Vitamin A plays an important role in vision, bone growth, reproduction, cell division and cell differentiation, which is the process by which a cell decides what it is going to become. It helps maintain the surface linings of the eyes and the respiratory, urinary, and intestinal tracts. When those linings break down, bacteria can enter the body and cause infection. Vitamin A also helps maintain the integrity of skin and mucous membranes that function as a barrier to bacteria and viruses.
Vitamin A helps regulate the immune system. Vitamin A may help lymphocytes, a type of white blood cell that fights infections, function more effectively.
It is important to regularly eat foods that provide vitamin A or beta-carotene even though vitamin A is stored in the liver. Stored vitamin A will help meet needs when intake of provitamin A carotenoids or preformed vitamin A is low.
In the United States, RDAs for vitamin A are listed as Retinol Activity Equivalents (RAE) to account for the different activities of retinol and provitamin A carotenoids. In the table below, RDAs are also listed in International Units (IU) because food and some supplement labels list vitamin A content in International Units (1 RAE in micrograms (ug) = 3.3 IU). The 2001 RDAs for adults and children (21) in ug RAE and IUs are:
300 ug or 1000 IU per day in children aged 1-3,
400 ug or 1333 IU per day in children aged 4-8,
600 ug or 2000 IU per day in children aged 9-13,
900 ug or 3000 IU per day in those 14 and over.
There is no RDA for beta-carotene or other provitamin A carotenoids. The Institute of Medicine report suggests that consuming 3 to 6 mg of beta-carotene daily will maintain plasma beta-carotene blood levels in the range associated with a lower risk of chronic diseases. A diet that provides five or more servings of fruits and vegetables per day and includes some dark green and leafy vegetables and deep yellow or orange fruits should provide recommended amounts of beta-carotene.
Vitamin A deficiency rarely occurs in the United States, but it is still a major public health problem in the developing world.There is increased interest in subclinical forms of vitamin A deficiency, described as low storage levels of vitamin A that do not cause overt deficiency symptoms. This mild degree of vitamin A deficiency may increase children’s risk of developing respiratory and diarrheal infections, decrease growth rate, slow bone development, and decrease likelihood of survival from serious illness.
Low plasma retinol concentrations indicate depleted levels of vitamin A. This occurs with vitamin A deficiency but also can result from an inadequate intake of protein, calories and zinc. These nutrients are needed to make Retinol Binding Protein (RBP), which is essential for mobilizing vitamin A from your liver and transporting vitamin A to your general circulation.
Fat malabsorption can promote diarrhea and prevent normal absorption of vitamin A. This is most often seen with cystic fibrosis, sprue, pancreatic disorders, and after stomach surgery. Healthy adults usually have a reserve of vitamin A stored in their livers and should not be at risk of deficiency during periods of temporary or short term fat malabsorption. Long-term problems absorbing fat, however, may result in deficiency, and in these instances physicians may advise vitamin A supplementation.
Signs, symptoms & indicators of Vitamin A Requirement
Reduced sense of taste or smell
History of infections
Thin/thick uncracked heel calluses or thin/thick cracked heel calluses
Bumps on backs of arms
Keratosis pilaris (KP) is a common mild condition in which the backs of the upper arms look rather like dried out, plucked chicken flesh. KP is hereditary. The characteristic rash is caused by firm little plugs forming in the hair follicles. The plugs themselves are made of bits of keratin, the main protein found in the outermost protective layer of skin These plugged follicles give the skin a raised, stippled appearance, usually called goosebumps. The bumps are usually skin color or slightly pinker, and do not itch. The rash is often not noticeable to others, except on close inspection.
The condition usually appears in early childhood, often around the age of two or three. Since the rash is associated with and worsened by dryness of the skin, most people experience a clear-cut seasonal variation, generally worse in the winter. Adults who still have keratosis pilaris often experience further improvement during the middle decades. The average age when spontaneous improvement is first noted is sixteen. [British Medical Journal, June 1994]
The rash is more common in those with eczema, dry skin, or vitamin A deficiency. The most common spot on the body for KP is the backs of the upper arms (92%), followed by the thighs (59%), and it can also occur on the face, buttocks, and eyebrows.
Higer doses of Vitamin A may be needed, and to avoid toxicity, a water soluble form should be used.
Patients may turn to prescription vitamin A creams such as Retin A / Tazorac / Avita / Differin to help restore a smooth texture in recalcitrant cases or as a way to help treat KP complicated by acne. Potent retinols such as Afirm are nonprescription options.
