涵養眼睛的學習: Eye health and 維生素Vitamin D
Low blood levels of vitamin
D are associated with an increased risk of age-related macular degeneration,
says a new study.
Deficient or suboptimal concentrations of vitamin D in
the blood were associated with a 2.6 and 1.5 fold increased risk of AMD,
according to findings published in JAMA Ophthalmology .
Researchers led by Dr Amy Millen from The University
of Buffalo also found an association with polymorphisms in vitamin D genes and
the odds of AMD in participants of the Carotenoids in Age-Related Eye Disease
Study (CAREDS).
The researchers found that deficient vitamin D levels
plus the high-risk genotype were associated with a 6.7 fold increase in the
odds of developing AMD.
Suppressing inflammation
The benefits of vitamin D are thought to be linked to
suppressing an inflammatory response in the eye, which may be aggravated by
select genotypes.
“Macular degeneration has been found to be
strongly associated with genetic risk,” explained Millen in a press
release. Among many genes linked to AMD, one of the strongest is a specific
genetic variant (Y402H) in the complement factor H (CFJ) gene, which codes for
the CFH protein that is involved in the body’s immune response.
“People who have early stage AMD develop drusen,
lipid and protein deposits that build up in the eye. Your body sees this drusen
as a foreign substance and attacks it, in part via the complement cascade
response,” she said. “CFH is one of the proteins involved in
this response. We see more AMD in people who have certain variants in the gene
which encodes a form of this CFH protein that is associated with a more
aggressive immune response.”
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“We hypothesize that vitamin D suppresses a
pro-inflammatory state in the retina via its genomic functions,” wrote
the researchers in JAMA Ophthalmology .
“Calcitriol is thought to modulate the adaptive immune response to suppress
damaging inflammation by decreasing immune cell pro-inflammatory cytokine
production, inhibiting dendritic cell maturation, inhibiting T- and B-
lymphocyte proliferation, and inducing T-regulatory cell function.”
Eye health
Image © iStockPhoto
The macula is a yellow spot of about five millimeters
diameter on the retina. As we age, levels of the pigments in the macula
decrease naturally, thereby increasing the risk of AMD. The yellow color is due
to the content of the carotenoids lutein and zeaxanthin.
AMD is the leading cause of legal blindness in people
over 50, and affects over 10 million Americans, according to the American
Macular Degeneration Foundation.
The majority of the research has focused on the
macular carotenoids, but the new study suggests that vitamin D status and
genetics may also be linked with AMD risk.
“To our knowledge, this is the first study that’s
looked at the interaction between genetic risk and vitamin D status in the
context of age-related eye disease,” said Millen, in a release
from The University of Buffalo.
Study details
Dr Millen and her co-workers analyzed data from 913
women, 550 of whom had adequate levels of vitamin D (at least 20 ng/mL). A
further 275 were considered to have inadequate levels (between 12 and 20
mg/mL), while the remaining 88 were deemed deficient (lower than 12 ng/mL).
While the results showed that the odds of having AMD
were higher in women who were vitamin D deficient, increasing vitamin D levels
beyond 12 ng/mL did not further lower the odds of AMD to any meaningful extent,
said Millen
“Our message is not that achieving really high
levels of vitamin D are good for the eye, but that having deficient vitamin D
levels may be unhealthy for your eyes,” she said.
The researchers were affiliated with The University of
Buffalo, The University of Wisconsin, Madison, The University of Iowa, Kaiser
Permanente Research, Fred Hutchinson Cancer Research Center, and Case Western
Reserve University.
Source: JAMA Ophthalmology
Published online ahead of print, doi:10.1001/jamaophthalmol.2015.2715
“Association Between Vitamin D Status and Age-Related Macular Degeneration
by Genetic Risk”
Authors: A.E. Millen, et al.
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Low blood levels of vitamin D are
associated with an increased risk of age-related macular degeneration, says a
new study.
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