Vitamin A:Vitamin A is a colorless substance found only in animal foods. It is formed in the animal or human body from a yellow pigment, carotene, found in carrots, apricots, yams, all green vegetables, green pasture crops and seaweeds, the quantity roughly paralleling the intensity of the color. We get vitamin A itself from such animal foods as liver and fish-liver oils; egg yolks, butter, and cream supply both carotene and vitamin A.
Mild deficiencies of vitamin A are so common that you have probably experienced them. A slight deficiency impairs vision. A substance containing vitamin A, visual purple, is formed in the eyes; any light reaching the eyes breaks down part of the visual purple (this includes TV, computer screens, sunlight, glaring lights etc), and the products of this purposeful breakdown set up nerve impulses which tell the brain what the eyes see. More visual purple is formed and again destroyed.
This cycle of regeneration and breakdown continues throughout life. Vitamin A is therefore somewhat like the film in a camera in that it photographs what you see but the “film” is used up.
Both day and night vision require vitamin A, but night vision depends on the vitamin-A mechanism entirely; therefore a subtle vitamin-A deficiency first causes difficulty in seeing in the dark. You can test your vitamin-A adequacy any time you drive at night. The lights of on-coming cars destroy vitamin A in your eyes; if your ocular fluid contains ample vitamin, you can see again almost immediately; if you are deficient, you will be blinded, the length of time depending on the severity of your deficiency. Tests have shown that persons having auto accidents at night are pathologically deficient in this vitamin. When better lighting of highways results in fewer accidents, it is because day vision rather than night vision is used and vitamin A is less relied upon.
There are varying degrees of night blindness. The person with a mild deficiency believes his vision to be normal but sees more efficiently in daylight. With a slightly greater deficiency, he experiences eye fatigue after watching television, for example, but he usually assumes that others have similar difficulty. If his need for vitamin A is still greater, he may suffer pain in his eyes, especially after long use, and experience nervousness, headaches, and visual fatigue. A severe deficiency can cause such discomfort and eyestrain that he may refuse to drive at night.
Such a person is sensitive to bright light during the day and feels more comfortable wearing dark glasses; thus less light reaches his eyes and less vitamin is destroyed. The majority of people who wear dark glasses eat too little vitamin A to allow normal vision.
People who work in bright light, which destroys vitamin A quickly, or dim light, which requires night vision entirely, use relatively more vitamin A than do persons working in moderate light. Typists and bookkeepers who face the glare of light on white paper frequently suffer from eyestrain preventable by diets richer in vitamin A; persons who sew, read, or watch television a great deal, miners working in dim light, welders facing flashing fire, photographers working both with bright lights and in darkrooms, and people living on the desert or beach where the sunlight is reflected by white sand often have visual difficulties because their need for vitamin A is unusually great. Perhaps no glare is so destructive to the vitamin A in the eyes as sunlight on clean snow; trappers, hunters, and skiers are often too familiar with this vitamin deficiency.
When the lack becomes severe, burning, itching, and inflamed eyelids, eyestrain, perhaps severe pain in the eyeballs themselves or frequently occurring sties are experienced in addition to nervousness and exhaustion. Mucus may accumulate in the corners of the eyes, ulcers or sores sometimes appear on the covering of the eye, or cornea.
Although eye symptoms may be the first to be noticed in a mild vitamin-A deficiency, even earlier changes take place in the skin. Cells in the lower layers of skin die and slough off. They plug the oils sacs and pores, thus preventing oil from reaching the surface; the skin may become so dry and rough that the entire body sometimes itches. The pores plugged with dead cells cause the skin to have the appearance of “goose pimples” although they are unaffected by temperature changes.
This roughness usually occurs first on the elbows, knees, buttocks, and back of the upper arm.
Pores enlarged by an accumulation of dead cells and oil are spoken of as whiteheads or blackheads. If these cells become infected, pimples may result. The skin is likewise susceptible to such infections as impetigo, boils, and carbuncles. These abnormalities can usually be corrected by increased amounts of vitamin A, provided the diet is adequate in other respects.
When vitamin A is under-supplied, the hair becomes dry and lacks sheen and luster. Dandruff usually accumulates on the scalp. The nails may be affected and peel easily or become ridged.
Simultaneously with the visual difficulties and the changes in the skin, a vitamin-A deficiency allows abnormalities to occur in the tissues spoken of as mucous membranes. These tissues line the body cavities such as the throat, nose, sinuses, middle ears, lungs, the gall bladder, and the urinary bladder. If the diet is adequate in vitamin A, these membranes continuously secrete a liquid, or mucus, which covers the cells and prevents bacteria from reaching them and also cleanses the surface.
Furthermore, bacteria cannot live in mucus. Worn tissues are digested by enzymes, and the wastes are removed; therefore healthy tissues contain no accumulation of dead cells. Because of substances known as antienzymes which counteract the effect of the enzymes produced by bacteria, live cells can protect themselves from bacterial destruction. Millions of bacteria find their way to these healthy tissues but cannot reach the cells because of the mucus covering or are made ineffective by the mucus; they are offered no food and/or are rendered harmless by the antienzymes. Since they cannot get a foothold, no infection occurs.
Individuals deficient in vitamin A allow conditions ideal for bacterial growth to be set up in their bodies; bacteria can grow only when they are provided with warmth, moisture, and food. During vitamin-A deficiency the cells of the mucous membrane grow more rapidly than usual but quickly die. These cells are crowded forward by other rapidly growing cells which likewise die until there accumulates a cheesy-like surface of layer upon layer of packed, dead cells. Since dead cells cannot secrete mucus or produce antienzymes their surface is no longer washed and their self-protective mechanisms are gone. Heat, moisture, and a continually replenished food supply combine to set up conditions ideal for bacterial growth; bacteria themselves are ever present. Infections are usually the result.
Changes in the mucous membranes occur early in the bronchial tubes and lungs, where air sacs may be completely plugged with dead cells, and in the middle ears, sinuses, kidneys, urinary bladder, and prostate gland. What has been described as an “accumulation of profuse debris” may cause irritation or obstruct narrow ducts, such as those from the salivary gland or the pancreas; the mouth may become dry; the pancreatic juices may fail to reach the intestine. Dead cells from the uterus and vagina may slough off, causing leucorrhea, often accompanied by profuse menstruation. Cysts may be formed around the accumulated dead cells in almost any part of the body.
Taken from Adelle Davis “Let’s Eat Right to Keep Fit”