Vitamin A is a vital nutrient indispensable for a range of body functions. As a fat-soluble vitamin, it is necessary for cell development and vision. It also acts as a potent antioxidant, helping prevent and repair cellular damage caused by oxidative stress.
Preformed vitamin A (retinol, retinyl esters) and provitamin A carotenoids, like beta-carotene, that get converted to retinol are the two main forms of vitamin A in the human diet. Animal products, fortified foods, and vitamin supplements are sources of preformed vitamin A.[1]
Natural plant foods include carotenoids. Lycopene, lutein, and zeaxanthin, a few more types of carotenoids present in the diet, are not turned into vitamin A but have positive effects on health.
Vitamin A is a crucial nutrient for overall health and well-being. Vitamin A contributes to eye health, specifically in the formation of rhodopsin which is necessary for color and low light vision, and in maintaining the health of the cornea and conjunctiva.
It also helps maintain other surface tissues such as the skin, intestines, lungs, bladder, and inner ear. Additionally, Vitamin A supports the growth and distribution of T cells, which aid in protecting the body from infection, as well as skin cell health, reproductive health, and fetal development.[2]
Provitamin A carotenoids like alpha-carotene, beta-carotene, and beta-cryptoxanthin are predecessors to vitamin A and possess antioxidant qualities. These carotenoids shield the body from free radicals, the highly reactive molecules that can cause harm through oxidative stress.
Oxidative stress has been linked to chronic diseases like diabetes, cancer, heart disease, and cognitive decline. A diet rich in carotenoids has been shown to reduce the risk of these conditions, including diabetes, heart disease, and lung cancer. [4] [5] [6]
As previously discussed, vitamin A plays a critical role in vision and eye health. Consuming enough of this nutrient through diet can help guard against certain eye conditions, such as age-related macular degeneration (AMD).
Research has shown that higher levels of beta carotene, alpha carotene, and beta cryptoxanthin in the blood may reduce the risk of AMD by as much as 25%. This reduction in risk is thought to be a result of the protective effects of carotenoid nutrients on macular tissue by reducing oxidative stress.[7]
Observational studies have shown that a higher intake of carotenoids from fruits and vegetables is linked to a reduced risk of lung cancer in nonsmokers and current or former smokers. However, three large clinical trials have not found that beta-carotene or vitamin A supplements help prevent or reduce the risk of lung cancer. In fact, two of the trials actually found an increased risk of lung cancer among participants who took supplements containing beta-carotene or retinyl palmitate (a form of vitamin A).[2] The U.S. Preventive Services Task Force recommends against the use of beta-carotene supplements for cancer prevention due to potential harm outweighing any potential benefits.[8]
Lycopene is a carotenoid that gives fruits and vegetables a pink or red color and has been studied for its potential impact on cancer due to its antioxidant properties. Observational studies have shown a reduced risk of prostate cancer in men who consume high amounts of fruits and vegetables. The evidence on the specific effect of lycopene is mixed, with some studies showing a protective effect and others showing no effect. Accurate reporting of lycopene intake is tricky, and the results may also suffer the impact of other cancer-protective compounds in lycopene-rich foods.[9]
Vitamin A is crucial for reproduction in both men and women, as it plays a vital role in sperm and egg development. It is also of utmost importance for placental health, the growth and development of fetal tissues, and overall fetal growth. It is a critical component for the health of pregnant individuals, their unborn babies, and those trying to conceive.[10]
Vitamin A contributes to a healthy immune system by activating protective responses against illnesses and infections. It assists cell production, such as B and T cells, which are paramount for immune responses. A lack of vitamin A leads to higher levels of pro-inflammatory molecules that weaken the immune system's response and ability to function.[11]
The following foods are rich in vitamin A:
Fruits and vegetables with deeper or brighter colors contain higher levels of carotenoids. Vegetable sources of beta-carotene are fat and cholesterol-free and better absorbed when eaten with a small amount of fat.
The daily recommended intake of vitamin A for men is 900 mcg, and for women is 700 mcg, which is achievable through a diet rich in whole foods. Avoid excessive consumption and do not surpass the Tolerable Upper Intake Level of 3,000 mcg (10,000 IU) per day for adults to prevent toxicity.[2]
Excessive intake of vitamin A through supplements or treatment with certain medications, such as isotretinoin, can lead to toxicity.[12] Acute toxicity occurs with a single high dose, while chronic toxicity occurs with excessive doses over an extended period.[13]
Among the side effects of chronic vitamin A toxicity (often hypervitaminosis A) are poor appetite, joint and bone pain, vision disturbances, sunlight sensitivity, hair loss, and nausea and vomiting.
