VITAMIN A

Vitamin A is a fat-soluble vitamin crucial for maintaining healthy vision, immune function, skin integrity, and thyroid health. It helps regulate the metabolism of thyroid hormones, supporting their production and release, which are essential for metabolic processes.

The body obtains vitamin A from dietary sources like liver, fish oils, and colorful fruits and vegetables such as carrots and spinach.

Vitamin A primarily exists in two forms: retinoids (such as retinol and retinoic acid) and carotenoids (such as beta-carotene). These forms are already biologically active or can be converted into active forms within the body.

vitamin shop

Foods Rich in Vitamin A

Vitamin A can be found in both animal-based and plant-based foods. Here are some examples of foods rich in vitamin A:

Animal-Based Sources (Retinoids):

Liver: Beef liver and chicken liver are among the richest sources.
Fish: Especially oily fish like salmon, mackerel, and tuna.
Dairy Products: Milk, cheese, and butter.
Eggs: Particularly the yolk.

Plant-Based Sources (Carotenoids, which convert to Vitamin A):

Carrots: A well-known source of beta-carotene.
Sweet Potatoes: Particularly the orange-fleshed varieties.
Pumpkin: Also high in beta-carotene.
Dark Leafy Greens: Such as spinach, kale, and collard greens.
Red and Orange Bell Peppers: Rich in carotenoids.
Mangoes: Contain a good amount of beta-carotene.
Apricots: Fresh or dried, both are good sources.
Butternut Squash: Another excellent source of beta-carotene.

Including a variety of these foods in your diet can help ensure you get adequate amounts of vitamin A, supporting vision, immune function, and overall health. Animal-based sources provide vitamin A in its readily usable retinoid form, while plant-based sources provide carotenoids, which the body can convert into retinoids.

PROCESSES INVOVLED

Vitamin A is essential for a variety of chemical processes in the body, playing crucial roles in vision, immune function, reproduction, and cellular communication.

Vision

Visual Cycle: Vitamin A is vital for the visual cycle, which occurs in the retina of the eye. Retinal, a form of vitamin A, combines with opsin to form rhodopsin, a pigment in the photoreceptor cells. Rhodopsin is essential for low-light vision. When light hits rhodopsin, it changes shape, triggering a signal that is sent to the brain, allowing vision in dim light.

Immune Function

Immune Cell Differentiation and Proliferation: Vitamin A regulates the differentiation and proliferation of immune cells. Retinoic acid, the active form of vitamin A, influences the growth and differentiation of T cells and B cells, which are crucial for adaptive immunity.

Cell Growth and Differentiation

Gene Expression Regulation: Retinoic acid acts as a hormone to regulate gene expression by binding to nuclear receptors (retinoic acid receptors, RARs) and activating or repressing specific genes. This regulation is crucial for cell growth, differentiation, and apoptosis, especially in epithelial cells.

Reproduction and Embryonic Development

Spermatogenesis and Fetal Development: Vitamin A is essential for reproductive health. In males, it is necessary for spermatogenesis, while in females, it supports embryonic development. Retinoic acid regulates the expression of genes critical for the development of the heart, eyes, and limbs.

Skin and Mucous Membranes

Maintenance of Epithelial Tissues: Vitamin A helps maintain the integrity and function of epithelial tissues, including the skin and mucous membranes. It promotes the differentiation of epithelial cells and prevents keratinization, ensuring the barrier function of these tissues.

Antioxidant Activity

Protection Against Oxidative Stress: As an antioxidant, vitamin A helps protect cells from oxidative stress by neutralizing free radicals. This protective effect is important for preventing cellular damage and reducing the risk of chronic diseases.

Vitamin A is essential for vision, immune function, cell growth and differentiation, reproduction, skin health, and protection against oxidative stress.

Its active forms, retinol, retinal, and retinoic acid, participate in various biochemical processes that are crucial for maintaining overall health.

VITAMIN A & THYROID

Vitamin A and retinoids help the immune system and the development of certain immune cells called Treg cells. They can influence how these cells grow and respond, especially when there are high levels of a substance called IL-2. Vitamin A helps balance immune responses by reducing inflammation and supporting gut health, which protects against diseases like type 1 diabetes and multiple sclerosis.

Hashimoto's thyroiditis (HT) is a common autoimmune disease that affects the thyroid. It starts with inflammation driven by Th17 cells and later involves Th1 cells. In some cases, Th2 cells are also involved. A study found that certain genes related to vitamin A can affect how severe HT is and who is more likely to get it.

In HT patients, an imbalance in gut bacteria (dysbiosis) affects nutrient absorption and triggers autoimmunity. This imbalance and a leaky gut barrier are major factors in autoimmune diseases. Although more research is needed, vitamin A seems to protect the gut barrier, suggesting it may play a regulatory role in managing Hashimoto's thyroiditis.

REFERENCES

Vitamin A Overview and Functions:
National Institutes of Health (NIH) Office of Dietary Supplements. "Vitamin A: Fact Sheet for Health Professionals." NIH.

Vitamin A and Thyroid Health:
Arthur JR, Beckett GJ. "Role of selenium in thyroid hormone metabolism and effects of selenium deficiency on thyroid hormone and iodine metabolism." Biological Trace Element Research, 1999. PubMed.

Stoltzfus RJ, Dreyfuss ML. "Guidelines for the Use of Iron Supplements to Prevent and Treat Iron Deficiency Anemia." International Nutritional Anemia Consultative Group (INACG), 1998. WHO.

Sources of Vitamin A:
Harvard T.H. Chan School of Public Health. "The Nutrition Source: Vitamin A." Harvard
Von Lintig, J. (2012). Provitamin A metabolism and functions in mammalian biology. The American Journal of Clinical Nutrition, 96(5), 1234S-1244S.
Hall, J. A., & Blomhoff, R. (2009). Vitamin A. In F. Firestone (Ed.), Vitamins in Health and Disease (pp. 61-75). CRC Press.
Chambon, P. (1996). A decade of molecular biology of retinoic acid receptors. The FASEB Journal, 10(9), 940-954.
Clagett-Dame, M., & Knutson, D. (2011). Vitamin A in reproduction and development. Nutrients, 3(4), 385-428.
Blaner, W. S. (2001). Retinoid metabolism and function. The FASEB Journal, 15(5), 170-185.
During, A., & Harrison, E. H. (2004). Intestinal absorption and metabolism of carotenoids: insights from cell culture. Archives of Biochemistry and Biophysics, 430(1), 77-88.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9592814/

DISCLAIMER

The contents presented here are solely for neutral information and general education. The texts make no claim to completeness, nor can the timeliness, accuracy, and balance of the information provided be guaranteed. The texts in no way replace professional advice from a doctor or pharmacist, and they may not be used as a basis for independent diagnosis or initiation, modification, or termination of treatment for diseases. Always consult your trusted physician for health-related questions or complaints! I assume no liability for inconveniences or damages arising from the application of the information presented here.