Fat Soluble Vitamin:
Vitamin A is a fat-soluble vitamin. Naturally it is found in many foods.
Functions of Vitamin A:
Vitamin A is important for the immune system, reproduction and normal vision. Vitamin A is also involved in the proper functioning of lungs, heart, and kidneys.
Types of Vitamin A:
Vitamin A is present in two different forms which are discussed below:
Preformed Vitamin A:
Preformed Vitamin A is found in poultry, dairy products, fish and meat.
This form of vitamin A is found in vegetables, fruits and other plant based products. In foods and dietary supplements most common type of provitamin A is beta-carotene.
|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|
|19–50 years||900 mcg RAE||700 mcg RAE||770 mcg RAE|
|51+ years||900 mcg RAE||700 mcg RAE|
Daily Requirements of Vitamin A:
List of upper limits of preformed vitamin A in International Units are given in table above. These levels are not applied to the people who are consuming vitamin A for medical reasons. Upper limits for some forms of provitamin A and beta-carotene have not been established.
Amount of vitamin A required depends upon age and reproductive status. For people with 14 year and older age recommended intakes of vitamin A range between 700 and 900 micrograms per day of retinol activity equivalents(RAE). Women who are nursing recommended intakes for vitamin A range between 1200 and 1300 RAE. Infants and children younger than 14 years’ lower values of vitamin A are recommended.
However, content of vitamin A in the dietary supplements and foods is given in international units(IU) on product labels. It is not given in mcg RAE. Conversion of IU into mcg is not easy. For example, a diet containing variety of food will have 900 mcg RAE content of vitamin A and it will provide 3000 and 36000 IU of vitamin A depending upon the amount of food consumed.
US Food and Drug Administration has established a Daily Value(DV) of vitamin A. for Adults and children of 4 year and older age the daily value of vitamin A obtained from a mixed diet of animal and plant food should be 5000 IU according to US FDA. DVs are not considered as recommended intakes for example they don’t vary by sex and age. But, on average it will be useful in getting enough vitamin A if a person try to reach 100% of the recommended daily value every day.
Naturally vitamin A is found in many foods. It is also artificially added to some foods such as cereal and milk. Recommended amount of vitamin A can be obtained by getting variety of foods. Some of the foods rich in vitamin A are listed below:
- Organ meats and beef liver, but these foods are high in cholesterol so limited amount should be consumed.
- Some kinds of fish, like salmon
- Green leafy vegetables and other yellow, orange and green vegetables such as carrots, squash, and broccoli.
- Fruits like apricots, mangoes and cantaloupe.
- Major sources of vitamin A such as dairy products
- Fortified cereals of breakfast
|mcg RAE per|
|Sweet potato, baked in skin, 1 whole||1,403||28,058||561|
|Beef liver, pan fried, 3 ounces||6,582||22,175||444|
|Spinach, frozen, boiled, ½ cup||573||11,458||229|
|Carrots, raw, ½ cup||459||9,189||184|
|Pumpkin pie, commercially prepared, 1 piece||488||3,743||249|
|Cantaloupe, raw, ½ cup||135||2,706||54|
|Peppers, sweet, red, raw, ½ cup||117||2,332||47|
|Mangos, raw, 1 whole||112||2,240||45|
|Black-eyed peas (cowpeas), boiled, 1 cup||66||1,305||26|
|Apricots, dried, sulfured, 10 halves||63||1,261||25|
|Broccoli, boiled, ½ cup||60||1,208||24|
|Ice cream, French vanilla, soft serve, 1 cup||278||1,014||20|
|Cheese, ricotta, part skim, 1 cup||263||945||19|
|Tomato juice, canned, ¾ cup||42||821||16|
|Herring, Atlantic, pickled, 3 ounces||219||731||15|
|Ready-to-eat cereal, fortified with 10% of the DV for vitamin A, ¾–1 cup (more heavily fortified cereals might provide more of the DV)||127–149||500||10|
|Milk, fat-free or skim, with added vitamin A and vitamin D, 1 cup||149||500||10|
|Baked beans, canned, plain or vegetarian, 1 cup||13||274||5|
|Egg, hard boiled, 1 large||75||260||5|
|Summer squash, all varieties, boiled, ½ cup||10||191||4|
|Salmon, sockeye, cooked, 3 ounces||59||176||4|
|Yogurt, plain, low fat, 1 cup||32||116||2|
|Pistachio nuts, dry roasted, 1 ounce||4||73||1|
|Tuna, light, canned in oil, drained solids, 3 ounces||20||65||1|
|Chicken, breast meat and skin, roasted, ½ breast||5||18||0|
Dietary supplements of Vitamin A:
In dietary supplements vitamin A is usually available in the form of beta-carotene (provitamin A), retinyl palmitate (preformed vitamin A) or combination of both preformed and provitamin A. vitamin A can also be obtained from multivitamin-mineral supplements. Solely vitamin A containing dietary supplements are also available.
