We know vitamins are good for us, but do you know exactly what each one is good for? Sure, we know vitamin C is good for a cold, but do you know why? In this series, we will take a look at each vitamin and delve into what role each one has to play in nutrition.
Vitamin A is a fat-soluble vitamin. There are two forms in which it is found: as provitamin A (retinoids), and as performed vitamin A (carotenoids). Retinoids – which include retinol, retinal, and retinoic acid – are readily used by the body and are found in animal sources. It is retinol, however, that is most used as it can convert into retinal and retinoic acid.
Retinol affects the immune system and vision. When the body uses retinol for vision, it is absorbed and transported to the retina of the eye. From there, it is oxidized into retinal, which helps the eye with night vision. A lack of retinol can result in poor night vision, or night blindness.
Retinoic acid plays an important role in gene expression. According to Nutri-Facts, “retinoic acid can bind to different nuclear receptors to initiate or inhibit gene expression. Through the regulation of the expression of specific genes, retinoic acid plays a major role in cellular differentiation; the specialization of cells for highly specific physiological roles.” It's the conversion of retinol into retinoic acid that is important not only in the differentiation of cells, but in their growth as well.
The other compound of vitamin A, carotenoids, comes from plant food sources. They are the reason our fruits and vegetables come in pigments of bright yellow, orange, and red. There are over 600 carotenoids, but it's the carotenoid beta-carotene that is the most sought after part of vitamin A. Most known for being found in carrots, this special antioxidant plays an important role in immune system, healthy skin, and vision.
The antioxidants in beta-carotene combat free-radicals, preventing damage that could cause disease such as cardiovascular disease. When beta-carotene is ingested into the body, it is converted into retinol. The body will, however, only convert as much beta-carotene as it needs, so it's considered to be a safe source of vitamin.
Beyond supporting vision, vitamin A is taken for skin conditions, bone growth, leukemia, cell growth, and maintenance of vital organs such as the heart and lungs. There are studies that have been conducted to determine if vitamin A plays a significant role in various conditions such as HIV, but results are inconclusive.
Studies have, however, shown a possible link to cancer prevention . People who eat more foods with beta-carotene are possibly at a lower risk for various cancers. The reason for this is the antioxidants found in beta-carotene attack the damaging free-radicals that are responsible for cancerous cell growth. It has not been proven, however, that it will prevent cancer.
The recommended dose of vitamin A is 700 mcg in an adult female and 900 mcg in an adult male. In order to obtain vitamin A, supplements and food rich in vitamin A should be consumed. Sweet potatoes, black-eyed peas, carrots, pumpkins, spinach, fortified cereal, and beef liver all contain high amounts of vitamin A.
Vitamin A deficiencies are rare, but they do occur. A common symptom in deficiency is xerophthalmia, which is the inability to see in low light conditions. High intakes can have adverse reactions as well. According to the National Institutes of Health, symptoms include “dizziness, nausea, headaches, coma, and even death. High intakes of preformed vitamin A in pregnant women can also cause birth defects in their babies.” When pregnant, talk to your doctor about how much vitamin A you should be taking.
On the other hand, too much vitamin A can have adverse effects. In fact, it can be toxic as it can lead to liver failure. Other symptoms of too much vitamin A include dry skin, headache, fatigue, nausea, diarrhea, and hair loss. If you are experiencing these symptoms and you feel it may be from too much vitamin A, then consult your physician.
As always, it's best to consume nutrients through food. Supplements should be used as a second source if consuming adequate levels through food, or other health related issues, prevents one from achieving the daily requirements.