Cracking skin
Conditions that suggest Vitamin A Requirement
Conjunctivitis
Vitamin A deficiency has been reported in people with chronic conjunctivitis. It is unknown whether vitamin A supplementation can prevent conjunctivitis or help people who already have the condition. [Int J Vitam Nutr Res 1976;46: pp.454-7 {in German}]
Cystitis, Bacterial Bladder Infection
Retinoic acid (an analogue of vitamin A) is needed for the differentiation of basal cells into mucus epithelial cells. A deficiency results in keratinization of mucus membranes that line the respiratory tract, intestines, urinary tract and epithelium of the eye. This in turn decreases the protective barrier role played by these membranes, resulting in an increased number of infections and other pathologies.
Night Blindness
Night blindness is commonly caused by a deficiency in vitamin A. It is considered one of the first indicators of vitamin A deficiency.
Increased Risk of Prostate Cancer
Carotene compounds called lycopenes, which are found in high amounts in tomatoes, have been shown to protect against prostate cancer. Several studies have shown that males consuming tomato sauce receive some protection against cancer.
Boils, Abscesses, Carbuncles
The addition of zinc supplements and vitamin A to the diet is reported to be effective in treating boils.
Keratosis pilaris
Keratosis pilaris (KP) is a common mild condition in which the backs of the upper arms look rather like dried out, plucked chicken flesh. KP is hereditary. The characteristic rash is caused by firm little plugs forming in the hair follicles. The plugs themselves are made of bits of keratin, the main protein found in the outermost protective layer of skin These plugged follicles give the skin a raised, stippled appearance, usually called goosebumps. The bumps are usually skin color or slightly pinker, and do not itch. The rash is often not noticeable to others, except on close inspection.
The condition usually appears in early childhood, often around the age of two or three. Since the rash is associated with and worsened by dryness of the skin, most people experience a clear-cut seasonal variation, generally worse in the winter. Adults who still have keratosis pilaris often experience further improvement during the middle decades. The average age when spontaneous improvement is first noted is sixteen. [British Medical Journal, June 1994]
The rash is more common in those with eczema, dry skin, or vitamin A deficiency. The most common spot on the body for KP is the backs of the upper arms (92%), followed by the thighs (59%), and it can also occur on the face, buttocks, and eyebrows.
Higer doses of Vitamin A may be needed, and to avoid toxicity, a water soluble form should be used.
Patients may turn to prescription vitamin A creams such as Retin A / Tazorac / Avita / Differin to help restore a smooth texture in recalcitrant cases or as a way to help treat KP complicated by acne. Potent retinols such as Afirm are nonprescription options.
Female Infertility
Vitamin A is involved in steroid hormone synthesis and cell differentiation. It is important for healthy growth, normal reproduction and lactation.
Motherhood Issues
See link between Female Infertility and Vitamin A Deficiency.
Menorrhagia (Heavy Periods)
One study found serum retinol levels (a measure of vitamin A levels) to be significantly lower in women with menorrhagia than in healthy controls. 92% of those with lower levels experienced either complete relief or significant improvement after 25,000 IU of vitamin A was taken twice per day for 15 days.
Risk factors for Vitamin A Requirement
Alcohol-related Problems
Excess alcohol intake depletes vitamin A stores. Also, diets high in alcohol usually do not provide recommended amounts of vitamin A. It is very important for anyone who consumes excessive amounts of alcohol to include good sources of vitamin A in his or her diet. However, Vitamin A supplementation may not be recommended for individuals who abuse alcohol because alcohol may increase liver toxicity associated with excess intakes of vitamin A . A doctor would need to evaluate this situation and determine the need for vitamin A supplementation.
Protein Deficiency
A deficiency of protein or zinc can reduce the amount of vitamin A released from the liver.
Digestive Enzyme Need
90% of all dietary retinol is in the form retinyl palmitate which requires action by pancreatic enzymes before it can be absorbed.
Parasite Infection
Different types of parasites can cause a deficiency of vitamin A, vitamin B12, and iron.
Zinc Requirement
A deficiency of protein or zinc can reduce the amount of vitamin A released from the liver.
Vitamin A supplementation
Multiple vitamin supplement use
Vegan diet
Vegetarians who do not consume eggs and dairy foods need greater amounts of provitamin A carotenoids to meet their need for vitamin A. It is important for vegetarians to include a minimum of five servings of fruits and vegetables daily and to regularly choose dark green leafy vegetables and orange and yellow fruits to consume recommended amounts of vitamin A.
