Eye health and vitamins: Supplement intake ‘can increase degeneration’, review reveals

By Cheryl Tay contact

- Last updated on GMT

Related tags: Vitamin c, Nutrition

An antioxidant-rich diet is preferable to antioxidant supplements for lowering eye disease risk, say researchers. ©iStock
An antioxidant-rich diet is preferable to antioxidant supplements for lowering eye disease risk, say researchers. ©iStock
Scientists have cautioned that antioxidant consumption in supplement form is not as effective as a nutrient-rich diet to improve eye diseases, with some evidence suggesting they can actually worsen existing conditions.

According to a review undertaken by the University of Auckland, antioxidants are thought to lower the risk of eye disease, since oxidative stress aids their progression, especially in the case of cataracts and age-related macular degeneration (AMD).

However, while they found that food-based antioxidants provided benefits, this wasn’t mirrored when they were consumed in supplement form.

The review found “probable evidence that dietary intake of fruits and vegetables, and vitamin C lowered (the) incidence of cataracts and AMD”, ​but “in high supplemental doses, vitamin C increases macular degeneration risk”​.

Vitamin A, on the other hand is “protective for cataracts and glaucoma, but not in supplemental form”​, and is associated with a reduced risk of AMD. In addition, dietary calcium and iron appear “protective against glaucoma, but not in supplemental form”​.

Cataracts

The review observed a link between higher fruit and vegetable intake and reduced cataract risk, as well as higher meat intake and increased cataract risk.

It stated that the “the protective association identified between higher intakes of fruit and vegetables with reduced risk of cataracts​ may be attributed to their composition”​, as they are antioxidant-rich dietary sources.

The most consistent inverse association between dietary antioxidant intake and lower cataract risk was seen with vitamins C and E. However, “conflicting findings surrounding vitamin E supplementation”​ were also discovered.

Age-related macular degeneration

As with cataracts, several studies drew a link between high fruit and vegetable intake and lower AMD risk, as well as high meat intake and higher AMD risk, but the review said the “findings are not as clear”​.

Two studies found that vitamin E in particular lowered AMD risk, one of which also pointed to a high intake of combined pro-vitamin A carotenoids as lowering AMD risk. It further stated that there was no significant link between vitamin C intake and AMD risk.

Other studies were unable to identify any statistically significant association between antioxidant intake and AMD risk. However, calcium intake “may modulate the risk of AMD”​, but only if less than 800mg is taken daily; an intake exceeding 800mg a day could increase AMD risk.

Glaucoma

Seven studies on the effect of dietary and supplementary antioxidant intake on glaucoma were reviewed: four showed an inverse association, while the other three showed “no statistically significant effect, regardless of intake”​.

Dietary calcium and iron intake, however, seems to “modulate the risk”​ of glaucoma, but “supplemental intake of both micronutrients elevates the risk”​.

The consumption of vitamins A and C had the most consistent overall impact on lower glaucoma risk. Dietary intake of vitamin E, on the other hand, was not found to reduce glaucoma risk.

The review concluded that “while a nutrient-rich diet high in fruit and vegetables, and associated antioxidants, appeared to be protective, we would caution intake of supplementary antioxidants for those with ocular disease”​.

 

Source: Asia Pacific Journal of Clinical Nutrition

https://doi.org/10.6133/apjcn.082016.01

“Food components and ocular pathophysiology: a critical appraisal of the role of oxidative mechanisms”

Authors: Reinlesh Raman, Ehsan Vaghefi, Andrea J Braakhuis

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