Vitamin D, is in fact, not a vitamin. Vitamins are things that cannot be made by humans. Vitamin D is a secosteroid hormone. The active from of Vitamin D, 1,25-D, is the powerful steroid hormone made by the human body.
Let’s be clear from the beginning; cholecalciferol, in pill form, DOES NOT replace light.
“The radiation of the sun delivers the energy to maintain all processes of life on earth. But light is, from the viewpoint of living matter, more than a source of energy. It is the means to recognize the world…”(Clayton, Roderick K. 1970). Sunlight reaches the human body through the eyes, the skin, and in the gut. Photosynthesis links the food that we eat with the light in our environment. The light we surround ourselves with plays such an influential role in human biology that industrial light manufacturing has engineered lighting in specific ways to increase productivity in the workplace. Have you ever heard the phrase “genetics loads the gun, environment pulls the trigger?” If I’ve heard it once, I’ve heard it a thousand times. Our understanding of Circadian Biology and the physics of light has completely changed the meaning of this phrase. What do we know now that we did not know 10-15 years ago? Our zip code controls our genetic code. Genes are designed to respond directly to the environment around us. In this case, when I say environment I am talking about light and electromagnetic radiation. You see, one of the most important things that we know now that we did not know 10-15 years ago is that the mitochondria directly control genetic expression. Previously, we have been under the impression that the nucleus was the primary control arm of genetic expression, but now we know through Redox, reactive oxygen species (ROS), Calcium (Ca2+), pH, and Mitochondrial Unfolded Protein Response (UPRmt), the mitochondria communicate directly to the nucleus of our cells. This communication to Cytosolic-Nuclear Signal Integration facilitates Nuclear Signal Interpretation, and in turn, Nuclear Response Output. You might be wondering how any of this relates to light? Mitochondria are heavily influenced by, and even responsive to, many different frequencies of light. To fully understand how light can impact human biology, you must first realize that surface topology influences the biochemistry beneath it. Quantum Physics, biochemistry, endocrinology and nutrition all intersect in the study of Circadian Biology.
Ultraviolet light touches the brain and central neuroendocrine system through the eyes and the skin. The human body has the ability to transduce ultraviolet electromagnetic energy into chemical, hormonal, and neural signals. UV radiation on the skin upregulates neuroendocrine axes, locally inducing proopiomelanocortin-peptides, corticotropin-releasing hormone, and cytokines, just to name a few. Once released into circulation, exerting systemic effects activating the hypothalamic-pituitary-adrenal axis, immunosuppression independent of vitamin D, and even opioidogenic effects. UV light also has profound impacts on circadian rhythm, directly reaching the paraventricular and arcuate nuclei of the hypothalamus through the retino-hypothalamic tract of the eyes.
UVA and UVB radiation both are biologically relevant portions of the electromagnetic spectrum. Constituting major cutaneous stressors. UVB, though only representing a small fraction of the Sun’s energy reaching the Earth’s surface, is very efficient at exerting biological effects. UVB is absorbed mostly by the upper layers of the human epidermis, but also penetrates to the papillary dermis. UVA penetration reaches the reticular dermis but is 1000 times less efficient at inducing biological effects at the minimal erythemal dose than UVB. VIS deeply penetrates the skin reaching the hypodermis, but it does not inflict substantial photodamage, due to poor absorption in the epidermis. The wavelengths of solar light reaching the Earth have similar photon energy (eV): VIS: 1.65 to 3.1, UVA = 3.10 to 3.94, UVB = 3.94 to 4. The magnitude of the biological response is defined by two key mechanisms:
1) the chromophore absorbing the light
2) the quantum mechanics of electron excitation.
A chromophore is an atom or a group that is responsible for the color of a compound. Beta-carotene, for example, is a strongly colored orange-red pigment found in carrots, pumpkins, and yams. Beta-carotene absorbs green light, and reflecting others, giving it its red-orange appearance. What are some biologically relevant chromophores you have probably heard of before?
- Aromatic amino acids (phenylalanine, tyrosine, tryptophan, and histidine)
- Biogenic amines (histamine, serotonin, epi and norepinephrine, and dopamine)
- Pyrimidines and Purines (adenine (ATP) and guanine (GTP))
- Quinones (Vitamin K, CoQ10)
- 7-dehydrocholesterol (required to form cholecalciferol)
The primary chromophore for the VIS part of the spectrum, is located in the retina. In conjunction with opsin proteins, is involved in the phototransduction necessary for vision and/or regulation of circadian rhythm. In conjunction with cryptochromes, flavins and pterines absorb shorter wavelengths of VIS and are involved in photoreception and phototransduction and may affect circadian rhythm.