Potential Role of Vitamin C in Cataract Prevention - Coursework Example

Potential Role of Vitamin C in Cataract Prevention Introduction: The high rate of incidence of cataract has made it a worldwide problem. Cataract when left untreated could lead to blindness. The rate of incidence and the possible consequences have led to investigations into means to prevent cataract. Antioxidants are believed to be beneficial in the prevention of cataract and in retarding the progress of the disease and this has led to Vitamin C being considered for a role on the prevention of cataract. However, evidence emerging from studies on the potential role of vitamin C in the prevention of cataract has been contradictory, with some finding beneficial effects and the others failing to do so. This has led to a controversy on the possible role of vitamin C in the prevention of cataract. Evaluation of Article in Support of the Potential Role of Vitamin C: Valero et al, 2002, conducted a case controlled study to test the hypothesis, as suggested in other studies that higher levels of antioxidant vitamins, including vitamin C, and mineral micronutrients were protective for cataract. The study extended over a period of fourteen months in Valencia, a Mediterranean region. The inclusion criteria were patients between the ages 55-74 and having been diagnosed with nuclear, cortical, posterior, sub-capsular, or mixed cataract in at least one eye. Controls were frequency matched on age, gender, and with suitable lens opacity grading. Exclusion criteria were any patients on special diets and eye conditions or medical treatments that increased the risk for cataract. Trained study teams were employed in data collection in terms of ophthalmic examination and administration of the questioner. The questionnaire collected data on education levels, occupation, occurrences of diarrhea, life style habits, dietary habits, and the past and present use of vitamin supplementation. The interviewing teams that administered the questionnaire were kept oblivious of the case-control status of the subjects. An adequate protocol was employed to collect blood samples of the subjects for analysis of vitamin C. Blood and dietary details were treated as separate entities for statistical analysis and variables in both groups were logarithmically transformed and these standardized values analyzed statistically employing Stata 6 software. There were 347 case and 345 controls in the study. The results from the study indicated that a blood plasma level of ascorbic acid more than 49umol had significant association with a reduction of 64% in the risk for cataract. This association was found in the univariate analysis as well as the analysis after adjustment for potentially confounding factors like education. Such an association has a minimal probability of being a result of chance. There are three important factors that stand out in this study, which need to be considered. The first is the case controlled design of the study employing an adequate number of subjects to increase the validity of the findings. The second is that it employed blood serum analysis to ascertain the levels of ascorbic acid and not the intake levels of ascorbic acid. The third factor is that the study was conducted in the Mediterranean region, where the population is known to have a high intake of citrus fruits high in vitamin C content, and where the supplemental use of Vitamin C is to the minimum. However the weakness in the study is that there has been no exclusion of the other antioxidant vitamins and minerals, which leaves the findings of the beneficial aspects of vitamin C open to the question of whether these benefits observed were derived from vitamin C only or from any of the other antioxidant vitamins and minerals (Valero, et al, 2006). Evaluation of Article not in Support of the Potential Role of Vitamin C: On contrast to the above study Christen et al, 2008 examining prospective data of dietary carotenids, vitamin C and E on the risk of cataract in women based found no significant benefits from dietary vitamin C in reducing the risk of cataract. The study was conducted with the objective of testing the oxidative hypothesis of cataract formation suggestion that damage to the lens proteins and cell membranes occurs from reactive oxygen species and that nutrients with antioxidant properties offer protection against these changes. The subjects selected were willing women participants from the women enrolled in the recently completed randomized double masked, placebo-controlled Women’s Health Study (WHS) of low-dose aspirin, vitamin E, and beta carotene in the primary prevention of cardiovascular disease in apparently healthy female health professionals in the age group 45 years and older. The assessment of nutrient intake in the original study was based on subject response to the average consumption of a standard unit or portion size for each of the food items. Food tables were used to convert these responses to provide average daily intake of each nutrient. Data on the supplemental use of vitamins was also collected from the subjects and added to provide the total intake of antioxidants. Data from food sources alone were thus available for vitamin C. The SFFQ estimates have been found to be similar to plasma levels of these nutrients and estimates from food records, and