Feb 14, · Vitamin A is a fat-soluble vitamin that is naturally present in many foods. Vitamin A is important for normal vision, the immune system, and reproduction. Vitamin A also helps the heart, lungs, kidneys, and other organs work properly. There are two different types of vitamin A. Vitamin A is essential for your health in a number of ways. Your body cannot produce vitamin A from scratch, which makes it an essential micronutrient. That means that you need to get this vitamin Estimated Reading Time: 3 mins.
Get the latest public health information from CDC. Have a question? This is a fact sheet intended for health professionals. For a reader-friendly overview of Vitamin A, see our consumer fact sheet on Vitamin A. Vitamin A how to do saraswati puja the ritual the name of a group of fat-soluble retinoids, including retinol, retinal, and retinyl esters [ ].
Vitamin A is involved in immune function, vision, reproduction, and cellular communication [ 145 ]. Vitamin A is critical for vision as an essential component of rhodopsin, a protein that absorbs light in the retinal receptors, and because it supports the normal differentiation and functioning of the conjunctival membranes and cornea [ ].
Vitamin A also supports cell growth and differentiation, playing a critical role in the normal formation and maintenance of the heart, lungs, what vitamin a good for, and other organs [ 2 ].
Two forms of vitamin A are available in the human diet: preformed vitamin A retinol and its esterified form, retinyl ester and provitamin A carotenoids [ ]. Preformed vitamin A is found in foods from animal sources, including dairy products, fish, and meat especially liver. By far the most important provitamin A carotenoid is beta-carotene; other provitamin A carotenoids are alpha-carotene and beta-cryptoxanthin.
The body converts these plant pigments into vitamin A. Both provitamin A and preformed vitamin A must be metabolized intracellularly to retinal and retinoic acid, the active forms of vitamin A, to support the vitamin's important biological functions [ 23 ].
Other carotenoids found in food, such as lycopene, lutein, and zeaxanthin, are not converted into vitamin A. The various forms of vitamin A are solubilized into micelles in the intestinal lumen and absorbed by duodenal mucosal cells [ 5 ].
Both retinyl esters and provitamin A carotenoids are converted to retinol, which is oxidized to retinal and then to retinoic acid [ 2 ]. Most of the body's vitamin A is stored what vitamin a good for the liver in the form of retinyl esters. Retinol and carotenoid levels are typically measured in plasma, and plasma retinol levels are useful for assessing vitamin A inadequacy. However, their value for assessing marginal vitamin A status is limited because they do not decline until vitamin A levels in the liver are almost depleted [ 3 ].
Liver vitamin A reserves can be measured indirectly through the relative dose-response test, in which plasma retinol levels are measured before and after the administration of a small amount of vitamin A [ 5 ]. For clinical practice purposes, plasma retinol levels alone are sufficient for documenting significant deficiency. A plasma retinol concentration lower than 0.
In some studies, high plasma or serum concentrations of some provitamin What vitamin a good for carotenoids have been associated with a lower risk of various health outcomes, but these studies have not definitively demonstrated that this relationship is causal.
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:. RDAs for vitamin A are given as retinol activity equivalents RAE to account for the different bioactivities of retinol and provitamin A carotenoids, all of which are converted by the body into retinol see Table 1.
One mcg RAE is equivalent to 1 mcg retinol, 2 mcg supplemental beta-carotene, 12 mcg dietary beta-carotene, or 24 mcg dietary alpha-carotene or beta-cryptoxanthin [ 5 ].
For example, the RDA of mcg RAE for adolescent and adult men is equivalent to 3, IU if the food or supplement source is preformed vitamin A retinol or if the supplement source is beta-carotene.
Therefore, a mixed diet containing mcg RAE provides between 3, and 36, IU vitamin A, depending on the foods consumed. Concentrations of preformed vitamin A are highest in liver and fish oils [ 2 ]. Other sources of preformed vitamin A are milk and eggs, which also include some provitamin A [ 2 ]. Most dietary provitamin A comes from leafy green vegetables, orange and yellow vegetables, tomato products, fruits, and some vegetable oils [ 2 ].
