Vitamin A
We introduced the types of micro-nutrients in our last post . They were classified as either vitamins or minerals. We’ll explore a vitamin –vitamin A in this post, and determine its functions and sources.
Vitamin A is a fat-soluble vitamin. Contained in 2 forms as either;
- Pro-vitamin A –found in plant sources –including beta-carotene
- Pre-formed Vitamin A -found in animal sources
The 3 active forms of vitamin A in the body include:
- Retinal
- Retinol
- Retinoic acid
Retinol can be converted in the body to retinal which then undergoes oxidation to produce retinoic acid (vitamin A).
Nevertheless, while the conversion of retinol to retinal is reversible, that of retinal to retinoic acid is irreversible.
Functions Of Vitamin A
Protects eye health-Vitamin A is essential for preserving eye health. It contributes to healing dry eyes and fights against eye infections. You also minimize the risk of macular degeneration when you consume adequate amounts of Vitamin A.
Has anti-oxidant properties-It possesses anti-inflammatory properties significant in neutralizing free radicals in your body that have the potential for cell or tissue damage. In turn, it lowers the probability of inflammation, which tends to lead to diseases.
Maintains immunity-Vitamin A is important in fighting against infections as it influences the regulation of your immune responses.
Enhances cell development and preserves skin health– Sufficient intake of Vitamin A ensures proper wound healing and skin maintenance. It promotes collagen production, ensuring your skin looks healthy and supple, and decreases the risk of acne.
Sources of Vitamin A
Vitamin A is contained in a variety of foods. These foods especially those from plant sources are colourful. They include;
Plant sources
- Pumpkin
- Squash
- Mangoes
- Pineapples
- Tomatoes
- Carrots
- Dark green leafy vegetables- spinach, kales
- Melon
- Broccoli
- Pawpaw
- Sweet potatoes
- Peppers
- Avocado
Animal sources
- Eggs
- Cheese
- Meat
- Fish
RDA
- 900 micrograms for males
- 700 micrograms for females
Anything above 3000 micrograms per day can be deemed excessive.
Individuals At Risk Of Vitamin A Deficiency
Pregnant women –As a result, of their increased needs of Vitamin A for their own metabolism,foetal development, and tissue maintenance, poor dietary intake predisposes them to the risk of Vitamin A deficiency.
Chronic alcoholics-Chronic alcoholism can contribute to the depletion of liver stores of Vitamin A.
Individuals with certain health conditions-Conditions that interfere with Vitamin A absorption such as a leaky- gut syndrome, pancreatic disorders, auto-immune disorders, and inflammatory bowel disease predisposes one to Vitamin A deficiency.
Vitamin A deficiency may also result from the following reasons:
- Inadequate intake
- Infections
- Worm infestations
- Protein–energy malnutrition– either kwashiorkor or marasmus.
Signs And Symptoms Of Vitamin A Deficiency
Impaired vision. Lack of Vitamin A leads to xerophthalmia (dryness of conjunctiva and cornea ), which develops as follows:
- Night blindness-An early indication of Vitamin A deficiency is characterized by an inability to see properly in dim light.
- Conjunctival Xerosis-dryness of the conjunctiva.
- Bitot’s spots form – they are oval, triangular, or irregular foamy patches on the eye ball.
- Corneal Xerosis- This is drying of the cornea.It leads to increased risk of infection as the mucous membranes become dry.
- Keratomalacia – is the softening of the cornea.
Acute Respiratory infections – The lack of or inadequate intake of Vitamin A leads to impaired immunity. We asserted that Vitamin A is important for immunity hence a lack of it impedes the proper functioning of the immune system. In fact, the younger the patient, the more the severity of effects. Children with severe Vitamin A deficiency are more susceptible to high mortality rates, infections, and growth retardation.
Diarrhoea –Especially among children, diarrhoea may present.
Vitamin A Toxicity
On the other hand, excess intake of Vitamin A can also occur leading to toxicity.Vitamin A toxicity is mainly resultant of supplementation rather than dietary intake. Therefore, if supplementation is necessary, guidance should be sought from a qualified dietitian.
Beta-carotene(converted to Vitamin A in the body and found in most vegetables and fruits) does not cause toxicity, though an excessive amount of it can lead to hypercarotaenamia which is characterized by the yellowing of the skin.
Toxicity presents as Hypervitaminosis that can either be acute or chronic.
- Acute hypervitaminosis – results from the intake of high amounts of vitamin A within a short period i.e. a few hours or days.
- Chronic hypervitaminosis– Occurs due to a high intake of vitamin A over a long period.It can cause birth defects during pregnancy and liver damage.
Let us look into the reasons for Vitamin A supplementation:
- Other people use it to treat eye disorders such as glaucoma and cataracts.
- Some people use the vitamin in managing gastrointestinal ulcers, Crohn’s disease, sinus infections, and urinary tract infections.
- Some apply it to the skin with the intent of promoting wound healing, reducing wrinkles, and protecting it against UV radiation.
- Others use it for the treatment of skin conditions such as eczema and acne.
So, people supplement with Vitamin A for a variety of reasons. Some of the reasons may not be proven or lack conclusive research because whereas supplements can enhance health in certain cases, they cannot assert to heal or prevent a condition. Anyway, it is crucial that supplementation be prescribed by a dietitian.
Symptoms Of Vitamin A Toxicity
Abnormal softening of the skull bone (in infants and children)
- Lack of weight gain (in infants and children)
- Double vision (in young children)
- Blurred vision
- Bone pain
- Reduced alertness
- Lack of appetite
- Dizziness
- Hair changes, such as hair loss and oily hair
- Irritability
- Vomiting
- Nausea
- Drowsiness
- Skin changes- cracking at corners of the mouth, itching ,yellowing of the skin
- Headaches
- Liver damage
Nutrient Interactions With Vitamin A
Zinc
- Zinc deficiency facilitates the decreased production of retinol-binding protein(RBP)- a protein involved in the transportation of retinol through the peripheral tissues; hence reducing the probability of retinol toxicity .
- Zinc deficiency also interferes with the release of retinol in its storage form (retinol palmitate) from the liver.
- Zinc and Vitamin A are essential for bone remodeling, preventing stunting incidences.
Iron
- In multiple instances, Vitamin A deficiency co-exists with iron deficiency. As such, it can further exacerbate iron-deficiency aneamia because it interferes with iron metabolism.
Vitamin K
- Intake of excess Vitamin A impedes Vitamin K absorption. Hence, the Vitamin K level in your blood undergoes a decrease when Vitamin A is in excess.
Vitamin D
- Vitamin A toxicity promotes Vitamin D deficiency, causing reduced bone density.
Drug Interactions With Vitamin A
- Oral contraceptives enhance Vitamin A levels.
- Orlistat, a weight loss treatment drug lowers Vitamin A absorption rates, as well as the utilization and absorption of other fat-soluble vitamins and beta-carotene.
- Cholesterol-lowering medications such as cholestyramine (Questran) and colestipol (Colestid) may decrease the body’s ability to absorb vitamin A, leading to low levels of Vitamin A in the body. However, Statins- also cholesterol-lowering medications may increase vitamin A levels in the blood.
- Neomycin (Mycifradin) – This antibiotic decreases the body’s capacity to absorb vitamin A, notably when ingested in large doses.
In recommendation, Vitamin A should be consumed in adequate amounts to avoid excesses or inadequacies. Preferably, obtain your vitamin A from its natural sources rather than supplements to minimize the likelihood of excess intake that could lead to toxicity. In case there is a need for supplementation, consult with a dietitian. Include a variety of Vitamin A sources in your diet.