We all know that there are certain substances called vitamins and minerals that we are supposed to consume in certain amounts each day in order to achieve and maintain good health. But if you haven’t been in a health class in a few years you may have forgotten the benefits, recommended daily allowances and sources of these substances. Consider this article a refresher on the first in the alphabet of vitamins, vitamin A.
What we know as vitamin A is actually a family of fat-soluble vitamins such as retinol, which is considered one of the most usable forms of vitamin A. It is found in animal products, such as eggs and liver.
Plant sources of vitamin A have what is known as provitamin A carotenoids, which are the dark pigments in plants such as dark leafy greens. This provitamin A carotenoids can be converted into vitamin A, which is important for vegetarians and others who might not eat the animal products that are rich in this vitamin.
Carotenoids have been in the news a lot lately, particularly forms such as beta carotene, lycopene and lutein, which are powerful antioxidants that protect the body’s cells from damage caused by pollution, aging and other factors. While lycopene and lutein are not provitamin A carotenoids, they are still important to a healthy diet and have been shown to have health benefits such as preventing heart disease and protecting eye health. Beta carotene is the carotenoid most easily converted into vitamin A. One source for beta carotene that everyone probably is familiar with is carrots.
Vitamin A is beneficial to the body because it helps cells. It aids in cell division and differentiation (helping a cell know what job it is supposed to do or what it will become) and maintains the surface lining of the intestinal, urinary and respiratory tracts. It also plays a role in immune-system support, helping your body fight off disease by producing white blood cells. Vitamin A also plays a role in reproduction, bone growth and in vision (your mother wasn’t kidding when she told you to eat your carrots so you could see well).
But how much vitamin A is enough?
The recommended daily intake is measured in micrograms, a very small unit of measurement. Toddlers need about 300 micrograms, older children about 400, pre-teens 600, teen and adult men about 900 micrograms, and non-nursing or pregnant women need about 700 micrograms a day. The needed amount goes up slightly during pregnancy and jumps dramatically (to about 1,300 micrograms) when nursing.
How much is that when you’re talking about actual food? You can get 100 percent of your daily allowance of vitamin A from a cup of raw cantaloupe. A standard serving of canned chunky vegetable soup will probably give you slightly more than 100 percent. A carrot gives you 400 percent and 3 ounces of cooked beef liver gives you 610 percent (chicken liver would give you 280 percent of the recommended allowance). Other animal sources of vitamin A include eggs and whole milk.
If you don’t want to resort to eating liver, there are many vegetables that are high in vitamin A. In addition to cantaloupe and carrots, servings of sweet potatoes, spinach and mango will give you more than 100 percent of the daily allowance of vitamin A. Other good sources are kale, fortified oatmeal or cereal and tomato juice.
Don’t worry if your diet includes a lot of these foods. It takes a fair amount of vitamin A to make you sick, and it usually has to be consumed over a long period of time. Because vitamin A is fat soluble, the excess is stored in the liver, so that is where damage will occur if you get too much vitamin A for a long time. A common cause of what is called hypervitaminosis A is getting too much A through supplements or from animal products. The vitamin A that comes from beta carotene is not associated with this ailment, so if your big doses of A come from veggies, you should be fine.
The upper tolerance level has been measured at more than twice the recommended daily amount of vitamin A. Consuming more than this won’t necessarily make you sick, but you might want to cut back if you’re regularly eating a lot more than that, or stop taking any vitamin supplements containing vitamin A if you get enough through food.
Signs of acute vitamin A toxicity include nausea, lack of muscle coordination, headache, dizziness and blurred vision. Hypervitaminosis A can cause liver abnormalities, birth defects and bone loss that could result in osteoporosis.
Vitamin A deficiency is rare in the industrialized world, but in developing countries this lack can cause xeropthalmia, damage to the cornea, and it often causes children to go blind. Night blindness is often thought of as one of the warning signs of vitamin A deficiency. Lack of vitamin A can also make it harder for the body to fight infection, which can lead to other health problems, particularly pneumonia and other respiratory or diarrheal infections.
Vegetarians who do not consume animal products may need to supplement (make sure the vitamin A pills you are using come from a vegetarian source) or make sure to eat a variety of vegetables, including dark leafy greens and other dark vegetables each day. It is certainly possible to get enough vitamin A from vegetables without using supplements or fortified foods, but if you don’t like greens or carrots you may need some extra help.
Some studies suggest that diets high in vitamin A and beta carotene can reduce the risk of lung cancer. Others show that high doses of vitamin A may interfere with calcium and vitamin D absorption, thus increasing risk for osteoporosis. Most of these studies had to do with supplements and animal products eaten at more than three times the recommended allowance for vitamin A, so it’s likely that this is not a major concern for people who get vitamin A in moderation or from animal sources.
Vitamin A is an important building-block of our bodies and it is easy to get enough from a variety of sources, even if you don’t like liver.
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