Harvard Study Shows Zeaxanthin Good for AMD

BOSTON--Researchers from Harvard, Columbia University and other colleges worldwide reported that retinal levels of zeaxanthin may influence the risk of age-related macular degeneration (AMD). Led by C. Kathleen Dorey, Ph.D., researchers tested their hypothesis that retinal zeaxanthin prevented light-induced photoreceptor cell death by absorbing blue light. Results from the study appear in the November issue of Investigative Ophthalmology & Visual Science (43, 11:3538-49, 2002) (www.iovs.org).

The study's authors used quail in their experiment, since the birds' retinas resemble humans' maculae more so than rats or mice. Over the course of six months, 16 quail were fed a carotenoid-deficient diet supplemented with 35 mg/d of zeaxanthin for one, three or seven days; one group of the birds stayed on the deficient diet. Half of each group was then exposed to intermittent 3,200-lux white light for 10 one-hour intervals separated by two-hour periods of darkness. Afterward, one retina from each quail was collected for HPLC analysis.

Retinal zeaxanthin was found to have increased significantly on day three but then plateau. It was found that after seven days of zeaxanthin supplementation, carotenoid concentrations in serum, liver and fat increased by factors of 50.8, 43.2 and 6.5, respectively.

Researchers found that the number of apoptotic rods and cones in light-damaged eyes held an inverse relationship with retinal zeaxanthin levels, although not with serum zeaxanthin. Retinas with low concentrations of zeaxanthin were found to have suffered severe light damage, as evidenced with a very high number of apoptotic photoreceptor (rod and cone) cells.

"These data provide the first experimental evidence that xanthophyll carotenoids protect photoreceptors in vivo," the authors concluded.

Dorey added that she believes zeaxanthin has potential to eventually complement other strategies to improve the treatment of AMD. "The retina is constantly exposed to oxidative injury, a leading candidate for initiating or accelerating retinal degeneration," she said. "Our studies showed that light damage was strongly influenced by the amount of zeaxanthin in the retina, and that significantly greater retinal protection was provided at dietary levels higher than those normally occurring in the diet."