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Vitamin C and Eye Health
Abstract
Vitamin C is a water-soluble vitamin that is essential for the biosynthesis of collagen, carnitine, and catecholamines. It serves as a strong antioxidant and protects proteins, lipids, and DNA from oxidative damage. The eye contains the highest concentrations of vitamin C found in the human body. Vitamin C is important to eye health because of its role in protecting the proteins of the crystalline lens from oxidation, in serving as a free radical scavenger in the retina, and in promoting wound healing in the cornea. Scurvy, the classic syndrome of vitamin C deficiency, includes some findings of ophthalmological importance, including vascular abnormalities of the conjunctiva, dry eyes, and hemorrhages of the conjunctiva, orbit, anterior chamber, and retina. Vitamin C may become increasingly important to ocular health with demographic changes such as increasing life span and a larger aging population, and with the continued depletion of the stratospheric ozone layer (1).
... Ascorbic acid (AA) is absorbed in the main form of vitamin C in most vegetables, constituting in summer squash about 80%À90% of the total vitamin C (Semba, 2007). Thus in scallop fruits, in which the vitamin C content is close to 21 mg 100 g 21 FW (Balbierz and Kolota, 2015), around 86% of this value is AA (18 mg/100 g FW), as shown in (Blanco-Díaz et al., 2016) and the pumpkin and vegetable marrow had the lowest AA content (B9 mg 100 g 21 FW) (Sargent and Maynard, 2012;Blanco-Díaz et al., 2015). ...
The main economic value of the Cucurbita species resides in the consumption of its immature fruits as vegetables, commonly known as summer squashes. The beneficial health effects of summer squash are attributed to their bioactive compounds, contributing positively to the daily nutritional intake and also protecting against some diseases, including diabetes, cardiovascular diseases, accelerated aging, and some types of cancer. This chapter provides an overview of nutritional composition, antioxidant properties, as well as the health benefits of the eight summer squash morphotypes (pumpkin, vegetable marrow, cocozelle, zucchini, acorn, scallop, crookneck, and straightneck). We also highlight the influence of ripening stage, agronomic conditions, and environmental variation that can contribute to increase desirable summer squash attributes as well as the potential contribution to the required daily intake by compiling the most recent works found in the literature on this subject.
A wide variety of the roots and tubers plays a major role in human diet, animal feed,
and industrial raw materials. Sweet potatoes (SPs) play an immense role in human diet
and considered as second staple food in developed and underdeveloped countries.
Moreover, SP production and management need low inputs compared to the other
staple crops. The color of SP flesh varied from white, yellow, purple, and orange.
Scientific studies reported the diversity in SP flesh color and connection with nutritional and sensory acceptability. Among all, orange-fleshed sweet potato (OFSP)
has been attracting food technologists and nutritionists due to its high content of
carotenoids and pleasant sensory characteristics with color. Researchers reported
the encouraging health effects of OFSP intervention into the staple food currently
practicing in countries such as Uganda, Mozambique, Kenya, and Nigeria. Scientific
reviews on the OFSP nutritional composition and role in vitamin A management
(VAM) are hardly available in the published literature. So, this review is conducted to
address the detailed nutritional composition (proximate, mineral, carotenoids, vitamins, phenolic acids, and antioxidant properties), role in vitamin A deficiency (VAD)
management, and different food products that can be made from OFSP.
Despite the recorded rarity of ocular vascular lesions in human scurvy, conjunctival lesions appeared during deprivation of ascorbic acid in five of nine volunteers who participated in two studies of experimental scurvy in man, three of four men in the first study and two of five men in the second. The ocular lesions often appeared early in the development of clinical scurvy and were first noted after deprivation of ascorbic acid for 74–95 days.
These lesions varied from minute bulbar conjunctival hemorrhages and varicosities to a large subconjunctival hemorrhage accompanied by palpebral petechial hemorrhages, and conjunctival congestion.
