Dr. Nuria Roda / Alberto Tejero
We spend most of our time indoors, illuminated by artificial light, with our eyes fixed on screens—whether due to remote work, studying, or leisure. This digital connection and lack of exposure to nature is altering the lifestyle maintained by our ancestors. It is precisely in this modern scenario where the duo of vitamins A and D becomes highly relevant, as both are intimately linked to light.
Nowadays, we live in an era of digital sedentarism and spend more of our lives inside homes or offices. We spend most of our time indoors, illuminated by artificial light, with our eyes fixed on screens—whether for remote work, study, or leisure. This digital connection and lack of exposure to nature has altered our lifestyle. It is in this scenario where the duo of vitamins A and D becomes highly relevant, since both are intimately linked to light. In Spain, some research reports deficiencies exceeding 76% in vitamin D among certain population groups, and globally, the WHO estimates that around 190 million preschool-aged children lack vitamin A.
To understand the magnitude of this modern disconnection, it is very helpful to observe our evolutionary history, as mentioned by Dr. Morley Robbins. Our physiological relationship with light and these nutrients is very ancient:
- An ancestral heritage: According to data from astrobiologists, vitamin A arrived on our planet about 700 million years before vitamin D. This indicates to us that our biology first adapted to interact visually and cellularly with light, with Vitamin A functioning as a true “light sensor.”
- The cycle of the seasons: Later, we developed a dependence on vitamin D, which he refers to as a “sun filter.” Evolutionarily, our body is designed to take advantage of the seasonal sun: we produce large amounts of Vitamin D during the summer, the liver is responsible for storing it, and that reserve lasts us approximately 6 months to face the winter.
The great contemporary problem is that we have broken this natural cycle. While sunlight changes naturally with the seasons, we subject our “sensors” to constant artificial light all year round, without going outside to recharge our natural reserves. Furthermore, modern medicine often tries to fix this lack of light with isolated supplementation, which can unbalance our metabolism. For example, synthetic vitamin D consumption can end up blocking vitamin A. This underscores a golden rule in nutrition: we cannot compensate for a lifestyle disconnected from nature by taking isolated compounds without understanding how they interact with each other inside our body.
Both belong to the group of fat-soluble vitamins, which means they are absorbed better when consumed along with lipids. They travel through the bloodstream and are stored in tissues such as the liver, muscle, and adipose tissue. Below, their properties will be discussed:
Vitamin A (Retinol and Provitamin A)
Vitamin A, known in its active form as retinol, or in its plant precursor form as provitamin A (beta-carotenes), is much more than the “eyesight vitamin”. Its functions are:
- Vision and cellular differentiation: It is essential for vision. Its metabolites act directly on our ability to process light. The body takes the retinol you consume and converts it into a molecule called retinal. This retinal binds to a protein in your eyes to form rhodopsin, which is the key visual pigment. When a light ray enters your eye in the dark, it hits this molecule. The impact of the light causes vitamin A to physically change shape, generating an electrical impulse that travels directly through your optic nerve to the brain, translating into the image you see.
- Immunological Shield: It participates in the development of helper T cells and B cells, making it important for adaptive immunity. Its contribution to the regeneration of the mucosal epithelium and the functioning of neutrophils, macrophages, and natural killer cells also makes it important for innate immunity.
- Cellular energy: Robbins elevates its importance to the most basic cellular level. He points out that retinol is fundamental inside the mitochondria. It acts as an essential bridge that allows electrons to move and generate energy. According to this view, a lack of retinol forces the cell to use inefficient energy methods (Warburg effect).
- Mineral Metabolism (Iron and Copper): While this is traditionally not emphasized, Dr. Robbins highlights that vitamin A is indispensable for producing Transferrin and for making Copper bioavailable in the body.
Its deficiency is severe. If there is not enough vitamin A, the eye runs out of visual pigments, causing night blindness. Furthermore, on a physical level, the lack of this vitamin prevents proper eye lubrication, which can lead to extreme dryness (xerophthalmia) and corneal ulceration. In addition, it weakens the immune system and can cause fertility problems. From Robbins’ perspective, its deficiency profoundly affects energy metabolism and has even been proposed as a factor in the development of cancer.
Vitamin D (Cholecalciferol)
Vitamin D functions in our body as a steroid hormone (derived from cholesterol). It is produced endogenously when sunlight comes into contact with 7-dehydrocholesterol in our skin. Among its benefits are:
- The architect of bones: Its best-known function is to maintain calcium and phosphorus homeostasis. Its action is to mobilize calcium from the bone and inhibit the secretion of parathyroid hormone (PTH), which indirectly stimulates osteoclasts (the cells responsible for extracting calcium from bone); in this way, it facilitates bone mineralization and, therefore, strengthens our bones.
- Immune Support: Beyond bones, it plays a prominent role in regulating our immune system. Almost all white blood cells in the body (macrophages, T cells, and B cells) have vitamin D receptors. When vitamin D binds to them, it activates the production of antimicrobial peptides. A healthy immune system must not only know how to attack, but also when to stop. Vitamin D helps modulate this response, preventing the immune system from overreacting.
Chronic deficiency, caused mainly by lack of sunlight, causes rickets in children and osteomalacia or osteoporosis in adults. However, an excess also brings problems, although it is rarer. Clinically, it causes soft tissue calcification, nausea, and kidney problems. Dr. Robbins adds a profound warning regarding excessive supplementation with synthetic vitamin D: he states that it can “block” vitamin A and that, in very high doses, it can increase iron storage in tissues, decreasing cellular energy production (ATP).
In conclusion, little is known about the shared history between our cells, light, and these nutrients. To properly absorb and take advantage of these benefits, it is ideal to consume these vitamins along with healthy fats (such as avocado or olive oil), as fatty acids are their natural transport vehicle.
Bibliographic references:
- Navarro Valverde, C., & Quesada Gómez, J.M.. (2014). Vitamin D deficiency in Spain: reality or myth? Revista de Osteoporosis y Metabolismo Mineral, 6(Supl. 1), 5-10. https://dx.doi.org/10.4321/S1889-836X2014000500002
- Song, P., Adeloye, D., Li, S., Zhao, D., Ye, X., Pan, Q., Qiu, Y., Zhang, R., Rudan, I., & Global Health Epidemiology Research Group (GHERG) (2023). The prevalence of vitamin A deficiency and its public health significance in children in low- and middle-income countries: A systematic review and modelling analysis. Journal of Global Health, 13, 04084. https://doi.org/10.7189/jogh.13.04084
- Robbins, M. (2021). Cure Your Fatigue: The Root Cause and How to Fix It on Your Own. BenBella Books.
- López-Picadoa A., Fernández Torresa M., Martínez Santosa M., Marina Ruiza I. (2009). Fat-soluble vitamins. Guide for correct dispensation. Farmacia Profesional, Vol. 23. 6. pages 41-44.
- McEldrew, E. P., Lopez, M. J., & Milstein, H. (2022). Vitamin A. In StatPearls. StatPearls Publishing.
- Tuckey R.C et al. The serum vitamin D metabolome: What we know and what is still to discover. J Steroid Biochem Mol Biol. 2019 Feb; 186:4-21.