Basic Concepts:
- Vitamin A has a strong regenerative effect on the skin, promotes cellular differentiation, and regulates sebaceous gland activity.
- Vitamin A deficiency is common in developing countries but rare in developed ones. Conversely, vitamin A hypervitaminosis is more frequent and is mainly caused by excessive consumption of supplements containing vitamin A.
- Common cosmetics contain substances like Retinol and Retinyl Palmitate, which need to be metabolized into retinoic acid in the skin to become biologically active; however, this conversion may not always occur extensively.
- The beneficial effect of retinoic acid on hair follicles is well known but has certain limitations
Vitamin A Overview:
Vitamin A is a fat-soluble vitamin with a broad spectrum of actions, regulating many essential functions in the human body. Ancient Egyptians already knew that consuming liver could treat vision problems, but the active substance, vitamin A, was only discovered in 1922 by Mori.
Vitamin A exists naturally in various chemical forms (alcohol, aldehyde, acid), with retinol (alcohol) being the most common and biologically active form. Vitamin A from animal sources is found as retinyl esters, while plant-based vitamin A exists as retinal (two aldehyde molecules forming one β-carotene molecule). Vitamin A from mixed sources is in the form of retinol.
In the human body, vitamin A circulates as retinyl ester, is mainly stored in the liver (50–90%), and is rapidly transported by hepatic stellate cells (also called star-shaped liver cells)
Vitamin A & Its Actions
Vitamin A is essential for the normal growth of the body and the proper functioning of the eyes, skin, gonads, and immune system. It is crucial for the functions of the mucous membranes in the respiratory, urinary, and gastrointestinal systems, as well as for hormone synthesis. Moreover, vitamin A plays a key role in cellular division and differentiation. It also helps maintain skin integrity, while retinoids are vital for visual acuity, especially in low-light conditions.
Vitamin A acts as a regulator of the immune system, supporting lymphocytes and white blood cells in combating bacterial and viral infections. Additionally, it has been shown to possess significant in vivo pro-oxidant and antioxidant properties, and to inhibit carcinogenesis both in vitro and in vivo.
The effects of vitamin A on gene expression are mediated through protein kinases and tRNA synthases. Its action on the skin is strongly regenerative, promoting cellular differentiation of both epidermal and mesenchymal cells. Vitamin A also regulates the quality and quantity of secretions from the sebaceous glands.
Vitamin A and Dietary Sources
High amounts of vitamin A are found in all dairy products, meats—especially liver and kidneys—as well as in fish oils and eggs. Carotenoids, which are precursors to vitamin A, are abundant in carrots, pumpkins, and all dark green vegetables (e.g., spinach). Unfortunately, most animal-based foods rich in vitamin A also tend to have a high fat content.
Vitamin A Requirements
Vitamin A is typically measured in International Units (IU) or Retinol Activity Equivalents (RAE), with the conversion being 1 µg = 1 RAE = 3.3 IU. The Recommended Daily Allowance (RDA) for an adult male is 3,000 IU or 900 µg, the Adequate Intake (AI) is 500 µg (1,650 IU), and the Tolerable Upper Intake Level (UL) is set at 3,000 µg (10,000 IU).
Vitamin A Deficiency
Serum vitamin A levels do not necessarily reflect the total vitamin A status in the body, and patients with hypervitaminosis A may present with low, normal, or high serum vitamin A levels. Vitamin A deficiency is common in developing countries but rare in developed ones. The liver, the main storage site for vitamin A, can store enough to meet an adult’s needs for approximately 12 months, making deficiency from a typical Western diet very uncommon.
For context, 100 grams of cooked beef liver contains six times the recommended daily allowance (RDA) of vitamin A, while a large carrot provides four times the RDA of carotenoids. However, individuals on severely restrictive diets and strict vegans may rarely develop symptoms of vitamin A deficiency, such as decreased visual acuity, mucous membrane dryness, and frequent respiratory infections.
