Is Vitamin D3 Made From Humans? Unpacking the Science of the Sunshine Vitamin

November 10, 2025 •

4 min read

Fact: The human body can, and does, synthesize its own vitamin D3 when exposed to sunlight. The question, is vitamin D3 made from humans?, is based on a misunderstanding, as humans are the ones who produce it in their skin, triggering a vital process for bone and immune health.

Quick Summary

The human body naturally synthesizes its own vitamin D3, or cholecalciferol, in the skin when exposed to UVB radiation. It is also obtained through dietary sources like fatty fish, eggs, and fortified foods, as well as supplements derived from animals or plants.

Key Points

Endogenous Production: The human body produces its own vitamin D3 in the skin when exposed to UVB radiation from sunlight.
Activation in Organs: The vitamin D3 synthesized in the skin is inactive until it undergoes two processing steps in the liver and kidneys to become the active hormone.
Dietary Sources: Fatty fish, eggs, and fortified products are key dietary sources of vitamin D3, supplementing what the body produces naturally.
D3 vs. D2: Vitamin D3 from animal sources is generally more effective at raising and sustaining blood vitamin D levels than vitamin D2 from plant sources.
Vital Functions: Adequate vitamin D3 levels are essential for bone health, immune function, and regulating calcium and phosphorus in the body.
Multiple Factors: The amount of vitamin D3 produced by the skin depends on skin pigmentation, age, geographical latitude, and sunscreen use.

How Humans Synthesize Their Own Vitamin D3

When asking, "Is vitamin D3 made from humans?", the most accurate answer is that humans have the capability to produce it within their own bodies. This fascinating process occurs primarily in the skin and is a perfect example of our biological adaptation to our environment. When our skin is exposed to ultraviolet B (UVB) radiation from sunlight, it converts a cholesterol precursor called 7-dehydrocholesterol into previtamin D3. This previtamin D3 then undergoes a temperature-dependent rearrangement to form vitamin D3, or cholecalciferol. The amount of vitamin D3 produced this way is influenced by several factors, including the intensity of the sun, the season, the person's skin pigmentation, and age. For example, a person with darker skin requires longer sun exposure than someone with a lighter complexion to synthesize the same amount of vitamin D3.

The Activation Process: Liver and Kidneys

After its initial synthesis in the skin, the vitamin D3 is still in an inactive form. To become biologically active, it must undergo two hydroxylation steps in the body. First, it travels to the liver, where it is converted into 25-hydroxyvitamin D. This is the major circulating form of vitamin D, and it's what healthcare providers typically measure to determine an individual's vitamin D status. The second and final step occurs in the kidneys, which convert 25-hydroxyvitamin D into the active hormone, 1,25-dihydroxyvitamin D, or calcitriol. Calcitriol plays a critical role in regulating calcium and phosphorus levels in the bloodstream, which is essential for bone health.

Dietary Sources of Vitamin D3

While the sun is the most efficient source for synthesizing vitamin D3, dietary intake is also crucial, especially during months with limited sun exposure or for those who avoid the sun. Few foods naturally contain significant amounts of vitamin D, but several are fortified to help meet daily requirements. A balanced nutrition diet can provide a necessary boost, particularly from animal-based sources.

List of Foods with Vitamin D3

Fatty Fish: Excellent sources include salmon, mackerel, herring, and sardines. A single serving of salmon can provide a substantial portion of the daily recommended intake.
Cod Liver Oil: This supplement is a highly concentrated source of vitamin D3.
Egg Yolks: Eggs from chickens with access to sunlight produce yolks with higher vitamin D content. This is a simple and versatile way to increase intake.
Beef Liver: Though it contains smaller amounts of vitamin D3 compared to fatty fish, it is still a contributing source.
Fortified Foods: Many common products are fortified with vitamin D, including milk (dairy and plant-based), some cereals, yogurts, and orange juice.
Mushrooms: Some mushrooms, when exposed to ultraviolet light, can provide vitamin D, though mostly D2. However, some treated mushrooms can contain some D3.

The Vitamin D3 vs. Vitamin D2 Debate

When looking for supplements or fortified foods, you might encounter two main forms: vitamin D3 (cholecalciferol) and vitamin D2 (ergocalciferol). The main difference lies in their origin and effectiveness in the body.

Comparison Table: Vitamin D3 vs. Vitamin D2


Feature	Vitamin D3 (Cholecalciferol)	Vitamin D2 (Ergocalciferol)
Origin	Naturally produced by animals (including humans) and obtained from animal products like fatty fish, liver, and eggs.	Primarily produced by plants and fungi, such as mushrooms, and used to fortify certain foods.
Sourcing	Typically sourced from lanolin (sheep's wool) for supplements, but vegan versions from lichen are also available.	Derived from yeast, and therefore is a vegan-friendly option for supplementation.
Efficacy	Often considered more potent and effective at raising blood vitamin D levels and sustaining them for a longer period.	Less effective at increasing and maintaining blood vitamin D concentrations compared to D3.
Absorption	More easily absorbed by the body.	Also well-absorbed, but generally raises serum levels less effectively than D3.

Why Adequate Vitamin D3 is Important

Beyond its role in calcium absorption and bone health, vitamin D3 is vital for numerous other physiological functions. It helps regulate the immune system, modulate cell growth, and may play a role in reducing inflammation. A deficiency can lead to bone conditions like rickets in children and osteomalacia in adults. Furthermore, some studies have linked low vitamin D status to an increased risk of certain autoimmune diseases and conditions like type 2 diabetes. Ensuring you have adequate levels through sun exposure and a proper nutrition diet is a key step towards overall wellness.

Conclusion

In summary, the notion of Is vitamin D3 made from humans? is based on a literal truth: our bodies are natural vitamin D3 factories. While sun exposure is a primary source for internal synthesis, a balanced nutrition diet rich in D3-containing foods is equally important for maintaining healthy levels. The body requires active vitamin D3 to perform critical functions, from strengthening bones to supporting the immune system. With modern lifestyles limiting sun exposure, many individuals turn to dietary sources and supplements to bridge the gap. By understanding the science of how our bodies make and utilize this vital nutrient, we can make more informed decisions to support our overall health and well-being. Harvard Health offers further insights on the topic.

Frequently Asked Questions

You can get vitamin D3 from both sources. Your body synthesizes it in the skin upon exposure to UVB radiation, and you can also obtain it from certain foods, particularly fatty fish and egg yolks, and fortified products.

Many experts and studies indicate that vitamin D3 is more effective than vitamin D2 at raising and maintaining adequate blood levels of vitamin D. However, both forms are used in supplements and fortified foods.

The process begins when UVB rays from sunlight hit the skin, converting a compound called 7-dehydrocholesterol into previtamin D3, which is then converted into vitamin D3.

Many vitamin D3 supplements are produced by irradiating lanolin, a fatty substance from sheep's wool. Vegan D3 supplements, however, can be sourced from lichen.

After the skin produces vitamin D3, the liver converts it to 25-hydroxyvitamin D. This is then sent to the kidneys, where it is converted into the active hormone, calcitriol, which the body can use.

For many, especially those with limited sun exposure, it can be challenging to get enough vitamin D from food alone, as few foods are naturally rich in it. Fortified foods and supplements are often necessary to meet daily needs.

Vegetarians who consume dairy and eggs can get vitamin D3 from egg yolks and fortified milk and yogurt. Plant-based sources are primarily vitamin D2, but fortified cereals and some mushrooms exposed to UV light can also contribute.

Symptoms can include fatigue, bone pain, muscle weakness, and mood changes. A deficiency can also increase the risk of conditions like osteoporosis and rickets.