Ascorbic acid (vitamin C) is commonly used as a dietary supplement, often in megadoses. However, as the daily oral dose is increased, the concentration of ascorbic acid in the plasma and other body fluids does not increase proportionally, but instead tends to approach an upper limit. For example, when the daily dose is increased from 200 to 2500 mg (from 1.1 to 14.2 mmol) the mean steady state plasma concentration increases only from approximately 12 to 15 mg/L (from 68.1 to 85.2 mumol/L). Published data were reanalyzed with an integrated modeling approach to shed new quantitative light on this phenomenon. This analysis is based on the renal clearance of ascorbic acid, which rises sharply with increasing plasma concentrations as a result of saturable tubular reabsorption. The analysis indicates that both saturable gastrointestinal absorption and nonlinear renal clearance act additively to produce the ceiling effect in plasma concentrations. As a consequence of this ceiling effect, there is no pharmacokinetic justification for the use of megadoses of ascorbic acid.
The lens, being devoid of blood vessels in postnatal life, is dependent on its surrounding media for nutrition and respiration. However, because of its internal oxidative mechanism, it is partly independent of the aqueous for its respiration. It is fortunate that this is so, for, according to Duke-Elder,¹ the oxygen tension of the aqueous is insufficient to meet the requirements of the lens. The internal oxidative system of the lens functions through the agencies of glutathione and vitamin C, or cevitamic acid. The latter is present in the aqueous and lens, while the former is found only in the lens.
These substances are capable of being reversibly oxidized and reduced, thus forming a so-called "redox" system. This property depends on the ability of glutathione and vitamin C to accept hydrogen, and in this process the hydrogen donor (the lens) is oxidized. That the reversibly oxidized vitamin C is
Objective
To determine if there is an association between the surgical outcome of trabeculectomy and uric acid and ascorbic acid concentrations in the aqueous humor at the time of the procedure.
Patients, Materials, and Methods
Aqueous humor samples were collected from the eyes of 169 of 249 adult patients who underwent trabeculectomy alone for any type of glaucoma between April 1989 and July 1995. Postoperatively, all medical records were reviewed and outcomes were classified as successful, unsuccessful, or indeterminate. The ascorbic acid and uric acid concentrations were determined in masked fashion by high-pressure liquid chromatography. Factors associated with surgical outcome were determined.
Results
Uric acid concentration was higher in unsuccessful eyes (mean±SD, 0.21±0.08 mmol/L, n=26) than in successful eyes (0.15±0.09 mmol/L, n=91, 95% confidence interval for difference, 0.02-0.10 mmol/L). Ascorbic acid levels were not significantly different in the eyes with unsuccessful (1129.9±601.9 µmol/L) and successful (1334.3±511.0 µmol/L) surgery (95% confidence interval for difference, −475.2 to 66.4 µmol/L, P=.13) surgery. Other factors associated with failure were previous surgery and surgery performed at the inferior limbus. A multiple polytomous logistic regression analysis was performed, after excluding the small number of operations performed at the inferior limbus. The odds ratio for failure increased by a factor of 1.68 for every 1-mmol/L increase in uric acid (95% confidence interval, 1.16-2.43, P=.006).
Conclusions
Uric acid levels were higher at the time of surgery in eyes that had unsuccessful outcomes than in those with successful outcomes. No significant difference in ascorbic acid levels was detectable. A higher uric acid level in the aqueous humor is a risk factor for trabeculectomy failure and might be tested as a prognostic indicator. Understanding the host characteristics that determine whether a trabeculectomy will be successful in a given eye is important. Data from the Fluorouracil Filtering Surgery Study Group suggest that in eyes with previous surgery the following are risk factors for surgical failure: time elapsed since the last procedure involving a conjunctival incision, the number of previous procedures involving conjunctival incisions, high preoperative intraocular pressure, and Hispanic ethnicity. In addition, previous intraocular surgery itself, age, race, and the diagnosis of uveitic or neovascular glaucoma are generally considered risk factors for trabeculectomy failure.
