Why DHA Failed: The Fatty Acid That Actually Restored Vision in Mice
In one group, the mice could distinguish increasingly smaller stripes. In the other, the lines blurred together. The only difference was the type of fatty acid.
If you are taking omega-3 supplements for your eyes, you may be taking the wrong fatty acid.
Researchers at the University of California, Irvine have found evidence that a specific class of hard-to-get fatty acids reversed age-related vision decline in aged mice, while the more common omega-3 supplement DHA produced no benefit at all. The findings, published in Science Translational Medicine, also identified genetic variants in a key enzyme that correlate with faster progression of age-related macular degeneration in humans, lending weight to the idea that lipid metabolism is central to how the eye ages.
The work builds on years of research into ELOVL2, an enzyme that drops sharply with age and is considered one of the most reliable molecular markers of biological aging. In earlier work, increasing ELOVL2 activity in older mice improved vision by raising levels of the omega-3 fatty acid DHA in the eye. That led to a reasonable assumption: give DHA directly, and you could achieve the same effect.
You could not. What is important is that we did not see the same effect with DHA, said Dorota Skowronska-Krawczyk, corresponding author and associate professor in the Departments of Physiology and Biophysics and Ophthalmology and Visual Sciences at UC Irvine, speaking in a university news release.
The UCI team instead turned to very-long-chain polyunsaturated fatty acids, VLC-PUFAs, which are the direct biochemical products of the ELOVL2 enzyme and are found in the retinas photoreceptor membranes. As the body ages, VLC-PUFA levels in the retina decline. When the researchers injected aged mice with VLC-PUFAs intravitreally, visual function improved for up to four weeks, measured by electroretinography and behavioral assays sensitive to visual acuity and contrast sensitivity.
The distinction matters. Decades of research have pointed to DHA as protective for retinal health, and large clinical trials have tested that hypothesis directly. The Age-Related Eye Disease Study 2, AREDS2, run by the National Eye Institute, enrolled roughly 4,000 patients with intermediate AMD and found that adding omega-3 fatty acids DHA and EPA to the standard antioxidant formulation had no additional effect on progression to advanced AMD. The trial was considered disappointing for the field.
The UCI researchers findings suggest a narrower problem: not that fatty acid supplementation fails in AMD, but that the specific VLC-PUFAs that decline with age are not the same as the DHA in fish oil and most commercial supplements. VLC-PUFAs are present in retinal tissue at much higher concentrations than DHA but are harder to obtain through diet because they are synthesized locally by ELOVL2. When ELOVL2 activity falls with age, so does the retinas supply of these molecules.
The team also found that two genetic variants in the ELOVL2 gene are associated with faster onset of intermediate AMD. One variant, rs911196, correlates with 4.7 months earlier onset in people of European ancestry. And in a separate collaboration with researchers at UC San Diego, the group found that loss of ELOVL2 function accelerates aging of immune cells, with near-total loss of ELOVL2-expressing blood stem and progenitor cells in people over 60. That suggests the fatty acid pathway may not be limited to the retina.
We show the potential for reversing age-related vision loss, Skowronska-Krawczyk said. The molecular evidence, she said, shows that VLC-PUFA supplementation actually reverses the aging features in retinal tissue.
The study stops well short of suggesting VLC-PUFAs are ready for human testing. The mice received intravitreal injections, direct delivery into the eye, not anything close to an oral supplement or pill. VLC-PUFAs have not been tested in larger animals, and whether the molecular rejuvenation seen in mouse retinas will translate to human vision is unknown. The AREDS2 result also does not prove DHA does not work; the trial tested high-dose oral supplementation in patients with established intermediate AMD, not early intervention in people with genetic risk.
What the research does suggest is a more specific target: VLC-PUFAs, not DHA, appear to be what the aging retina is actually missing. Our work really confirms the fact that DHA alone cannot do the work, Skowronska-Krawczyk said, but we have this other fatty acid that is seemingly working.
The supplement industry already markets DHA and EPA extensively for eye health. The UCI findings will not disrupt that market in the near term, but they sharpen the distinction between what is commercially available and what the biology may actually require.
