Vitamin A
Vitamin A is a fat-soluble vitamin that plays several key roles in the body.
Key Role
Vision:
One of the most well-known functions of vitamin A is its role in supporting vision. Specifically, vitamin A is essential for the proper functioning of the retina, a layer of tissue at the back of the eye that detects light and color. Vitamin A is a component of rhodopsin, a pigment in the retina that helps with low-light vision (night vision). [1,2]
Immune function:
Vitamin A plays a crucial role in maintaining the health of the immune system. It helps regulate the immune response to infections and is involved in the production and function of various immune cells, including white blood cells.[1,2]
Skin health:
Vitamin A is important for maintaining healthy skin and mucous membranes. It supports the production of new skin cells, regulates oil production in the skin, and promotes wound healing. Vitamin A derivatives, such as retinoids, are commonly used in skincare products for their anti-aging and acne-fighting properties.[1,2]
Reproduction and growth:
Vitamin A is essential for normal growth and development, including embryonic development, fetal growth, and postnatal growth. It plays a role in the development of various tissues and organs, including the lungs, heart, kidneys, and skeletal system.[1,2]
Gene expression:
Vitamin A is involved in the regulation of gene expression, influencing the activity of numerous genes involved in cell differentiation, proliferation, and apoptosis (programmed cell death).[1,2]
Rec Amount/day
The optimal amount of vitamin A intake varies depending on factors such as age, sex, and overall health. However, the Recommended Dietary Allowance (RDA) for vitamin A established by the Institute of Medicine (now the National Academy of Medicine) provides general guidelines for daily intake:
For adult men: 900 micrograms (mcg) of retinol activity equivalents (RAE) per day [1]
For adult women: 700 micrograms (mcg) of RAE per day [1]
These recommendations are based on maintaining overall health and meeting the body's needs for vision, immune function, and growth. However, individual requirements may vary, and certain populations, such as pregnant or lactating women, may have higher vitamin A needs. [1]
It's important to note that vitamin A is available in two forms in the diet: preformed vitamin A (retinol and its esterified form, retinyl ester) found in animal-based foods, and provitamin A carotenoids (such as beta-carotene) found in plant-based foods. The RDA is expressed in micrograms of RAE to account for the differences in bioavailability between these forms. Excessive intake of vitamin A supplements can lead to toxicity, so it's important to follow recommended doses and consult with a healthcare professional if considering supplementation.[1,4]
Co-factors
Several cofactors work synergistically with vitamin A to support its functions in the body:
Zinc: Zinc is involved in the metabolism of vitamin A and helps convert beta-carotene (a precursor of vitamin A) into retinol (the active form of vitamin A). Zinc also plays a role in immune function and wound healing, complementing the functions of vitamin A in these processes.[1,3]
Vitamin D: Vitamin D works in conjunction with vitamin A to regulate gene expression and support various physiological processes, including immune function, bone health, and cell growth and differentiation.[1,3]
Vitamin E: Vitamin E is an antioxidant that works synergistically with vitamin A to protect cells and tissues from oxidative damage. The two vitamins may enhance each other's antioxidant activity and contribute to overall health and well-being.[1,3]
Protein: Adequate protein intake is necessary for the synthesis and transport of retinol-binding protein (RBP), a carrier protein that facilitates the transport of vitamin A in the bloodstream. Protein deficiency can impair the body's ability to utilize vitamin A effectively.[1,3]
Fat: Since vitamin A is a fat-soluble vitamin, dietary fat is necessary for its absorption and transport in the body. Consuming vitamin A-rich foods with sources of healthy fats, such as nuts, seeds, avocado, and olive oil, can enhance its bioavailability.[1,3]
Iron: Iron is involved in the metabolism of vitamin A and supports various physiological processes, including oxygen transport, immune function, and energy metabolism. Adequate iron status is important for the utilization of vitamin A and overall health.[1,3]
These cofactors work together with vitamin A to optimize its various functions, including vision, immune function, skin health, and growth. A balanced diet that includes a variety of nutrient-rich foods can help ensure adequate intake of these cofactors and support overall health and well-being.
Food Sources
Liver: Liver, particularly beef liver, is one of the richest sources of vitamin A. It contains a highly bioavailable form of vitamin A called retinol.[1]
Eggs: Egg yolks are rich in vitamin A, providing both retinol and carotenoids.[1]
Dairy products: Milk, cheese, and yogurt contain vitamin A, particularly in the form of retinyl esters.[1]
Fatty fish: Certain fatty fish, such as salmon and mackerel, contain small amounts of vitamin A, primarily in the form of retinol.[1]
Fortified foods: Some foods, such as breakfast cereals, margarine, and milk substitutes, may be fortified with vitamin A to enhance their nutritional value.[1]
Orange and yellow fruits and vegetables: Carotenoids, such as beta-carotene, are found in fruits and vegetables with orange, yellow, and red hues. Examples include carrots, sweet potatoes, pumpkin, mangoes, and apricots.[1]
Dark green leafy vegetables: Certain leafy greens, such as spinach, kale, and Swiss chard, contain carotenoids like beta-carotene, as well as other forms of vitamin A. [1]
Red and orange bell peppers: Bell peppers, particularly red and orange varieties, are rich in beta-carotene and other carotenoids. [1]
Including a variety of these foods in your diet can help ensure that you meet your daily vitamin A needs. It's important to note that vitamin A is available in different forms, including preformed vitamin A (retinol) found in animal-based foods and provitamin A carotenoids found in plant-based foods. Consuming a mix of both types of foods can provide a balanced intake of vitamin A.
Cooking Method
To preserve the vitamin A content in foods during cooking, it's best to use methods that involve minimal heat exposure and shorter cooking times. Steaming, sautéing, and stir-frying are preferable to boiling, as they expose foods to lower temperatures and less cooking duration. These methods help retain the delicate structure of vitamin A, which can be easily degraded by heat. Additionally, blanching vegetables before cooking can help preserve their color, texture, and nutrient content, including vitamin A. Consuming fruits and vegetables raw or lightly cooked, such as in salads or as snacks, further ensures the retention of their vitamin A content. By adopting these cooking methods, individuals can maximize the nutritional benefits of their foods and maintain adequate intake of vitamin A for overall health and well-being. [5]
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Vitamin A Fact Sheet for Health Professionals. (2018, March ). US Department of Health and Human Services. https://ods.od.nih.gov/factsheets/VitaminA-HealthProfessional/
H. Herschel Conaway, Petra Henning, Ulf H. Lerner, Vitamin A Metabolism, Action, and Role in Skeletal Homeostasis, Endocrine Reviews, Volume 34, Issue 6, 1 December 2013, Pages 766–797, https://doi.org/10.1210/er.2012-1071
O'Connor C, Varshosaz P, Moise AR. Mechanisms of Feedback Regulation of Vitamin A Metabolism. Nutrients. 2022 Mar 21;14(6):1312. doi: 10.3390/nu14061312. PMID: 35334970; PMCID: PMC8950952.
Olson JM, Ameer MA, Goyal A. Vitamin A Toxicity. [Updated 2023 Sep 2]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2024 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK532916/
Yuan GF, Sun B, Yuan J, Wang QM. Effects of different cooking methods on health-promoting compounds of broccoli. J Zhejiang Univ Sci B. 2009 Aug;10(8):580-8. doi: 10.1631/jzus.B0920051. PMID: 19650196; PMCID: PMC2722699.