hence used in this study as the means of providing data on the plasma levels of these nutrients from food and supplemental intake. The unit of for data analysis was the individuals and not the eyes. Participants were classified based on the status of the worse eye in keeping with the severity of cataract. Nutrient intake was taken to be a categorical variable adjusted to total energy employing the residual method. The independent impact of each nutrient on the risk of cataract was evaluated on the basis of simultaneously entering all the nutrients in a Cox regression model employing the median scores from the quintiles and adjusting for other cataract risks. An elimination method using a backward selection procedure was employed to arrive at those nutrients that had a significant association with cataract. Based on the results of data analysis the study found a weak and statistically insignificant inverse association of vitamin C with risk of cataract, and allows the conclusion that there is no beneficial association of vitamin C in cataract. The study has gone through an elaborate design to ensure the properness of the data and an adequate use of statistical processes in an attempt to improve the validity of its findings. Such a design is appreciated. However, exactness of data on nutrient intake is based on responses of subjects and their ability to recall and evaluate nutrient intake. This data which is the basis of all further estimations and analysis thus becomes questionable. Furthermore, there are absorption issues with vitamin C, and intake of vitamin C only may not be truly reflective of plasma levels of vitamin C, which is critical to the evaluation of the beneficial potential of vitamin C. Finally, there is a gender bias in the study, as it is evaluation of data taken only from women (Christen et al, 2008). Discussion on the Nutrient Controversy: The oxidative hypothesis in cataract formation suggests that antioxidants may have a beneficial role in to play in cataract. Vitamin A, C, and E are known to have antioxidant properties and are free radical scavengers, which have made them the main subjects of the testing of this hypothesis. Vitamin C is also known to absorb ultraviolet rays and provides preventive action against the accumulation of free radicals (Kuzniarz, Mitchell, Cumming & Flood, 2001). Several studies have gone into testing the hypothesis and the results have been contradictory leading to the development of controversy in the role of antioxidants in cataract. Epidemiological data points to the use of antioxidants including vitamin C proving beneficial in cataract, but this promise has not been held out due to the contradictory evidence from the several studies that have been undertaken to test these beneficial effects (Gritz, et al, 2006). The growing contradictory evidence suggests that differences in the methodologies employed in these different studies may be a factor in this disparate evidence. For instance, it is the amount of vitamin C that is present in the lens that could provide the protective influence in cataract (Varma & Hegde, 2004). Intake of vitamin C is not correctly reflective of the plasma levels of vitamin C, and furthermore there is the issue of vitamin C intake from natural food sources and through supplemental efforts (West, Oren & Moroi, 2006). Testing of the oxidative hypothesis in the case of vitamin C using different parameters involving these factors may lead to contradictory results. n the Valero et al, 2002, supplemental use of vitamin C was avoided by concentrating on a population that had a naturally high intake of vitamin C and plasma levels of vitamin C were ascertained by blood tests. In contrast, in the Christen et al, 2008 study both natural intake and supplemental intake were considered in total for the calculation of vitamin C intake, and the conversion of this intake using SFFQ estimates were employed to get the plasma levels of vitamin C. These differences could have had a role to play in the contradictory findings of the two studies. Literary Resources Christen, G. W., Liu, S., Glynn, J. Robert, Gaziono, J. M., & Buring, E. J. (2008). Dietary Carotenids, Vitamin C and E, and Risk of Cataract in Women. Archives of Ophthalmology, 126(1), 102-109. Gritz, D. C., Srinivasan, M., Smith, D.S., Kim, U., Lietman, T. M., Wilkins, J. H., Priyadharshini, B. John, R. K., Aravind, S. Prajna, N. V., Thulasiraj, R. D. & Whitcher, J. P. (2006). The Antioxidants in the Prevention of Cataracts Study: effects of antioxidant supplements on cataract progression in South India. British Journal of Ophthalmology, 90, 847-851. Hegde, K. R. & Varma, S. D. Protective effect of ascorbate against oxidative stress in the mouse lens. Biochimica et Biophysica Acta, 1670, 12-18. Kuzniarz, M., Mitchell, P., Cumming, G. R. & Flood, M. V. (2001). Use of Vitamin Supplements and Cataract: The Blue Mountains Eye Study. Vitamins and Cataract, 132(1), 19-25. Valero, P. M., Fletcher, E. A., De Stavola, L. B., Vioque, J. & Alepuz, C. V. (2006). Vitamin C Is Associated with Reduced Risk of Cataract in a Mediterranean Population. THE JOURNAL OF NUTRITION, 132, 1299-1306. West, L. A., Oren, A. G. & Moroi, E. S. (2006). Evidence for the Use of Nutritional Supplements and Herbal Medicines in Common Eye Diseases. 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