Having had a small bowel resection
Pancreas mostly/pancreas completely removed
History of adult acne
Vitamin A Requirement suggests the following may be present
Parasite Infection
Different types of parasites can cause a deficiency of vitamin A, vitamin B12, and iron.
Vitamin A Requirement can lead to
Cancer / Risk - General Measures
Analogues of vitamin A are known as retinoids. Numerous studies have shown that retinoid deficiency enhances the risk of cancer in humans. Retinoids are being used in humans to treat cancers (particularly skin, lung, bladder, cervical or breast) which involve epithelial tissues. Vitamin A can be used to both treat and prevent cancers and there have been a number of studies showing beta carotene‘s protective effects against cancer.
Menorrhagia (Heavy Periods)
One study found serum retinol levels (a measure of vitamin A levels) to be significantly lower in women with menorrhagia than in healthy controls. 92% of those with lower levels experienced either complete relief or significant improvement after 25,000 IU of vitamin A was taken twice per day for 15 days.
Recommendations for Vitamin A Requirement
Key
| Weak or unproven link |
| Strong or generally accepted link |
| Proven definite or direct link |
| Strongly counter-indicative |
| May do some good |
| Likely to help |
| Highly recommended |
Glossary
Vitamin A
A fat-soluble vitamin essential to one's health. Plays an important part in the growth and repair of body tissue, protects epithelial tissue, helps maintain the skin and is necessary for night vision. It is also necessary for normal growth and formation of bones and teeth. For Vitamin A only, 1mg translates to 833 IU.
Bacteria
Microscopic germs. Some bacteria are "harmful" and can cause disease, while other "friendly" bacteria protect the body from harmful invading organisms.
Mucous Membranes
The membranes, such as the mouse, nose, anus, and vagina, that line the cavities and canals of the body which communicate with the air.
Virus
Any of a vast group of minute structures composed of a protein coat and a core of DNA and/or RNA that reproduces in the cells of the infected host. Capable of infecting all animals and plants, causing devastating disease in immunocompromised individuals. Viruses are not affected by antibiotics, and are completely dependent upon the cells of the infected host for the ability to reproduce.
Immune System
A complex that protects the body from disease organisms and other foreign bodies. The system includes the humoral immune response and the cell-mediated response. The immune system also protects the body from invasion by making local barriers and inflammation.
White Blood Cell
(WBC): A blood cell that does not contain hemoglobin: a blood corpuscle responsible for maintaining the body's immune surveillance system against invasion by foreign substances such as viruses or bacteria. White cells become specifically programmed against foreign invaders and work to inactivate and rid the body of a foreign substance. Also known as a leukocyte.
Beta-Carotene
The most abundant of the carotenoids, beta-carotene has strong provitamin A activity and is a stronger antioxidant than vitamin A. It is widely accepted today as a cancer preventative. It is found in leafy green and yellow vegetables, often missing in children's diets. Beta-Carotene is believed to be a superior source of Vitamin A because it is readily converted into a more active form of the substance: your body converts it to Vitamin A as needed.
Provitamin
A substance found in certain foods, that the body may convert into a vitamin. Also called previtamin.
IU
International Units. One IU is 1/40th (0.025) of a microgram (mcg).
Microgram
(mcg): 1/1,000 of a milligram in weight.
RDA
Recommended Daily Allowance of vitamins or other nutrients as determined by the FDA. U.S. RDAs are more widely used than RDAs, and focus on 3 age groups: Infants of 0-12 months; Children of 1-4 years; Adults and children of more than 4 years.
Milligram
(mg): 1/1,000 of a gram by weight.
Chronic
Usually Chronic illness: Illness extending over a long period of time.
Subclinical
Not manifesting characteristic clinical symptoms. Pertaining to a disease or condition.
Protein
Compounds composed of hydrogen, oxygen, and nitrogen present in the body and in foods that form complex combinations of amino acids. Protein is essential for life and is used for growth and repair. Foods that supply the body with protein include animal products, grains, legumes, and vegetables. Proteins from animal sources contain the essential amino acids. Proteins are changed to amino acids in the body.
Zinc
An essential trace mineral. The functions of zinc are enzymatic. There are over 70 metalloenzymes known to require zinc for their functions. The main biochemicals in which zinc has been found to be necessary include: enzymes and enzymatic function, protein synthesis and carbohydrate metabolism. Zinc is a constituent of insulin and male reproductive fluid. Zinc is necessary for the proper metabolism of alcohol, to get rid of the lactic acid that builds up in working muscles and to transfer it to the lungs. Zinc is involved in the health of the immune system, assists vitamin A utilization and is involved in the formation of bone and teeth.
