Acute or chronic vitamin A toxicity is defined as retinol levels greater than 100 mcg/dl.
Hypervitaminosis A has been reported in almost 50% of patients taking 150% of the RDA for vitamin A, in the form of retinol, between 6 to 12 months after laparoscopic sleeve gastrectomy. Chronic vitamin A toxicities are associated with loss of hair; dry mucous membranes; dry, rough skin; and even cortical bone loss and fractures.
It’s only a semi-myth that eating carrots will help you see in the dark. A carrot’s main nutrient, beta-carotene (responsible for this root vegetable’s characteristic orange color), is a precursor to vitamin A and helps your eyes to adjust in dim conditions. Vitamin A can’t give you superpowers of night vision or cure your dependence on contact lenses, but eating an adequate amount will support eye health.
Vitamin A also stimulates the production and activity of white blood cells, takes part in remodeling bone, helps maintain healthy endothelial cells (those lining the body’s interior surfaces), and regulates cell growth and division such as needed for reproduction.
The two main forms of vitamin A in the human diet are preformed vitamin A (retinol, retinyl esters), and provitamin A carotenoids such as beta-carotene that are converted to retinol. Preformed vitamin A comes from animal products, fortified foods, and vitamin supplements. Carotenoids are found naturally in plant foods. There are other types of carotenoids found in food that are not converted to vitamin A but have health-promoting properties; these include lycopene, lutein, and zeaxanthin.
Vitamin A (retinol, retinoic acid) is a nutrient important to vision, growth, cell division, reproduction and immunity. Vitamin A also has antioxidant properties. Antioxidants are substances that might protect your cells against the effects of free radicals — molecules produced when your body breaks down food or is exposed to tobacco smoke and radiation. Free radicals might play a role in heart disease, cancer and other diseases.
Vitamin A is found in many foods, such as spinach, dairy products and liver. Other sources are foods rich in beta-carotene, such as green leafy vegetables, carrots and cantaloupe. Your body converts beta-carotene into vitamin A.
As an oral supplement, vitamin A mainly benefits people who have a poor or limited diet or who have a condition that increases the need for vitamin A, such as pancreatic disease, eye disease or measles. If you take vitamin A for its antioxidant properties, keep in mind that the supplement might not offer the same benefits as naturally occurring antioxidants in food.
The recommended daily amount of vitamin A is 900 micrograms (mcg) for adult men and 700 mcg for adult women.
Vitamin A is currently listed on the Nutrition Facts label measured in international units (IU). However, the Institute of Medicine lists the Recommended Dietary Allowances (RDA) of vitamin A in micrograms (mcg) of retinol activity equivalents (RAE) to account for different absorption rates of preformed vitamin A and provitamin A carotenoids. Under the Food and Drug Administration’s (FDA) new food and dietary supplement labeling regulations, as of July 2018 large companies will no longer list vitamin A as IU but as “mcg RAE.”
- RDA: The Recommended Dietary Allowance for adults 19 years and older is 900 mcg RAE for men (equivalent to 3,000 IU) and 700 mcg RAE for women (equivalent to 2,333 IU).
- UL:The Tolerable Upper Intake Level is the maximum daily intake unlikely to cause harmful effects on health. The UL for vitamin A from retinol is 3,000 micrograms of preformed vitamin A.
The evidence suggests that eating a variety of foods rich in vitamin A, especially fruits and vegetables, is protective from certain diseases, though the health benefit of vitamin A supplements is less clear.
Many breakfast cereals, juices, dairy products, and other foods are fortified with retinol (preformed vitamin A). Many fruits and vegetables and some supplements contain beta-carotene, lycopene, lutein, or zeaxanthin.
- Leafy green vegetables (kale, spinach, broccoli), orange and yellow vegetables (carrots, sweet potatoes, pumpkin and other winter squash, summer squash)
- Red bell pepper
- Cantaloupe, mango
- Beef liver
- Fish oils
- Fortified foods
Vitamin A deficiency is rare in Western countries but may occur. Conditions that interfere with normal digestion can lead to vitamin A malabsorption such as celiac disease, Crohn’s disease, cirrhosis, alcoholism, and cystic fibrosis. Also at risk are adults and children who eat a very limited diet due to poverty or self-restriction. Mild vitamin A deficiency may cause fatigue, susceptibility to infections, and infertility. The following are signs of a more serious deficiency.
- Xerophthalmia, a severe dryness of the eye that if untreated can lead to blindness
- Nyctalopia or night blindness
- Irregular patches on the white of the eyes
- Dry skin or hair