The top food sources of vitamin A in the U. Table 2 suggests many dietary sources of vitamin A. How to make a fish batter foods from animal sources in Table 2 contain primarily preformed vitamin A, the plant-based foods have provitamin A, and the foods with a mixture of ingredients from animals and plants contain both preformed vitamin A and provitamin A.
FDA developed DVs to help consumers compare the nutrient contents of foods and dietary supplements within the context of a total diet. FDA does not require food labels to list vitamin A content unless vitamin A has been added to the food. The U. Department of Agriculture's USDA's FoodData Central [ 9 ] lists the nutrient content of many foods and provides a comprehensive list of foods containing vitamin A in IUs arranged by nutrient content and by food nameand foods containing beta-carotene in mcg arranged by nutrient content and by food name.
Vitamin A is available in multivitamins and as a stand-alone supplement, often in the form of retinyl acetate or retinyl palmitate how can i convert avi to mp4 2 ]. A portion of the vitamin A in some supplements is in the form of beta-carotene and the remainder is preformed vitamin A; others contain only preformed vitamin A or only beta-carotene.
Supplement labels usually indicate the percentage of each form of the vitamin. The amounts of vitamin A in stand-alone supplements range widely [ 2 ]. Multivitamin supplements how to do the frog kick contain —3, mcg RAE 2,—10, IU vitamin A, often in the form of both retinol and beta-carotene.
Adults aged 71 years or older and children younger than 9 are more likely than members of other age groups to take supplements containing vitamin A. Although these intakes are lower than the RDAs for individual men and women, these intake levels are considered to be adequate for population groups. The adequacy of vitamin A intake decreases with age in children [ 4 ]. Furthermore, girls and African-American children have a higher risk of consuming less than two-thirds of the vitamin A RDA than other children [ 4 ].
Frank vitamin A deficiency is rare in the United States. However, vitamin A deficiency is common in many developing countries, often because residents have limited access to foods containing preformed vitamin A from animal-based food sources and they do not commonly consume available foods containing beta-carotene due to poverty [ 2 ]. According to the World Health Organization, million preschool-aged children and In these countries, low vitamin A intake is most strongly associated with health consequences during periods of high nutritional demand, such as during infancy, childhood, pregnancy, and lactation.
In developing countries, vitamin A deficiency typically begins during infancy, when infants do not how to create a staff rota adequate supplies of colostrum or breast milk [ 12 ]. Chronic diarrhea also leads to excessive loss of vitamin A in young children, and vitamin A deficiency increases the risk of diarrhea [ 513 ]. The most common symptom of vitamin A deficiency in young children and pregnant women is xerophthalmia.
One of the early signs of xerophthalmia is night blindness, or the inability to see in low light or darkness [ 214 ]. Vitamin A deficiency is one of the top causes of preventable blindness in children [ 12 ]. People with vitamin A deficiency and, often, xerophthalmia with its characteristic Bitot's spots tend to have low iron status, which can lead to anemia [ 312 ]. Vitamin A deficiency also increases the severity and mortality risk of infections particularly diarrhea and measles even before the onset of xerophthalmia [ 51214 ].
In developed countries, clinical vitamin A deficiency is rare in infants and occurs only in those with malabsorption disorders [ 15 ]. However, preterm infants do not have adequate liver stores of vitamin A at birth and their plasma concentrations of retinol often remain low throughout the first year of life [ 1516 ].
Preterm infants with vitamin A deficiency have an increased risk of eye, chronic lung, and gastrointestinal diseases [ 15 ]. In developed countries, the amounts of vitamin A in breast milk are sufficient to meet infants' needs for the first 6 months of life. But in women with vitamin A deficiency, breast milk volume and vitamin A content are suboptimal and not sufficient to maintain adequate vitamin A stores in infants who are exclusively breastfed [ 17 ].
