Does Sun Give You Vitamin D?

“You need to leave your room and go out to get that vitamin D from sunlight” is something that you may have heard quite often. But here are two things you might not have heard before: 1) The sun doesn’t give us Vitamin D. 2) Human skin can use the use the sunlight to do something similar to photosynthesis carried out by plants.


So, where does the vitamin D come from? Let’s answer this question, and along the way get to know a bit more about the D-lightful origin of Vitamin D.

Kids running in forest
Kids running in forest, Credit: Rawpixel. License: CC0

Table of Contents

The Sunshine Vitamin

The origin story of this D-lightful hormone goes way back to the time when we had no idea what time was because we didn’t exist back then.


Imagine: it’s 750 million years in the past, and we are now deep in the oceans of a much younger Earth. Most creatures are living in water, and there are no big land organisms yet. The microscopic water-dwellers called phytoplankton are busy soaking up UV-B rays from the sunlight. They need the sunrays to power their biochemical mills and produce sterol—a chemical essential to their growth and survival. This process also created two by-products—Vitamins D3 and D2. Phytoplankton did not need Vitamin D2 and D3 for their metabolism. But soon these substances became major drivers in the evolutionary journey of life.

Phytoplankton and their sterol synthesis by-products (Left: Vitamin D2,
Phytoplankton and their sterol synthesis by-products Vitamin D2, Credit: Siskopoulos
Phytoplankton and their sterol synthesis by-products (Left: Vitamin D2,
Phytoplankton and their sterol synthesis by-products Vitamin D3, Credit: Wikipedia

Fast forwarding to 550 million years ago; life has evolved a long way, and we now have core proteins that can act as Vitamin D receptors, or VDRs. These VDRs allow Vitamin D to act as a hormone and participate in the endocrine system—a system of glands and organs that use hormones as messengers to regulate important functions like growth and metabolism via the circulatory system of blood and body fluid. Over a period of millions of years, Vitamin D’s signaling functions have moved up the food chain, from plankton to fishes like cod and salmon.

Vitamin D receptors started evolving in marine life
Vitamin D receptors started evolving in marine life, Credit: Wikimedia/Jawahar Swaminathan and MSD staff
Vitamin D receptors started evolving in marine life
Vitamin D receptors started evolving in marine life, Credit: KWDesigns

All this had been happening while life was exclusively underwater; but now organisms are slowly (over 100s of millions of years) evolving towards the land. Since these new land creatures don’t have water to protect them from the ball of fire in the sky, they need highly effective sunscreen. Vitamin D came to the rescue and started protecting the life of land from the harmful rays of the sun. As we moved towards the origin of human-like species, Vitamin D became more and more essential to the survival of life on earth.

Why do we need Vitamin D?

Vitamins are essential nutrients that our body needs to make sure all the organs are working properly. There are 13 essential vitamins, further divided into two categories: water-soluble vitamins and fat-soluble vitamins. The first category consists of vitamin C and 8 different vitamin B complexes. The second group consists of vitamins A, D, E, and K. All these vitamins have different purposes in our body. Some repair cells, some maintain energy, and some keep diseases at bay. Now that we have a general idea about vitamins, let’s dive into Vitamin D.


Ever since modern humans have walked this land, they have spent long hours outdoors in the sun, hunting, gathering, and, with the development of agriculture, farming. However, the industrial revolution (1740–1860) changed the way humans lived. More and more people were spending their time inside, working with machines, rather than outside, farming. Even the children weren’t getting enough sunlight because pollution from the industries was choking the clear skies. A new disease called rickets started to affect children who were around the industrial towns. More and more children were being diagnosed with bone malfunction or disorder. After a lot of investigation, doctors discovered that rickets was caused by a lack of exposure to sunlight and Vitamin D deficiency.

Vitamin D deficiency can lead to several bodily disfunctions
Vitamin D deficiency can lead to several bodily disfunctions, Credit:

Wait, didn’t we say that sunlight does not give us vitamin D? Then why is lack of sun exposure causing vitamin D deficiency? All plants’ and animals’ bodies, including humans’, manufacture a pre-cursor of vitamin D. Sunlight just helps us convert that precursor into a biologically useful form. We will get into the details in a minute, but for this section, all we need to know is we need sunlight to reap the benefits of vitamin D.


