Table of Contents
- What is Vitamin A?
- Signs Of a Vitamin A Deficiency
- Health Benefits of Vitamin A
- Other Vitamin A Benefits
- Best Vitamin A Foods
- Vitamin A Precautions
- Vitamin A Risks
- Vitamin A Dosing
- Vitamin A Interactions
Vitamin A also called retinol and retinal, is vital to many functions within the human body.
The eyes and immune system, for example, can’t function properly without sufficient amounts of Vitamin A.
In fact, vitamin A deficiency is the most common cause of childhood blindness.
However, vitamin A in excess is counterproductive to health in many cases and can result in vitamin toxicity.
Before starting a vitamin A regimen, it’s important for you to understand the full role vitamin A plays within the body, its health benefits, recommendations for dosing for your age and gender, high-risk groups, and vitamin A’s interactions with other disease processes and medications.
Knowing these facts can help you achieve safe and beneficial health rewards from vitamin A.
What is Vitamin A?
If you’re like most people, you’ve seen vitamin A called by various names on food and product labels, and you’ve probably wondered if it’s all the same thing or not.
While all the name-calling is unavoidable from a medical and biologic standpoint, the various names associated with vitamin A can cause a great deal of confusion for the medical layperson just trying to read a label and make an informed decision about their vitamin A intake.
Retinal, retinol, and beta-carotene, for example, are often used interchangeably with vitamin A.
Let’s look at what this all means.
What is vitamin A? It’s is a fat-soluble vitamin.
Vitamin A is an umbrella term for a group of compounds that are either found naturally in food sources, or that is converted to vitamin A within the body.
The two types of vitamin A that are found in the diet are provitamin A carotenoids and preformed vitamin A.
The most commonly known and important provitamin A carotenoid is beta-carotene, a plant pigment the body later converts into vitamin A.
Provitamin A carotenoids are found in plant-based foods, such as fruits and vegetables.
You’ve probably heard beta-carotene mentioned if your ophthalmologist has ever told you why carrots are so fantastic for your eye health.
Preformed vitamin A, which consists of retinol and retinyl ester, are found in animal-based foods, including meats, fish, and dairy.
The body uses retinol to make other retinoids.
While some carotenoids, like lutein, are not converted into vitamin A, both preformed vitamin A and provitamin A, for the most part, must be metabolized within the body in order to be utilized for health purposes as “vitamin A.”
It’s first converted to the active form of vitamin A, which is retinal.
For storage in the liver, it’s then converted into retinoic acid and retinyl esters.
And this is why the complex little vitamin is often called vitamin A and retinal (the active form) interchangeably.
Vitamin A plays an important role in reproduction, immunity, cell development, skin health, bone development and growth, vision, and heart, lung, and kidney function.
Retinol is particularly essential to skin health. More on the details of these benefits in a minute.
Signs Of a Vitamin A Deficiency
Because of its abundance in plant and animal sources, vitamin A deficiency in developed countries like the United States is a rarity.
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Such nutritional vitamin deficiencies are most commonly seen in underdeveloped and low-income countries where famine is common and food varieties are limited for adults, children, and pregnant women.
The World Health Organization, or WHO, has some interesting data on vitamin A deficiency, including:
- It’s the leading cause of preventable blindness in children, affecting anywhere from 250,000 to 500,000 children each year, and half of these children will die from complications within a year of going blind.
- It increases the risk of death and disease from illness and infection.
- It can cause night blindness in pregnant women.
- It’s an escalating problem in half the world’s countries, particularly South-East Asia and Africa.
- Estimates show around 250 million preschool-aged children suffer a deficiency of vitamin A (2).
In developed countries, like the U.S., vitamin A deficit can be seen when individuals alter their diets in highly restrictive ways.
If you’ve ever undergone an elimination diet, then you certainly know about restrictive diets.
It’s essentially when a food source or groups of food sources are eliminated and then reintroduced to determine the root of allergies and health problems.
Such diets are excellent diagnostic tools, but they can also easily lead to nutritional deficiency if maintained long-term without additional supplementation of the missing vitamins and nutrients.
A deficiency secondary to a disease process is the most common cause of retinol deficiency in adults in developed countries.
