Eye Disease and Oxidative Stress: Can You Reduce Your Risk?
Cataract is the worldwide leading cause of visual impairment, being responsible for a little under half of all cases according to the World Health Organisation. Cataract develops when the lens in the eye is damaged over time, and risk factors include older age, cigarette smoking and exposure to UV light. Although cataract can be treated surgically, there are barriers that prevent access in many countries. People also may suffer from impaired vision for years before they are treated for the condition. As the causes of lens damage are related to increased oxidative stress, researchers have been investigating whether dietary antioxidants can be protective. The human lens contains antioxidants such as alpha- and gamma-tocopherol, and the carotenoids lutein and zeaxanthin, according to Yeum and co-workers. As these nutrients are essential and therefore must be supplied by the diet, they are natural foci of research attention. As antioxidants also work together (for example, vitamin C is needed to regenerate alpha-tocopherol), a diet that includes higher levels of antioxidants in general may also protect against oxidative damage, therefore protecting the lens as well.
A group led by Christen recently published additional results of the Physicians Health Study II. The primary results of this large, long-term clinical study in older male physicians were presented last year and showed that multivitamin supplements taken over a period of 11 years modestly reduced risk of cancer (Gaziano et al.), but had no effect on cardiovascular disease endpoints or total mortality (Sesso et al.). Rates of eye diseases were a secondary endpoint.
The study found that long-term multivitamin use significantly reduced the risk of cataracts, and these results appear to be more pronounced in the older group of men (those aged over 70, compared with age groups 50-59, and 60-60), and for people with nuclear sclerotic cataract (the most common type). When looking at the risk of age-related macular degeneration however, there appeared to be no effect. These results also agree with another large trial in a similar population of older Americans, that found multivitamin use (but not high-dose supplements) moderately reduced cataracts (see Milton and AREDS Research Group publications).
This study was fairly unique in that it used a multivitamin supplement that contained vitamin and mineral at recommended levels over a long period of time in a well-nourished population. As well as not showing harm, this supplementation regimen appears to result in a reduction in incidence of cancer and cataracts. There was also a small, non-significant reduction in overall mortality in the group of men randomized to the multivitamin supplements. The authors cite research that shows a reduction or delay in lens opacities due to antioxidants or micronutrients as a possible reason for these results.
Aside from a balanced diet, other behaviors associated with reduced risk of cataract include reducing the eyes’ exposure to UV light (for example, by wearing sunglasses with an effective UV filter on sunny days) and not smoking. Regular visits to the optician will also help pick up the signs of cataract early and avoid loss of quality of life due to visual impairment.
Christen WG, Glynn RJ, Manson JE, Macfadyen J, Bubes V, Schvartz M, Buring JE, Sesso HD, Michael Gaziano J. A Multivitamin Supplement and Cataract and Age-Related Macular Degeneration in a Randomized Trial of Male Physicians. Ophthalmology. 2013 Nov 20. pii: S0161-6420(13)00883-X. doi: 10.1016/j.ophtha.2013.09.038. [Epub ahead of print] http://www.ncbi.nlm.nih.gov/pubmed/24268861
Age-Related Eye Disease Study Research Group. A randomized, placebo-controlled, clinical trial of high-dose supplementation with vitamins C and E, beta carotene, and zinc for age-related macular degeneration and vision loss: AREDS report no. 8. Arch Ophthalmol. 2001 Oct;119(10):1417-36. http://www.ncbi.nlm.nih.gov/pubmed/11594942
Milton RC, Sperduto RD, Clemons TE, Ferris FL 3rd; Age-Related Eye Disease Study Research Group. Centrum use and progression of age-related cataract in the Age-Related Eye Disease Study: a propensity score approach. AREDS report No. 21. Ophthalmology. 2006 Aug;113(8):1264-70. http://www.ncbi.nlm.nih.gov/pubmed/16877067
Yeum KJ, Taylor A, Tang G, Russell RM. Measurement of carotenoids, retinoids, and tocopherols in human lenses. Invest Ophthalmol Vis Sci. 1995 Dec;36(13):2756-61. http://www.ncbi.nlm.nih.gov/pubmed/7499098