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About Vitamin A Retinol

Vitamin A exists in two forms: preformed vitamin A, exclusively occurring in animal products, and provitamin A carotenoids (e.g. beta-carotene) found in vegetal products. Both forms of vitamin A are converted to retinal and retinoic acid, the active forms of vitamin A.

Vitamin A affects the body in different ways. It greatly impacts the immune system, brain, mucous membranes, skin, teeth, eyes and bones. Adequate vitamin A intake also plays a crucial role in the fetal development and genital health of women and men. Vitamin A is a critical factor in night vision, color perception, cell growth and differentiation; it is also responsible for erythropoiesis. Vitamin A is an important antioxidant for the whole body, protecting eyes and skin from UV radiation. In addition, vitamin A is important in supporting epithelial cells of the intestinal tract surface.

Vitamin A is stored in the liver, which is then released in required amounts through enzymatic reactions. For this, zinc is needed, therefore the body in a deficiency state cannot efficiently benefit from vitamin A storage in the liver.

Vitamin A affects different tissues, among other things, through the retinoic acid receptor (RAR), retinoid X-receptor (RXR) and vitamin A receptor (STRA6). Retinoid X-receptor is required for activation of the vitamin D receptor. Hence, adequate vitamin A intake along with adequate vitamin D intake has a synergistic effect on the target tissues. Moreover, thyroid hormone receptors (TR) are fully activated when the intake of both vitamins A and D is balanced or adequate. RAR and RXR are important DNA-binding proteins or transcription factors necessary for gene expression. Both vitamins D and A act as hormones in the body.

The following factors decrease the absorption of vitamin A:

• Iron deficiency
• Excessive alcohol consumption
• Fat absorption disorders (for example, biliary tract obstruction) • Liver diseases
• Celiac disease
• Cystic fibrosis
• Pancreatic insufficiency
• Prolonged diarrhea
• Giardiasis

One can easily meet daily requirements for vitamin A by regularly eating liver, kidney, eggs, dairy products, salmon, butter, caviar, cheese, sweet potato, carrot, sweet red pepper and spinach. Since vitamin A is fat-soluble, it is more efficiently absorbed into the bloodstream when eaten with fat. Thankfully, most animal-sourced foods rich in vitamin A are also high in fat. After consumption, most of the vitamin A is stored in our liver for future use.

TOP FOODS HIGH IN VITAMIN A
Source: The National Food Composition Database in Finland (Fineli)


• Beef and reindeer liver (19,674 mcg / 100 g)
• Chlorella algae (about 15,400 mcg / 100 g)
• Other liver products (vitamin A levels vary between 2,000 and 10,000 mcg / 100 g)
• Dried carrot (6,758 mcg / 100 g)
• Eel (2,500 mcg / 100 g)
• Seaweed (nori) (1,237.5 mcg / 100 g)
• Carrot (774.1 mcg / 100 g)

• Curly kale (765.8 mcg / 100 g)
• Sweet potato (764 mcg / 100 g)
• Butter (705.3 mcg / 100 g)
• Rosehip (522.9 mcg / 100 g)
• Parsley (468.7 mcg / 100 g)
• Cod liver oil (250–750 mcg / 5–15 ml portion)

Biostarks reference ranges for vitamin A

  • Vitamin A Retinol (VitA-S): 2.0-10 umol/L

Scientific references:

  • Penniston, K. & Tanumihardjo, S. (2006). The acute and chronic toxic effects of vitamin A. The American Journal of Clinical Nutrition 83 (2): 191–201.
  • Higdon, J. & Tan, L. (2015). Vitamin A. The Linus Pauling Institute’s Micronutrient Information Center (MIC).
  • John, D. A., & Brundha, M. P. (2016). Awareness of Vitamin A Deficiency among Middle Aged Men-Research. Vitamins & Minerals, 5(2): 144.
  • Gattu, S., Bang, Y. J., Pendse, M., Dende, C., Chara, A. L., Harris, T. A., ... & Hooper, L. V. (2019). Epithelial retinoic acid receptor β regulates serum amyloid A expression and vitamin A-dependent intestinal immunity. Proceedings of the National Academy of Sciences, 116(22), 10911-10916.
  • Al Tanoury, Z., Piskunov, A., & Rochette-Egly, C. (2013). Vitamin A and retinoid signaling: genomic and nongenomic effects: thematic review series: fat-soluble vitamins: vitamin A. Journal of lipid research, 54(7), 1761-1775.