These diseases affecting the liver, pancreas, gallbladder, and intestines, such as seen with IBS, celiac disease, chronic diarrhea, giardiasis, bile duct obstruction, cirrhosis, and cystic fibrosis, can create vitamin A deficiencies due to the body being unable properly to absorb, store, or convert vitamin A (3).
The National Institute of Health, Office of Dietary Supplements, cites studies showing that as many as 40% of cystic fibrosis patients suffer from a vitamin A deficit.
Preterm infants may also be at risk for vitamin A deficiency.
Often the infants are not born with sufficient vitamin storage, such as of retinol, because of their underdeveloped system.
Studies have shown that these levels often stay low in premature infants for the first year of their lives, leaving them at increased risk for respiratory, gastrointestinal, and eye diseases.
The symptoms of a retinol deficiency include:
- Visual impairment, disturbance, and blindness.
- Drying, scaling, and thickening of the skin.
- Impaired immunity.
- Keratinization of the mucous membranes of the GI, urinary, and respiratory tracts.
- Growth retardation in children (5).
The American Academy of Ophthalmology describes the visual disturbances associated with vitamin A deficit as a process that begins with night blindness and difficulty seeing in low-light settings.
As the deficiency continues, the conjunctiva dries out and is prone to ulcerations.
And, if the deficiency goes untreated, it can cause complete vision loss and permanent blindness (6).
Other reported symptoms include dull hair, dandruff, fatigue, depression, and insomnia.
Health Benefits of Vitamin A
As an antioxidant and powerful systematic player in everything from vision and skin to immunity and the skeletal system, vitamin A’s benefits are quite numerous.
Here are some of the most highly researched and proven health benefits of topical, supplemental, and dietary forms of retinol.
Clearly, a sufficient amount of vitamin A is essential to prevent vision problems.
However, you should also know that the benefits of retinol can stave off many other vision disease processes.
Vitamin A keeps the eye moist and enables it to adjust to bright and dark changes in light, thereby improving night vision.
Retinol helps to nourish the retina in the eye.
Vitamin A has been studied in improving glaucoma and decreasing the risk of macular degeneration with significant success rates.
Look no further than a six-year, $5 million dollar retinitis pigmentosa study that specifically focused on vitamin A, to show you just how interconnected the eyes and vitamin A are; it’s almost unprecedented for a vitamin study to take this much time and funding.
Retinitis pigmentosa affects about 1.5 million people worldwide.
It’s an inherited group of eye diseases affecting the retina that begins with night vision blindness, peripheral vision loss, and tunnel vision, before eventually leading to complete blindness.
Most with the disease are blind by their early 40s.
Investigators in the abovementioned clinical trial found that a 15,000 IU vitamin A supplement helped RP suffers stave off the disease process and retain useful vision longer.
The study, by Berman-Gund Laboratory for the Study of Retinal Degenerations at Harvard Medical School, The National Eye Institute, and The Foundation Fighting Blindness, was published in the June 1993 issue of Archives of Ophthalmology (7).
Vitamin A is becoming more commonly prescribed by eye surgeons following laser eye surgery to improve healing and recovery times.
A May 2001 British Journal of Ophthalmology article describes a double-blind clinical trial of vitamin A supplementation following 40 photorefractive keratectomies.
It universally found that the group given vitamin A all had faster healing times, reported less post-op hazing, and had better visual acuity than the group given a placebo.
The retinol benefits are echoed in other post eye surgery trials with vitamin A.
You’ve probably heard that breastfeeding provides an infant with an immune system boost.
But do you know why?
It’s partly because retinol benefits are passed to the infant through the mother’s breastmilk.
Vitamin A supports the immune system in both its prevention of infection-causing germs from entering the body and its post-lymphatic response to infection once germs do get inside.
Retinol does this mainly by keeping mucous membranes strong and moist and enhancing white blood cell function.
Moist membranes make it harder for germs to attack and make you sick.
The American Society for Microbiology published a report in 2005 on the effects of vitamin A and the immune system, whereby numerous studies and clinical trials were investigated.
Overall, the body of research suggests that vitamin A can have a multi-level impact on immunity by actions such as antibody production, lymphocytic proliferation, and sustaining the integrity of mucosal epithelia in the gut (8).
Vitamin A is an antioxidant that helps promote skin integrity by inhibiting the oxidation of other harmful molecules.
The components of vitamin A work to keep your body free of toxins and free radicals that commonly damage the skin.