The prevalence of vitamin A deficiency in developing countries begins to increase in young children just after they stop breastfeeding [ 3 ]. The most common and readily recognized symptom of vitamin A deficiency in infants and children is xerophthalmia. Pregnant women need extra vitamin A for fetal growth and tissue maintenance and for supporting their own metabolism [ 18 ]. The World Health Organization estimates that 9.
Other effects of vitamin A deficiency in pregnant and lactating women include increased maternal and infant morbidity and mortality, increased anemia risk, and slower infant growth and development. Most people with cystic fibrosis have pancreatic insufficiency, increasing their risk of vitamin A deficiency due to difficulty absorbing fat [ 1920 ].
However, improved pancreatic replacement treatments, better nutrition, and caloric supplements have helped most patients with cystic fibrosis become vitamin A sufficient [ 21 ]. Several studies have shown that oral supplementation can correct low serum beta-carotene levels in people with cystic fibrosis, but no controlled studies have examined the effects of vitamin A supplementation on clinical outcomes in patients with cystic fibrosis [ ].
This section focuses on three diseases and disorders in which vitamin A might play a role: cancer, age-related macular degeneration AMDand measles. Because of the role vitamin A plays in regulating cell growth and differentiation, several studies have examined the association between vitamin A and various types of cancer.
However, the relationship between serum vitamin A levels or vitamin A supplementation and cancer risk is unclear. Several prospective and retrospective observational studies in current and former smokers, as well as in people who have never smoked, found that higher intakes of carotenoids, fruits and vegetables, or both are associated with a lower risk of lung cancer [ 123 ]. In the Carotene and Retinol Efficacy Trial CARET18, current and former smokers including some males who had been occupationally exposed to asbestos took daily supplements containing 30 mg beta-carotene and 7, mcg RAE 25, IU retinyl palmitate for 4 years, on average [ 24 ].
In the beta-carotene component of the Physicians' Health Study, 22, male physicians took mg aspirin plus 50 mg beta-carotene, 50 mg beta-carotene plus aspirin placebo, mg aspirin plus beta-carotene placebo, or both placebos every other day for 12 years [ 26 ]. In all three of these studies, taking very high doses of beta-carotene, with or without 7, mcg RAE 25, IU retinyl palmitate or mg aspirin, did not prevent lung cancer.
How to use a shubb capo fact, both the CARET and ATBC studies showed a significant increase in lung cancer risk among study participants taking beta-carotene supplements or beta-carotene and retinyl palmitate supplements. The evidence on the relationship between beta-carotene and prostate cancer is mixed. However, the ATBC study found that baseline serum beta-carotene and retinol levels and supplemental beta-carotene had no effect on survival [ 28 ].
The ATBC and CARET study results suggest that large supplemental doses of beta-carotene with or without retinyl palmitate have detrimental effects in current or former smokers and workers exposed to asbestos. The relevance of these results to people who have never smoked or to the effects of beta-carotene or retinol from food or multivitamins how to do a essay format typically have modest amounts of beta-carotene is not known.
How to gain more traffic research is needed to determine the effects of vitamin A on prostate, lung, and other types of cancer. Age-related macular degeneration AMD is a major cause of significant vision loss in older people. AMD's etiology is usually unknown, but the cumulative effect of oxidative stress is postulated to play a role.
If so, supplements containing carotenoids with antioxidant functions, such as beta-carotene, lutein, and zeaxanthin, might be useful for preventing or treating this condition. Lutein and zeaxanthin, in particular, accumulate in the retina, the tissue in the eye that is damaged by AMD. A follow-up AREDS2 study confirmed the value of this supplement in reducing the progression of AMD over a median follow-up period of 5 years but found that adding lutein 10 mg how to make a leprechaun costume zeaxanthin 2 mg or omega-3 fatty acids to the formulation did not confer any additional benefits [ 31 ].
