People with a genetic predisposition
for age-related macular degeneration (AMD) significantly increased their odds
of developing the blinding eye disorder if they had a history of heavy smoking
and consistently did not exercise or eat enough fruits and vegetables,
according to an observational study of women funded by the National Eye
Institute, part of the National Institutes of Health.
Eating a healthy diet and getting
exercise have been shown in earlier studies to protect against AMD, a leading
cause of vision loss among people age 50 and older. Findings from this latest
study, conducted by a team of investigators at the University of Wisconsin-Madison,
suggest that genetic and lifestyle factors may contribute to AMD in a
synergistic way. The findings were published online in the journal Ophthalmology.
If you have a family history of AMD,
the good news is that the study findings suggest that there are things you can
do to potentially lower your risk of developing AMD yourself,.
The researchers studied the risk
among women ages 50 to 79 years who had participated in the Carotenoids in
Age-Related Eye Disease Study (CAREDS), an ancillary investigation of the much
larger Women's Health Initiative, an observational study that has tracked the
health-related behaviors and outcomes of more than 160,000 women since 1991.
For the current study, first author
Kristin J. Meyers, Ph.D., and her team evaluated the diet and exercise patterns
of 1663 women and categorized them into lowest-, moderate- and highest-risk
groups. They also evaluated whether the women smoked and, if so, how many years
they smoked a pack of cigarettes or more each day. They also assessed genetic
data from the women to determine whether they carried known genetic risk
factors for AMD. They looked most closely at an allele (version) of the
complement factor H (CFH) gene that is known to be associated with greater AMD
risk, probing whether the women had zero, one, or two copies of the allele.
A total of 337 women in the study
developed AMD, of whom 91 percent had early-stage disease.
Among women with stable diets, those
who carried two high-risk genetic alleles, smoked at least seven pack-years,
and were in the highest-risk diet and exercise categories were more than four
times more likely to have AMD compared to those women who did not have genetic
risk factors and who ate a healthy diet and got at least 10 hours/week of light
exercise (such as housework or walking at a pace you could sing to) or at least
eight hours of moderate activity (such as brisk walking).
In addition to lifestyle
contributions, vitamin D levels may play a synergistic role with genetic
factors, according to the findings of another study by the same team involving
913 CAREDS participants. Amy E. Millen, Ph.D., that study's first author, found
that blood levels indicating vitamin D deficiency (less than 12 ng/mL of 25 hydroxyvitamin
D) were associated with a 1.8-fold increase in the odds of having AMD among
women with no risk alleles, but a 6.7-fold increase in the odds of having AMD
among women with two risk alleles, compared with women who had no genetic risk
alleles and adequate levels of vitamin D. The findings of the vitamin D study,
which was also funded by NEI, were published in JAMA Ophthalmology.
"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," said Dr. Mares.
"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 processes both directly and indirectly."
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