We know that our bones are made of calcium, right? But our body does not make its own calcium. We get it from different food sources, like leafy vegetables, dairy, or fish. No matter how much calcium we get from food, it’s of no use in the absence of vitamin D. Vitamin D, specifically D3, allows our intestines to absorb the calcium from our food, and hence is essential to our bone and teeth health. Since vitamin D is also a hormone, it helps with the regulation of blood pressure, energy production from food, and even the working of our immune system. Does that mean we need to consume a ton of vitamin D every day to make sure everything is functioning properly? We do need to include vitamin D-rich foods in our diet. However, that source would make up only a tiny fraction of what we actually need.

Vitamin D-rich foods. Licence: CC
Vitamin D-rich foods, Credit: Wikimedia/Ashashyou. Licence: CC

Then where does the rest come from? A process that, like photosynthesis, is powered by the sun.

“Photosynthesis” in Humans

We might not be able to make food via photosynthesis from sunlight like plants, but our skin can pump out 90% of all our Vitamin D3 needs with the help of the sun. Hidden under the layers of our skin is a light-sensitive steroid called 7-dehydrocholesterol. When we go out on a sunny day, UV-B radiation can penetrate through the skin and break one of the bonds in these photosensitive steroids. This gives rise to a new molecule called pre-vitamin D3. The warmth in our skin from soaking up the sunlight breaks down the pre-vitamin D3 into vitamin D3 (chemical name cholecalciferol). However, it’s not body-ready yet. For it to become easily absorbable, cholecalciferol has to be broken down into a simpler active chemical.

Vitamin D synthesis process. Licence: CC
Vitamin D synthesis process, Credit: Wikimedia/Hbf878.Licence: CC

Once our skin releases vitamin D3 it enters the bloodstream and eventually reaches our liver and kidneys. By the combined effort of these two organs, the vitamin is then converted to its final absorbable form, called calcitriol. The calcitriol is then absorbed by Vitamin D binding proteins, or DBPs, and transported throughout our body to fulfill its duties.


However, we must tread with caution. Sunlight is essential to vitamin D formation, but it also has the potential to damage our skin. Spending 10–20 minutes outside on a sunny day should do the trick. And what to do if you live somewhere that doesn’t have a lot of sunshine? Well, ask your doctor, they always know best!


Hormones: biologically active chemicals released by the endocrine glands. They have highly specific functions regulating and controlling functions in our body such as metabolism, growth, and the sleep cycle.


Metabolism: chemical reactions that our cells carry out to convert food into energy, which is then used for essential functions, like breathing, digesting, and growing.


Photosensitive: an object or material that reacts to light via physical or chemical responses.


Phytoplankton: chlorophyll-containing organisms that live in the ocean and use sunlight to live and grow just like terrestrial plants


Steroids: natural or man-made biologically active organic molecules that act as signalling molecules and have various physiological effects, such as suppression of the immune system and reducing inflammation.

Grade Level: 8.8


Reading Ease: 61.6

• Carlberg, C. (2022). Vitamin D in the Context of Evolution. Nutrients, 14(15), 3018. (Accessed on 6th November 2022)


• Cowart, L. (2016, May 12). The weird history of vitamin D — and what it actually has to do with sun. Washington Post. ( Accessed on 6th November 2022)


• Holick, M. F. (2008). Vitamin D: a D-Lightful health perspective. Nutrition Reviews, 66, S182–S194. ( Accessed on 6th November 2022)


• How much sun is good for our health? (n.d.). ScienceDaily. Retrieved November 7, 2022, from ( Accessed on 6th November 2022)


• Seeker. (2016, April 19). How Does Our Skin Turn Sunlight Into Vitamin D? [Video]. YouTube. ( Accessed on 6th November 2022)


• Vitamin D (Calcitriol). (n.d.). Retrieved November 7, 2022, from ( Accessed on 6th November 2022)


  • Sanjukta Mondal
    : Author
    Sanjukta Mondal (she/her) has a Master's degree in Industrial Chemistry and loves to explore the world through the lens of chemistry and her trusty camera. During postgraduate research, she worked on the development of functional materials for battery technology and water treatment. Currently, she is trying to navigate through the labyrinth of scientific writing and science writing, fuelled by coffee and her fascination for the extraordinary science and stories hidden behind everyday objects. Writing for SmoreScience will allow her to explore the enthralling world of science and share it with other curious minds.

Copyright @smorescience. All rights reserved. Do not copy, cite, publish, or distribute this content without permission.

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