Poor vision is a problem that affects many people around the world. Some of the conditions that result in poor vision include age-related macular degeneration (AMD) and cataracts. AMD affects the macula, a central part of the retina. As a result, one’s vision becomes blurry. Cataracts, on the other hand, are a clouding of eye lenses that blocks light from reaching the retina, causing an individual’s vision to become blurry (Whatham et al., 2008). Research shows that vitamin A supplementation helps to deal with vision problems. Vitamin A supplementation is a health strategy that is used to eliminate the deficiency of vitamin A in the body and its consequences. The topic of this review paper is Vitamin A supplementation and vision. The objective is to determine how vitamin A supplementation affects vision.
Vitamin A Supplementation will help vision related problems.
Data and Results
In their study, Tiruvalluru, Ananthathmakula, Ayyalasomayajula, Nappanveettil, Ayyagari and Reddy (2013) investigate vitamin A supplementation ameliorate obesity-related retinal degeneration among rats. The sample used consisted of 32 lean and 32 obese rats of the WNIN/OB strain. Each group was divided into four categories and subjected to various levels of vitam A supplementation. Data was analyzed using SPSS, and they established that body weights of the lean rats remained unchanged after treatment with vitamin A supplementation. On the other hand, the body weight of the obese rats in category 3 and 4 reduced significantly. It was also established that the level of plasma glucose in the obese groups was higher and that vitamin supplementation did not influence the level of plasma glucose. The level of plasma retinol was higher in obese groups than in the lean groups. Like in the case of plasma glucose, vitamin A supplementation did not affect the level of plasma retinol.
Gene expression was also analyzed in this study and it was established that there was increased expression of rod-specific genes in the obese groups as a result of vitamin A supplementation. However, the increased level for various genes differed depending on the dose of vitamin A administered. In terms of retinal morphology, the researchers established that, while there is limited change in retinal morphology of the lean groups, there were significant changes in retinal morphology in the obese groups.
In another study, Rotenstreich et al. (2013) examined the effect of oral treatmen with 9-cis β-carotene on the visual function of patients of Retinitis pigmentosa (RP). In the study, 34 eligible patients were selected in a cross-over, placebo-controlled, and double-masked clinical trial that ran from 1st April 2008 to 31st May 2009. The participants were assigned randomly to a 90-day regime of 4 capsules daily, each capsule containing 300 mg of placebo or 9-cis β-carotene-rich bardawi. The β-carotene comprised of equal amounts of all-trans and 9-cis isomers. Dunaliella capsules were given to 16 participants while remaining participants receive placebo. Out of the 34 participants selected, 29 completed the study. Out of the 29, 21 were men and 8 were women. The mean age was 46.7, with standard deviation of 16.9. The age of participants ranged from 21 to 74 years. Ethnically, two participants were Israel-born, 10 were from either America or Europe, and 17 were born from either Africa or Asia.
Treatment with Dunaliella resulted in significant increase in the plasma content of all-trans β-carotene, both in the placebo-first group and in the Dunaliella-first group. Al-trans β-carotene was reduced after washout. However, the baseline remained higher as compared to the initial. The researchers also established that the interocular difference in the ERG b-wave responses was not significant in 27 participants out of the 29 who completed the study. However, when they analysed the eyes of the participants separately, they established that the placebo-first group showed a higher b-wave response. On the impact of treatment on maximal dark-adapted and light-adapted ERG b-wave amplitudes, the researchers established the Dunaliella treatment resulted in significant increase in the maximal dark-adapted ERG b-wave amplitude, +7.8 μV for the left eyes and +8.9 μV for the right eyes. On the other hand, the placebo treatment led to a reduction in the ERG b-wave, with the reduction more significant in the right eyes as compared to the left ones (-3.9 μV for the left eyes and -7.9 μV for the right eyes). The treatment of dunaliella also resulted in positive change in binocular mean (+8.4 μV) and visual field areas. On the other hand, placebo treatment reduced binocular mean change (-5.9 v μV).
In their study, Akuffo et al. (2017) examined the effect of supplemental macular carotenoids and coantaxidants on visual function among individuals suffering from age-related macular degeneration. They used 121 participants whom after being subjected to the treatment, they significantly improved in terms of visual function for both primary and secondary outcome measure (P=0.013 for primary outcome measure). It was also established that there were significant rise in macular pigment over time (P˂0.005).
Lastly, in their study, Wolf-Schnurrbusch, Zinkernagel, Munk, Ebneter and Wolf (2015) examined the effect of oral lutein supplementation on macular pigment density and contrast sensitivity. In the study, 79 patients were randomly assigned to two treatment groups, with 40 participants assigned to the lutein only treatment and 39 subjected to a combination of lutein and omega treatment. Six of the participants were smokers, 23 of them ex-smokers while 50 had never smoked. All participants had AMD or drusen pigmentary abnormalities. In the first 6 months, all participants took 10 mg of lutein with omega-3 fatty acids for the group subjected to the combination treatment. The macular pigment optical density (MPOD) level at baseline was 0.54+/- 0.19 D.U for the group subjected to the Lutein treatment and 0.56 +/- 0.21 D.U. After 6 months, the MPOD level for the lutein group increased to 0.66 DU and 0.60 DU for the lutein and omega group. The change in the lutein was significant (P˂0.005). On the other hand, the change in the lutein and omega was not significant (P=0.059). The authors also established that the contrast sensitivity (CS) score increased from 1.29 to 1.69 for the lutein group but did not change for the lutein and omega group. Plasma levels of zeaxanthin and lutein showed changes in the lutein group, but remained unchanged for the lutein and omega group.
