Which Disease Is Caused By Lack of Vitamin A/Vitamin A is a group of unsaturated nutritional organic compounds that includes retinol, retinal, retinoic acid, and several provitamins A carotenoids (most notable beta-carotene). Vitamin A has multiple functions: it is important for growth and development, for the maintenance of the immune system and good vision. Vitamin A is needed by the retina of the eye in the form of retinal, which combines with protein opsin to form rhodopsin, the light-absorbing molecule necessary for both low-light (scotopic vision) and color vision. Vitamin A also functions in a very different role as retinoic acid (an irreversibly oxidized form of retinol), which is an important hormone-like growth factor for epithelial and other cells.
Vitamin A is a fat-soluble vitamin that is essential for humans and other vertebrates. Vitamin A comprises a family of molecules containing a 20 carbon structure with a methyl-substituted cyclohexenyl ring (beta-ionone ring) and a tetraene side chain with a hydroxyl group (retinol), aldehyde group (retinal), carboxylic acid group (retinoic acid), or ester group (retinyl ester) at carbon-15. The term vitamin A includes provitamin A carotenoids that are dietary precursors of retinol. The term retinoids refer to retinol, its metabolites, and synthetic analogs that have a similar structure. Carotenoids are polyisoprenoids, of which more than 600 forms exist. Of the many carotenoids in nature, several have provitamin A nutritional activity, but food composition data are available for only three (α-carotene, β-carotene, and β-cryptoxanthin) [rx].
How much vitamin A do I need?
The amount of vitamin A adults (19-64 years) need is:
- 0.7mg a day for men
- 0.6mg a day for women
Vitamin A can be found in two principal forms in foods
- Retinol, the form of vitamin A absorbed when eating animal food sources, is a yellow, fat-soluble substance. Since the pure alcohol form is unstable, the vitamin is found in tissues in a form of retinyl ester. It is also commercially produced and administered as esters such as retinyl acetate or palmitate.
- The carotenes alpha-carotene, beta-carotene, gamma-carotene; and the xanthophyll beta-cryptoxanthin (all of which contain beta-ionone rings), but no other carotenoids, function as provitamin A in herbivores and omnivore animals, which possess the enzyme beta-carotene 15,15′-dioxygenase which cleaves beta-carotene in the intestinal mucosa and converts it to retinol.
The three forms of active preformed vitamin A differ in purpose within the body and in their oxidation levels.
- Retinol – Also known as vitamin A1. This is common in supplements and also associated with vitamin A toxicity in extremely high doses.
- Retinal – Essential to your vision, this form of vitamin A converts light into electrical input to your brain.
- Retinoic acid – Retinoic acid is critical in cell differentiation. When your cells are very young and still not sure if they will become eye cells, heart cells or brain cells, they depend on retinoic acid to tell them what to turn into.
Deficiency Symptoms of Vitamin A
- Night Blindness – Low levels of vitamin A can cause a lack of rhodopsin, which is a light-sensitive protein present in your eye. And the lack of this protein impairs vision in dim light. You may, therefore, find it difficult to see properly at night when you have vitamin A deficiency. Watch out for telltale signs like difficulty driving at night. Night blindness is harder to notice in children because they may not know enough to complain about it. As a parent, have you noticed your child behaves differently once there’s no light or when they are in a dark room? If the child is inactive or apprehensive about moving around, probe further.
- Dry Eyes – Changes in the way you see are usually the first and most prominent sign of vitamin A deficiency. “Xerophthalmia” is the term used to indicate the range of eye problems triggered by vitamin A deficiency.ated can point to a vitamin A deficiency.
- Dry Skin, Rashes, Broken Nails – Fatigue or constant tiredness may be another early sign. Though it may seem non-specific, like itching or dry skin, probe further, especially if there are clear eye-related symptoms accompanying these
- White Or Silver Gray Foamy Spots In The Eye – Another sign of a vitamin A deficiency is the formation of foamy spots known as Bitot’s spots in the whites of your eyes. Bitot’s spots can be triangular or irregular in shape and usually appear at the 3 o’clock or 9 o’clock positions. They will appear slightly raised and look more like skin rather than a mucous membrane. They are essentially formed from a buildup of keratin because of the drying out of the cornea.