People suffering from vitamin A deficiency:
deficiency of vitamin A is rare. Most of the people in Unite States get sufficient amount of vitamin A from the foods they eat. However, there are certain groups of people who feel trouble in getting sufficient amount of vitamin K. these are discussed below:
- Premature infants who mostly have lower vitamin A levels in their first year.
- In developing countries, young children, breast feeding women, infants and pregnant women
- People suffering from cystic fibrosis
Deficiency of vitamin A is rare in United States, however commonly it is found in many developing countries. Deficiency of vitamin A in pregnant women and young children result in a condition termed as xerophthalmia. In this condition individual is unable to see in low light and if it is not treated it can also lead to blindness.
Health effects of vitamin A:
Scientists are studying the health effects of vitamin A for better understanding. Some of these are discusses below:
People who consume foods rich in beta-carotene might be at low risk of developing certain types of cancer such as prostate cancer or lung cancer. But updated studies did not provide any evidence that beta-carotene or vitamin A supplements can help in preventing cancer or lowering the chances of death from this disease. In fact some studies demonstrate that smokers who consume high doses of beta-carotene supplements are at an increased risk of developing lung cancer.
Age-Related Macular Degeneration:
In older people one of the most common cause of vision loss is Age-Related Macular Degeneration (AMD) or as the aging occurs in people loss of central vision can also be the reason. People who are at a high risk of developing advanced AMD a supplement composed of zinc, copper and anti-oxidants with or without the combination of beta-carotenes has shown the promising effects for slowing down the rate of vision loss.
Vitamin A deficiency is rare in north America. When children suffering from deficiency of vitamin A get measles, they show severe symptoms of disease. If these children take high doses of vitamin A supplements it will help in reducing the diarrhea and fever caused due to measles. Vitamin A deficiency is common in developing countries. In these countries, vitamin A supplements help in reducing the death risk in children suffering from measles.
High intakes of some forms of vitamin A seems to be harmful.
Preformed Vitamin A:
Excessive intake of preformed vitamin A mostly from certain medicines and supplements can cause various symptoms such as:
· Nausea and even death
|Life Stage||Upper Limit|
|Birth to 12 months||2,000 IU|
|Children 1–3 years||2,000 IU|
|Children 4–8 years||3,000 IU|
|Children 9–13 years||5,667 IU|
|Teens 14–18 years||9,333 IU|
|Adults 19 years and older||10,000 IU|
In pregnant women, high intakes of preformed vitamin A can result in birth defects in new born babies. Pregnant women should not consume high doses of vitamin A supplements.
If beta-carotene or some other forms of provitamin A is consumed in high amounts the skin color turns to yellow-orange, but this is a harmless condition. Consumption of high amounts of beta-carotene don’t causes any birth defects or some other serious conditions that are mostly caused by consuming too much amounts of preformed vitamin A.
Interactions of Vitamin A with other medications:
· A weight-loss drug named Orlistat (Alli®, Xenical®) decreases the vitamin A absorption and result in low blood levels of vitamin A in some people.
· Some doctors also prescribe synthetic forms of vitamin A as medicines examples include acitretin (Soriatane®) for treatment of psoriasis and bexarotene (Targretin®) for treatment of T-cell lymphoma effects on the skin. If patient consumes these medicines in combination with supplements of vitamin A it can result in dangerously elevated levels of vitamin A in the blood.
Before taking any supplements, patient should talk to his/her pharmacist, health care provider so that they will provide guideline regarding the interactions of various medicines or drugs with the supplements.
Healthful eating and Vitamin A:
Dietary Guidelines of federal government for Americans advised that the people should obtain most of their nutrients by consuming healthy food. Healthy diets contain dietary fibers, minerals, vitamins as well as other substances that are beneficial for health. In certain cases dietary supplements and fortified foods may help in providing nutrients that in other cases may be consumed in amounts that are less than recommended values.
This fact paper by Office of Dietary Supplements gives a piece of knowledge that should not replace the medical prescription. We foster you to communicate with your healthcare adviser (doctor, pharmacist, dentist etc.) for your interest in, queries about, or use of supplements and what could be best for your health.
