Research from Tufts University, Boston, has indicated that evidence remains inconclusive in regards to whether or not zinc intake from foods and supplements is beneficial in the primary prevention and treatment of AMD. Analysis, published in the journal, Investigative Ophthalmology & Visual Science (Vishwanathan et al, Vol. 54, No. 6, pp 3985-3998) show that while the results on zinc intake for the prevention of AMD did not paint a clear picture, comprehensive data from AREDS (a large scale US-based multi-centre clinical Age-related Eye Disease Study, sponsored by the National Eye Institute) suggest that zinc treatment may be effective in preventing the progression of the disease to advanced AMD. The authors conclude in their publication that, “zinc supplementation alone may not be sufficient to produce clinically meaningful changes in visual acuity”.
Given that AMD is the leading cause of blindness among the elderly in industrialized countries, several national healthcare systems are keen to uncover any associations with incidence or treatment that can minimize the social and economic burden of the disease. As it stands, there is currently no cure for AMD and while anti-VEGF treatments have made a significant impact on the disorder in recent years, their cost and efficacy across all patients continue to present a challenge in optimizing patient care. According to several independent studies, including that of Tufts University, the greatest risk factor for AMD is age, with prevalence growing dramatically with increasing age. “Nearly 24% of Americans over the age of 80 have intermediate signs of AMD and 12% have advanced AMD, whereas the respective prevalence among people 40 to 49 years old are 2% and 0.1%”, reports Tufts researchers.
The comprehensive systematic study published in IOVS examined data from randomized controlled trials (RCTs), prospective cohort, retrospective cohort, and case-control studies that had investigated zinc intake from foods and/or supplements, covering AMD in males and females with a mean age of 50 years or older. According to the study authors, the research represented the first systematic review focused on the independent effects of zinc for the prevention and treatment of AMD. Previous studies had evaluated the effect of zinc in combination with other antioxidant nutrients which meant that the results presented challenges in teasing out which specific components could be clearly linked to study observations. In the Tufts study, the authors suggested that the strongest evidence for zinc in the treatment of AMD arises from AREDS, a large scale clinical study which indicated that zinc supplementation alone “reduced the risk of progression to advanced AMD in those with intermediate AMD and those with advanced AMD in one eye”. Data from the other three RCTs showed that while zinc intake might improve visual acuity in early AMD patients, the results in patients with advanced AMD were less supportive.
In concluding their evaluation on the use of zinc the Tufts investigators commented that, “zinc treatment can be effective in preventing progression to advanced AMD, which is critical in preventing complete vision loss in patients with early, intermediate, and advanced AMD. Zinc in combination with antioxidants, rather than zinc alone, can be used to achieve clinically and statistically significant improvements in visual acuity in AMD patients. Evidence thus far on zinc intake for the prevention of AMD is insufficient to draw any overall conclusions.”