- Corneal Ulcers And Blindness – Without proper treatment, a deficiency in vitamin A can lead to the development of sores or ulcers in the eyes. An ulcer in the eye may look like a tiny punched-out area or have a fluffy appearance. Eventually, damage to the eyes can result in blindness. In fact, vitamin A deficiency is the main cause of preventable blindness in children – but one that is more commonly observed in the developing world.
- Frequent Infections – Frequent throat, chest, bladder, or stomach infections accompanied by eye problems may indicate a vitamin A deficiency. Vitamin A has earned the name “the anti-infective vitamin” because of its vital role in the proper functioning of the immune system. Your skin and the mucosal cells which line your urinary tract, digestive tract, and airways function as a barrier and first line of defense against infection.
- Growth Retardation In Children – In children with severe vitamin A deficiency, normal growth and development can slow down.
- Poor eye health
- Chronic gut
- Dry, thick or scaling skin
- Macular degeneration
- Dry mucous membranes
- Weak fingernails
- Low vitamin D levels
- Respiratory infections
- Immune system dysfunction
- Leaky gut or other gut health issues
- Autoimmune disease
- Excessive sun exposure
- Vegetarian diet
- Low-fat diet
- Being a woman of childbearing age
- Having cystic fibrosis
Food Sources of Vitamin A
Vitamin A is found in many foods, including the following list. Bracketed values are retinol activity equivalences (RAEs) and percentage of the adult male RDA, per 100 grams of the foodstuff (average). Conversion of carotene to retinol varies from person to person and bioavailability of carotene in food varies.
- Cod liver oil (30000 μg 3333%)
- Liver (turkey) (8058 μg 895%)
- Liver (beef, pork, fish) (6500 μg 722%)
- Liver (chicken) (3296 μg 366%)
- Ghee (3069 μg 344%)
- Sweet potato (961 μg 107%)
- Carrot (835 μg 93%)
- Broccoli leaf (800 μg 89%)
- Butter (684 μg 76%)
- Kale (681 μg 76%)
- Collard greens (frozen then boiled) (575 μg 64%)
- Butternut squash (532 μg 67%)
- Dandelion greens (508 μg 56%)
- Spinach (469 μg 52%)
- Pumpkin (426 μg 43%)
- Collard greens (333 μg 37%)
- Cheddar cheese (265 μg 29%)
- Cantaloupe melon (169 μg 19%)
- Bell pepper/capsicum, red (157 μg 17%)
- Egg (140 μg 16%)
- Apricot (96 μg 11%)
- Papaya (55 μg 6%)
- Tomatoes (42 μg 5%)
- Mango (38 μg 4%)
- Pea (38 μg 4%)
- Broccoli florets (31 μg 3%)
- Milk (28 μg 3%)
- Bell pepper/capsicum, green (18 μg 2%)
- Spirulina (3 μg 0.3%)
Intake recommendations for vitamin A and other nutrients are provided in the Dietary Reference Intakes (DRIs) developed by the Food and Nutrition Board (FNB) at the Institute of Medicine of the National Academies (formerly National Academy of Sciences) [rx]. DRI is the general term for a set of reference values used for planning and assessing nutrient intakes of healthy people. These values, which vary by age and gender, include:
- Recommended Dietary Allowance (RDA) – Average daily level of intake sufficient to meet the nutrient requirements of nearly all (97%–98%) healthy individuals; often used to plan nutritionally adequate diets for individuals.
- Adequate Intake (AI) – Intake at this level is assumed to ensure nutritional adequacy; established when evidence is insufficient to develop an RDA.
- Estimated Average Requirement (EAR) – Average daily level of intake estimated to meet the requirements of 50% of healthy individuals; usually used to assess the nutrient intakes of groups of people and to plan nutritionally adequate diets for them; can also be used to assess the nutrient intakes of individuals.
- Tolerable Upper Intake Level (UL) – Maximum daily intake unlikely to cause adverse health effects.
