Vitamin A is needed for healthy vision, bones, reproduction, cell division and building immunity. Vitamin A comprises a group of compounds in our body that help fight infections and destroy harmful viruses and bacteria. It also aids the maintenance of healthy surface linings of our intestines, respiratory and urinary tracts and skin and mucous membranes and eyesight.
Vitamin A is a fat-soluble vitamin and that means the body can store it for future use and it is best consumed through food. Our daily diet should be the best provider of Vitamin A. The recommended dosage of Vitamin A in our diet is:
- 0.7 mg a day for men
- 0.6 mg a day for women
Sources of Vitamin A
Vitamin A is available both through animal and plant sources. But Vitamin A is better absorbed in the body when it comes from animal products than plant sources. Vitamin A from animal sources is called preformed Vitamin A. Preformed Vitamin A is absorbed in human bodies in the form of retinol, an active form of Vitamin A. Retinol sources include whole milk and beef liver, eggs, cheese, oily fish and fortified food products like yoghurt and margarine and some breakfast cereals.
Vitamin A that is available from plant sources, namely colourful vegetables and fruits is called provitamin A carotenoids. These are also converted into retinol in the body. Provitamin A is available through plants that have beta carotene and alpha carotene. These are also said to serve as antioxidants and hence protect cells from free radicals and help fight illnesses. Carrots, spinach, sweet potatoes and fruits like cantaloupes, apricots, papaya, mango are rich in carotenoids.
The DV (Daily Value) recommended dietary allowance for Vitamin A is 5000 IU (International Units). Food providing less than 5 % of the DV is a low source of Vitamin A while 10 % of more is a good source according to U.S. Department of Agriculture's Nutrient Database. However nutritionists suggest that foods that provide a lower percentage of Vitamin A can contribute to a healthy diet.
Approximately 250,000 to 500,000 malnourished children in the developing world become blind each year from a deficiency of vitamin A. In countries like United States Vitamin A deficiency is usually associated with excess alcohol in take or dietary intake deficiencies.
Deficiencies in Vitamin A can lead to lack of immunity in fighting disease and viruses. In poorer nations, children often die of complications arising of infectious disease like measles or pneumonia due to Vitamin A deficiency. Night blindness, damage to the retina and cornea are also attributed to Vitamin A deficiency. In children it can lead to slow bone development, diarrhea and low metabolic activity.
Vegetarians who do not consume dietary products or eggs need to have their needs for Vitamin A met. To do this they must include atleast five servings of fruits and vegetables to offset the lack of the vitamin.
Excess doses of Vitamin A about 10 times of the RDA or Recommended Dietary Allowance can lead to toxicity. This will manifest itself through dry itchy skin, loss of appetite and nausea. Bone and joint pain can also be a sign of excess vitamin A. the elderly and women past menopause suffering from osteoporosis and limited exposure to sunlight can also suffer due to excess Vitamin A as it weakens bones and can lead to fractures. Lack of vitamin D is also likely to be harmful as it acts upon Vitamin A absorption.
Pregnant women in low doses can cause birth defects in pregnant women and it is usually suggested that pregnant women do not consume Vitamin A supplements without doctor supervision. Pregnant women are often suggested to avoid consuming liver as it contains high levels over the recommended dose of 1.5 mg per day of Vitamin A.
The association between Vitamin A intake and diets rich in beta carotene helping to lower cancer is being debated as many studis have not proved that it helps protect against diseases like cancer. Researchers are also debating the link between osteoporosis and excessive presence of Vitamin A in the body.
There is no evidence that Vitamin A supplements can prevent cancer or heart attacks. Health practitioners and nutritionists recommend that the best way to include vitamin a is through a healthy and balanced diet. They suggest the intake of a multivitamin which will also include the necessary 5000 IU of vitamin A. Additional vitamin A supplements are not recommended for normal people.
Did You Know?
- Dietary Supplement Fact Sheet: Vitamin A and Carotenoids
- Vitamin A
- USDA National Nutrient Database