- Some of the leading causes of sight loss affect the part of the eye called the retina.
- Supplementation with a certain type of omega fatty acid known as docosahexaenoic acid, or DHA, can reduce the incidence of retinal disease, however, improving DHA levels in the retina is challenging due to the retina-blood barrier.
- A group of researchers has now shown that a different form of DHA they have developed can enter the retinal tissue— at least in mice.
- If the same effect is shown in humans, the supplement could be used to reduce risk and potentially even treat some retinal diseases.
Loss of sight is believed to have a global cost of $411 billion annually due to medical and care costs, as well as lost work and productivity, according to the World Health Organization.
Most people who lose their sight are over the age of 50, and globally the leading causes of vision impairment are:
- age-related macular degeneration
- diabetic retinopathy
- uncorrected refractive errors.
Age-related macular degeneration and diabetic retinopathy both affect the retina, which is found at the back of the eye and contains many light-sensitive cells which allow us to see.
Age-related macular degeneration affects the macula—a part of the retina—and results in central vision being blurred. Meanwhile, diabetic retinopathy is seen in patients with both type 1 and type 2 diabetes and is caused by high blood sugar levels affecting blood flow to the retina, and if untreated, can cause blindness.
Of all the tissues in the body, the retina and brain have the highest concentration of a certain type of omega-3 fatty acid known as docosahexaenoic acid or DHA. This fatty acid has to be provided through diet or supplementation as the body can only make small amounts of it.
While the importance of omega-3 fatty acids in the diet are well known, and epidemiological studies have shown the beneficial effects of DHA supplementation on reducing the risk of development of retinal disease, actually getting this molecule into the retina in order to support normal functioning is much harder.
This is because it is challenging to get DHA in the form used for supplements, that cross the intestinal barrier, to also penetrate the blood-retinal barrier.
Now, new research offers a ray of hope to treat and possibly prevent visual declines related to Alzheimer’s disease, diabetes, and other disorders after scientists created a new form of DHA that can cross into the eye’s retina.
The research was funded by an Alzheimer’s Association Research Grant (AARG).
A new form of DHA
The group of researchers behind the study were from the University of Illinois at Chicago and presented their data at the annual meeting of the American Society for Biochemistry and Molecular Biology, March 25–28 in Seattle.
They showed that a new form of DHA they have developed could be used to cross both the intestinal and retinal blood barrier.
To do this, the researchers created a new lysophospholipid form of DHA or LPC-DHA. They gave this supplement to mice at a low dose for 6 months, equivalent to about 250 to 500 milligrams of omega-3 fatty acids per day in humans.
This resulted in a 100% increase in the amount of DHA found in their retinas. Researchers compared the effect of supplementation with LPC-DHA to other forms of DHA supplementation such as fish oil and krill oil and found it to be superior.
Improved eyesight with DHA
Further studies by the team in mice bred to exhibit some of the symptoms of Alzheimer’s showed that after six months of daily supplementation with LPC-DHA, these mice exhibited a 96% improvement in retinal DHA levels as well as preserved retinal structure and function.
When compared to conventional DHA supplements, they found these had no effect on retinal DHA levels or function in the mice.
As this form of DHA has only been tested in mice and not humans, it is unclear whether this LPC-DHA would have the same effect in humans.
Low DHA in Alzheimer’s
Low levels of DHA have been found in the retinas of individuals with both age-related macular degeneration and diabetic retinopathy as well as those with Alzheimer’s disease.
Dr. Mohammed Zeeshan Afzal, primary care doctor and dermatologist with over 14 years of experience, and medical officer at Welzo, who was not involved in the study, told Medical News Today:
“DHA (docosahexaenoic acid) is an omega-3 fatty acid that is essential for proper retinal function. DHA levels have been linked to several retinal conditions, including age-related macular degeneration (AMD), retinopathy of prematurity (ROP), and retinitis pigmentosa (RP).”
“Diabetic retinopathy is a complication of diabetes that affects the blood vessels in the retina. DHA has been shown to have a protective effect on these blood vessels, reducing inflammation and oxidative stress that can contribute to the development of diabetic retinopathy,” Dr. Afzal explained.
Dr. Barry Sears, founder of the Inflammation Research Foundation, who was also not involved in the study, told MNT that the effect of DHA on inflammation is seen, “virtually all because DHA is the building block required to make certain hormones (resolvins) that are necessary to reduce excess inflammation in the neurons.”
Can DHA benefit Alzheimer’s-related visual impairment?
The authors of the study claim that the findings could be of benefit to people with Alzheimer’s disease. People with Alzheimer’s disease often have vision impairment, though the causes are myriad.
Dr. Sears told MNT that the vision impairment seen in Alzheimer’s disease patients could be due to the same inflammatory processes that cause Alzheimer’s disease in general, and Dr. Zeeshan Afzal told MNT that there are many potential causes.
“The visual impairment seen in people with Alzheimer’s disease is caused by damage to the brain’s visual processing centers. As the disease progresses, it can affect a person’s ability to recognize faces, read, and navigate their environment. This is due to the buildup of amyloid plaques and tau tangles in the brain, which disrupt communication between neurons and cause cell death,” he explained.
The authors point out that retinal DHA levels have been discovered to be low in Alzheimer’s patients as well as others with visual impairment.
Finding a way that could raise these levels could help to prevent Alzheimer’s-related declines in visual function.
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