Can You Get Vitamin A Toxicity From Food?
Article by Namrata Ashok
In the US, 60,000 vitamin toxicities, also known as hypervitaminosis, are reported every year. Vitamin A can be present in the body through topical absorption or oral ingestion via supplementation or food intake. The two predominant forms of vitamin A are preformed vitamin A (retinol and retinyl esters) present in egg yolk, liver, fish liver oils dairy, fortified foods, and vitamin supplements, as well as provitamin A, present in carotenoids, such as beta-carotene. Carotenoids, once ingested, get converted into Vitamin A in the body. Beta-carotene is present in various fruits and vegetables, such as leafy green vegetables, red, orange, and yellow vegetables and fruits, tomatoes, mangoes, and cantaloupe (8). Moreover, the western diet is comprised of approximately 70% preformed vitamin A and 30% provitamin A (6). Yet, what implication does this have on vitamin toxicity levels?
Metabolism of vitamin A
Research suggests that Vitamin A accounts for 80% absorption if consumed with adequate levels of fat. 50 to 85% of the total retinol in the body is stored in the liver when Vitamin A is in adequate amounts. Preformed vitamin A (e.g retinyl esters) gets converted to retinol in the intestine by pancreatic and intestinal enzymes, and retinol is readily absorbed by cells lining the intestine. The excess retinol gets converted back to retinyl esters and stored in the liver. On the other hand, Provitamin A carotenoids require the presence of fat in a meal to be dissolved in fat droplets, taken up by micelles in finite capacity, and absorbed intestinally for physiological use. Excess Provitamin A carotenoids are stored in the liver. Ultimately, the bioconversion and bioavailability of Provitamin A carotenoids in the gut is affected by the carotenoid species, amount of carotenoid in a meal, the cellular properties of the plant containing the carotenoid, food preparation method, genetic influence, and nutrition status of the individual (6).
Functions of vitamin A
Retinol plays a vital role in the light-sensitive nerve cells of the retina in the eye, protects the skin and lining of the lungs, intestine, and urinary tract, and supports bone re-modeling. Furthermore, vitamin A helps the production and activity of white blood cells for adequate immune function, as well as cell growth and cell division for reproduction. Although vitamin A has its own functions, vitamin A deficiency is known to disrupt vitamin D function in bone and immune health.
Toxicity vs deficiency
Vitamin A deficiency occurs when an insufficient quantity of vitamin A is absorbed and allocated to its physiological functions. On the other hand, vitamin A toxicity occurs when an excess quantity of Vitamin A is ingested, and therefore stored in fat or the satellite cells of the liver. The recommended vitamin A dose from food is 700 ug of retinol equivalents a day for men and 600 ug of retinol equivalents a day for women. Guidelines suggest a maximum intake of 3000 ug preformed vitamin A a day. Celiac disease, Crohn’s disease, Cirrhosis, Alcoholism, and Cystic Fibrosis are conditions that disrupt digestion, possibly contributing to vitamin A malabsorption. Furthermore, adults and children who consume a less diverse diet are at high risk of vitamin A deficiency (2).
Toxicity typically occurs from high doses of preformed vitamin A in supplements. These supplements are used to treat acne and skin disorders and are found in over-the-counter supplements. However, excess levels of preformed vitamin A is toxic. Although research suggests no correlation between high intakes of provitamin A carotenoids in foods and vitamin A toxicity, as beta-carotenes are converted slowly, carotenoids in the palms and soles is an indication of excess beta-carotene consumption (2). Currently, supplement companies have transitioned to beta-carotene as a source of Vitamin A instead of preformed vitamin A. Although this transition may decrease the risk of toxicity, some research concludes an association between high doses of beta-carotene in supplements and increased risks of cancer. This association is not apparent with fruit and vegetables, containing beta-carotene, but needs to be further investigated to establish a stronger association (1).
What kind of vitamin A supplements should we take?
Observational studies conclude lower lung cancer risks with higher consumption of carotenes from fruits and vegetables, but heightened susceptibility to lung cancer when exposed to high dose beta-carotene and retinol palmitate (Vitamin A alternative) supplements. These findings affect current and former smokers to a greater extent (1). All in all, the U.S. Preventive Services Task Force advises against the use of beta-carotene with its potential greater harm than any suggested benefit, due to cancerous associations (11), and that vitamin A deficiency can be supported through a diverse diet with adequate fat intake.
Symptoms of vitamin A toxicity
Chronic vitamin A toxicity manifests in symptoms, such as fatigue, infertility, dry skin and hair, liver disorders, excess collagen production, fibrosis, nausea, sensitivity to light, and eye disorders, as well as Vitamin D functions, such as the susceptibility to infection and weakened bones (1). These symptoms are typically seen with large intakes of 20,000 - 50,000 IU through supplementation (6). Some research suggests that the chronic and average consumption of 1.5mg of Vitamin A a day increases the risk of fractures to a greater extent with age and for women approaching menopause (10).
Can vitamin A in creams cause toxicity?
Vitamin A, in the form of retinol and retinol palmitate, is used in sunscreens, moisturizers, and lip balms. As these forms of Vitamin A are absorbed through the skin and not directly through the bloodstream, the correlation between topical Vitamin A in creams and toxic levels of Vitamin A in the body is weak. However, it is advised to apply creams with Vitamin A at night to prevent skin sensitivity and skin damage with exposure to bright light during the day (1).
Can I eat liver and liver products?
Liver is one of the richest sources of Vitamin A. Guidelines recommend liver consumption in small portions or less frequently, once a week, or consumed without supplementation (10). For pregnant women, preformed Vitamin A sources from vegetables, fruits, and fortified dairy products may be more suitable as liver and liver products are not recommended during pregnancy, with a maximum supplemental intake of 700 ug a day (9).
Summary
Vitamin A is present as preformed vitamin A, found in many supplements, animal products, and fortified foods, or provitamin A, found as carotenoids in fruits and vegetables.
Toxicity from naturally-occurring provitamin A has been minimally reported.
High doses of beta-carotene intake from supplements have been linked to cancer, especially amongst smokers.
The primary contributor to hypervitaminosis A is a high-dose supplement.
For specific nutrition needs, please seek dietary recommendations from an registered Dietitian or GP. Other resources available to you include the NHS, British Nutrition Foundation and British Dietetics Association websites.
This blog was written by Namrata Ashok, a Sports Science and Nutrition BSc student at University of Glasgow. Currently involved in two internships, work experience, podcasts, and further reading, alongside her studies, Namrata is enthusiastic about helping individuals heal and restore from the inside out, honing in on approaching the root cause. She is determined to explore the world of health, nutrition, and movement by combining research, theory, and practical experience.
References:
(1) https://www.hsph.harvard.edu/nutritionsource/vitamin-a/
(3) https://dergipark.org.tr/en/download/article-file/864941
(4) https://jamanetwork.com/journals/PEDS/articlepdf/496120/archpedi_85_3_007.pdf
(5) https://academic.oup.com/nutritionreviews/article/58/5/138/1832501
(6) https://cot.food.gov.uk/sites/default/files/cot/cotstavita.pdf
(7) https://www.liebertpub.com/doi/pdf/10.1089/vim.2020.0330
(8) https://www.ncbi.nlm.nih.gov/books/NBK532916/
(9) https://www.bfwh.nhs.uk/wp-content/uploads/2015/08/healthy-eating-vit-suppl-preg.pdf