Vitamin A

Vitamin A is a general term classification given to a number of naturally occurring, fat soluble nutrients that assist the body in performing a wide range of critical activities. It is particularly important for vision and immune system functions. Vitamin A is readily available from many sources (dairy products, some fish, and meat, as well as fruits and vegetables and fortified breakfast cereals). A balanced diet typically supplies enough vitamin A for most people. It can also be taken as a dietary supplement, either standalone as retinyl acetate, retinyl palmitate, or beta-carotene, or as part of a multivitamin.

Because research has suggested vitamin A's potential role in preventing, treating, or at least ameliorating conditions such as poor vision, infertility, chronic heart disease, acne, skin cancer and pancreatic cancer, depression, insomnia, and fatigue, the vitamin has on occasion been touted as something of an all-purpose wonder drug. Except for vitamin C, the vitamin is the most recommended nutrient for general health and maintenance of the body’s systems against the vulnerabilities and deteriorations associated with the otherwise normative processes of aging. However, the effects of vitamin A as a supplement are not fully understood or proven and research is ongoing. Miracle claims such as overarching anti-cancer properties have been largely debunked. It has also been shown that high doses of some forms of vitamin A can have negative effects, and supplements can also interact with medications; anyone interested in taking a dietary supplement should consult a doctor.

Background

Broadly speaking, vitamin A falls into two classifications: preformed vitamin A and provitamin A. Preformed vitamin A, which include substances known as retinoids (particularly retinol), is found in eggs, meat, cheeses, most fish (especially tuna and cod), processed dairy products (such as milk and cottage cheese), and poultry. Provitamin A, which includes several substances known as carotenoids, is found in most orange and yellow fruits and vegetables (carrots, sweet potatoes, chili peppers, pumpkins, grapefruits, and oranges) as well as in most dark green leafy vegetables (such as spinach and kale). In addition, vitamin A has been processed into a diet supplement, most often marketed as retinyl acetate or beta-carotene. Nutritionists, however, are quick to point out that the wide accessibility of vitamin A in natural forms means that a healthy and varied diet will assure the body adequate amounts of usable vitamin A. The Food and Drug Administration (FDA) recommends about 800 micrograms of vitamin A as part of a daily diet. Three average-sized carrots, for instance, provide that and more.

As nutrients, both classifications of vitamin A are directed by the body to widely different functions at the molecular level. The retinoids, for instance, are critical in red blood cell production and maintenance, although researchers are still working out the how and why. This means that retinoids help the body’s immune system respond quickly and effectively to imbalances caused by invading bacteria and viruses. They assist the body in tissue growth maintenance particularly after injuries or surgery, and they assist in promoting fertility and improving the chances of pregnancy. Retinoids also promote effective and efficient food processing and digestive function. But perhaps the most widely known function of the retinoids stem from their promotion of vision acuity. There is truth in the old adage that eating carrots keeps vision strong. Retinoids help the retina manufacture rhodopsin pigment rod cells. Those rod cells are particularly responsible for detecting muted light and for responding to sudden drops in available bright light. Vitamin A₁ (retinol) is widely used to preserve and enhance night vision and to treat xerophlthalmia (an inability to see in low light that can lead to blindness). Retinoids are also used, both topically and orally, to treat skin conditions, including psoriasis and acne. Research is being conducted on the possibility of their use in skin cancer treatments.

Carotenoids, on the other hand, can act as antioxidants, which are believed to potentially assist cells in halting and even stopping the damage done long-term by cellular exposure to oxygen. When a molecule suddenly loses an electron, it becomes what is called a free radical. Inherently unstable, free radicals seek any available electron to return it to stability and integrity, most often by simply stealing an electron from any readily available oxygen molecules in the cell. That triggers a kind of domino effect where the robbed cell now needs an electron, thus creating a sustained long-term chain of cellular destruction that helps account for any of a wide variety of slow-motion catastrophic ailments, such as cancers, and diabetes, Alzheimer's disease and other dementias, aging (specifically the skin folds characteristic with aging), and blindness. As an antioxidant, vitamin A simply contributes an electron to the process, thus halting the destructive interaction with oxygen. Research has not entirely agreed what impact vitamin A has—whether it retards the process, controls it, or entirely halts it—but the presence of antioxidants is thought to help the body’s molecular structures maintain their efficiency and their structural integrity.

Overview

Because vitamin A appears to be such a boon for the body, consumers are often tempted to take amounts far in excess of recommended dosages as a way to ward off the effects of aging or to prevent the onset of cancer. Ironically, excessive intake can actually create significant problems. Too much vitamin A has been shown to actually usurp the body’s normative immunity operations. Vitamin A in supplement form has shown no ability to prevent or fight cancer, and some studies have even suggested that excess beta-carotene supplements increase the risk of lung cancer in smokers. Excess vitamin A intake has also been linked to an increase in bone fractures, particularly hip fractures in the elderly, and in actually advancing eye disorders such as macular degeneration. Additionally, vitamin A has been implicated in birth defects in the babies of mothers who consumed excessive amounts.

Another potential problem with vitamin A overconsumption is that most of the retinoid variations are found in foods that are high in saturated fats and cholesterol. These sources pose their own health risks. Fortunately, with rare exceptions, the body is capable of converting carotenoids into retinoids. Body systems impaired by genetic deficiencies and disorders, poor diet or malnutrition, those regularly exposed to industrial pollutants and chemical particulates, or those compromised by massive infectious diseases or excessive alcohol intake may struggle to complete the conversion efficiently.

Vitamin A Deficiency

Vitamin A is frequently among those food supplements most administered in diet programs that target developing nations. Whereas in developed countries diet and nutrition are regular and food products readily available, in developing countries, where food supplies are often compromised by catastrophic weather conditions, inadequate or inefficient agricultural processes, or political or military disruption, vitamin A deficiencies have been linked to widespread viral infectious disease outbreaks (particularly measles), as the lack of vitamin A weakens the immune system. It also causes eye problems, including night blindness, the whites of the eyes becoming dry and thick, and a condition known as keratomalacia. Keratomalacia, if untreated, leads to the cornea becoming opaque, and is a leading cause of blindness in developing countries, especially in children. The skin can also become dry, damaged, and more prone to infection. A lack of vitamin A during pregnancy can increase the risk of maternal mortality. That these conditions are largely preventable through diet gives special urgency to international relief efforts addressed particularly to children.

Vitamin A deficiency is estimated to affect approximately one-third of children under five worldwide, and a 2008 study estimated that 670,000 children die of causes related to Vitamin A deficiency each year.

Bibliography

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