Old age blindness issue & antioxidant friendly food habit
Old age blindness:
Macular degeneration & Cataract are the two important issue of old age blindness till present moment. Diabetic retinopathy, glaucoma are other contenders. Though cataract can be easily deal with surgical intervention; Macular degeneration is quiet challenging. With the increasing of life expectancy macular degeneration burden is growing globally.
Vision is a special sense by which the qualities of an object (as color, luminosity, shape & size) constituting its appearance are provided through a process in which light rays entering the eye are transformed by the retina in to electrical signals that are transmitted to brain via optic nerve and the brain interprets the signal and helps to see the surrounding.
Oxidative stress: The active process of image formation and conversion of light to electrical signal and its propagation to brain causes huge amount oxygen consumption in the retinal tissue. During oxygen consumption or oxidative reaction oxygen derived free radicals or reactive oxygen species (ROS) like singlet-oxygen, hydroxyl ion, hydrogen peroxide etc are liberated at the site. These free radicals are injurious to retinal tissue. The tissue damage caused by free radicals is called oxidative stress. Retina is highly vulnerable to oxidative stress due to its high oxygen consumption; high proportion of polyunsaturated fatty acid and constant exposure to visible light. To minimize the damaging effect of free radical injury it is very urgent to detoxify the free radicals immediately after their production. The detoxification is naturally done by the antioxidant. Level of ROS in eye is usually regulated by intracellular antioxidant defense system. Reduced glutathione (GSH) and antioxidant enzymes like superoxide dismutase & Glutathione Peroxidase (GSH-Px) are the important antioxidant defense system in the eye.
Free radicals– are atom/ group of atoms with an odd number of electrons and can be formed when oxygen interact with certain molecules. Once formed these highly reactive radical can start a chain reaction with important cellular components such as DNA or the cellular membrane. Cell may function poorly or die.
Antioxidants– are molecules which can safely interact with free radicals and terminate the chain reaction before vital molecules are damaged. Antioxidants are vit-C, vit-E, betacarotene (vit-A), other carotenoids (Lutein, Lycopene,Selenium, Zeaxanthin, Astraxanthin etc); Zn, Cu, Mn etc.
Two special important factors accelerate the oxidative stress. These are smoking and electromagnetic radiation exposure (EMR). Smoking is more relevant with macular degeneration and EMR is more relevant with cataract formation. They also aggravate the retinopathy with their oxidative effects.
Smoking- cigarette smoking is one of the strongest factors associated with the development of most severe ARMD. Pyridines are predominant constituents of cigarette smoke and its most toxic derivative is 2-ethylpyridine (2-EP). It is well accepted that the cumulative effects of cigarette toxicants over time causes cell death and increases susceptibility to oxidative damage. In addition, there is a well recognized relationship between pack-years and new vascular ARMD, which follows a dose-response effect.
Electromagnetic radiation (EMR): EMR exposure of eye results in overproduction of ROS (reactive oxygen species) which can damage cellular components such as lipids, nucleic acid and protein. EMR signals consist of extremely low frequency fields (between 1Hz-100 KHz) and high frequency fields, in the band of the radio frequency fields (RF, 100 kHz- 3GHz) and of the microwaves (MW, above 3 GHz). Wi-Fi exposed field of 2.45 GHz. Oxidative stresses mediated by ROS thus produced are believed to be a principal cause of non-congenital cataract.
Food habit: prehistoric human lived as pure hunter gatherer and ate only the natural food that could be obtained from hunting and collecting vegetable materials such as roots, fruits, nuts, grains and seeds. In ancient days man used to take raw food such as fruits, vegetable items, animal flashes and fishes. As the invention of fire the living style changed abruptly. Human learn to smoke the animal flashes and fishes. Cooking makes eating easier and faster. As the development of agriculture man started to plant his own food and produce cereals (wheat, rice, barely, pulse, vegetables, fruits etc). Ultimately human accustomed with a variety of recipe with the advancement of civilization. But they do not know why food is so essential for life or how food helps us to live. With the advancement of science it is now revealed how food act or play in human body. Now a day food is a luxurious item in living style of human. Food habit is a trend of the society where scientific basis or issue of real need is frequently ignored.
Ingredients of food: six basic ingredients of food are- Carbohydrate, Protein, Fat, Vitamin, Mineral and water.
Carbohydrate is the source of sugar or calorie. This sugar or calorie is the fuel for the thousands of chemical reaction occurring consistently in the body.