This type of damage is typically associated with premature and natural aging, such as that of fine lines and wrinkles.
It’s moisturizing and moisture retention actions help to keep the skin soft and prevent drying and keratinization.
Wrinkles are particularly responsive to topical retinol treatments.
The first prescription FDA-approved retinoid to treat wrinkles was Tretinoin.
It was proven effective to increase collagen, stimulate the growth of new blood vessels, fade age spots, reduce actinic keratosis, and improve the appearance of sun-damaged skin.
Since then, a number of other retinoid products have also become available over-the-counter and by prescription.
A quick word of caution – some of these are associated with adverse fetal reactions in pregnant women.
You should consult your dermatologist if you’re of childbearing age and not on birth control.
Good skin integrity is beneficial to you from a cosmetic and daily living standpoint, but it’s particularly of importance with respect to preexisting diseases.
Diabetes, for example, often compromises the skin’s ability to heal and regenerate properly.
Maintaining good skin integrity is of the utmost importance in preventing and healing skin issues associated with the disease process, such as a diabetic ulcer.
Application of topical vitamin A and D ointment is a common practice in tattoo aftercare.
It’s a preferred treatment because it keeps the skin properly moisturized and protected to promote healing.
Topically applied in the form of retinol, vitamin A has been used to treat acne, psoriasis, and hyperpigmentation with great success.
In acne, for example, vitamin A treatments 1) reduce the production of sebum that clogs the pores; 2) decrease the size of sebaceous glands; 3) reduce the number of bacteria in the skin ducts, and 4) increase the proliferation and differentiation of keratinocytes.
In turn, this all decreases the inflammatory response to the acne and speeds recovery from it (9).
The first retinoid was approved for acne in 1971.
Today, retinoids are in many of the most successful acne topical treatments.
Oral retinol supplements are also available by prescription.
A dermatologist can help you determine if you have an acne problem and if retinoids are a suitable treatment option.
Bones need vitamin A to grow and stay strong and healthy.
Vitamin A influences the production and efficiency of osteoblasts, which are the bone-building cells within the body.
Without enough vitamin A, the bones can be brittle, porous, and be less dense.
This process is of particular importance if you have a degenerative joint disease or other orthopedic condition.
However, it’s important to note that vitamin A in excess can trigger osteoclasts, which are the cells that break down bones and lower bone density.
Lower bone density leaves bones vulnerable to fractures.
Muscles are attached to bones via ligaments and tendons.
For muscles to preform and grow, they must have strong bones.
Vitamin A provides a lubricating effect on the membranes surrounding muscles, tendons, ligaments, and joints to help avoid friction-related problems.
Vitamin A plays a significant role in the strength of teeth through its role in dentin production.
Dentin is the second hard layer of the tooth, located directly under the enamel.
Tubular dentin is produced throughout your entire life.
It serves as a patching system where the enamel is worn and cavities have begun.
Vitamin A plays a role in keeping the urinary tract properly moisturized and healthy.
Vitamin A also prevents urinary calculi that lead to the formation of kidney stones.
Vitamin A has been researched as a cancer preventative and treatment measure because of its cell regrowth properties, interactions with white blood cells, antioxidant properties, and because the moisture it provides to membranes makes them more resistant to cellular damage.
It’s a common part of treatment for a certain form of leukemia and has been researched for effectiveness in treating other forms of cancer, such as breast cancer, lymphomas, and colon cancer.
A recent study published by Science Daily explored vitamin A as a tool to counteract colon cancer relapses.
Colon cancer is infamous for its resistance to conventional treatment, making it one of the leading causes of cancer deaths worldwide.
The researchers used vitamin A to reactivate a lost protein that would eliminate cancer cells and their metastasis.
The results were astounding (10).
Tissue cells are constantly shedding and being replaced with new, fresh skin cells.
This is not only a necessary biological process for skin health but is also a vital component in wound healing.
Vitamin A helps repair damaged tissues.
Retinoic acid is a vitamin A component that works as a growth factor for epithelial cells.
It basically activates genes that turn immature skin cells into mature epidermal cells, thereby expediting the skin cell turnover rate (11).
Measles has been linked to vitamin A deficiency.
Intake of vitamin A has also been linked to relieving diarrhea, pneumonia, and fever side effects of measles.
In clinical studies, treatment of measles that included vitamin A significantly reduces the morbidity rate in children.