A woman who embraced a Zen macrobiotic philosophy with its rigid nutritional system was completely bedridden and near death with the classical manifestations of scurvy and severe folic acid and protein deficiency. This rigid diet is a threat to life and should be condemned.
A 13-YEAR-OLD white girl had an 18-hour history of spontaneous right proptosis (Figure 1) and significant periorbital and retrobulbar discomfort. This had developed while she was resting quietly. She had not recently taken aspirin, nonsteroidal anti-inflammatory drugs, or anticoagulants.Figure 1.Appearance of patient at time of presentation with right-sided proptosis. The superior sulcus was expanded and tense to palpation.
Excised guinea pig ciliary body-iris preparations accumulated 1J <C-labeled L-ascorbate. The concentrating mechanism required glucose as well as Na+, K+, and Ca++ ions in the media and is inhibited by ouabain, dinitrophenol, iodoacetate, cyanide, fluoride, desoxycorticosterone, and hydrocortisone. It demonstrates saturation kinetics with increasing concentrations of L-ascorbate in the media and is competitively inhibited by D-isoascorbate. Ascorbate is secreted into the aqueous humor of the guinea pig's posterior chamber. By raising the plasma ascorbate level, saturation kinetics can be demonstrated. T, .he high ascorbate concentration of aqueous humor in guinea pigs, rabbits, sheep, and many other species including most primates has been a subject of con-siderable research effort and interest. In the Living rabbit eye it has been postulated that ascorbate is secreted into the posterior chamber aqueous humor, and saturation kinetics have been demonstrated by raising the plasma ascorbate level. 1 ' 2 In addition L-ascorbate has been shown to be accumu-lated by rabbit ciliary body-iris prepara-tions incubated in vitro. 3 ' 4 It was the purpose of this study to further elaborate upon the in vitro accumulation of L-ascorbate by the guinea pig ciliary body and to relate this to in vivo ascorbate trans-port into the guinea pig eye.
L-ascorbic acid (ascorbate or vitamin C) is a required nutrient for humans. Absorption, transport, and disposition of ingested ascorbate involve the following: (1) bioavailability and absorption in the gastrointestinal tract; (2) presence in the circulation; (3) tissue distribution; (4) excretion; and, (5) metabolism. Fundamental to each of the above are ascorbate chemistry and mechanisms of transport of ascorbate across membranes. Ascorbate can be reversibly oxidized to dehydroascorbic acid, which can be irreversible degraded. Both reduced and oxidized forms cross cell membranes. Differences in transport kinetics, tissue specificity, and Na+ and energy dependence strongly support the existence of separate transport mechanisms. An important consideration in the analysis of ascorbate transport iss that of substrate availability. Reduced ascorbate is by far the most predominant form found in plasma and tissues. Dehydroascorbic acid is rapidly reduced intracellularly to ascorbate by both enzymatic and chemical mechanisms. Despite constitutively low levels of dehydroascorbic acid, conditions that promote oxidation of ascorbate can profound alter both the nature and availability of substrate. Elucidation of mechanisms that modulate the delivery of ascorbate to tissues and its utilization under different metabolic conditions will be invaluable for making recommendations for ascorbate ingestion. Published by Elsevier science Inc. 1998.
In the aqueous humour and the corneal epithelium of rabbits, the ascorbic acid levels were investigated using the photometric assay with 2,6-dichlorophenolindophenol. After injection of 300 mg/kg body weight of ascorbate, the aqueous humour ascorbic acid levels were slightly elevated, showing the well-known saturation kinetics. In the corneal epithelium the ascorbic acid levels were increased by twice the amount of that of the aqueous humour. The significance of an ascorbic acid therapy in corneal diseases is discussed
Scurvy is caused by a deficiency of vitamin C (ascorbic acid) and still occurs in developed countries. Those most at risk of scurvy are elderly people, men who live alone, people who are dependent on alcohol, people with fadish diets,1 mentally ill patients, and those undergoing peritoneal dialysis and haemodialysis.2 Scurvy is not usually reported in patients with cancer but its frequency is probably underestimated.
