Vitamin A is one of the four fat-soluble vitamins which are essential for good health. It has an important role as an antioxidant that prevent damage to cells by free radicals. Adequate levels are important for good vision, and poor night vision is one of the first symptoms of deficiency of this vitamin.It is also necessary for proper function of the immune, skeletal, respiratory, reproductive systems, and connective tissue (skin, hair and nails).
Adequate amounts of this vitamin are undoubtedly necessary for maintaining good health. It is essential for proper functioning of retina, where it may act to prevent night blindness and to reduce the risk of macular degeneration which is the most common cause of blindness in the elderly. There is also evidence that adequate amounts in the form of carotenoids can reduce the risk of certain cancers, heart attack and stroke.
How much we need?
Intake of supplements of vitamin A will prevent deficiency in most cases, and it is best to take supplements in the form of carotenoids to avoid the toxicity of the active form this vitamin.
Recommendations for daily intake of beta carotene varied between 6 and 30 mg per day, and usually is 15mg a day.
Vitamin A sources
There are two primary forms of vitamin A.
Retinoids, the active form of vitamin A, are found in animal products like meat, whole milk and eggs. The liver is particularly rich in this vitamin, given that it is a repository for excess of this vitamin.
Precursors of vitamin A – carotenoids are found in orange vegetables and herbaceous plants such as sweet potatoes, carrots, spinach, zucchini, cabbage, kale and turnip.
Richest in Vitamin A are fresh vegetables, while frozen and canned vegetables loose some quantities of this vitamin. Alpha and beta carotene, as well as some lesser known carotenoids can be converted into vitamin A in the small intestine. This happens when the body needs vitamin A, and therefore is no possibility of an overdose, as is the case with active forms of this vitamin.
Supplements may contain the active form of vitamin A or its precursor. The active form may be better for those who have problem with converting carotenoids into active vitamin, such as in people older than 55 years who have problems with absorption of fat. In such cases, it can also be used retinyl palmitate, a form of vitamin A that is soluble in water.
Symptoms include loss of appetite, decreased function of the immune system by frequent infections (especially respiratory), hair loss, rashes, dry skin and eyes, vision problems including night blindness, poor growth and fatigue. Usually symptoms appear after longer lasting deficiency of this vitamin.
Lack of vitamin A is more likely to occur in people who are malnourished, alcoholic, chronically ill, and those with disturbed absorption of fat. Another group of people with increased risk of deficiency of vitamin A is people with type 1 diabetes, which is not well controlled.
Risk factors for deficiency
Those who consume alcohol beverages are more likely to have a shortage of vitamin A, also higher doses of this vitamin need people who take certain medications, including birth control pills, methotrexate, cholestyramine and other drugs that sequester bile.
Other risk group are people who are malnourished, chronically ill, people in postoperative stage or chemotherapy. Also chronic diarrhea, cystic fibrosis, and liver or kidney disease can lead to vitamin A deficiency. Diabetics are often deficient in this vitamin, but also more vulnerable to its toxic effects, so before they start using any supplements they should consult a doctor.
Vitamin A Toxicity
Overdose can occur when taking large doses of the active form of vitamin A, and big part of these quantities that will not be used by the body are stored in the liver and fatty tissues. Symptoms include dry lips and skin, pain in bones and joints, diarrhea, vomiting, headaches, blurred or double vision, confusion, irritability, fatigue and tense fontanel in babies, as well as very high levels can lead to a deficiency of vitamin C, E and K. Symptoms are usually reversible, but request medical advice. They usually appear after 6 hours of acute overdose and it takes several weeks to disappear.
Children are more sensitive to high levels of vitamin A than adults, and because of that it should be paid particular attention to dosage. It is especially important to avoid overdose during pregnancy because it may cause miscarriage and fetal malformations. People with kidney disease are also at high risk for vitamin A toxicity and should not take supplements without consulting a doctor.