Importantly, the study revealed that beta-carotene was not a required ingredient; the original AREDS formulation without beta-carotene provided the same protective effect against developing advanced AMD. Measles is a major cause of morbidity and mortality in children in developing countries. About half of all measles deaths happen in Africa, but the disease is not limited to low-income countries. Vitamin A deficiency is a known risk factor for severe measles.
The World Health Organization recommends high oral doses 60, mcg RAE [, IU] of vitamin A for two days for children over age 1 with measles who live in areas with a high prevalence of vitamin A deficiency [ 32 ].
A Cochrane review of eight randomized controlled trials of treatment with vitamin A for children with measles found that 60, mcg RAEIU of vitamin A on each of two consecutive days reduced mortality from measles in children younger than 2 and mortality due to pneumonia in children [ 32 ]. Vitamin A also reduced the incidence of croup but not pneumonia or diarrhea, although the mean duration of fever, pneumonia, and diarrhea was how to scan email for viruses with norton in children who received vitamin A supplements.
A meta-analysis of six high-quality randomized controlled trials of measles treatment also found that two doses of 30, mcg RAEIU in infants and 60, mcg RAEIU in older children significantly reduced measles mortality [ 33 ]. The vitamin A doses what is the final break on prison break in these studies are much higher than the UL.
What is vitamin A and what does it do?
Apr 21, · Vitamin A is important for the eyes and skin, the immune system, and for normal growth. Vitamin A is a fat-soluble vitamin that is absorbed with fats in your diet and stored in your body's fatty tissue. Vitamin A is used to treat vitamin A lovedatingstory.com names: Palmitate-A, Aquasol A. Feb 14, · Vitamin A is critical for vision as an essential component of rhodopsin, a protein that absorbs light in the retinal receptors, and because it supports the normal differentiation and functioning of the conjunctival membranes and cornea [ ]. Oct 04, · Vitamin A is essential for your health, supporting cell growth, immune function, fetal development and vision. Perhaps one of the best-known functions of Author: Jillian Kubala, MS, RD.
Vitamin A retinol, retinoic acid is a nutrient important to vision, growth, cell division, reproduction and immunity. Vitamin A also has antioxidant properties. Antioxidants are substances that might protect your cells against the effects of free radicals — molecules produced when your body breaks down food or is exposed to tobacco smoke and radiation. Free radicals might play a role in heart disease, cancer and other diseases.
Vitamin A is found in many foods, such as spinach, dairy products and liver. Other sources are foods rich in beta-carotene, such as green leafy vegetables, carrots and cantaloupe. Your body converts beta-carotene into vitamin A.
As an oral supplement, vitamin A mainly benefits people who have a poor or limited diet or who have a condition that increases the need for vitamin A, such as pancreatic disease, eye disease or measles.
If you take vitamin A for its antioxidant properties, keep in mind that the supplement might not offer the same benefits as naturally occurring antioxidants in food. The recommended daily amount of vitamin A is micrograms mcg for adult men and mcg for adult women. Beyond use as an oral supplement, vitamin A is used in topical creams to reduce fine wrinkles, splotches and roughness and treat acne. A healthy and varied diet will provide most people with enough vitamin A.
If you're interested in the antioxidant properties of vitamin A, food sources are best. It's not clear if vitamin A supplements offer the same benefits as naturally occurring antioxidants in food. Too much vitamin A can be harmful and excess vitamin A during pregnancy has been linked to birth defects.
Too much vitamin A can be harmful. Even a single large dose — over , mcg — can cause:. If you are or might become pregnant, talk to your doctor before taking vitamin A. Excess use of vitamin A during pregnancy has been linked to birth defects. Mayo Clinic does not endorse companies or products. Advertising revenue supports our not-for-profit mission.
This content does not have an Arabic version. See more conditions. Request Appointment. Vitamin A. Products and services. Free E-newsletter Subscribe to Housecall Our general interest e-newsletter keeps you up to date on a wide variety of health topics. Sign up now. Show references Vitamin A. Accessed Aug. Duyff RL. Use supplements wisely. New York, N. Micromedex 2. Vitamin A oral. Beta-carotene oral.
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