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Their study of identical twins from the US World War II Twin Registry also found that the more a person smoked, the higher their risk of developing macular degeneration.
The study, “Smoking, Dietary Betaine,
Methionine, and Vitamin D in Monozygotic
Twins with Discordant Macular Degeneration:
Epigenetic Implications” published
in the journal Ophthalmology on
July 1, is the first to look at identical
twin pairs in which one twin had early
age-related macular degeneration (AMD), and
the other had late stage AMD. AMD is highly heritable, with genetic factors determining up to 71 percent of the disease’s severity as determined by a previous study of this twin registry by this same research team. By examining identical twins with the same genes but whose disease was at different stages, researchers were able to identify environmental and behavioral factors that may contribute to severity of the disease.
“We wanted to know why, if they have the
same genes, do they have different stages of
the disease?’’ said lead researcher Johanna
M. Seddon, MD, ScM, Director of the
Epidemiology and Genetics Service, Tufts
Medical Center, and Professor of
Ophthalmology, Tufts Universtity School of
Medicine.
“Eat a healthy diet with lots of fruits and
vegetables, and that can make a difference -
even if you have a genetic susceptibility to
macular degeneration,’’ said Seddon, a
specialist in macular degeneration, and, of
course, don’t smoke.’’
Macular degeneration is one of the leading
causes of vision loss in older Americans. It
occurs when cells in the macula, the part of
the eye responsible for clear central
vision, gradually die. Macular degeneration
can progress so slowly it takes years for
serious vision loss to occur but it can also
develop rapidly, causing severe vision loss
that can make it difficult to drive, read or
conduct daily tasks. Each twin completed a questionnaire about nutritional and health behaviors. The study found that twins whose macular degeneration was at the early stages tended to consume more vitamin D from dietary sources such as fish or milk than their brothers. Vitamin D may reduce the risk of macular degeneration because it has anti-inflammatory properties. It may also block the formation of new blood vessels that can grow under the macula, leaking blood and causing vision loss in the more severe stages of the disease. Similarly, Dr. Seddon’s research team also found that higher intakes of betaine and methionine were linked to a slower progression of the disease.
These nutrients have also been linked to
epigenetic mechanisms, which is a change in
DNA, not attributable to a change in the
actual DNA sequence. Betaine is found in
fish, grains and spinach, while methionine
is found in poultry, fish and dairy foods.
The study also found that among the pairs of
twins, the twin who was the heavier smoker
tended to have the more severe case of
macular degeneration. These results indicate
that both genetic susceptibility and
environmental factors are important, that
epigenetic factors may also be involved, and
further underscores the importance of
modifiable behaviors, especially avoiding
smoking and eating a healthy diet, to help
prevent or delay the progression of macular
degeneration.
The study evaluated pairs of elderly male twins and used a survey
of personal dietary and health habits to
determine variations.
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