Vitamin A inadequacy risk in certain groups:
Some groups which suffer from inadequate supply of vitamin A are discussed below:
In infants of developed countries vitamin A deficiency is rarely observed. People with malabsorption disorder of vitamin A only suffer from its deficiency. 
However, at birth adequate stores of vitamin A are not found in liver of preterm infants and throughout their first year of life retinol concentration in plasma also remains low. [16,17]
Preterm infants suffering from deficiency of vitamin A are at increased risk of developing chronic lung, eye and gastrointestinal disease.
Young Children and Infants in Developing countries:
In developed countries, sufficient amount of vitamin A is found in breast milk and this amount fulfills the infant’s requirement of vitamin A for first six months of life. But infants who are exclusively feeding on breast milk from mother suffering from vitamin A deficiency or having sub-optimal levels of vitamin A will not get adequate amount of vitamin A. 
In developing countries, prevalence of vitamin A deficiency increases in young children after they stopped breast feeding. 
In infants xerophthalmia is the readily recognized and most common symptom of vitamin A deficiency.
Lactating and Pregnant women in developing countries:
Extra vitamin A is needed by the pregnant women for tissue maintenance and fetal growth. It is also required by the pregnant women to support their own metabolism. 
According to the estimation of World Health Organization about 9.8 million pregnant women around the world suffer from xerophthalmia due to deficiency of vitamin A. 
In lactating and pregnant women some other effects caused due to deficiency of vitamin A include increased risk of anemia, increased infant and maternal mortality and morbidity rate and slower growth and development rate in infants.
People suffering from cystic fibrosis:
Pancreatic insufficiency is observed in most of people suffering from cystic fibrosis. These people are at high risk of developing vitamin A deficiency because of their difficulty in absorbing fats. [20,21]
It is found through several cross-sectional studies that 15-40% of patients suffering from cystic fibrosis have deficiency of vitamin A. 
However, improved treatment for pancreatic replacement, caloric supplements and better nutrition have helped most of the patients suffering from cystic fibrosis to become sufficient in vitamin A.  Several studies have shown that people suffering from cystic fibrosis can be treated through oral supplementation which will help in correcting low serum levels of beta-carotene. But no control studies have performed regarding these findings. [21-23]
In this section three disorders or diseases are focused in which vitamin A has a role. These include Age-Related Macular Degeneration (AMD), cancer and measles.
Vitamin A plays an important role in regulation of cell growth and differentiation because of this role link between vitamin A and various types of cancer is examined by several studies. However, the relationship between vitamin A supplementation or serum levels of vitamin A and cancer risk is not clear.
Several studies such as prospective and retrospective observational studies are performed in current and former smokers. People who have never smoked were also included in these studies. Results showed that higher intakes of carotenoids, vegetables and fruits or both are linked with the lower risk of developing lung cancer. [1,24]
However, clinical trials didn’t provide any evidence that supplements of beta-carotene or vitamin A help in preventing lung cancer. Several trials were performed on this. In first trial named Carotene and Retinol Efficacy Trial (CARET), 18 current and 314 former smokers which also includes some males who had been exposed occupationally to asbestos were given daily 30 mg supplement of beta-carotene and retinyl palmitate 25,000 IU for the duration of 4 years, on average .
In the second trial named Alpha-Tocopherol, Beta-Carotene (ATBC) study for Cancer Prevention 29,133 male smokers took 20 mg/day beta-carotene, 50 mg/day alpha-tocopherol and 20 mg/day beta-carotene, or placebo, 50 mg/day alpha-tocopherol for the period of 5–8 years .
In the beta-carotene constituent of Health Study of the Physicians 22,071 male physicians consumed 50 mg beta-carotene plus 325 mg aspirin, 325 mg aspirin plus beta-carotene placebo, 50 mg beta-carotene plus aspirin placebo or both placebos were taken every other day for duration of 12 years .
results from all these three studies showed that consuming very high doses of beta-carotene in combination with or without retinyl-palmitate 25000 IU or aspirin 325 mg don’t help in preventing lung cancer. In fact, results of both studies ATBC and CARET showed that consuming high amounts of beta-carotene supplementation or retinyl-palmitate and beta-carotene supplements significantly increase the risk of developing lung cancer in the participants. Participants taking supplements of beta-carotene in physician’s health study didn’t show the risk of increased lung cancer in participants. Possible explanation of these results is that in the study only 11% of physician were former or current smokers.
