Vitamin A, also known as retinol, was first discovered in 1913 by two American biochemists, Elmer Verner McCollum and Marguerite Davis. They conducted experiments on animals and observed that a fat-soluble factor was essential for growth and overall health. This discovery was a significant milestone in nutritional science, as it marked the identification of the first fat-soluble vitamin, initially called “fat-soluble factor A.” Later, in 1931, Swiss chemist Paul Karrer determined the chemical structure of vitamin A, which further advanced the understanding of its role in human health. Vitamin A is now known to be crucial for vision, immune function, and maintaining healthy skin and mucous membranes.
Functions Of Vitamin A
- Vision: Vitamin A is crucial for maintaining healthy eyesight. It helps form the light-absorbing molecule called retinal, which is essential for both low-light and colour vision.
- Immune System: Vitamin A supports the immune system by playing a vital role in the development and function of white blood cells, which help protect the body against infections. It also maintains the structural integrity of mucosal cells, which serve as a first line of defence against pathogens.
- Cell Growth and Differentiation: Vitamin A is necessary for the growth and differentiation of cells, including the maintenance of healthy skin, hair, and nails. It is also involved in the development of bone tissue and the production of red blood cells.
- Reproduction: Vitamin A is essential for both male and female reproductive systems, as well as embryonic development during pregnancy.
- Antioxidant Activity: As an antioxidant, vitamin A helps neutralise harmful free radicals that can cause cellular damage, reducing the risk of chronic diseases such as cancer and cardiovascular disease.
- vitamin A is involved in bone remodelling, the process by which old bone is broken down and new bone is formed. This process is essential for maintaining strong and healthy bones throughout life. Vitamin A influences bone health through its impact on osteoblasts (cells responsible for bone formation) and osteoclasts (cells responsible for bone resorption).
Good Sources Of Vitamin A
Vitamin comes in two forms: preformed vitamin A (retinol) found in animal-based foods, and provitamin A (carotenoids) found in plant-based foods. Here are some good sources of vitamin A from both categories:
Animal-based sources (preformed vitamin A):
- Liver (beef, pork, chicken, or turkey)
- Fish liver oils (cod liver oil)
- Fatty fish (salmon, mackerel, herring, and tuna)
- Dairy products (milk, yogurt, cheese, and butter)
Plant-based sources (provitamin A – carotenoids):
- Sweet potatoes
- Dark leafy greens (kale, spinach, collard greens, and Swiss chard)
- Squash (butternut, acorn, and pumpkin)
- Red and yellow bell peppers
How Much Vitamin A Do We Need?
The recommended daily intake of vitamin A varies based on age, sex, and life stage. The National Institutes of Health (NIH) provides the following guidelines:
- Infants 0-6 months*: 400 mcg per day (micrograms)
- Infants 7-12 months*: 500 mcg per day
- Children 1-3 years: 300 mcg per day
- Children 4-8 years: 400 mcg per day
- Children 9-13 years: 600 mcg per day
- Teens 14-18 years (males): 900 mcg per day
- Teens 14-18 years (females): 700 mcg per day
- Adults 19 years and older (males): 900 mcg per day
- Adults 19 years and older (females): 700 mcg per day
- Pregnant women: 770 mcg per day
- Breastfeeding women: 1,300 mcg per day
* Adequate intake (AI)
Please note that individual needs may vary, and it’s important to consult with a healthcare professional or registered dietitian for personalised recommendations. Also, remember that consuming excessive amounts of preformed vitamin A can lead to toxicity, so it’s crucial to stay within the recommended guidelines.
For more information, you can refer to the official guidelines on the National Institutes of Health (NIH) Office of Dietary Supplements website:
What Are The Signs Of Vitamin A Deficiency?
Vitamin A deficiency can lead to various symptoms, as it plays a vital role in vision, immune function, and maintaining healthy skin and mucous membranes. Severe vitamin A deficiency can result in a condition called xerophthalmia. Some of the signs and symptoms of vitamin A deficiency include:
- Night blindness: A lack of vitamin A can lead to night blindness, making it difficult to see in low light conditions.
- Dry, scaly skin: Vitamin A is essential for maintaining healthy skin, and deficiency can cause skin to become dry, rough, and scaly.
- Dry eyes: A deficiency in vitamin A can result in dry and irritated eyes, due to a lack of moisture and lubrication on the eye’s surface.
- Frequent infections: Inadequate vitamin A levels can weaken the immune system, making individuals more susceptible to infections and illnesses.
- Slow wound healing: Vitamin A is essential for proper wound healing, and deficiency can lead to slow or impaired recovery from injuries.
- Poor bone growth: Vitamin A deficiency can affect bone development, potentially leading to stunted growth and an increased risk of fractures in children.
- Difficulty conceiving and increased risk of miscarriage: Vitamin A is necessary for proper reproductive function, and deficiency can contribute to difficulty conceiving and an increased risk of miscarriage in pregnant women.
What Happens If I Take Too Much Vitamin A?
Consuming excessive amounts of vitamin A, particularly preformed vitamin A (retinol), can lead to a condition known as hypervitaminosis A or vitamin A toxicity. This condition can cause a range of symptoms and health issues, some of which can be severe. Symptoms of vitamin A toxicity can be acute (short-term) or chronic (long-term).
Acute vitamin A toxicity symptoms include:
- Nausea and vomiting
- Loss of appetite
- Blurred vision
- Fatigue and drowsiness
- Abdominal pain
Chronic vitamin A toxicity symptoms and health issues may include:
- Dry and itchy skin
- Cracked lips
- Hair loss
- Brittle nails
- Bone and joint pain
- Osteoporosis and increased risk of bone fractures
- Liver damage or cirrhosis
- Enlarged liver or spleen
- Birth defects during pregnancy
It is important to note that toxicity is more commonly associated with preformed vitamin A, which is found in animal-based foods and supplements. The provitamin A carotenoids found in plant-based foods, like beta-carotene, are less likely to cause toxicity because the body only converts these compounds into vitamin A as needed.
To prevent vitamin A toxicity, it’s essential to stay within the recommended dietary allowances (RDA) and avoid consuming large amounts of preformed vitamin A. If you’re considering taking vitamin A supplements, consult with a healthcare professional or registered dietitian to determine the appropriate dosage for your needs.