Kiwifruit and Age-Related Macular Degeneration
Kiwifruit is a naturally good source of lutein and zeaxanthin, 2 phyotnutrients that scientists believe may protect against age-related macular degeneration (AMD).
AMD is the leading cause of irreversible blindness among older Americans. Mild AMD affects nearly 30% of Americans over 75 years of age. There are 2 types of AMD: dry and wet. Ninety percent of AMD patients have dry AMD, which is caused by deposits on the macula in the center of the retina, where vision is sharpest. In wet AMD, tiny blood vessels bleed into the macula, partially or completely blocking out central vision. Although the central vision is blocked, AMD patients usually retain peripheral vision but cannot see well enough to read or drive.
Because there is no cure for AMD, it is critical to prevent eye damage leading to this condition. Research studies have cited carotenoids named lutein and zeaxanthin as potential inhibitors. Data from human studies suggest that dietary intake of these carotenoids can lead to their accumulation in the retina and, therefore, may provide protection against retinal degeneration. Within the central macula, zeaxanthin is the dominant component; in the peripheral retina, lutein predominates.
In a recent small-scale study, 11 subjects modified their usual daily diets by adding 60 g/d of spinach for 15 weeks. Spinach was selected because of its high lutein content. Eight subjects had increases in serum lutein and macular pigment density, 2 subjects showed substantial increase in serum lutein but not macular pigment, and 1 subject showed no change.
Another study, by the Eye Disease Case-Control Study Group, reported that patients in the group with the highest level of plasma lutein zeaxanthin had a lower risk ratio for AMD. Subjects in the highest quintile for their intake of lutein zeaxanthin demonstrated a 57% lower risk of advanced AMD compared to those in the lowest quintile.
As antioxidants, lutein and zeaxanthin may also play a second important role in eye health, by protecting the macula against the effects of free radicals. Their antioxidant properties may help limit the oxidative stress on the eye tissue that results from metabolism and light.
The increased interest in the protective effects of lutein and zeaxanthin has sparked a need for information about the carotenoid content of specific foods. Kale and spinach rank as the two highest food sources of lutein and zeaxanthin; kiwifruit tops the list of fruits that contain these phytonutrients, thus providing an enjoyable method of delivery for consumers who prefer fruit sources or for those who wish to select a variety of dietary sources.
This article is an executive summary of an article by Professor Elizabeth J. Johnson, Tufts University, Boston, MA.