We describe six cases of scurvy in patients with cancer.
From January 1993 to September 1996 we observed six cases of scurvy in 3723 patients with non-cancerous conditions and six cases in 219 patients with cancer. Tables 1 and 2 give details of the six cases in the patients with cancer. All of the patients were men. Two of them (cases 2 and 4) lived alone and three (cases 1, 2, and 4) drank heavily. …
MOST of the recorded measurements of the reduced glutathione content of tissues have been made by Tunnicliffe's method of titration with iodine on the assumption that the trichloracetic extracts of tissue contain little else but glutathione capable of reducing iodine in acid solution. A method depending upon a different principle was introduced by Mason, who found that the reduced glutathione content of liver, kidney and yeast extracts determined by titration against iodine is 120-200 per cent of the true value. His method has however been neglected, and the iodine method has been used almost exclusively. Recently, Bierich has evolved a third method for the estimation of reduced glutathione and has also obtained values much lower than those obtained by iodine titration. Ever since the discovery of ascorbic acid, it has been evident (as is mentioned by these workers) that where ascorbic acid occurs in the tissues, it will be estimated as glutathione in the iodine titration; but it has been assumed without any evidence that ascorbic acid occurs only in traces except in the suprarenal cortex.
IN previous communications a method has been described for estimating the hexuronic (ascorbic) acid content of foodstuffs, based on titration in acid solution with the oxidation-reduction indicator 2-6-dichlorophenolindophenol after preliminary extraction with trichloracetic acid1, 2, 3. Judging from the fact that this method when applied to some forty common sources-mostly fruit and vegetable materials-enabled the `minimal antiscorbutic doses' to be calculated to give results in excellent agreement with the values determined directly by biological tests, it is evident that the method has a considerable range of specificity. A number of necessary conditions and provisions were set out, which unfortunately there seems to have been some tendency to overlook, and it would appear advisable therefore to direct attention to certain considerations which must be borne in mind if the possibility of misleading conclusions is to be avoided.
Purpose: To better understand wound healing after glaucoma filtration surgery by measuring the production of type I and type III collagen in cultured Tenon's fibroblasts and determine the effect of ascorbic acid on collagen subtype production. Methods: An ELISA-type dot blot assay was used to directly measure the production of types I and III collagen by subconfluent cultures of fibroblasts from human Tenon's capsule. Because ascorbic acid is both high in aqueous humor and necessary for the production of collagen, we measured the dose response of type I and type III collagen production to ascorbic acid. Results: Ascorbic acid stimulated an increase in collagen production that reached a maximum level at 100 [mu]g/ml. This is approximately half of the ascorbic acid concentration found in human aqueous humor. Unlike previous reports, we found no toxic effects from ascorbic acid at concentrations as high as 250 [mu]g/ml over a 24-hour period. The lack of toxicity may result from the use of serum-free media in the assay. Conclusions: This culture system will be useful for exploring factors that may alter collagen production and could potentially affect wound healing.
Objective
To review the spectrum of patients with alkali burns admitted over an 11-year period and to assess the clinical outcomes after the introduction of a standard alkali burn treatment protocol.
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By experimenting with the “one-sided” diets which were used in the experiments, mentioned in the foregoing paper on polyneuritis in poultry, we found that guinea-pigs also contract a disease, and that this disease is accompanied by very characteristic changes.
Studies on the ultraviolet ray absorption in the aqueous humour of rabbit, cat, monkey, guinea pig, and rat showed marked species differences. In the rabbit aqueous the ascorbic acid, the proteins, and some amino acids (tyrosine, phenylalanine, cystine, and tryptophane) are together responsible for the total absorption, and a very great part of it refers to the ascorbic acid content. Accordingly, species with significant amounts of ascorbic acid in the aqueous (monkey, rabbit, guinea pig) have a greater absorption capacity towards ultraviolet radiation than species (cat, rat) lacking this substance. This effect of the ascorbic acid may contribute in protecting the lens against the most biotoxic ultraviolet rays. It seems that the ascorbic acid concentration is highest in the aqueous of typical day animals and lowest in species being active in the dark, indicating a correlation between the aqueous' ascorbic acid level and the quantity of incident light on the eye. The possible significance of changed aqueous ultraviolet ray absorption in the pathogenesis of human cataract development is discussed.
