Vitamin A, often referred to as retinol, belongs to the group of essential vitamins known as fat-soluble vitamins, which dissolve in and get absorbed with fat molecules. Although the body can store fat-soluble vitamins in the fatty tissues and liver, you still need the daily recommended amount of vitamin A.
Daily Intake
The daily recommended intake of vitamin A varies based on age and gender. Children between ages 9 and 13 should consume 600 micrograms, or mcg, of vitamin A per day, according to The National Institutes of Medicine Food and Nutrition Board. Women 14 and older need 700 mcg per day, while men in the same age range need 900 mcg per day. Vitamin A produces pigments in the retina of the eye, making it vital to good vision, especially in low-light situations. Vitamin A also supports the production of healthy tissues, including skin, teeth, mucous membranes and bones. Vitamin A contributes to a healthy immune system by producing white blood cells that fight infection.
Sources
Many different foods contribute to daily vitamin A intake. Animal sources, such as eggs, milk and liver, contain pre-formed vitamin A. The human body absorbs this type of vitamin A as retinol, the most active form of vitamin A. Plants also contain vitamin A, but in the form known as a provitamin A carotenoid. Beta-carotene, the most common type of provitamin A carotenoid, is found in orange vegetables and fruits, including carrots, cantaloupe and apricots. Other sources include green leafy vegetables such as spinach and sweet red peppers. In the U.S., carotenoids account for approximately 26 percent of a man's daily vitamin A intake and 34 percent of a woman's daily vitamin A intake.
Deficiency
The typical American diet provides the recommended daily intake of vitamin A, making deficiency rare. Less-developed countries, however, suffer from vitamin A deficiencies. Although the body can store some vitamin A, consistently failing to consume the recommended intake due to a lack of food causes 250,000 to 500,000 children to go blind each year, according to the National Institutes of Health Office of Dietary Supplements. Children in these countries also develop complications from infectious diseases due to a diminished immune system caused by vitamin deficiency.
Tolerable Upper Limit
Consuming too much vitamin A through diet is not a concern. When the stores of vitamin A in the body are high, the body stops converting carotenoids into vitamin A. Because much vitamin A intake comes from carotenoids, this reduces the risk of reaching the tolerable upper limit, which describes the amount necessary to cause adverse health effects. Taking vitamin A supplements can lead to too much vitamin A in the body. The National Institutes of Health sets the tolerable upper limit for vitamin A at 3,000 mcg per day for adult men and women.
Member Comments