Vitamin A is a fat-soluble vitamin. Vitamin A helps form and maintain
healthy teeth, skeletal and soft tissue, mucous membranes, and skin. It
is also known as retinol because it generates the pigments in the retina.
Vitamin A promotes good vision, especially in dim light. It may also be
required for reproduction and breast-feeding.
Vitamin A does much more than help you see in the dark. It stimulates
the production and activity of white blood cells, takes part in remodeling
bone, helps maintain the health of endothelial cells (those lining the
body's interior surfaces), and regulates cell growth and division. This
latter role had researchers exploring for years whether insufficient vitamin
A caused cancer. Several studies have dashed this hypothesis,(1) as have
randomized trials of supplements containing beta carotene, a precursor
of vitamin A.
Beta-carotene, which has antioxidant properties, is a precursor to Vitamin
A. Antioxidants destroy free radicals, which are unstable substances that
can react with and damage cells, tissues and organs. Free radicals are
believed to be associated with many of the degenerative changes seen with
aging. However, it is not yet known whether antioxidants can prevent these
changes and studies have been conflicting. For example, one study found
increased cancer risk in smokers who took high doses of beta carotene.
If you don't get enough Vitamin A, you are more susceptible to infectious
diseases and vision problems. However, large doses of Vitamin A can be
toxic. Large doses can also cause abnormal fetal development in pregnant
women. Increased amounts of beta-carotene can turn the color of skin to
yellow or orange. The skin color returns to normal once the increased
intake of beta-carotene is reduced.
Food Sources: Vitamin A comes from animal sources, such as eggs, meat,
milk, cheese, cream, liver, kidney, cod and halibut fish oil. However,
all of these sources - except for skim milk that has been fortified with
Vitamin A - are high in saturated fat and cholesterol.
The precursor form, beta-carotene, is found in plants. Sources of beta-carotene
are carrots, pumpkin, sweet potatoes, winter squashes, cantaloupe, pink
grapefruit, apricots, broccoli, spinach, and most dark green, leafy vegetables.
The more intense the color of a fruit or vegetable, the higher the beta-carotene
content. These vegetable sources of beta-carotene are free of fat and
cholesterol.
The body regulates the conversion of beta-carotene to Vitamin A based
on its needs.
