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Studies Confirm Interaction of Genetics, Diet, Exercise Affect Age-Related Macular Degeneration Risk

NEW YORK(GenomeWeb) ─ Researchers from the University of Wisconsin-Madison published the results of an observational study of women with a genetic predisposition for age-related macular degeneration in the journal Ophthalmology.The study revealed that the odds of developing the blinding eye disorder significantly increases if a person has a history of heavy smoking and consistently did not exercise or eat enough fruits and vegetables.                                   

Age-related macular degeneration (AMD), when the central portion of the retina deteriorates, is a leading cause of vision loss among people age 50 and older. Previous studies have shown that eating a healthy diet and getting exercise protect against developing the disease. The recent study suggests that genetic and lifestyle factors may contribute to AMD in a synergistic way, when different factors work together to enhance or lower risk. 

Collaborating with researchers form the University of Iowa, Iowa City and Oregon Health Science University, 1,663 women ages 50 to 79 years had their diet and exercise patterns evaluated and were then categorized into risk groups. The women who had participated were part of a larger study in the Carotenoids in Age-Related Eye Disease Study (CAREDS), an ancillary investigation of the Women's Health Initiative. 

The researchers also ascertained whether the women smoked and, if so, how many years they smoked a pack of cigarettes or more each day. Then researchers assessed genetic data from the women to determine whether they carried known genetic risk factors for AMD. They looked closely at the allele of the complement factor H gene, known to be associated with greater AMD risk, probing to see if women had zero, one, or two copies of the allele. 

Of the women studied, 337 developed AMD, 91 percent of whom had early-stage disease. Those who carried two high-risk genetic alleles, smoked at least one pack per day for at least seven years, and were in the highest-risk diet and exercise categories were more than four times more likely to have AMD compared to women who did not have genetic risk factors, ate a healthy diet, and got 10 hours/week of light exercise or eight hours of moderate activity. 

The same team of scientists also published findings in JAMA Ophthalmology that found that vitamin D levels may also play a synergistic role with genetic factors in disease development. This study involved 913 CAREDS participants and found that blood levels indicating vitamin D deficiency ─ less than 12 ng/mL of 25 hydroxyvitamin D ─ were linked with a 1.8-fold increase in the odds of having AMD among women with no risk alleles compared to women with no genetic risk and adequate vitamin D levels. However, there is a 6.7-fold increase in the odds of having AMD among women with two risk alleles. 

"The findings of both studies support the notion of biologic synergy. That is, that one's genes, lifestyle factors and nutrition all come together in a synergistic way to mediate inflammation, which is a key mechanism involved in AMD," Julie Mares, a professor in the department of ophthalmology and visual sciences at the UW-Madison School of Medicine and Public Health, said in a statement. "There's a large body of evidence that unhealthy lifestyle habits are associated with inflammation and that CFH risk alleles augment inflammatory responses. Vitamin D is believed to suppress inflammation, which is thought to enhance the AMD disease process both directly and indirectly." 

Both studies were funded by grants from the National Eye Institute, part of the National Institutes of Health.