RDAs for vitamin A are given as mcg of retinol activity equivalents (RAE) to account for the different bioactivities of retinol and provitamin A carotenoids (see Table 1). Because the body converts all dietary sources of vitamin A into retinol, 1 mcg of physiologically available retinol is equivalent to the following amounts from dietary sources: 1 mcg of retinol, 12 mcg of beta-carotene, and 24 mcg of alpha-carotene or beta-cryptoxanthin. From dietary supplements, the body converts 2 mcg of beta-carotene to 1 mcg of retinol.
Currently, vitamin A is listed on food and supplement labels in international units (IUs) even though nutrition scientists rarely use this measure. Conversion rates between mcg RAE and IU are as follows [rx]
- 1 IU retinol = 0.3 mcg RAE
- 1 IU beta-carotene from dietary supplements = 0.15 mcg RAE
- 1 IU beta-carotene from food = 0.05 mcg RAE
- 1 IU alpha-carotene or beta-cryptoxanthin = 0.025 mcg RAE
However, under FDA’s new labeling regulations for foods and dietary supplements that take effect by January 1, 2020 (for companies with annual sales of $10 million or more) or January 1, 2021 (for smaller companies), vitamin A will be listed only in mcg RAE and not IUs [rx,rx].
An RAE cannot be directly converted into an IU without knowing the source(s) of vitamin A. For example, the RDA of 900 mcg RAE for adolescent and adult men is equivalent to 3,000 IU if the food or supplement source is preformed vitamin A (retinol). However, this RDA is also equivalent to 6,000 IU of beta-carotene from supplements, 18,000 IU of beta-carotene from food, or 36,000 IU of alpha-carotene or beta-cryptoxanthin from food. So a mixed diet containing 900 mcg RAE provides between 3,000 and 36,000 IU of vitamin A, depending on the foods consumed.
|U.S. RDAs or
Adequate Intakes, AI,
retinol activity equivalents (μg/day)
|Infants||0–6 months||400 (AI)||500 (AI)|
- ULs are for natural and synthetic retinol ester forms of vitamin A. Beta-carotene and other provitamin A carotenoids from foods and dietary supplements are not added when calculating total vitamin A intake for safety assessments, although they are included as RAEs for RDA and AI calculations.[rx][rx]
|0–6 months*||400 mcg RAE||400 mcg RAE|
|7–12 months*||500 mcg RAE||500 mcg RAE|
|1–3 years||300 mcg RAE||300 mcg RAE|
|4–8 years||400 mcg RAE||400 mcg RAE|
|9–13 years||600 mcg RAE||600 mcg RAE|
|14–18 years||900 mcg RAE||700 mcg RAE||750 mcg RAE||1,200 mcg RAE|
|19–50 years||900 mcg RAE||700 mcg RAE||770 mcg RAE||1,300 mcg RAE|
|51+ years||900 mcg RAE||700 mcg RAE|
* Adequate Intake (AI), equivalent to the mean intake of vitamin A in healthy, breastfed infants.
Health Benefits of Vitamin A
Essential for Good Eyesight
- Your eyes are delicate and hence require extra care and protection. Vitamin A is widely known to treat weak eyesight, keeping the eyes nice and moist. It is also evident that regular consumption of vitamin A enhances night vision preventing you from night blindness. According to eye specialists, retinol is the only nutrient that helps the development of ‘visual purple’ in your eyes. You will be delighted to know that vitamin A has the potential to reduce risks of cataracts and macular degeneration, which are age-related eye problems.
It Prevents Urinary Stones
- Urinary stones are a troublesome health problem. You should try every possible precaution to avoid it. However, an effective way of steering clear of the health complication is to consume a diet rich in vitamin A. It is known to work as a shield against factors that form urinary calculi by producing calcium phosphate in your body. Vitamin A also keeps the urinary tract in shape that minimizes the chance of urinary stone reoccurrence.
For Healthy Bones
- Dairy products and vitamin D are known to keep your bones and teeth stronger. This is why experts recommend incorporating dairy products into your routine and drinking a glass of milk regularly to avoid bones problems. After thorough research and spending considerable time, scientists have found that regular consumption of vitamin A is effective for your bones and teeth as well. Combined with other nutrients, vitamin A produces a solid layer called dentin below the surface of your teeth. This layer strengthens your teeth against various oral health problems.
