Vitamin A in the diet
Vitamin A is a yellow primary alcohol that is derived from carotene. The recommended daily allowance of Vitamin A is 3 mg for men and 2.4 mg for women.
Where can vitamin A be obtained in the diet?
One way vitamin A can be obtained is by manufacturing it from provitamin A carotenoids. The most efficient carotenoid is beta-carotene which is found in many darkly colored fruits and vegetables such as carrots, broccoli, squash, spinach, kale, and sweet potatoes. Vitamin A is also found in animal products such as milk, butter, cheese, eggs and liver. Most fat free milk products are fortified with vitamin A to replace the vitamin A lost when the when the fat is removed. Many breakfast cereals are also fortified with vitamin A.
Vitamin A's role in the body
Vitamin A is necessary for the formation and maintenance of skin, mucous membranes, bones, and teeth. Vitamin A also effects reproduction, cell division and cell differentiation. Vitamin A influences vision by helping to increase night vision (the ability to see in the dark). Vitamin A may also help regulate the immune system by increasing the effectiveness of lymphocytes which are a type of white blood cell that fights infections. Some carotenoids have also been shown to function as antioxidants as well as being a source of Vitamin A.
Results of a vitamin A deficiency in the diet
The primary symptom of vitamin A deficiency is difficulty adapting to darkness, also known as night blindness. Vitamin A deficiency also makes the cornea very dry and thus promotes damage to the retina and cornea. A deficiency in vitamin A causes the cells lining the lungs to lose their ability to remove disease-causing microorganisms. This increases susceptibility to bacterial infection. Skin dryness may also occur as a result of vitamin A deficiency.
Results of vitamin A toxicity in the diet
High storage levels of vitamin A in the body can lead to birth defects, liver abnormalities and reduced bone mineral density which can lead to osteoporosis. Excessive amounts of Vitamin A can also stop menstruation and cause skin rashes. It is also dangerous to consume very large amounts of vitamin A over a short period of time. Effects of doing this include nausea, vomiting, headache dizziness and blurred vision.