Antioxidants mitigate cataract risk and progression

By Cheryl Guttman

Fort Lauderdale - Antioxidant supplements may have an important role to play in slowing the rate of cataract progression, according to new data presented at the Association for Research in Vision and Ophthalmology

The latest findings of the Nutrition and Vision Project (NVP) indicate that prolonged use of vitamin E supplements slows the rate of progression of nuclear cataract, but its benefit appears to be greatest in lenses with more advanced early opacities, reported

Allen Taylor PhD, Director of the Laboratory for Nutrition and Vision Research, and Professor of Nutrition, Biochemistry and Ophthalmology, Tufts University, Boston.

The study showed that persons who took vitamin E supplements (minimum intake 90 mg/day) for 10 years or more had a 29% lower increase in nuclear mean density (NMD) score and a 70% reduced risk of achieving significant opacity compared to never users (intake less than or equal to 6.7 mg/day).

Between 1993 and 1995, the NVP enrolled 603 Boston area residents who were participants in the Nurses' Health Study (NHS). Volunteers eligible for entry in the NVP were aged 54 to 73 years, had both natural lenses intact, and no history of cancer except for non-melanoma skin cancer. Complete nutritional data (dietary and supplement) was available from a series of questionnaires completed as part of the NHS protocol.

For the study evaluating nuclear opacity progression, lens photographs were taken upon NVP entry and five years later. Nuclear opacity was measured using computerised image analysis and a NMD score was generated and expressed in pixel density units (PDUs).

Researchers divided the participants into subgroups by duration of intake of the different vitamins. They compared mean change in NMD after adjustments for age, diabetes status, alcohol intake, baseline body mass index, smoking history and sun exposure. The researchers based their analyses on data from 407 participants for whom all of this data was available.

NMD scores at baseline ranged from 19 to 102 PDUs (maximum possible 256). Final scores ranged from 32 to 213 PDUs. Looking at adjusted geometric mean of the change in NMD scores from follow-up to baseline by type and duration of supplement intake showed a significant benefit for decreasing progression among women using vitamin E for ten years or more.

Among 262 women who never used vitamin E supplements, the NMD score increased by 17 PDUs compared to a +12.0 PDU change among the 29 subjects with an intake history of 10 or more years.
Further analyses showed that women using vitamin E supplements for ten or more years had about a 70% decreased risk of developing opacity relative to never users, whether opacity was defined using an NMD score of 60 PDUs or 70 PDUs.

However, when the cut-off was set at the denser score, use of vitamin E supplements for five to nine years was also associated with a significant 62% decreased risk of developing opacity compared to those never using vitamin E.

The data also showed that the advantage of longer history of vitamin E intake for reducing NMD score progression was most robust among women who had more advanced early opacities at baseline.
With eyes stratified into three groups by entry PDU (less than 39 in both eyes; 39 to 50 in one eye; and 50+ in one eye), researchers observed a significant benefit of prolonged vitamin E supplement use for delaying progression only among women who had a baseline NMD score of 50 PDU or greater in one eye.

The change from baseline NMD score in that subgroup was +11.7 PDUs compared to +20 PDUs in never users within the same baseline NMD category.

However, there was a trend for a significant reduction in opacity progression for prolonged vitamin E intake among persons with one eye with a baseline PDU of 39 to 50. Change from baseline in that group was +12.5 PDUs among persons taking vitamin E at least 10 years compared to +16.4 PDU among never users.

In a related paper published in the American Journal of Clinical Nutrition [Taylor A, et al. AJCN 2002; 75:540-9], Dr Taylor and his NVP colleagues reported data suggesting a role for vitamin C intake in lowering the risk of developing cortical opacities among women aged under 60 years.
Dr Taylor explained that understanding the effects of nutrient intake on cataract development and progression begins with an appreciation of the fact that with ageing, the structural proteins of the lens and also the proteases responsible for removing the photo-oxidised lens constituents are subject to oxidative stress.

The end result is accumulation and aggregation of damaged proteins which lead to cataracts.
Various nutrients, including vitamins C and E, carotenoids, and lutein/zeaxanthin function as antioxidants and might be expected to be beneficial in counteracting oxidative stress.

Research confirms that these nutrients get to the lens when they are ingested in the diet or with supplements. The findings of epidemiological studies have indicated that a higher intake of antioxidants is beneficial in decreasing rates of cataract development and progression, Dr Taylor said.
Nevertheless, two large intervention studies failed to corroborate these observations.

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