Vitamin A is an essential fat-soluble nutrient that plays a fundamental role in maintaining various aspects of our health. It is crucial for maintaining sharp vision and promoting optimal eye health, as well as aiding in the formation of strong bones and teeth. Its contributions go further, including strengthening the immune system and enhancing the body's antioxidant defense mechanisms. Moreover, vitamin A is required for the proper functioning of both the male and female reproductive systems.
Vitamin A is abundant in a diverse range of healthy foods and is also available in synthetic form as dietary supplements. Incorporating a well-balanced diet rich in sources like carrots, sweet potatoes, leafy greens, eggs, and liver can provide ample amounts of natural vitamin A. However, for individuals who may have difficulty obtaining sufficient vitamin A through diet alone, dietary supplements can be a convenient alternative.
In this article, we will cover the essentials of vitamin A, including recommended daily intake for individuals at different life stages, the numerous health benefits attributed to this essential nutrient, the best food sources, and the risk factors that make some people more susceptible to vitamin A deficiency. We will also look into strategies to avoid toxicity by monitoring our intake.
What is Vitamin A ?
Although commonly regarded as a single nutrient, vitamin A is actually a group of fat-soluble compounds called retinoids, primarily including retinol and retinyl esters.
The human diet contains two types of vitamin A:
What is Vitamin A ?
Although commonly regarded as a single nutrient, vitamin A is actually a group of fat-soluble compounds called retinoids, primarily including retinol and retinyl esters.
The human diet contains two types of vitamin A:
- Preformed vitamin A
Preformed vitamin A includes retinol and retinyl esters. It is exclusively found in foods of animal origin, such as dairy products, eggs, meat, liver and fish. These sources are rich in preformed vitamin A which is easily absorbed and utilized by the body.
- Provitamin A carotenoids
Provitamin A carotenoids are found in plant-based foods, such as carrots, sweet potatoes, spinach, and other colorful fruits and vegetables. The most well-known provitamin A carotenoid is beta-carotene. In the body, provitamin A carotenoids can be converted into retinol and provide a source of vitamin A.
It is important to note that while preformed vitamin A is readily available in animal-based foods, provitamin A carotenoids from plant sources offer an alternative means of obtaining vitamin A, particularly for individuals following a vegetarian or vegan diet.
In Western countries, around 30% of the total daily vitamin A intake comes from provitamin A carotenoids found in plant sources. However, in developing countries, this ratio increases significantly to approximately 70%.(1)
By including a variety of foods rich in both preformed vitamin A and provitamin A carotenoids, individuals can ensure an adequate intake of this essential nutrient.
How Much Vitamin A Do We Need Daily?
The daily requirement of vitamin A varies depending on factors such as age and gender.
The recommended dietary allowances (RDAs) for vitamin A are typically measured in micrograms of retinol activity equivalents (RAE).
For adult men, the RDA is about 900 mcg RAE per day, while adult women require roughly 700 mcg RAE.(2)
During pregnancy, the RDA increases to 770 mcg RAE, and during lactation, it rises further to 1300 mcg RAE. It's important to note that these values may vary slightly depending on specific guidelines and individual overall health.(2)
Health Benefits of Vitamin A
# Vision and eye health
Vitamin A is widely recognized as a key contributor to vision and eye health.
Retinal, the active form of vitamin A, combines with the protein opsin to form rhodopsin, a crucial molecule enabling the absorption of photons and facilitating our ability to perceive light. This process is vital for vision, especially in low light conditions.(3)
Additionally, a deficiency in vitamin A can hinder the function of rods, a specific type of photoreceptor cell in the retina responsible for vision in dim light. Such impairment can lead to night blindness, affecting our ability to see clearly during nighttime conditions.(4)
Furthermore, research has demonstrated that a diet rich in carotenoids can help lower the risk of certain eye diseases, particularly Age-Related Macular Degeneration (AMD), a condition that can lead to the blurring of central vision. Carotenoids act primarily by scavenging free radicals and reducing oxidative stress, which are potential threats to overall eye health.(5)
# Vitamin A is a potent antioxidant
Carotenoids, such as beta-carotene, alpha-carotene and cryptoxanthin, possess remarkable antioxidant properties that provide protection against the detrimental effects of free radicals and oxidative stress.
