Vitamin A is a fat-soluble nutrient, a group of retinoids (primarily retinol and retinyl esters). This essential vitamin is stored mainly in the liver, serving as a reservoir. It is fundamental for numerous biological processes, supporting overall human health.
Recommended Daily Amounts
Daily vitamin A needs vary significantly by age, gender, and life stage. These recommendations are typically expressed in micrograms (mcg) of Retinol Activity Equivalents (RAE) to account for different forms of vitamin A. For infants aged 0 to 6 months, the recommended daily intake is 400 mcg RAE, increasing to 500 mcg RAE for infants 7 to 12 months.
Children aged 1 to 3 years generally require 300 mcg RAE daily, while those 4 to 8 years old need 400 mcg RAE. For older children aged 9 to 13 years, the recommendation rises to 600 mcg RAE per day. Adult males aged 14 years and older should aim for 900 mcg RAE daily, and adult females in the same age group require 700 mcg RAE.
During pregnancy, the daily recommended amount for teens is 750 mcg RAE, and for adult pregnant women, it is 770 mcg RAE. Breastfeeding teens need 1,200 mcg RAE daily, while breastfeeding women require 1,300 mcg RAE.
Key Roles of Vitamin A
Vitamin A plays multiple roles, contributing to several physiological systems. It is essential for vision, particularly in low-light conditions, forming a component of rhodopsin in the retina. It helps maintain eye moisture, preventing dryness and potential corneal damage.
Beyond vision, vitamin A supports a robust immune system. It influences the production and activity of white blood cells, which are part of the body’s defense against illness and infection. Adequate vitamin A levels help maintain the integrity of mucous membranes lining the respiratory, gastrointestinal, and urinary tracts, forming protective barriers against pathogens. This nutrient guides cellular growth and specialization, a process known as cell differentiation.
Cell differentiation is important for the normal formation and maintenance of various organs, including the heart, lungs, skin, and mucous membranes. It supports reproductive health, including fertility, embryonic development, and placental development during pregnancy.
Dietary Sources
Vitamin A is available from two main types of dietary sources: preformed vitamin A and provitamin A carotenoids. Preformed vitamin A, also known as retinol, is found in animal-based foods. This form is readily used by the body without conversion.
Rich sources of preformed vitamin A include beef liver and other organ meats, fish and fish oils like cod liver oil and salmon, and dairy products such as milk, cheese, and butter. Eggs are a good source. Many breakfast cereals and some dairy products are fortified with preformed vitamin A.
Provitamin A carotenoids are plant pigments the body converts into vitamin A, with beta-carotene being the most common. They are abundant in colorful fruits and vegetables like carrots, sweet potatoes, pumpkin, squash, mangoes, cantaloupe, and papayas. Dark green leafy vegetables such as spinach, kale, and broccoli contain provitamin A carotenoids, though their color may be masked by chlorophyll.
Understanding Deficiency and Excess
An insufficient intake of vitamin A can lead to various health problems, with vision issues often being among the first signs. Night blindness, characterized by difficulty seeing in dim light, is an early indicator. If left unaddressed, deficiency can progress to xerophthalmia, a condition causing severe dryness of the eyes, potentially leading to corneal damage, foamy spots on the whites of the eyes (Bitot spots), ulcers, and ultimately permanent blindness. Vitamin A deficiency is a leading cause of preventable blindness, particularly in children globally.
Beyond vision, a lack of vitamin A can result in dry skin and compromise the immune system, increasing susceptibility to infections, especially respiratory and diarrheal illnesses. Infertility and delayed growth and development in children are potential consequences.
Conversely, excessive preformed vitamin A intake can lead to toxicity (hypervitaminosis A) because the body stores excess amounts in the liver. Acute toxicity, often from a single large dose, can cause severe headaches, nausea, vomiting, dizziness, irritability, drowsiness, abdominal pain, and increased brain pressure, especially in children.
Chronic toxicity develops from prolonged high-dose intake. Symptoms include dry, rough, or peeling skin, hair loss, cracked lips, and mouth ulcers. Bone pain and swelling are common, and chronic excess can increase the risk of fractures and osteoporosis, particularly in older adults. Liver damage, confusion, blurred vision, and sun sensitivity are potential effects.
For pregnant individuals, high doses of preformed vitamin A are concerning due to the risk of severe birth defects. While large amounts of provitamin A carotenoids can cause harmless skin yellowing, they do not lead to vitamin A toxicity. Therefore, avoid high-dose supplementation without professional medical guidance.