Omega-3 Benefits: Omega-3 and Sight

Omega-3 benefits to sight

Docosahexaenoic acid (omega-3 DHA) and arachidonic acid (AA) represent over 30% of the lipid structure of the brain and the cones and rods in the retina. Both contribute to the fluidity of the cell membranes, which is extremely important in the nerve tissue morphogenic process, particularly in the brain.(1) Furthermore, omega-3 DHA increases the photoreceptors sensitivity to light, is involved in neurogenesis, stimulates pre- and post-natal development of glial cells and stimulates neuronal migration and synaptogenesis.(2-7) The external membranes of the retinal cones and rods accumulate large amounts of long-chain polyunsaturated fatty acids (LC-PUFAs), particularly omega-3 DHA; its fluidity is essential for the light signal transduction process and its conversion into an electrical signal which is then processed by the brain. The photoreceptors are concentrated in the external membranes of the cones and rods and are mobilised through the membrane when they receive a light signal (photons), modifying the concentration of cyclic guanosine monophosphate (cGMP). The decrease in cGMP stimulates closure of the sodium channels, producing hyperpolarization of the membrane, thus generating the electrical impulse that is sent to the brain. Here, once again, membrane fluidity is essential for signal transduction to occur and this fluidity requires phospholipids with a high omega-3 LC-PUFA content.(8,9)

Development of sight in infants and omega-3

It is estimated that the foetus, during the last trimester of gestation, and the newborn, during the first six months of life, require an extraordinary amount of AA and omega-3 DHA (which concentrate particularly in the axonal growth cones and synaptic vesicles, which contain the neurotransmitters) because the speed of precursor transformation in the liver is not sufficient to cover the metabolic requirements of these fatty acids.(1) Thus, if the mother has an adequate intake of omega-3 LC-PUFAs with an adequate Omega-6/Omega-3 ratio in her diet, she can provide the foetus, through the placenta, and the newborn, through breast milk, with the necessary amounts for normal development of the nervous and visual system.(10) Various clinical studies have shownimprovements in visual acuity and cognitive development in children with larger amounts of omega-3 DHA during breastfeeding and in premature infants after supplements in formulas.(11-13) The decrease in omega-3 DHA in the brain and retina interferes with normal neurogenesis and neuron function, as well as the sight signalling csascades.(14)
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Age-related macular degeneration (AMD) and omega-3

Long-chain polyunsaturated fatty acids, essential to the vision process, also affect factors and processes involved in the pathogenesis of vascular and neural disease of the retina. Omega-3 DHA is the largest structural lipid in the photoreceptor membranes and appears to facilitate accumulation of lutein in the retina, while insufficient omega-3 DHA in this tissue is associated with retinal function disorders. Both omega-3 DHA and EPA can act as protective agents due to their influence on genetic expression and retinal cell differentiation. Omega-3 EPA is capable of reducing concentrations of the protein vascular endothelial growth factor (VEGF), responsible for abnormal expansion and bursting of blood vessels.(15) 
An inverse relationship between Omega-3 LC-PUFA ingestion and advanced age-related macular degeneration has been found in six studies.(17-22) With respect to the prevalence of the disease, the highest and lowest odds ratios between ingesting Omega-3 LC-PUFA were 0.4 and 0.9, respectively. 
Recently, a study has been published on simultaneous ingestion of lutein (12 mg/d) and omega-3 DHA (800 mg/d) and placebo for 4 months in women aged between 60 and 80 years, assessing the effect on lutein and omega-3 DHA serum concentration and macular pigment density. The results show that lutein supplementation increases macular pigment density eccentrically, while omega-3 DHA supplementation produces in increase in the central area.  Furthermore, the combination of omega-3 DHA and lutein produces a combined effect.(16) 
The ARES 2 study (www.ares2.org) is currently in progress with 4,000 patients, lasting 5-6 years, to assess the effect of lutein/zeaxanthin and Omega-3 LC-PUFAs on the development of age-related macular degeneration (AMD).

Others conditions and Omega-3

The association of omega-3 DHA, vitamin E and vitamin B complex has produced statistically significant differences between visual fields and sensitivity to contrast in glaucoma patients compared to the control group who did not take the micronutritional supplement.(23) 
Various studies with animal models have shown the antiapoptotic protective function of DHA in photoreceptors, in both light-induced and ischaemic/reperfusion processed-related lesions and those produced by oxidative stress.(24) 
It has been suggested that omega-3 DHA may be useful as a protector in pigmentous retinosis(25), where low plasma and erythrocyte levels of DHA have been documented as contributing to the characteristic visual disorders of this disease.

  

Bibliography

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