Free radicals are unstable molecules that, when accumulated in excess, can induce a state of "oxidative stress". This condition plays a significant role in the pathogenesis of numerous chronic diseases, including diabetes, heart disease, obesity, cancer, and cognitive impairment, and more.(6)
By neutralizing free radicals, carotenoids help counteract oxidative stress, thereby contributing to the prevention of these chronic diseases and promoting overall well-being
# Vitamin A may help fight cancer
Carotenoids have been extensively studied for their potential in combating cancer, with notable findings indicating their beneficial effects.(7)
Research from the PubMed database highlights the significance of carotenoids like lycopene, beta-carotene, and cryptoxanthin in reducing risk factors associated with prostate, lung, and breast cancer. These carotenoids have shown promising potential in providing protective effects against the development and progression of these types of cancer.(8)
Moreover, one intriguing aspect is the anti-angiogenic activity observed specifically with beta-carotene. This property hinders the formation of new blood vessels by malignant cells, thereby impeding their ability to sustain growth and metastasis. By depriving cancer cells of vital blood supply, beta-carotene may help impede the progression and spread of the disease.(9)
# Vitamin A may help treat measles in children
Measles is a highly contagious respiratory disease that primarily affects children. Fortunately, the introduction of the measles vaccine in 1963 greatly reduced its prevalence.
Vitamin A deficiency is a major risk factor for severe measles infections. In addition, studies have shown that vitamin A supplementation plays a crucial role in reducing the risk of death from measles, particularly in children under the age of two. In fact, supplementation has been found to decrease mortality rates by as much as 87% in this age group. As a result, the World Health Organization (WHO) recommends the administration of an oral dose of 200,000 IU of vitamin A (100,000 IU for infants) daily for two days to children diagnosed with measles, particularly in regions where vitamin A deficiency is prevalent.(10)
By implementing this recommended vitamin A supplementation during measles outbreaks, healthcare providers and organizations aim to improve the outcomes and reduce the severity of the disease, ultimately protecting the health and well-being of affected children.
What Foods are Rich in Vitamin A?
Vitamin A is an essential nutrient that our bodies cannot produce, so it must be obtained through our daily diet. Both preformed vitamin A and provitamin A carotenoids are plentiful in a diverse range of nutritious and wholesome foods.
As a fat- soluble nutrient, vitamin A can be stored in the body for future use. Speaking of which, the majority of vitamin A in the human body is stored in the liver as retinyl esters.(11)
As previously indicated, preformed vitamin A is absorbed and utilized by the body more efficiently than provitamin A. In fact, the body can absorb approximately 75%-100% of retinol versus 10%-30% of beta-carotene from dietary sources.(12)
Furthermore, the efficient absorption of vitamin A depends on factors such as the presence of bile acids, pancreatic enzymes, and sufficient gastric acidity. Given that vitamin A is fat-soluble, consuming dietary fat alongside a meal rich in vitamin A can enhance its absorption by the body.(13)
# Foods high in preformed vitamin A
- Cod liver oil
- Liver and organ meats
- Some types of fish like tuna, herring, and salmon
- Dairy products like cheese, butter and milk
- Egg yolks
# Foods high in provitamin A carotenoids
- Brightly colored vegetables and fruits like spinach, sweet potatoes, pumpkin, carrots, kale, broccoli, lettuce, kale, red peppers, winter squash, apricots, cantaloupe, papaya, mangoes, pink grapefruit, and watermelon
- Nuts like pistachios, lotus seeds, and breadfruit seeds
- Tomato products
Is There a Synthetic Form of Vitamin A?
Yes, there are synthetic forms of vitamin A available in the form of supplements. These supplements often contain preformed vitamin A, typically in the form of retinyl acetate or retinyl palmitate, as well as provitamin A in the form of beta-carotene. Some supplements even combine both forms of vitamin A.
Furthermore, it’s worth noting that vitamin A is commonly included in multivitamin supplements, ensuring a comprehensive intake of essential nutrients.
By offering these synthetic options, supplements provide a convenient way to meet vitamin A requirements, particularly for individuals who may have specific dietary restrictions or limited access to natural food sources.
Remember, it’s always advisable to consult with a healthcare professional before starting any supplement regimen to determine the appropriate dosage and ensure it aligns with your individual health needs.
Who Is Most at Risk of Vitamin A Deficiency?
Vitamin A deficiency is rare in high-income and developed countries as most people tend to get enough of the vitamin in their daily diet. Unfortunately, this is not the case in developing countries where vitamin A deficiency is more common, especially in young children, according to the WHO.
Certain groups of people, for medical or socioeconomic reasons, may be at greater risk of developing vitamin A deficiency than others, including:
# Premature infants
Premature infants are particularly at risk of vitamin A deficiency due to several factors. Firstly, preterm infants often have insufficient vitamin A stores at birth, coupled with low blood levels of retinol during the first year of life. Their underdeveloped immune systems also render them more vulnerable to infections.(14)
While some studies suggest that vitamin A supplementation may help reduce the incidence of chronic lung disease and sepsis in this population, further research is required to substantiate these findings. Nonetheless, the importance of monitoring and addressing vitamin A status in premature infants is recognized as a crucial aspect of their overall care.
