The requirement of A vitamin was first suggested in 1881 as a possible factor needed for the maintenance of good health. Then, in 1900, nutritional studies on young rats reported an accessory food factor that was critical for the survival and growth of these animals. Currently, vitamin A is well known for its essential role in human health and nutrition, so much so that it receives considerable attention in targeted public health programs. Deficiency of A vitamins is characterized by both subclinical and clinical conditions, where anemia, corneal dryness, night blindness, impetigo, and fever are predominantly attributed. In tropical regions and in areas where sufficient vegetables and fruits are not regularly consumed, the prevalence of vitamin
A-related problem is quite severe. Not only are the problem of vitamin A restricted to any particular region but there are also serious issues of A vitamin in industrialized nations.
International organizations have realized that they need to monitor the possible side effects of excessive vitamin A intake in commercial preparations in industrialized nations. In summary, vitamin A is a well-known micronutrient that is essential for the regular functions of the human body. In this review, an extensive description of the status, the sources, and potential health issues surrounding vitamin A is provided.x”
Curiously enough, most oil-based supplements and food products that are generally consumed contain at least some free carotenoids, usually better absorbed than the bound carotenoids. The daily intake of vitamin A that meets the current RDA can be ensured by daily consumption of, for example, 85 and 135 g of beef liver, respectively, or 170 g of cooked spinach. Allowances are slightly increased during pregnancy and lactation. With other guidelines, the needs of the population could be reached by consuming an average of five or more servings a day of fruits and vegetables. Due to the fact that beta-carotene is effectively transformed into vitamin A, it is expressed not only by the international unit of retinol but also by micrograms of RAE. It is, however, important to outline that only a part of it can be transformed by the human body, and the individual bioavailability of provitamin A can be very different. The best way to reach the Nutritional needs of A vitamin foods products represent the full panel of nutrients necessary to reduce the risks of deficiency. Food may be the mixed-green leaves like salads and vegetables, yellow or orange sources, like carrots, and sources of fat, like some oil, that may elevate the final quantity of carotenoids available in food and enhance the availability of provitamin A from the provitamin A vitamin foods.
Vitamin A is one of those nutrients that have a wide variety of functions, from normal vision to immune function and healthy skin. Probably most known for its role in keeping eyes healthy, vitamin A enables the production of pigments in the retina and is critical for keeping the eye healthy for vision in low light and preventing age-related loss of vision. This is also one of the powerful antioxidant vitamins that helps to protect cells from damage caused by free radicals, besides helping in the reduction of inflammation. In this regard, it prevents chronic diseases related to heart conditions and certain cancers. The immune-enhancing properties of A vitamin benefits help the body to prevent infections, which particularly makes this vitamin useful for people vulnerable to respiratory and other infectious diseases.
In addition to eye health and immunity, vitamin benefits a significant role in skin health and cellular processes. Vitamin A is very essential to forming the primary underlying protein giving turgidity to the skin, elasticity, resilience, and healing. Good levels of vitamin A can improve skin conditions such as acne, dryness, and uneven pigmentation. Vitamin A maintains normal cellular proliferation and differentiation, therefore being important for organ health and the healing process in general. Vitamin A helps a developing fetus and keeps the heart, lungs, kidneys, and other organs working properly. Thus, proper intake of this vitamin, derived from carrots, sweet potatoes, spinach, and many types of fish, among others, is essential to health and in preventing conditions associated with nutrient deficiencies.
Global prevalence of A vitamin and energy arises because of low dietary intake coupled with poor absorption in developing countries. Vitamin A deficiency occurs along with typical eye and vision changes, including barely visible to complete corneal and conjunctival xerosis seen in a condition called xerophthalmia. Certain children may die from measles or diarrhea if they have subclinical vitamin A deficiency. It enhances maternal night blindness, mortality, maternal anemia, puerperal sepsis, and other related conditions because of the subclinical vitamin A deficiency among pregnant women. Pregnant women with subclinical vitamin A deficiency also have four times the chance of dying.
A vitamin and energy actions can be antagonized by some metals such as zinc, lead, and mercury. Symptoms of vitamin A toxicity are associated with extreme consumption either through the diet or the use of pharmacologic dosage. Excessive use of food or supplements can lead to hypervitaminosis A. Below 10,000 IU daily and 25,000-33,000 IU/day can be regarded.
As safe intake while tolerable upper limits are defined for long-term intakes from preformed vitamin A with almost no risk for advanced symptoms of hypervitaminosis A. One can get about 30 mg of beta-carotene safely, which hardly increases the risk of hypervitaminosis A because excessive blood beta-carotene is a yellowish color rather than reddish-orange. The establishment of upper limits for vitamin A intakes, as assessed by animal studies on the toxicological effect of chronic hypervitaminosis A, suggests that the intake of preformed vitamin A at 3000 μg retinol is approximately 100 times an adequate intake.
A vitamin is an essential micronutrient vital for growth, immune function, and reproduction. Its functions are largely tied to its active forms, which are involved in many processes such as vision, maintenance of epithelial tissues, and immune cell differentiation. While the importance of addressing vitamin A deficiency has been relatively well established, recent work has also highlighted cases of excess vitamin A intake leading to hypervitaminosis A or vitamin A toxicity, which can have serious negative health implications as well. Hence, both insufficient and excessive intake should be regarded when planning national and global strategies and health/nutrition policies and interventions involving A vitamin and energy. As the current evidence does not provide definitive conclusions on the safety and possible harm of high vitamin A levels, future research could investigate the possible impact of chronic vitamin A intake on mortality from many types of cancer, cardiovascular diseases, and neurodegenerative diseases, among others. Experimental research providing causal evidence of the effects of vitamin A beyond the growth and developmental period is still lacking.
Furthermore, another important area for future research involves the assessment of the effect of dietary guidelines and public health policies promoting the consumption of animal, fortified, or biofortified food sources containing vitamin A on vitamin intake and health outcomes at the population level. In low- and middle-income countries where many people rely on plant-based diets, research and intervention strategies are also needed to facilitate higher bioavailability of plant vitamin A precursors. Given the critical importance of vitamin A for human health, and the continuing evolution of the field of nutrition science, research on vitamin A seems as relevant today as when initial reporting brought it to the attention of the world.
English 
Deutsch 
Türkçe 
Español 
Italiano 
Français 
Português 
Português do Brasil 
Русский 
العربية