TUESDAY, Feb. 10, 2004 (HealthDayNews) -- Elevated blood levels of C-reactive protein, a molecular marker of inflammation already associated with heart disease and stroke, increase the risk of age-related macular degeneration, a new study finds.
But as is true of cardiovascular disease, it hasn't been proven yet that C-reactive protein (CRP) causes the eye condition, says study author Dr. Johanna M. Seddon, a surgeon in ophthalmology at Massachusetts Eye and Ear Infirmary.
Her report appears in the Feb. 11 issue of Journal of the American Medical Association.
"This study doesn't show that," she says. "We are doing a prospective study as well to see if there is evidence for that."
The macula is the central portion of the retina, which sends light signals to the brain through the optic nerve. For unknown reasons, it can begin to deteriorate with age, in the worst case causing a black hole in the center of the visual field.
Macular degeneration can occur early in life, but it is much more common in later years. It affects an estimated 13 million Americans, and nearly 20 percent of people over 75 have some degree of vision loss because of macular degeneration.
The link between CRP and the eye condition comes as no surprise, Seddon says, because a number of studies have shown that other factors linked to cardiovascular risk -- smoking, obesity and a fatty diet -- are also risk factors for macular degeneration.
But "to the best of our knowledge, this is the first study to implicate C-reactive protein as a systematic inflammatory marker for the development of age-related macular degeneration," the journal report says.
Its results come from the Age-Related Eye Disease Study, which has been following almost 5,000 people aged 55 and older for a number of years. This latest report tracked the condition of the macula in participants.
Only 183 of them experienced no macular degeneration, with another 200 having mild damage, 325 moderate damage and 222 with severe deterioration. CRP blood levels were significantly higher in the people with the most severe form of macular degeneration, the study finds.
Overall, the 25 percent of participants with the highest CRP protein levels were 65 percent more likely to have severe macular degeneration. Smoking added to the damage, more than doubling the risk for those with high CRP levels.
One purpose of the study is to see whether high doses of antioxidants -- beta carotene, zinc, and vitamins C and E -- can have beneficial effects against macular degeneration. The study has found that antioxidants can slow progression of the condition, Seddon says.p>
But Dr. Andrew K. Vine, a professor of ophthalmology at the University of Michigan Kellogg Eye Center, says that "good health is not just taking a vitamin pill. What older people need is a more active life."
The study "provides further information that one of the main causes of macular degeneration is a cardiovascular risk profile," Vine says. A study at the Kellogg center points in the same direction, he adds.
"Many of these factors can be corrected," Vine says. "Paying attention to our waistline, controlling blood pressure, reducing fat intake are among them. Older Americans are a very sedentary group. They need to change something."
"But that is not what they want to hear," Vine adds. "They'd rather take another pill.