Acute vitamin A toxicity is less frequent than chronic toxicity but results in more severe symptoms such as liver damage, increased cranial pressure, and even death. Besides, excessive intake of vitamin A by pregnant individuals can harm both them and their unborn child and may cause abnormal fetal development.[14]
1. Gilbert C. (2013). What is vitamin A and why do we need it?. Community eye health, 26(84), 65.
2. Office of Dietary Supplements. (2022, June 15). Vitamin A and Carotenoids - Health Professional Fact Sheet. National Institutes of Health. Retrieved February 16, 2023, from https://ods.od.nih.gov/factsheets/VitaminA-HealthProfessional/
3. Pizzino, G., Irrera, N., Cucinotta, M., Pallio, G., Mannino, F., Arcoraci, V., Squadrito, F., Altavilla, D., & Bitto, A. (2017). Oxidative Stress: Harms and Benefits for Human Health. Oxidative medicine and cellular longevity, 2017, 8416763. https://doi.org/10.1155/2017/8416763
4. She, C., Shang, F., Zhou, K., & Liu, N. (2017). Serum Carotenoids and Risks of Diabetes and Diabetic Retinopathy in a Chinese Population Sample. Current molecular medicine, 17(4), 287–297. https://doi.org/10.2174/1566524017666171106112131
5. Gammone, M. A., Riccioni, G., & D'Orazio, N. (2015). Carotenoids: potential allies of cardiovascular health?. Food & nutrition research, 59, 26762. https://doi.org/10.3402/fnr.v59.26762
6. Shareck, M., Rousseau, M. C., Koushik, A., Siemiatycki, J., & Parent, M. E. (2017). Inverse Association between Dietary Intake of Selected Carotenoids and Vitamin C and Risk of Lung Cancer. Frontiers in oncology, 7, 23. https://doi.org/10.3389/fonc.2017.00023
7. Wu, J., Cho, E., Willett, W. C., Sastry, S. M., & Schaumberg, D. A. (2015). Intakes of Lutein, Zeaxanthin, and Other Carotenoids and Age-Related Macular Degeneration During 2 Decades of Prospective Follow-up. JAMA ophthalmology, 133(12), 1415–1424. https://doi.org/10.1001/jamaophthalmol.2015.3590
8. US Preventive Services Task Force, Davidson KW, Barry MJ, et al. Screening for Colorectal Cancer: US Preventive Services Task Force Recommendation Statement. JAMA. 2021 May;325(19):1965-1977. DOI: 10.1001/jama.2021.6238. PMID: 34003218.
9. Prostate Cancer, Nutrition, and Dietary Supplements (PDQ®) – Health Professional Version. (2023, January 13). National Cancer Institute. Retrieved February 16, 2023, from https://www.cancer.gov/about-cancer/treatment/cam/hp/prostate-supplements-pdq
10. Bastos Maia, S., Rolland Souza, A. S., Costa Caminha, M. F., Lins da Silva, S., Callou Cruz, R. S. B. L., Carvalho Dos Santos, C., & Batista Filho, M. (2019). Vitamin A and Pregnancy: A Narrative Review. Nutrients, 11(3), 681. https://doi.org/10.3390/nu11030681
11. Hodge C, Taylor C. Vitamin A Deficiency. [Updated 2022 May 15]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK567744
12. de Oliveira M. R. (2015). Vitamin A and Retinoids as Mitochondrial Toxicants. Oxidative medicine and cellular longevity, 2015, 140267. https://doi.org/10.1155/2015/140267
13. Hammoud, D., El Haddad, B., & Abdallah, J. (2014). Hypercalcaemia secondary to hypervitaminosis A in a patient with chronic renal failure. The West Indian medical journal, 63(1), 105–108. https://doi.org/10.7727/wimj.2011.171
14. Bhattacharya, S., & Singh, A. (2017). Phasing out of the Universal Mega Dose of Vitamin-A Prophylaxis to Avoid Toxicity. AIMS public health, 4(1), 38–46. https://doi.org/10.3934/publichealth.2017.1.38