# Infants and young children
Breast milk usually provides sufficient vitamin A for breastfed newborns throughout the first six months of life. However, the risk of vitamin A deficiency is raised in children whose mothers are vitamin A deficient, particularly in cases of exclusive breastfeeding.
Research studies, including one published on PubMed, indicate that approximately one-third of preschool children experience vitamin A deficiency. This proportion significantly increases in developing countries and regions where vitamin A deficiency is more prevalent.
To address this important concern, efforts are focused on promoting breastfeeding while also ensuring that breastfeeding mothers receive adequate vitamin A intake themselves. Additionally, complementary feeding practices are emphasized to introduce a variety of foods rich in vitamin A to meet the nutritional needs of infants and young children.
# Pregnant and breastfeeding women
Pregnant and breastfeeding women are particularly at risk of vitamin A deficiency. Due to increased nutritional demands during these stages, higher levels of vitamin A are required to support their health and the development of their infants.
Meeting these increased requirements is crucial to prevent complications and health problems associated with vitamin A deficiency in this vulnerable population. In line with this, the World Health Organization (WHO) recommends that pregnant and lactating women increase their vitamin A intake to 770 mcg during pregnancy and 1300 mcg during lactation.(2)
Highlighting the severity of the issue, the WHO reports that 15% of all pregnant women globally suffer from xerophthalmia, a medical condition resulting from vitamin A deficiency. Xerophthalmia causes dryness of the conjunctiva and cornea, which, if left untreated, can progress to permanent blindness.(15)
# People with gastrointestinal disorders
Gastrointestinal disorders, such as Crohn’s disease, ulcerative colitis, celiac disease, inflammatory bowel disease, and chronic pancreatitis, can significantly impact vitamin A status. These conditions can impair the absorption, storage, and utilization of vitamin A in the body.
For instance, in a study conducted by the National Institutes of Health (NIH) involving 38 individuals with Crohn’s disease, it was revealed that 40% of them had insufficient hepatic stores of vitamin A, which was three times lower than the value observed in healthy controls.
# People with limited dietary diversity
People with low dietary diversity, limited access to a variety of foods, and specific dietary choices, such as vegetarians, are at risk of vitamin A deficiency.
For individuals following a vegetarian diet, who choose not to include animal-based products in their diet, obtaining adequate vitamin A can be challenging as it is primarily found in animal sources such as liver, dairy, and eggs.
While plant sources like fruits and vegetables contain sizeable amounts of provitamin A carotenoids, which can be converted to vitamin A in the body, the conversion efficiency varies among individuals. Therefore, vegetarians need to pay close attention to their vitamin A intake and ensure they include a variety of plant-based sources rich in carotenoids in their diet.
Enhancing dietary diversity and improving access to a wide range of nutritious foods are effective strategies to address and prevent vitamin A deficiency in these vulnerable populations.
# Individuals with cystic fibrosis
Cystic fibrosis is a genetic disorder that affects multiple organ systems, including the lungs, digestive system, and liver.
Due to the impairment in pancreatic function, individuals with cystic fibrosis often have a deficiency in pancreatic enzymes, which are crucial for the absorption of dietary fats.
As vitamin A is a fat-soluble vitamin, the inadequate absorption and utilization of vitamin A and other essential nutrients can increase the risk of vitamin A deficiency in individuals with cystic fibrosis.(16)
Given these challenges, individuals with cystic fibrosis face an elevated risk of insufficient vitamin A levels, which can have adverse effects on their overall health and well-being.
To address this health concern, people with cystic fibrosis typically receive regular vitamin A preparations from an early age as part of their therapeutic procedure. This proactive approach aims to ensure that individuals with cystic fibrosis maintain adequate levels of vitamin A and mitigate the risk of deficiency.(16)(17)
# People with liver issues
People with liver issues, such as cirrhosis or hepatitis, may be at an increased risk of vitamin A deficiency. The liver plays a crucial role in storing and metabolizing vitamin A. When liver function is compromised, it can affect the body’s ability to properly store and utilize this important vitamin. Consequently, individuals with liver issues may require specific attention to their vitamin A levels.
Healthcare professionals may recommend adjustments to their vitamin A intake or prescribe appropriate vitamin A supplementation to ensure they meet their nutritional needs.
# People following extremely low or fat-free diets
Individuals with extremely low or fat-free diets are at an increased risk of vitamin A deficiency. Vitamin A is a fat-soluble vitamin, which means it requires dietary fats for proper absorption and utilization by the body.
When fat intake is extremely low or absent, the absorption of vitamin A can be hindered. Therefore, individuals who follow these types of diets may have reduced absorption of vitamin A, potentially leading to a deficiency.