Name of authors
Type of study
Tiruvalluru, Ananthathmakula, Ayyalasomayajula, Nappanveettil, Ayyagari and Reddy
Vitamin A supplementation positively affects vision
Rotenstreich, Belkin, Sadetzki, Chetrit, Ferman-Attar, Sher and Harats
Oral treatment with 9-cis β-carotene has a positive effect on visual function
Akuffo, Beatty, Peto, Stack, Stringham, Kelly and Nolan
Randomized controlled study
Supplemental antioxidants positively affects visual function
Wolf-Schnurrbusch, Zinkernagel, Munk, M. R., Ebneter and Wolf
Randomized, open label study
Lutein treatment increases both MPOD and CS levels
The studies upheld the stated hypothesis because all of them show a positive effect of vitamin A supplementation on visual function. However, the results show that not all forms of supplementation results in positive visual function. For example, in their study Rotenstreich et al (2013) established that placebo treatment resulted in negative visual function in terms of maximal dark-adapted ERG b-wave. On the other hand, in their study, Wolf-Schnurrbusch et al (2015) established that treatment, which involves a combination of lutein and omega-3, does not have any effect on MPOD and CS levels. The negative effects of some of supplementation as well as lack of effect of other supplementations raise the question as to why this is the case. As such, there is need for more research to be carried out to determine why the placebo treatment, for instance, causes reduced ERG b-wave.
The reviewed studies provide valuable information on the role played by vitamin A supplementation and other forms of supplementation on the vision improvement. The varying types of study allow for comparison. Moroever, the fact that there is a general agreement among the studies on the role of vitamin A supplementation in vision improvement provides significant proof that vitamin A supplementation is effective in treating vision problems among people. However, the studies also had various limitations. For example, Tiruvalluru et al (2013) focused only on how vitamin A supplementation affects retinal morphology. The researchers, therefore, examined the retinal morphology of the rats and drew conclusions. While the comparison between obese and lean rats lends credence to the findings, the study does not consider other factors that may have affected the retinal morphology. For instance, the obese rats reduced weight significantly over the period. However, the researchers failed to examine the possibility that changes in the retinal morphology could have been due to changes in weight rather than the vitamin A supplementation.
The general limitation of the studies is their lack of analysis of why and how the various supplementations determine the various aspects of visual function. For instance, while Rotenstreich et al (2013) established that placebo treatment has a negative effect on maximal dark-adapted ERG b-wave, they did not explain why this is the case. Similarly, Wolf-Schnurrbusch et al (2015) failed to examine why lutein treatment improves MPOD and CS levels. The number of participants in each study was also small and less diverse. For example, Tiruvalluru et al (2013) used only 64 rats from one strain; thus it is not possible to determine whether the strain could have influenced the results. Such shortcomings are witnessed in all the other studies. Despite the limitations, the studies provide valuable knowledge on vitamin A supplementation and the role it plays in visual function. The knowledge provides a basis for more research on the subject. For example, researchers can focus on the specific details, using the knowledge in these studies as a foundation.
Akuffo, K. O., Beatty, S., Peto, T., Stack, J., Stringham, J., Kelly, D., … & Nolan, J. M. (2017). The impact of supplemental antioxidants on visual function in nonadvanced age-related macular degeneration: a head-to-head randomized clinical trial. Investigative ophthalmology & visual science, 58(12), 5347-5360.
Rotenstreich, Y., Belkin, M., Sadetzki, S., Chetrit, A., Ferman-Attar, G., Sher, I., … & Harats, D. (2013). Treatment With 9-cis β-Carotene–Rich Powder in Patients With Retinitis Pigmentosa: A Randomized Crossover Trial. JAMA ophthalmology, 131(8), 985-992.
Tiruvalluru, M., Ananthathmakula, P., Ayyalasomayajula, V., Nappanveettil, G., Ayyagari, R., & Reddy, G. B. (2013). Vitamin A supplementation ameliorates obesity-associated retinal degeneration in WNIN/Ob rats. Nutrition, 29(1), 298-304.
Whatham, A., Bartlett, H., Eperjesi, F., Blumenthal, C., Allen, J., Suttle, C., & Gaskin, K. (2008). Vitamin and mineral deficiencies in the developed world and their effect on the eye and vision. Ophthalmic and Physiological Optics, 28(1), 1-12.
Wolf-Schnurrbusch, U. E., Zinkernagel, M. S., Munk, M. R., Ebneter, A., & Wolf, S. (2015). Oral lutein supplementation enhances macular pigment density and contrast sensitivity but not in combination with polyunsaturated fatty acids. Investigative ophthalmology & visual science, 56(13), 8069-8074.
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