the maintenance of the overall health of an individual (1). Notably, numerous studies have focused on the role of vitamins in the prevention and treatment of visual disorders.
Vitamin deficiencies have been implicated in numerous ophthalmological diseases and have been shown to present various symptoms (2),(3). Of particular interest among the micronutrients is vitamin A, which has been extensively studied due to its role in photoreceptors and the phototransduction pathway. Light absorption by rhodopsin and cone opsin causes isomerization of the vitamin A form 11-cis retinal to all-trans retinal (4), which is then released from photoreceptor outer segments. All-trans retinal complexes with phosphatidylethanolamine (PE) to form N-retinylidene-phosphatidylethanolamine (N-ret-PE) and this is transported by the ABCA4 protein to the photoreceptor disk surface (5).
Vitamin A is abundant in leafy green vegetables, fish, and dairy. Clinical manifestations of vitamin A deficiency include night blindness, increased rates of infection, and softening of the cornea (keratomalacia) (6). Supplementation of vitamin A deficiency has been shown to boast numerous benefits including but not limited to the reduction of dry eye symptoms and improved dark adaptation (7).
On the other hand, vitamin overconsumption can result in toxicity. Rats that were orally administered abnormally high doses of vitamin A during gestation resulted in fetuses with eye abnormalities such as degeneration of the cornea, lens, and retina (8). In humans, Stargardt disease is an inherited autosomal recessive retinal disease characterized by mutations in the ABCA4 gene, which compromises the transport of N-ret-PE and results in the accumulation of bisretinoid (vitamin A dimer) compounds that ultimately leads to loss of retinal pigment epithelial and photoreceptor cells (5).
The key to proper eye health involves striking the right balance of vitamin levels in the human body. Nutrition guidelines based on scientific evidence set by Health Canada are readily available
online. So aim for a healthy, well-balanced diet and ensure you are consuming an appropriate amount of vitamins and minerals daily. Your eyes will thank you for it!
References
1. de Ridder, D., Kroese, F., Evers, C., Adriaanse, M. & Gillebaart, M. Healthy diet: Health impact, prevalence, correlates, and interventions. Psychol. Health 32, 907–941 (2017).
2. Preedy, V. R. Handbook of Nutrition, Diet, and the Eye. (Academic Press, 2014).
3. Whatham, A. et al. Vitamin and mineral deficiencies in the developed world and their effect on the eye and vision. Ophthalmic Physiol. Opt. 28, 1–12 (2008).
4. Birge, R. R. Rhodopsin and the First Step in Vision. in Encyclopedia of Condensed Matter Physics (eds. Bassani, F., Liedl, G. L. & Wyder, P.) 145–150 (Elsevier, 2005). doi:10.1016/B0-12-369401-9/00396-X.
5. Tanna, P., Strauss, R. W., Fujinami, K. & Michaelides, M. Stargardt disease: clinical features, molecular genetics, animal models and therapeutic options. Br. J. Ophthalmol. 101, 25–30 (2017).
6. McCullough, F. S. W., Northrop-Clewes, C. A. & Thurnham, D. I. The effect of vitamin A on epithelial integrity. Proc. Nutr. Soc. 58, 289–293 (1999).
7. Spits, Y., Laey, J.-J. D. & Leroy, B. P. Rapid recovery of night blindness due to obesity surgery after vitamin A repletion therapy. Br. J. Ophthalmol. 88, 583–585 (2004).
8.Padmanabhan, R., Singh, G. & Singh, S. Malformations of the Eye Resulting from Maternal Hypervitaminosis A during Gestation in the Rat. Cells Tissues Organs110, 291–298 (1981).
Comments