It Promotes Muscle Growth
- You might not pay attention to it, but muscle growth is essential specifically for children and growing teens. An accurate diet ensures proper muscle growth. Since vitamin A contains a lot of health benefits, promoting better muscle growth is it’s another health benefit. For proper muscle growth of children and growing teens, it is important to incorporate food items into their diet that contains plenty of vitamin A, which will help prevent the development of muscular dystrophy in the muscles.
Vitamin A Repairs Tissue
- Your body reproduces tissues and cells naturally, but it needs nutrients for the process. Without enough nutrients, this process can’t take place and your body remains unable to produce new tissues. Therefore, consume vitamin A in any form to enable this natural process as it replaces old tissues with the new ones effectively.
It Treats Measles
- Measles is neither rare nor a frequently occurring disease, but it is indeed draining. Child specialists suggest that children who are vitamin A deficient fall prey to measles. Hence, the solution is to incorporate food items that contain vitamin A into their diets. An adequate amount of this vitamin will relieve diarrhea and fever that comes with measles.
Vitamin A Delays Aging
- An occurrence of fine lines and wrinkles are common as you age. Although there are a number of treatments and products available to reduce these signs of aging, they cannot do what a nutrient can do. This is why beauty experts trust vitamin A. It is said to delay aging by reducing fine lines and wrinkles. Since it naturally contains moisture, it keeps your skin moist. When your skin absorbs this moisture, it becomes youthful again.
- Excessive sebum production cause acne, which is stressing as it might take months to heal. Taking vitamin A supplements are said to treat acne by limiting sebum production on the skin. The antioxidants in the vitamin rejuvenate dead skin cells leaving in smooth and baby soft.
It Strengthens Immune system
- Vitamin A works as an immunity booster. A powerful immune system keeps infectious bacteria at bay, but you need to maintain its functionality. Consuming vitamin A on a daily basis is said to increase lymphocytic responses that fight disease-causing antigens. It has properties that are necessary to keep mucus membranes moist. This moist mucus membrane ensures better immunity and promotes the activity of white blood cells. This process also prevents reentrance of germs and bacteria in your body.
For High Cholesterol
- High cholesterol levels are daunting due to their contribution to various cardio problems. There are numerous other severe health issues associated with high cholesterol. This is why nutritionists suggest diets loaded with vitamin A because it helps lower high levels of cholesterol. It is also known to widen arteries to ensure proper blood flow. Vitamin A can reduce the chances of blood clotting as well.
- All the vitamins are known to enhance the condition of skin – so does vitamin A. It has antioxidants and healing properties that are essential for your skin health. Consuming vitamin A enriched diet improves skin discoloration giving it a natural glow.
Boosts Bone Health
- This essential vitamin strengthens bones and teeth. Vitamin A helps in the formation of dentin, a layer of hard material just below the surface of the teeth, thereby enhancing its strength.
Prevents Urinary Stones
- Vitamin A prevents the formation of urinary calculi due to the formation of calcium phosphate. It also helps keep the lining of the urinary tract in shape, thereby reducing the recurring chance of stones.
Promotes Muscle Growth
- By keeping the bones healthy and retaining their shape, vitamin A plays an essential role in ensuring proper muscle growth in children and growing teens, thereby preventing the chances of developing muscular .
Reduces Risk of Acne
- Vitamin A helps cut down excess sebum production, thereby reducing the risk of acne. It also reinforces the protective tissues of the skin, thereby enhancing the overall health and vitality of the skin surface. It is also essential for the proper maintenance of the skin tissues and mucous membranes. It flushes out the toxins from your body and cleanses the system by virtue of its properties.
- Vitamin A is also a powerful antioxidant, which can prevent certain forms of cancer.
- Vitamin A plays an important role in replacing old and worn out tissues with new ones, as well as in keeping your bones and teeth strong.
- Vitamin A is famous for its wrinkle-eliminating properties, which can reduce age spots and fine lines. It can slow down the aging process by enhancing the overall health of the skin.
- Deficiency of vitamin A may cause measles in children. Intake of foods rich in this vitamin helps relieve the fever and diarrhea caused by measles.
Vitamin A plays a role in a variety of functions throughout the body, such as:
- Gene transcription
- Immune function
- Embryonic development and reproduction
- Bone metabolism
- Skin and cellular health
- Mucous membrane
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