Protein is the main structural component of the human body. Cells, muscle, bone, hormones, enzyme etc all are made up of protein. Protein acts as a building block of the human body.
Fat acts as a dual function in the body. It can provide calorie to function like sugar and also act as complementary to protein to form the structural component of the body like cells, hormones, enzymes etc.
Vitamins & minerals provide immunity to the body against different diseases or environmental effects. It also play role directly or indirectly in different chemical reactions in the body.
Water is the main bulk of the body. Without water every system within the body will be collapsed. Life cannot be thought of without water.
Antioxidants & its sources & RDA:
Vit-C: RDA- 90 mg/day for male & 75mg/day for female.
Main sources are-citrus fruits, strawberries, lemon, orange, mango, peppers, broccoli, spinach, cauliflower, kiwi fruits, cantaloupe, sweet potatoes.
Vit-E: RDA- 15 mg/day
Main sources are- nuts, seeds, lentils, bean, turnip green, spinach, broccoli, carrot, sunflower seeds, papaya, fish oil etc.
Vit-A: RDA- 900 mcg (FDA- 5000 IU)
beta carotene may be of preformed which is of animal source like beef liver, egg yolk, fish oil; or may be of pro-vit A which is of plant source like spinach (6288mcg/100g); carrot- 8332mcg/100g; sweat potatoes- 11509 mcg/100g; kale- 10625mcg/100g; mastard green- 10660 mcg/100g; collards green- 8575 mcg/100g; broccoli- 929 mcg/100g; cantaloupe melon- 2020 mcg/100g; romaine lettuce- 5226 mcg/100g.
Beta carotene only can be converted in to vit-A in the body and all other carotene like lycopene, leutein, zeaxanthin, astraxanthin etc are not be converted to vit-A in the body. Beta carotene and other carotenoids are efficient quencher of singlet oxygen. Beta carotene present in small amount in lens but absent in macula. It is the major carotenoid in skin. So it has limited role in lens to prevent cataract rather than to protect macula. Other carotenoids specially leutein has important role to protect macula thereby to prevent macular degeneration.
Leutein & xeaxanthin: are two types of yellow to red pigment found widely in vegetable and other plants effectively absorb and screen high energy blue light thus prevent cataract formation and macular degeneration.
Main sources are- cooked spinach 20.4 mg/ 1 cup; cooked kale 237 mg/ cup; turnip green 12.2 mg/cup; broccoli 1.7 mg/cup; egg yolk .15/large one;
Astraxanthin: source is red algae.
Selenium: FDA- 70 mcg. In human it is a trace element nutrient that functions as cofactor for glutathione reductase and certain forms of thioredoxin reductase.
Main sources are- garlic, shelfish, red meat, egg, sea food, white grain, lean meat.
Lycopene: sorces are- tomato, watermelon, guava etc.
Cu, Zn: these are actually co-factor. Main sources are- sea food, lean meat, nuts, legume, milk etc.
Few facts about antioxidants:
- Antioxidants are mainly of plant source.
- Bright colored fruits and vegetables mean more antioxidant.
- Highest antioxidant containing vegetables are spinach, broccoli, red cabbage.
- Best way to get dietary requirements of vitamin and antioxidants is to intake balance diet that contains variety of food.
- Consuming fish more than twice a week reduce macular degeneration (ARMD).
- Standard serve means: vegetable- 75 gm or 1 cup raw leafy vegetable / ½ cup other vegetable or juice; fruits- 1 medium size or ½ cup fruit juice; meat-2-3 ounce lean meat (meat containing less than 10gm fat/ serving); milk-1 cup fat free or low fat milk or yogurt. 5-9 servings of fruits & vegetables per day are needed.
- Any serving means 3 ounce or size of a small fist.
- Standard serve of meat containing 65 gm lean meat/ 80 gm poultry/100 gm fish/ 150 gm legume/ bean/ 170 gm tofu/30 gm nuts or seeds.
- Lean meat– skinless chicken breast, turkey cutlets, beef cut with loin or top round,rump roast, sirlon tip. Lean meat is the rich source of vit-B including vit-B12 (only animal source), Fe, Mn, Zinc etc which are easily absorbed.
Smokers should take antioxidant in a higher amount than ordinary people.
Dr. Md. Sayedul HoqueMBBS, FCPS, MS (ophth) National Eye Care Centre Ring Road, Shyamoli, Dhaka. Ex-Associate Professor National Institute of Ophthalmology & Hospital