Lowering Your Risk of AMD

Summarized by Robert W. Griffith, MD
January 16, 2006

Introduction

Age-related macular degeneration (AMD) is a serious cause of loss of vision in older people, affecting 11.5% of people over 80. As the population ages the number of people disabled by AMD is expected to rise accordingly. 'Oxidative stress' ¹ has been considered one of the major causes of AMD, and has led to recommendations that older people should take antioxidants to combat this process; it's already been shown that high-dose supplementation with beta carotene, vitamins C and E, and zinc slows the progression of the condition. The basis for this has received support from a publication in the Journal of the American Medical Association concerning the incidence of new cases of AMD in an aging population in the Netherlands. Here's a summary of the findings.

What was done

The Rotterdam Study is a prospective study of over 10,000 people aged 55 or older living in a middle-class suburb of Rotterdam, the Netherlands. Previous analyses have reported on common cardiovascular, neurological, and eye conditions in these participants.

About two thirds of the study participants had ophthalmologic exams at baseline (between 1990 and 1993), with follow-up exams at 4-year intervals. AMD was diagnosed on examination as early-stage or late-stage; no distinction into wet- and dry-type AMD was made.

The participants completed a food questionnaire at baseline, which defined their dietary habits, their supplement use, and any prescribed diets. This was complemented by an interview with a dietician, using a 170-item food frequency checklist. The results were converted into total energy intake and nutrient intake per day.

Information on possibly confusing factors, such as smoking, alcohol use, body mass index (BMI), lipid levels, blood pressure, and an assessment for atherosclerosis was collected at baseline.

The Rotterdam Study is a prospective study of over 10,000 people aged 55 or older living in a middle-class suburb of Rotterdam, the Netherlands. Previous analyses have reported on common cardiovascular, neurological, and eye conditions in these participants.

What was found

The average follow-up of the participants was 8 years. During follow-up 560 people (13%) developed AMD (mostly early-stage disease). Those with AMD were slightly older than those without it (average 68.2 years vs. 66.4 years), had smoked more, and had higher levels of high-density lipoprotein (HDL) cholesterol. There were no other differences between AMD and non-AMD people at baseline.

The risk of developing AMD was calculated in relation to the intake of antioxidant nutrients, including supplements. Trends were seen for the various carotenoids, although the only statistically significant links were seen for intake of vitamin E, iron, and zinc.

After making adjustments for possible interference by risk factors such as age, smoking, BMI, and so on, it was found that an 'above-midpoint intake' of beta carotene, vitamins C and E, and zinc, compared with a 'below-midpoint intake' of at least one of these nutrients, was associated with a 35% reduced risk of AMD. In persons with a below-midpoint intake of all four of these nutrients, the risk of developing AMD was increased by 20%.

In this study (as opposed to the study of antioxidants in slowing already-present AMD) taking antioxidants as supplements did not seem to affect the strength of the risk reduction.

What this study means

High dietary intake of vitamin E and zinc were linked with a lower risk of developing AMD. And a combination of above-the-midpoint intake of vitamins C and E, beta carotene, and zinc was linked to a 35% lower risk of developing AMD. So the secondary prevention seen in an earlier study with antioxidants was allied with a primary preventive effect on AMD.

It should be noted that the midpoint intakes (which were close to the average intakes) were at or above the Recommended Daily Allowance (RDA) for the specified nutrients. In other words, to gain protection from diet one must eat foods that are high in these nutrients.

Plenty of whole grains, vegetable oil, eggs, and nuts will ensure a high intake of vitamin E. Zinc is contained in meat, poultry, fish, whole grains, and dairy produce. Carrots, kale, and spinach contain plenty of beta carotene, while vitamin C is found in citrus fruits and juices, green peppers, broccoli, and potatoes. The results of this study suggest that a diet containing plenty of these foods will be more effective in preventing AMD than taking supplements.

Source

• Dietary intake of antioxidants and risk of age-related macular degeneration. VLR. van Leeuwen, BS. Boekhoorn , VJR. Vingerling ,  al., , 2005, vol. JAMA , pp. 3101--3017

Footnotes
1. Oxidative stress is a condition of increased oxidant production in the cells characterized by the release of free radicals and resulting in cellular degeneration.

Related Links
Age-Related Macular Degeneration (AMD) - An Overview
A Test of Risk for AMD?
Self-Help for AMD

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