It is crucial for these individuals to consider incorporating sources of healthy fats, such as nuts, seeds, avocados, and vegetable oils, into their diet. These fat sources can help facilitate the absorption of vitamin A and ensure they meet their nutritional requirements.
Vitamin A Deficiency Symptoms
Vitamin A deficiency can result from both insufficient intake and malabsorption syndromes, leading to a range of health issues.
Inadequate vitamin A levels can have a profound impact on various aspects of health, including vision, immune system function, susceptibility to infections, skin health, bone development, heart health, tooth integrity, and fertility.
One of the most common symptoms associated with vitamin A deficiency is xerophthalmia, a medical condition characterized by dry eyes and an inability to produce tears. If left untreated for an extended period, xerophthalmia can progress to night blindness, which manifests as difficulty adapting to low light conditions.
Prolonged vitamin A deficiency can further damage the cornea, ultimately leading to irreversible blindness. In fact, vitamin A deficiency remains one of the leading causes of preventable blindness, particularly among children (18).
Aside from vision problems, vitamin A deficiency can lead to a variety of other symptoms, including:
Dry skin: Vitamin A plays a role in maintaining the health and moisture of the skin. A deficiency can lead to dry, rough, and flaky skin.
Poor wound healing: Insufficient vitamin A levels can impair the body’s ability to heal wounds effectively, leading to delayed or impaired healing.
Increased susceptibility to infections: Vitamin A plays a crucial role in supporting immune system function. A deficiency can weaken the immune response, making individuals more prone to infections, particularly respiratory and gastrointestinal infections.
Impaired growth and development: In children, vitamin A deficiency can interfere with normal growth and development, resulting in stunted growth, delayed bone development, and a higher risk of skeletal abnormalities.
Changes in hair and nails: Vitamin A deficiency may cause dry and brittle hair, as well as brittle and spoon-shaped nails.
Impaired reproductive health: Inadequate vitamin A levels can affect fertility and reproductive health in both males and females.
How Can We Prevent Vitamin A Deficiency?
Preventing vitamin A deficiency is crucial, and early detection and intervention play a significant role. One of the primary ways to prevent vitamin A deficiency is by ensuring adequate intake of this essential nutrient through a well-balanced diet. Including foods rich in vitamin A, such as liver, dairy products, eggs, and a variety of colorful fruits and vegetables that are high in beta-carotene, can help maintain sufficient vitamin A levels and reduce the risk of deficiency and its related health consequences.
In cases where individuals are at higher risk of vitamin A deficiency or have persistent deficiency despite dietary efforts, healthcare professionals may recommend vitamin A supplementation. This can help restore optimal vitamin A levels in the body and alleviate associated symptoms.
Regular monitoring of vitamin A levels is important in identifying deficiencies and guiding appropriate interventions. Healthcare professionals can perform blood tests to assess vitamin A status and determine the most suitable course of action.
By addressing risk factors, maintaining a balanced diet rich in vitamin A sources, and considering appropriate supplementation when necessary, individuals can effectively manage and prevent the complications associated with vitamin A deficiency.
Can Excessive Vitamin A Intake Be Harmful?
Vitamin A toxicity can be just as harmful as a deficiency. When consumed in excessive amounts, vitamin A can lead to toxicity. Since vitamin A is a fat-soluble vitamin, it cannot be easily excreted in the urine like water-soluble vitamins. Instead, it is stored in the liver, and ingesting large doses of vitamin A over time, usually from supplements, can result in vitamin A poisoning.
Acute vitamin A toxicity occurs when high doses of preformed vitamin A from supplements or certain medications are consumed. This can lead to various symptoms, including nausea, dizziness, seizures, severe headaches, and blurred vision. On the other hand, chronic vitamin A toxicity is the result of long-term excessive intake and can cause symptoms such as weight gain, loss of appetite (anorexia), hair loss (alopecia), itching (pruritus), and muscle and bone pain.
Special caution should be taken by women who are pregnant or planning to have a baby. It is advised to avoid consuming excessive amounts of vitamin A, whether from supplements or foods high in vitamin A, such as liver and liver products. Excess vitamin A intake during pregnancy, particularly in the first trimester, can significantly increase the risk of birth defects.(19)
It’s worth noting that high intakes of carotenoids, which are provitamin A carotenoids found in plant sources, do not appear to cause major health issues. However, excessive consumption of beta-carotene over time can result in a condition called carotenemia. This condition causes the skin to turn a yellowish-orange color, but it is harmless and typically resolves once the intake of beta-carotene is reduced.
To ensure safe intake, the daily upper limit for preformed vitamin A is set at 3000 mcg. It’s important to note that this limit does not include doses taken for specific medical reasons. In contrast, there is currently no established upper limit for provitamin A carotenoids.(2)