To describe the content of water-soluble antioxidants in tear fluid.
We collected tear fluid from healthy subjects, either into borosilicate glass tubing or by absorption onto Schirmer strips. High pressure liquid chromatography with electrochemical detection provided data on several components in a single assay. The system was sufficiently sensitive to provide reliable values for components present in tear fluid collected at normal (basal) or stimulated rates of secretion.
Tear fluid at basal secretion was found to contain four compounds often considered to function in biology as antioxidants. Ascorbic acid (AA) is found at 665 microM, tyrosine at 45 microM and glutathione (GSH) at 107 microM. Cysteine (48 microM) and uric acid (328 microM) are reported for the first time; the latter is somewhat controversial as a physiologically active antioxidant. One peak on the chromatogram was consistently present but has not been identified. During stimulation of flow by brief inhalation of ammonium hydroxide fumes, the concentration of each compound was lower.
This work demonstrates the presence of electro-chemically active components that might function as antioxidants at the anterior surface of the cornea against potential damage from radiation, oxygen toxicity, abrasion and environmental chemicals.
Oxidative damage and antioxidant protection in ocular tissues has not been reviewed recently. Metabolism in the eye is of increasing interest because the organ is highly susceptible to damage by sunlight, oxygen, various chemicals, and pollutants. Interest is expected to increase because of an aging Western world population and a continued depletion of stratospheric ozone. Hydrogen peroxide is discussed because it is both a byproduct and a source of free radical reactions and is normally present in the aqueous humor. The metabolism of reactive oxygen species by enzymes, nutrients, pigments, and low molecular weight scavengers is evaluated. Ascorbic acid, because of its high concentration in the eye, is thought to be a primary substrate in ocular protection; progress in determining the mechanisms by which it is recycled and maintained in the useful, reduced state is discussed. Recent information is included about antioxidants not previously known to be present in the eye, and some importance is placed on the properties of the vitreous humor and tear fluid because of the previous lack of emphasis on these.
To determine if there is an association between the surgical outcome of trabeculectomy and uric acid and ascorbic acid concentrations in the aqueous humor at the time of the procedure.
Aqueous humor samples were collected from the eyes of 169 of 249 adult patients who underwent trabeculectomy alone for any type of glaucoma between April 1989 and July 1995. Postoperatively, all medical records were reviewed and outcomes were classified as successful, unsuccessful, or indeterminate. The ascorbic acid and uric acid concentrations were determined in masked fashion by high-pressure liquid chromatography. Factors associated with surgical outcome were determined.
Uric acid concentration was higher in unsuccessful eyes (mean+/-SD, 0.21+/-0.08 mmol/L, n=26) than in successful eyes (0.15+/-0.09 mmol/L, n=91, 95% confidence interval for difference, 0.02-0.10 mmol/L). Ascorbic acid levels were not significantly different in the eyes with unsuccessful (1129.9+/-601.9 micromol/L) and successful (1334.3+/-511.0 micromol/L) surgery (95% confidence interval for difference, -475.2 to 66.4 micromol/L, P=.13) surgery. Other factors associated with failure were previous surgery and surgery performed at the inferior limbus. A multiple polytomous logistic regression analysis was performed, after excluding the small number of operations performed at the inferior limbus. The odds ratio for failure increased by a factor of 1.68 for every 1-mmol/L increase in uric acid (95% confidence interval, 1.16-2.43, P=.006).
Uric acid levels were higher at the time of surgery in eyes that had unsuccessful outcomes than in those with successful outcomes. No significant difference in ascorbic acid levels was detectable. A higher uric acid level in the aqueous humor is a risk factor for trabeculectomy failure and might be tested as a prognostic indicator [corrected].