The evidence regarding the relationship between prostate cancer and beta-carotene is mixed. Participants of the CARET study who took supplements of retinyl palmitate and beta-carotene supplements showed 35% lower risk of developing non-aggressive prostate cancer as compared to men who are not consuming supplements. 
However, results from ATBC study showed that retinol levels and base-line serum beta-carotene as well as supplemental beta-carotene showed no effects on survival. 
Moreover, men with the high quintile level of baseline serum retinol were 20 times more susceptible to develop cancer of prostate than men with low level of quintile. 
Results from CARET and ATBC studies suggest that high doses of beta-carotene supplements with or without retinyl palmitate showed detrimental effects in former or current workers and smokers exposed to asbestos. Relevancy of these results to people who consumed retinol or beta-carotene from multivitamins or food or people who had never smoked at all is not known. To determine the vitamin A effects on lungs, prostate and other types of cancer more research is required.
Age-Related Muscular Degeneration:
In older people, major causes of significant vision loss is AMD. Etiology of AMD’s is unknown usually but it is postulated that cumulative effect of oxidative stress play an important role. If it is true than carotenoids supplements with anti-oxidant functions including lutein, beta-carotene and zeaxanthin might be helpful in treating or preventing this condition. Particularly, zeaxanthin and lutein accumulate in the eye tissue retina which is damaged specially by AMD. A large randomized clinical trial was performed. In this a study conducted termed The Age-Related Eye Disease Study (AREDS). This study found that participants at high risk of developing advanced AMD which include those with intermediate AMD or those suffering from advanced AMD in one eye. These participants decreased their risk of developing advanced AMD by 25% by consuming a supplement containing beta-carotene (15 mg) on daily basis, vitamin C (500 mg), vitamin E (400 IU dl-alpha-tocopheryl acetate), copper (2 mg) and zinc (80 mg), for the period of 5 years compared to participants on a placebo prescription .
Another follow-up study AREDS2 confirmed the worth of this supplement in decreasing the development of AMD over a median follow-up duration of 5 years. But it is also found out that adding zeaxanthin (2 mg) and lutein (10 mg) or omega-3 fatty acids to the formulation did not showed any additional benefits .
The study revealed the most important thing that beta-carotene supplementation was not a required ingredient; the original formulation of AREDS without beta-carotene provided the similar protective effect against development of advanced AMD. When the results were analyzed in more detail it showed that, supplementation with zeaxanthin and lutein reduced the risk of developing advanced AMD by 26% in participants with lowest dietary intakes of these two carotenoids .. Participants who took the modified AREDS supplementation containing zeaxanthin and lutein but not beta-carotene also showed the 18% reduced risk of developing advanced AMD than the participants who took the formulation with beta-carotene but not zeaxanthin or lutein.
Individuals who are developing or suffering from AMD should take advice of their health care provider about taking any of the formulations of supplements used in AREDS.
In developing countries, major cause of mortality and morbidity in children is measles. About half of deaths in Africa results from measles but it is not limited to countries with low-income. Deficiency of Vitamin A is a recognized risk factor for causing severe measles. High oral doses (200,000 IU) of vitamin A are recommended by the World Health Organization. It should be consumed by the children over the age 1 suffering from measles that are also living in areas with a high prevalence of vitamin A deficiency .
Eight randomized control trials were performed regarding treatment of measles with vitamin A. A Cochrane review of these studies were performed. Results showed that when 200,000 IU of vitamin A was used for two consecutive days it helped in reducing mortality rate of measles in children younger than 2 years. Furthermore, mortality due to pneumonia is also reduced in children. 
Vitamin A also helped in reducing incidence of croup but it did not reduce the incidence of diarrhea, or pneumonia, however the mean duration of pneumonia, diarrhea or fever was reduced in children who were getting vitamin A supplements. Another meta-analysis was performed on 6 high quality randomized control trial regarding the treatment of measles. This analysis showed that two doses of 100,000 IU vitamin A in infants and 200,000 IU in children of older age significantly reduce the mortality rate of measles. 
Much higher doses of vitamin A are used in these studies than the UL.
The effectiveness of vitamin A supplements for the treatment of measles in countries like United States where intake of vitamin A is usually in adequate amount is uncertain.
Vitamin A is needed by the body to maintain certain epithelial surfaces and corneas so the lower concentration of serum vitamin A associated with measles especially in people suffering from protein-calorie malnutrition can result in blindness. In a cochrane review none of the studies showed blindness as a primary outcome. 
Although, a clinical investigation was performed carefully on 130 African children suffering from measles showed that about half of all corneal ulcers and almost all bilateral blindness in these children occur due to deficiency of vitamin A.