Vitamin C has long been known to counter scurvy and be of general benefit as an antioxidant in human nutrition. It has been strongly associated with a reduction in cataract formation in the eye. Recently where there has been little understanding of the role of vitamin C is brain health. Interestingly, the research is linked back to eyes. Scientists at the Oregon Health & Science University (OHSU) and the University of Buenos Aires in Argentina have shown that the GABA type receptors in the cells of the retina require substantial amounts of vitamin to function well. The GABA type receptors that are found in the brain maintain communication links between neurones. When vitamin C is depleted the GABA type receptors in retinal cells stop working. Scientists are suggesting that retinal cells are indicators of brain functioning because of their close association with the central nervous system (CNS).

Vitamin C is a well known antioxidant and could simply act in the retinal cells as a protector against free radical damage. It is known that even when it has disappeared from other cells around the body, the CNS maintains levels as high as possible. It was postulated that a better understanding of the biochemical mechanisms in pathological eye disease such as glaucoma might be better understood.

There have been a couple of studies demonstrating that vitamin C protects eye proteins against oxidative damage induced by UV irradiation when judged by measuring histidine and thiol oxidation (Linetsky et al., 1998; Varma et al., 1997) but the evidence for reducing cataract dmage is controversial. In earlier epidemiological studies, cataract damage is claimed to be reduced by vitamin C supplementation as shown in the Nurses study (Chasan-Taber et al., 1999) , the Beaver Dam Eye study (Mares-Perlman et al., 2000), studies on the Mediterranean population (Valero et al., 2002), and the Japan Public Health Center (Yoshida et al., 2007). However most recently in the Physicians’ Health Study II (PHS II) (Christen et al., 2010) it was shown that both vitamin C and E supplementation had no appreciable effect on cataract formation. In fact in a study over 8 years long, vitamin C supplementation was associated with an increase in cataract damage (Rautiainen et al., 2010) because there was a 25% higher incidence of cataract extraction. Clearly, there is still plenty of research to be conducted on knowing whether vitamin C helps improve eye health.

References

Chasan-Taber, L., Willett, W. C., Seddon, J. M., Stampfer, M. J., Rosner, B., Colditz, G. A. & Hankinson, S. E. (1999) A prospective study of vitamin supplement intake and cataract extraction among US women. Epidemiology 10 pp. 679-684

Christen, W.G., Glynn, R.J., Sesso, H.D., Kurth, T. MacFadyen, J., Bubes, V., Buring, J.E., Manson, J-A E., Gaziano, J.M. (2010) Age-Related Cataract in a Randomized Trial of Vitamins E and C in Men. Arch. Opthalmology 128 (11) pp. 1397-1405

Hull, C., Li, G-L., Von Gersdorff, H. (2011) GABA Transporters regulate a Standing GABAc Receptor-Mediated Current at a Retinal Presynaptic Terminal. J. Neuroscience 31 (26) pp. 9672-9682

Linetsky, M., Ranson, N., Ortwerth, B. J. (1998) The aggregation in human lens proteins blocks the scavenging of UVA-generated singlet oxygen by ascorbic acid and glutathione. Arch. Biochem. Biophys. 351 pp. 180-188

Mares-Perlman, J., Lyle, B., Klein, B., Fisher, A. I., Brady, W. E., Van den Langenberg, G. M., Trabulsi, J. N. & Palta, M. (2000) Vitamin supplement use and incident cataracts in a population-based study. Arch. Ophthalmol. 118 pp. 1556-1563

Rautiainen, S., Lindblad, B.E., Morgenstern, R. Wolk, A. (2010) Vitamin C supplements and the risk of age-related cataract: A population-based prospective cohort study in women. Amer. J. Clin. Nutr. 91(2) pp. 487-493

Valero, M.P., Fletcher, A.E., De Stavola, B.L., Vioque, J., Alepuz, V.C. (2002) Vitamin C is associated with reduced risk of cataract in a Mediterranean population. J. Nutr. 132, pp. 1299-1306.

Varma, S. D., Ali, A. H., Devamanoharan, P. S., Morris, S. M. (1997) Nitrite-induced photo-oxidation of thiol and its implications in smog toxicity to the eye: prevention by ascorbate. J. Ocular Pharmacol. Ther. 13, pp. 179-187

Yoshida M, Takashima Y, Inoue M, et al. (2007) Prospective study showing that dietary vitamin C reduced the risk of age-related cataracts in a middle-aged Japanese population. Eur. J Nutr. 46(2): pp. 118–124