Metabolism of fatty acids and vitamins can help quell the inflammation behind ocular surface disease.
We know now that there are myriad causes of dry eye disease, all with a common denominator of underlying inflammation.[1,2] However, we now have more diagnostic tests and more treatment tools at our disposal, including nutritional input. A look at the science behind this approach to treating dry eye can offer us a complete picture of dry eye from an alternative perspective.
TWO ESSENTIAL ACIDS
Numerous studies have shown that omega-3 fatty acids (fish oil) are effective at treating dry eye disease.[3-9] However, they are not the only nutrient that addresses dry eye disease.
There are two essential (needed in our diet) fatty acids: alpha-linolenic acid (ALA), an omega-3, and linoleic acid (LA), an omega-6. Internal enzymes inside our bodies act upon these acids, producing functional molecules, including molecules that have pro- or anti-inflammatory reactions. Once metabolized, ALA and LA become prostaglandins E3 and E2 respectively. However, the progressive enzyme action is affected by many factors. For example, the delta-6 desaturase enzyme action on both omega molecules is reduced by aging, alcohol, nutrient deficiencies, trans fat, and elevated cholesterol. Thus, the metabolism of these molecules may not be as efficient as it appears.
THE RIGHT BALANCE
One of the most important aspects of this metabolism is the balance between the two omegas. Because omega-3 progresses to an anti-inflammatory prostaglandin, we might think our bodies need more of that one. However, we also need the pro-inflammatory prostaglandins to fight off infections, diseases and a whole host of conditions.
The ideal ratio of omega-6 to omega-3 should be about four to one (yes, more omega-6). However, the standard American diet maintains a ratio closer to 25 to one, which means that the pro-inflammatory pathway is pushed to the chronic inflammatory state. However, if the omega-3 balance is maintained, the omega-3 molecules of docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) will block off the conversion to arachidonic acid (AA). This will allow the omega-6 molecules gamma-linolenic acid (GLA) and dihomo-gamma-linolenic acid (DGLA) to convert to a mucus-specific anti-inflammatory prostaglandin E1. This reduces inflammation in all mucous membranes in the body, including those in the tear film.
So, should individuals increase the amount of omega-3 EFAs in the diet to balance out the ratio of omega-6 to omega-3 fatty acids? Not necessarily. Given the amount of omega-6 we currently consume, the additional amount of omega-3 required could lead to not-so-beneficial effects. For example, fish oil is a blood thinner, so ingesting excessive amounts could lead to easy bruising and other blood-thinning effects. A better approach is to reduce the amount of omega-6 fatty acids in our diet while moderately increasing the omega-3 fats in our diet.
DHA and EPA are formed when fish eat algae and are found in the triglyceride form.[12,13] A triglyceride consists of a three-carbon glycerol “backbone” with each carbon linked to a fatty acid molecule. Thus, each triglyceride molecule contains three fatty acids. In normally produced fish oil, about 20% to 30% of the fatty acids are EPA and DHA, while highly concentrated oils can contain 60% to 85% EPA and DHA. This is why it is important to check the label for the actual EPA/DHA concentrations in any particular formula.
Besides omega-3s and omega-6s, other nutrients also support the anterior segment of the eye, namely:
• vitamin A, which is vital for the health of the corneal and conjunctival epithelial cells of the cornea and conjunctiva, as well as the function of the immune system.[14-16] It is also necessary for goblet cell and lacrimal gland production of the large variety of mucins now associated with the base layer of the tear film.
• vitamin B6, which is one of the nutrient co-factors required to push the metabolic pathway conversion of GLA to DGLA.[17,18] It is also required for the neuronal blink response.
• vitamin C, which as ascorbyl palmitate (fat-soluble form) modulates PGE1 synthesis. This vitamin C form also enhances the production of immunoglobulin E concentrates in tears, the first line of basophil and mast cell defense against invading pathogens and allergens that frequently cause dry eye symptoms.
• vitamin E, which should be included in all fatty acid-based formulations to help prevent or slow lipid oxidation. This particularly includes any formulation that includes flaxseed oil or any type of fish oil.
• vitamin D, which improves tear hyperosmolarity and should be included in all formulations that include vitamin A due to an increased risk of fractures in older patients taking large amounts of supplemental vitamin A.[22,23]
Black currant seed oil is an excellent source of GLA due to its four-to-one balance of omegas and should be included in a full-spectrum dry eye formula.[24-27] Lactoferrin is one of the proteins that transfer iron to the cells and control the level of free iron in the blood. Adequate levels of tear lactoferrin, naturally produced by the lacrimal gland and neutrophils, are particularly important for eye surgery and contact lens patients, who are disposed to a risk of infection.
Quality dry eye products also contain minerals, mucin enhancers, antioxidants and natural anti-inflammatory ingredients. Making recommendations based on solid science will assure that your patients receive products that can make a significant as well as rapid resolution to their dry eye concerns.
Jeffrey Anshel, OD, FAAO, is founding president of the Ocular Nutrition Society and is in private practice in Encinitas, CA.
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