Diarrhea
Excessive discharge of contents of bowel.
Cystic Fibrosis
(CF) An incurable genetic disease involving a sticky buildup of mucus in the lungs (which makes breathing difficult and leads to infections), as well as pancreatic insufficiency (which leads to digestive problems). Symptoms include chronic cough producing thick mucus, excessive appetite combined with weight loss, intestinal disorders, salty sweat/skin and pneumonia. Lung-related problems are the most frequent cause of death. CF is a recessive disease, occurring only when a person inherits two mutated copies of the CF gene - one from each parent. Individuals with CF generally have a life expectancy of about 30 years.
Stomach
A hollow, muscular, J-shaped pouch located in the upper part of the abdomen to the left of the midline. The upper end (fundus) is large and dome-shaped; the area just below the fundus is called the body of the stomach. The fundus and the body are often referred to as the cardiac portion of the stomach. The lower (pyloric) portion curves downward and to the right and includes the antrum and the pylorus. The function of the stomach is to begin digestion by physically breaking down food received from the esophagus. The tissues of the stomach wall are composed of three types of muscle fibers: circular, longitudinal and oblique. These fibers create structural elasticity and contractibility, both of which are needed for digestion. The stomach mucosa contains cells which secrete hydrochloric acid and this in turn activates the other gastric enzymes pepsin and rennin. To protect itself from being destroyed by its own enzymes, the stomach’s mucous lining must constantly regenerate itself.
Eczema
Swelling of the outer skin of unknown cause. In the early stage it may be itchy, red, have small blisters, and be swollen, and weeping. Later it becomes crusted, scaly, and thickened.
Acne
A chronic skin disorder due to inflammation of hair follicles and sebaceous glands (secretion glands in the skin).
Cystitis
Inflammation of the urinary bladder.
Carotene
Converted into vitamin A in the body from a yellow pigment that has several forms (i.e., alpha-, beta-, and gamma-carotene).
Prostate
The prostate gland in men that surrounds the neck of the bladder and the urethra and produces a secretion that liquefies coagulated semen.
Cancer
Refers to the various types of malignant neoplasms that contain cells growing out of control and invading adjacent tissues, which may metastasize to distant tissues.
Steroid
Any of a large number of hormonal substances with a similar basic chemical structure containing a 17-carbon 14-ring system and including the sterols and various hormones and glycosides.
Hormones
Chemical substances secreted by a variety of body organs that are carried by the bloodstream and usually influence cells some distance from the source of production. Hormones signal certain enzymes to perform their functions and, in this way, regulate such body functions as blood sugar levels, insulin levels, the menstrual cycle, and growth. These can be prescription, over-the-counter, synthetic or natural agents. Examples include adrenal hormones such as corticosteroids and aldosterone; glucagon, growth hormone, insulin, testosterone, estrogens, progestins, progesterone, DHEA, melatonin, and thyroid hormones such as thyroxine and calcitonin.
Lactation
Production of milk; period after giving birth during which milk is secreted in the breasts.
Serum
The cell-free fluid of the bloodstream. It appears in a test tube after the blood clots and is often used in expressions relating to the levels of certain compounds in the blood stream.
Menorrhagia
Abnormally heavy menstrual period.
Enzymes
Specific protein catalysts produced by the cells that are crucial in chemical reactions and in building up or synthesizing most compounds in the body. Each enzyme performs a specific function without itself being consumed. For example, the digestive enzyme amylase acts on carbohydrates in foods to break them down.
Parasite
An organism living in or on another organism.
Cobalamin
Vitamin B-12. Essential for normal growth and functioning of all body cells, especially those of bone marrow (red blood cell formation), gastrointestinal tract and nervous system, it prevents pernicious anemia and plays a crucial part in the reproduction of every cell of the body i.e. synthesis of genetic material (DNA).
Iron
An essential mineral. Prevents anemia: as a constituent of hemoglobin, transports oxygen throughout the body. Virtually all of the oxygen used by cells in the life process are brought to the cells by the hemoglobin of red blood cells. Iron is a small but most vital, component of the hemoglobin in 20,000 billion red blood cells, of which 115 million are formed every minute. Heme iron (from meat) is absorbed 10 times more readily than the ferrous or ferric form.