Other causes of vitamin A deficiency include chronic diarrhea, malabsorption of fatty acids, and chronic alcoholism, which depletes liver vitamin A stores
Vitamin A Toxicity (Hypervitaminosis A)
Vitamin A toxicity occurs when the liver’s storage capacity is exceeded and plasma retinol-binding protein becomes saturated. Hypervitaminosis A is significantly more common than vitamin A deficiency and is primarily caused by excessive consumption of dietary supplements or foods rich in vitamin A.
Chronic intake of vitamin A supplements, even at levels insufficient to cause overt toxicity, has been linked to an increased risk of osteoporosis, histological liver damage, and congenital malformations in fetuses. Common symptoms of acute vitamin A toxicity include nausea, headache, dizziness, and blurred vision, often accompanied by a yellow-orange discoloration of the skin.
Modern medicine recognizes the “vitamin A paradox”: although vitamin A is essential for the development of mammalian and human embryos, excessive use of retinoids during pregnancy can lead to teratogenic effects. Additionally, while vitamin A supplementation has significantly reduced mortality in malnourished children, it has also been associated with immune system disturbances in healthy children.
Topical Use of Vitamin A
Vitamin A for skin is one of the most widely studied ingredients in dermatology and cosmetics, especially for its powerful anti-aging properties. Extensive clinical trials have confirmed the effectiveness of retinoic acid anti-aging in reducing wrinkles, improving skin texture, and repairing sun damage. However, because retinoic acid is considered a pharmaceutical drug, it is prescription-only in many countries.
For this reason, most cosmetic formulations rely on derivatives such as retinol and Retinyl Palmitate. Retinol is the most popular form, known for its multiple retinol benefits, although it is about 20 times less potent than retinoic acid. It must be converted within the skin into retinoic acid to become biologically active, which makes its effects slower but more suitable for regular over-the-counter use.
By contrast, Retinyl Palmitate efficacy remains controversial, as scientific evidence has not consistently confirmed significant clinical results. This leads to the ongoing debate of retinol vs retinoic acid: while retinoic acid provides rapid, proven anti-aging results, retinol is gentler, more widely accessible, and better tolerated for daily skincare.
Although these derivatives show promise, research continues to determine whether their conversion into sufficient levels of retinoic acid within the skin can reliably produce visible improvements.
Vitamin A and Hair Loss
Vitamin A and hair loss have been closely linked in both dermatology and cosmetic research. Topically applied retinol has the ability to counteract collagen reduction and increased metalloproteinases in the skin’s extracellular matrix caused by sun exposure. For this reason, retinol for hair may show some potential benefits in cases of androgenetic alopecia, helping improve scalp health and hair follicle support.
However, excessive intake of vitamin A supplements has been repeatedly associated with telogen effluvium, a temporary form of hair shedding where follicles prematurely enter the resting phase. In other words, while topical Vitamin A may improve scalp condition, oral overconsumption can be one of the hidden causes of hair loss.
Supporting this, a 2012 updated meta-analysis by Bjelakovic et al., published in the Cochrane Database and including 72 randomized trials with 296,707 participants, showed that chronic supplementation with beta-carotene (a precursor of Vitamin A) increased mortality from 11.1% to 13.8%. This applied to both healthy individuals and patients with digestive, cardiovascular, neurological, ocular, dermatological, rheumatoid, renal, and endocrine diseases.
In summary, oral vitamin A supplementation does not provide proven benefits for androgenetic alopecia, while excessive intake may trigger telogen effluvium and increase certain health risks. Chronic use of beta-carotene and possibly vitamin A has also been linked with a higher risk of cancer and overall mortality. Topical retinol benefits may exist for scalp and skin, but caution is essential with internal supplementation
Summary:
Oral vitamin A supplementation has no proven positive effect on androgenetic alopecia, and excessive vitamin A intake may cause telogen effluvium (hair shedding). Supplementation with beta-carotene and possibly vitamin A increases the risk of certain cancers.
Source: Konstantinos Anastassakis MD, PhD, “Androgenetic Alopecia from A to Z,” Nutritional Supplements and Androgenetic Alopecia, pp. 365–367, 2nd Edition, Zevelekakis Publications, Athens 2017.
0