Hyperlipidemia, or elevated cholesterol, is associated with a lack of vitamin A.
Adequate amounts can help reduce the risk of stroke and heart disease that are secondary to elevated cholesterol levels.
The American Heart Association has recommended a healthy dietary intake of antioxidants, including beta-carotene, for the prevention of heart-related diseases.
Fertility and Human Physiology
Sperm cell development can’t happen without vitamin A as a fetus develops.
A study published in the Journal of Biological Chemistry found that vitamin A activates the TR4 nuclear receptor responsible for embryo sperm cell production, lipid regulation, regulation of hemoglobin production, and the development of the central nervous system (12).
Fertility specialists often recommend vitamin A as a means for men to increase their sperm count.
As a ligand for nuclear receptors, vitamin A’s retinoic acid is essential for gene transcription regulation.
Recent evidence indicates that orphan nuclear receptors can also help discover drug targets for human disease processes.
Researchers from Harvard Medical School found that men who took beta-carotene supplements for at least 15 years were less likely to suffer cognitive decline.
Other studies have shown similar results with retinol in women.
This is because the cognitive decline is linked to oxidative stress.
Powerful antioxidants, such as vitamin A, combat the oxidation of free radicals.
Another study published in the Journal of Alzheimer’s Disease looked at the effect the lack of antioxidant vitamins, such as Vitamin A’s beta-carotene, had specifically on Alzheimer’s patients.
The study found that Alzheimer’s participants lacked sufficient beta-carotene levels across the board, raising the question of whether it could be useful in the prevention, onset, and/or treatment of Alzheimer’s disease (13).
The antioxidant properties of vitamin A make it a potent anti-inflammatory.
As retinol neutralizes free radicals and prevents them from becoming overactive, it helps prevent the tissue and cellular damage that can cause inflammation.
Other Vitamin A Benefits
Some studies have shown vitamin A to be beneficial in treating PMS, yeast infections, fibrocystic breast disease, and as a means to decrease the risk of transferring HIV to an unborn fetus.
Topical application of vitamin A is currently being researched as both a preventive and treatment for some forms of skin cancer.
Its use is common in underdeveloped countries to lessen the effects of malaria in children.
These claims all have medical evidence to support them, but they haven’t been studied thoroughly enough to be substantiated or refuted.
Topical retinoids are commonly prescribed for warts that fail to respond to other treatment options.
They work by disturbing the cell growth within the wart.
Studies have shown that stroke victims with high levels of vitamin A often recover faster, are less likely to have a long-lasting disability from the stroke, and have a higher survival rate than those lacking vitamin A.
Best Vitamin A Foods
Fish oils and liver contain the highest concentration of preformed vitamin A.
Milk and eggs contain both preformed and provitamin A.
Many kinds of cereal are fortified with vitamin A.
Here are the most common sources of vitamin A in the typical U.S. diet:
- cod liver oil
- egg yolk
- fortified milk
- cheddar cheese
- beef liver
- most yellow fruits and vegetables
- most orange fruits and vegetables
- most green leafy vegetables
Vitamin A Precautions
Too much retinol is just as harmful as not enough.
Excess vitamin A has been linked to a number of diseases, including osteoporosis.
In large doses, it can cause growth retardation and organ enlargement.
Vitamin A can expedite the effects of liver damage from habitual consumption and large amounts of alcohol.
It’s important to consider all sources of vitamin A and its derivatives.
For example, a common issue is when a person uses topical products with vitamin A active ingredients, takes supplements of vitamin A, and gets ample amounts from the plant and animal dietary sources.
Such overloads of retinol can often be the cause of headaches, nausea and vomiting, and skin rashes.
Also factor in any multi-vitamin you may take daily.
Most multivitamins contain vitamin A.
The product label will tell you the mcg per serving.
Vitamin A supplements and topical applications should be stored at room temperature, away from moisture, and out of direct sunlight.
Pregnant and lactating women need to monitor carefully their vitamin A intake.
Amounts exceeding 10,000 IU per day can cause birth defects, especially during the first three months of fetal development.
On the other hand, pregnant women are most likely to suffer from a vitamin A deficiency in the last trimester when the fetus’s demand is highest.
If you’re pregnant or lactating, always consult your pediatrician and prenatal care provider about your sources of retinol.
