Category: Health and Wellness
2. Omega-3 May Prevent Blindness
Increasing intake of the omega-3 fatty acids DHA and EPA, found
in popular fish-oil supplements, may protect against blindness resulting
from abnormal blood vessel growth in the eye, according to a study published
online by the journal Nature Medicine on June 24. The study was done in
mice, but a clinical trial at Children's Hospital Boston will soon begin
testing the effects of omega-3 supplementation in premature babies, who are
at risk for vision loss.
Abnormal vessel growth is the cause of retinopathy of
prematurity, diabetic retinopathy in adults, and "wet" age-related macular
degeneration, three leading causes of blindness. Retinopathy, affecting
about 4 million diabetic patients and about 40,000 premature infants in the
United States, is a two-step disease that begins with a loss of blood
vessels in the retina (the nerve tissue at the back of the eye that sends
visual signals to the brain). Because of the vessel loss, the retina becomes
oxygen-starved and sends out alarm signals that spur new vessel growth. But
the new vessels grow abnormally and are malformed, leaky and over-abundant.
In the end stage of the disease, the abnormal vessels pull the retina away
from its supporting layer, and this retinal detachment ultimately causes
blindness.
The researchers, led by Lois Smith, M.D., Ph.D., and Kip Connor,
Ph.D., of Children's Hospital Boston's Department of Ophthalmology and
Harvard Medical School, and John Paul SanGiovanni, Sc.D., of the National
Eye Institute (NEI), National Institutes of Health, studied retinopathy in a
mouse model, feeding the mice diets that emphasized either omega-3 fatty
acids (comparable to a Japanese diet) or omega-6 fatty acids (comparable to
a Western diet).
Mice on the omega-3 diet, rich in DHA (docosahexaenoic acid) and
its precursor EPA (eicosapentaenoic acid), had less initial vessel loss in
the retina than the omega-6-fed mice: the area with vessel loss was 40
percent to 50 percent smaller. As a result, the omega-3 group had a 40
percent to 50 percent decrease in pathological vessel growth.
"Our studies suggest that after initial loss, vessels regrew
more quickly and efficiently in the omega-3-fed mice," says Connor, the
study's first author. "This increased the oxygen supply to retinal tissue,
resulting in a dampening of the inflammatory 'alarm' signals that lead to
pathologic vessel growth."
Because omega-3 fatty acids are highly concentrated in the
retina, a mere 2 percent change in dietary omega-3 intake was sufficient to
decrease disease severity by 50 percent, the researchers note. Validating
their findings, results were virtually identical in mice whose omega-3 fatty
acid levels were increased through genetic means.
Omega-3 fatty acids like DHA and EPA are thought to dampen
inflammation in the body. They are often lacking in Western diets; instead,
omega-6 fatty acids predominate. The ideal omega-6:omega-3 ratio is thought
to be 2-to-1 to 5-to-1, whereas typical Western diets have ratios of 10-to-1
or higher. Premature infants are especially lacking in omega-3 fatty acids,
because they miss getting this nutrient from their mothers, a transfer that
normally happens in the third trimester of pregnancy.
The researchers demonstrated that the omega-3-based diet
suppressed production of TNF-alpha, reducing the inflammatory response in
the retina, whereas the omega-6-based diet increased TNF-alpha production.
The retinas of omega-3-fed mice also had increased production of the
anti-inflammatory compounds neuroprotectinD1, resolvinD1 and resolvinE1.
These compounds, derived from omega-3 fatty acids, also potently protected
against pathological vessel growth, and they were not detected in the
retinas of mice fed the omega-6 diet.
"If omega-3 fatty acids, or these anti-inflammatory mediators,
are as effective in humans and they are in mice, simple supplementation
could be a cost-effective intervention benefiting millions of people," says
Smith, the study's senior investigator. "The cost of blindness is enormous."
Aside from fish-oil supplements, the most widely available
source of omega-3 fatty acids is coldwater oily fish (wild salmon, herring,
mackerel, anchovies, sardines). The compounds can also be made synthetically
from algae or other non-fish sources.
Paul A. Sieving, M.D., Ph.D., director of the NEI, which
provided funding for the study, said, "This study shows the benefit of
dietary omega-3 fatty acids in protecting against the development and
progression of retinal disease. It gives us a better understanding of the
biological processes that lead to retinopathy and how to intervene to
prevent or slow disease. It will be interesting to see if human clinical
trials show similar beneficial effects."
In addition to retinopathy, the researchers speculate that
omega-3 fatty acids may help reduce vision loss in people with "wet" or
neovascular phase of age-related macular degeneration (AMD), a disease that
also involves abnormal vessel growth.