When we talk about vitamins, most people usually think about vitamin C and those in the ‘B’ family because of their popularity. You don’t often hear much about Vitamin A, despite is being one of the most important vitamins for your health.
Vitamin A is is essential for a variety of health aspects; it’s support eye function, aids in the differentiation of cells of the skin and mucous membranes, helps the body fight off infection through strengthening the immune system and supports growth and helps bones grow, which is why it’s especially important for children. Rickets, abnormal bone growth of the legs in children, is a direct result of Vitamin A deficiency.
Through its role with cell growth and division, Vitamin A has an important impact on the normal formation and maintenance of the heart, lungs, kidneys and other vital organs. A lack of Vitamin A in the diet can result in hair loss, skin problems, dry eyes, night blindness and increased susceptibility to infections.
Types of Vitamin A
There are two types of vitamin A.
Pro-vitamin A is found in plant-based foods such as fruits and vegetables. The most common type of pro-vitamin A is beta-carotene, a carotenoid that produces dark pigments in plant foods.
Preformed Vitamin A, also called retinol, is found in animal products. Notable sources of it include fortified milk, eggs, meat, cheese, liver, halibut fish oil, and kidneys.
Beta-carotene is a carotenoid. Carotenoids are naturally occurring pigments found in plants and are responsible for the vibrant colors of some fruits and vegetables. Beta-carotene, for example, gives carrots their orange color. As much as 50 percent of Vitamin A in a typical diet is provided by beta-carotene and other carotenoids derived from plants.
Once ingested, beta-carotene is either converted into Vitamin A (retinol), which the body can use in a variety of ways, or it acts as an antioxidant to help protect cells from the damaging effects of harmful free radicals.
A small number of carotenes, including beta-carotene, are often called “provitamin A” because they are a precursor to production of vitamin A in the body.
Retinol is sometimes called “true” Vitamin A because its natural form can easily be metabolized, making it easily absorbed.
As was previously mentioned, this class of Vitamin A compounds plays an important role for healthy vision, cell and bone tissue growth, as well as immune function.
Vitamin A in this form can only be found naturally in animal products like liver, eggs, and milk, so vegetarians and (especially) vegans need to be aware of where they’re getting their Vitamin A.
Gene expression refers to the process of the DNA being converted by enzymes in order to make a specific protein.
Not all components of DNA in a cell are expressed, only certain ones. They are expressed when an enzyme called DNA Polymerase III comes in and makes a single strand copy of DNA to make mRNA – the mRNA then goes on to make a protein, which is called a gene product.
Vitamin A in the retinoic acid form plays an important role in regulation of gene expression. Once retinol has been taken up by a cell it can be oxidized to retinal, which can be oxidized to retinoic acid.
Retinoic acid can bind to different nuclear receptors to initiate or inhibit gene expression. It calls the shots of which genes are expressed and which are suppressed, therefore it is highly important for the growth and development of the body. 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.
Vitamin A is required for normal functioning of the immune system, as retinol and its metabolites are necessary to maintain the integrity and function of skin and mucosal cells (lining airways, digestive and urinary tract), acting as a barrier and forming the body’s first line of defense against infection. Vitamin A is essential for the immune system’s overall function as it plays a central role in the development and differentiation of white blood cells such as lymphocytes, which play critical roles in immune response.
Foods Rich In Vitamin A
Foods rich in vitamin A are typically cheeses, leafy greens/mixed vegetables, fruits, fish and organ meats.
- Cheddar Cheese
- Roquefort Cheese
- Hard-Boiled Eggs
- Blue cheese
- Limburger cheese
- Goat Cheese
- Goose Liver Pate
- Bluefin Tuna
- Cod Liver Oil
- King Mackerel
- Liver Sausage
- Lamb Liver
- Beef Liver
- Cream Cheese
- Feta Cheese
- Passion Fruits
- Red Pepper
- Swiss Chard
- Romaine Lettuce
- Turnip Greens
- Winter Squash
Recommended Dietary Allowance (RDA)
Though everyone needs Vitamin A, the specific need for each person may vary.
The Recommended Dietary Allowance (RDA) for adult men (ages 19 and older) is 900 micrograms (mcg) per day.
For adult women (ages 19 and older), it is 700 mcg per day. Pregnant and breastfeeding women 19 years old and/or older have different daily dietary intakes, which are 770 mcg and 1,200 mcg respectively.
With this in mind, try to keep a balanced diet that contains varieties and combinations of the foods and food groups mentioned above.
Symptoms of Excessive Vitamin A
It is possible to get too much Vitamin A. Excessive intake of Vitamin A from vegetables (such as carrots) may result in a yellowing of the skin, but isn’t usually harmful.
Taking Vitamin A supplements can easily push you past your RDA. Symptoms of excess intake depend upon the duration of high Vitamin A intake and can include dry skin, rash, nausea, vomiting, fatigue, weakness, headaches, and hair loss.
Large doses of preformed Vitamin A (particularly in retinol supplements) can interfere with the function of Vitamin D and increase the risk for bone fractures and birth defects of fetuses when taken by pregnant women.
Beta-carotene supplements carry less risk, but some studies have found that large doses have been linked to higher risk of lung cancer among smokers.
Both types of supplements have been found to increase triglycerides (fats in the blood).
Risks of Taking VItamin A Supplements
Even when a Vitamin A supplement is taken within a recommended dose, it still may not be appropriate for everyone.
Diabetics and those with liver disease need to take Vitamin A supplements under the supervision of a health care provider. Smokers and heavy drinkers are advised not to take beta-carotene supplements. Women who are pregnant or hope to be soon are advised not to take additional vitamin A and to avoid synthetic forms of vitamin A. Children are at a greater risk for experiencing side effects from too much Vitamin A at lower levels.
Additionally, there are a number of recognized drug interactions that may hinder or amplify the effects of the medication when used in conjunction with Vitamin A. Other medications may block the absorption of vitamin A. If you are already on medication, you should talk to your health care provider before taking a Vitamin A in supplement.
It’s easy enough with our diet to get sufficient Vitamin A. Vitamin A is an essential vitamin that’s beneficial for many aspects of health.Share!