Those with medical conditions that affect how fat is absorbed, such as celiac disease, gluten allergies, and cystic fibrosis must take a water-soluble vitamin A supplement in order for it to be absorbed properly.
Certain intestinal infections, such as stomach worms, can also affect how vitamin A is absorbed.
Those with type V hyperlipoproteinemia forms of high cholesterol should not take vitamin A.
You shouldn’t consume animal liver more than once per week.
Eskimos and Arctic explorers have been found to suffer from hypervitaminosis due to the frequency with which they eat polar bear liver.
Topical retinoids are helpful for many common skin problems, but they can cause sensitivity issues, especially if used excessively or more often than recommended.
Common side effects are drying, redness, inflammation, skin discoloration, sensitivity to sunlight, and blistering or crusting.
Some studies have shown an increased risk of the HIV virus to replicate faster with high consumption of vitamin A in adult HIV patients.
Vitamin A Risks
Aside from the specific risks outlined above, your main risk of consuming vitamin A is hypervitaminosis, which is toxicity from having too much vitamin A in the body.
This can occur two ways: 1) consuming large amounts of vitamin A over a short period of time, or 2) from large amounts of vitamin A building up as it’s stored in your body.
The latter is most commonly seen when vitamin A is taken by those with liver disease.
Seek medical help immediately for symptoms of vitamin A toxicity, including vision changes, bone pain, headaches, nausea and vomiting, and skin changes.
Untreated toxicity can cause organ failure, create increased pressure on your brain, coma, and even death.
An important distinction in hypervitaminosis is that it’s particularly preformed vitamin A that can accumulate in the liver and cause toxicity; beta-carotene and provitamin carotenes can cause allergy but do not generally result in hypervitaminosis.
Vitamin A Dosing
The National Institute of Health recommends the following daily dietary allowances of vitamin A:
- 400 mcg for infants less than 6 months old.
- 500 mcg from 6-12 months old.
- 300 mcg from 12 months to age 3.
- 400 mcg from ages 4 to 8.
- 600 mcg from ages 9 to 13.
- 900 mcg for males from ages 14 to 18.
- 700 mcg for females from ages 14 to 18.
- 750 mcg for pregnant females ages 14 to 18.
- 1,200 mcg for lactating females ages 14 to 18.
- 900 mcg for males over 18 years old.
- 700 mcg for females over 18 years old.
- 770 mcg for pregnant females over 18 years old.
- 1,300 mcg for lactating females over 18 years old (14).
To provide some context, the following are typical amounts of vitamin A per serving in foods:
- 3 oz. of pan-fried beef liver = 6,582 mcg.
- 1 cup of skim ricotta cheese = 263 mcg.
- 1 baked sweet potato = 1,403 mcg.
- 1/2 cup of raw carrots = 459 mcg.
- 1 cup of fortified cereal = 127-149 mcg, depending on brand.
As you can see, a single sweet potato or liver serving can provide many times the recommended daily allowance of vitamin A.
For the average person, moderate dietary intake of vitamin A from a variety of plant and animal sources is harmless, even beneficial.
Vitamin A Interactions
Again, it’s important to look at how many sources of vitamin A and its components are in your life on a daily basis – topical, supplemental, and dietary.
Vitamin A in large quantities can interact with some antibiotics you take, such as tetracyclines, and cause increased inter-cranial pressure.
Always tell your physician if you take an oral dose of vitamin A, or heavily use retinol topical products.
Consult a physician before taking vitamin A with highly hepatoxic drugs, such as Tegretol, Dilantin, or Zocor.
There are many prescription drugs that have highly toxic side effects on the liver.
Be sure to clear any usage of vitamin A with your physician, especially if you have liver disease.
Consult a physician before taking vitamin A and using retinol topical products when taking Coumadin.
Both causes decreased blood clotting and could result in uncontrolled bleeding and bruising when you even lightly bump yourself.
As you can see, adequate amounts of vitamin A are very beneficial for a variety of your body’s biological systems.
It’s a key part of fetus development and continual good health throughout adolescence and adulthood.
In developed countries, plant and animal sources of vitamin A are readily available.
However, it isn’t a substance that everyone can supplement as they please; toxicity is a possibility, especially within certain groups like pregnant women and those with liver disease.
If in doubt, always consult your primary caregiver and nutritionist to determine how vitamin A will both benefit you and potentially interact with existing conditions and medications.