Notice: I’m happy to say that I’ll be reworking the Nutrition section of the site, including this post. More information, practical guidance. Stay tuned!
This first part in a series on nutrition focuses on omega-3, omega-6, and anti-oxidants in our diets. This Q&A series is based on notes provided by Yves Sauvé, Director of Research, Department of Ophthalmology, University of Alberta.
Question 1: The media and the internet are inundated with reports on nutrition to prevent, slow down and treat various retinal degenerations.
a. Sources of Vitamin A, omega 3’s/DHA, antioxidants etc:
- Vitamin A: green and yellow vegetables (converted from beta-carotene as the initial source, tightly regulated by the body), liver, egg yolks, fish oil, and margarine. Note a polar bear liver contains enough vitamin A (30-90grams) to kill an adult human.
- Omega-3’s
- DHA (docosahexaenoic acid): found in cold water oily fishes such as
salmon, herring, mackerel, anchovies and sardines; DHA is also commercially manufactured from microalgae (Crypthecodinium cohnii and Schizochytrium).
- EPA (eicosapentanoic acid): same source as DHA.
- ALA (alpha-linolenic acid): from flaxseed oil, hempseed oil, chia seeds, kiwi, and lingonberry. Note: no more than 5% of ALA can be converted into DHA (highly regulated conversion, in competition with saturated fatty acids)
- DHA (docosahexaenoic acid): found in cold water oily fishes such as
- Omega-6’s
- Arachidonic acid (AA): found in soybean oil (important additive in processed food) and corn oil (major food staple in the USA since most animals bred for food are fed corn, and most food additives are derived from corn), nuts, palm, rapeseed oil, sunflower oil, poultry, eggs, avocado, acai berry, pumpkin seed, and hempseed oil.
Antioxidants
- ⁃ Vitamin A: see above
- ⁃ Vitamin C (ie, ascorbic acid): found in citrus fruits and vegetables.
- ⁃ Vitamin E (ie, alpha-tocopherol): found in vegetable oil, nuts, sunflower, wheat, green leafy vegetables, and fish.
- ⁃ Lycopene: found in red tomatoes and watermelons.
- ⁃ Flavonoids (large family of antioxidants made by plants): found in tea, red wine, vegetables, and legumes.
- ⁃ Anthocyanins (a type of flavonoid): found in berries (acai, cranberry, blueberries, saskatoon berries, bilberries, etc…). The levels of anthocyanins in increases with ripening and are higher in the peel itself.
- ⁃ Polyphenols: found in fruit and berry beverages, coffee and soy. The levels of polyphenols in fruits and vegetables decreases with ripening.
- ⁃ Reservatrol: found in red wine; however you would have to drink 24 liters per day to reach a physiological effect (companies are purifying it).
- ⁃ Lutein and zexanthin: found in green vegetables (kale, swiss chard, collard greens, spinach, parsley, mustard greens, dill, celery, scallions, leek, broccoli, etc…) and in lower quantities in carrots.
- Alpha lipoic acid: made by the body (found in every cell); also found in red meat, organ meats (such as liver), and yeast.
- Curcumin: the indian spice (yellow powder).
- Anthraquinones: found in chinese teas such as Rheum, Qinghai Wild Dahuang tea, Semen Cassiae.
- Reduced L-glutathione: found in fruits, vegetables, meat (destroyed by intense heat).
- Quercetin: found in red wine, grapefruit, onions, apples, and black tea. It is also found in lesser amounts in leafy green vegetables and beans.
- coQ-10: found in fresh sardines and mackerel, the heart, liver and meat of beef, lamb and pork along with eggs; very small quantities (not sufficient for health) are found in spinach, broccoli, peanuts, wheat germ and whole grains.
- Lignan: found in oats, flax seeds, pumpkin seeds, sesame seeds, rye, soybeans, broccoli, beans, and some berries.
b. How do vitamins or other nutrients help eyesight?
- Vitamin A (retinol) is a precursor of the molecule (11 cis-retinaldehyde) that starts the process of transforming light into electrical changes in the eye (phototransduction); a balanced diet containing beta-carotene and/or vitamin A leads to sufficient amounts of 11 cis-retinaldehyde. Vitamin A also acts as an antioxidant (see below fro details). Note: intake of vitamin A is less desirable than of beta-carotene, from which the transformation into vitamin A is tightly regulated by the body needs (no chances of toxicity).
- DHA is an essential fatty acid (we need to get it directly from our diet), which represents close to 50% of all fatty acids essential for photoreceptor function. Byproducts of DHA (such as NPD1) have been shown to support the survival of photoreceptors; however, oxidation of DHA can lead to toxins (such as CEP). EPA is a precursor of very long chain n-3 fatty acids that are essential for photoreceptor function.
- Antioxidants are required to prevent oxidative damage due to the naturally high oxygen levels in the outer part of the retina where photoreceptors are localized. Some antioxidants (lutein and zeaxanthin) also help reducing the damaging effect of intense blue-light on the retina. A balanced diet contains sufficient amounts of antioxidants; there are multiple types and equally multiple natural sources.