Where Did We Get Vitamin D From? Sun, Diet, and Supplements Explained

January 8, 2026 •

4 min read

According to the National Institutes of Health, very few foods naturally contain vitamin D, making sun exposure and fortified products critical for most people. This crucial fat-soluble nutrient, nicknamed the "sunshine vitamin," is essential for bone health, immune function, and overall wellness. Understanding where did we get vitamin D from can help you ensure adequate levels.

Quick Summary

The three main sources of vitamin D are sunlight exposure, certain foods, and dietary supplements. Skin synthesizes vitamin D3 from UVB radiation, while diet provides D2 and D3 from fatty fish and fortified foods. Supplements are also a common way to ensure adequate intake, especially for those with limited sun exposure or specific dietary restrictions.

Key Points

Sunlight is primary: The skin synthesizes vitamin D3 from UVB rays, with synthesis affected by latitude, season, skin tone, and sunscreen use.
Food sources are limited: Few foods naturally contain vitamin D, but fatty fish like salmon, mackerel, and trout are good sources of D3.
Fortified foods help: Many common products, including milk, cereals, and orange juice, are fortified with vitamin D to aid public health.
Supplements are reliable: Dietary supplements containing D2 or D3 provide a consistent and precise way to ensure adequate intake, particularly for at-risk groups.
Activation is a multi-step process: Regardless of the source, vitamin D requires conversion by the liver and kidneys before the body can use it effectively.
Deficiency risks vary: Darker skin, older age, limited sun exposure, and certain medical conditions increase the risk of vitamin D deficiency.

The Primary Source: Sunlight

For most people, the skin's exposure to sunlight is the most significant natural source of vitamin D. The process is a marvel of biological engineering. When ultraviolet B (UVB) rays from the sun hit the bare skin, a cholesterol derivative called 7-dehydrocholesterol is converted into previtamin D3, which then thermally isomerizes into vitamin D3. This form of vitamin D is then transported to the liver and kidneys for further conversion into its active, usable form.

Factors Affecting Sun-Induced Vitamin D Production

Several factors influence how much vitamin D your skin can produce from sunlight:

Time of day: The sun is strongest between 10 a.m. and 4 p.m., which is the optimal time for vitamin D synthesis.
Latitude and season: The sun's angle varies with location and time of year. Those living at higher latitudes or experiencing winter months will have significantly reduced or no vitamin D synthesis from the sun.
Skin pigmentation: Melanin, the pigment that gives skin its color, acts as a natural sunscreen. People with darker skin require more sun exposure to produce the same amount of vitamin D as those with lighter skin.
Sunscreen and clothing: A high sun protection factor (SPF) lotion and protective clothing can effectively block the UVB rays necessary for production. Health professionals still recommend using sunscreen to mitigate skin cancer risk, balancing sun exposure with safety.

Dietary Sources: Food as Fuel

While sunlight is the primary source, dietary intake plays a crucial role, especially when sun exposure is limited. Few foods naturally contain significant amounts of vitamin D, but several options exist, including naturally rich foods and fortified products.

Naturally Occurring Sources

Natural sources of vitamin D are often the best, providing the more potent vitamin D3 form. These primarily include fatty fish and other animal products.

Fatty fish and fish oils: Excellent sources include salmon, mackerel, trout, and sardines. Cod liver oil is also a very rich source.
Egg yolks and beef liver: These contain smaller, yet still beneficial, amounts of vitamin D.
Certain mushrooms: Mushrooms exposed to ultraviolet (UV) light can produce vitamin D2, making them a plant-based option.

Fortified Foods

Food fortification has been a public health strategy since the 1920s to combat widespread deficiency diseases like rickets. Today, many common foods are voluntarily fortified with vitamin D.

Dairy and plant-based milks: Cow's milk, soy milk, and almond milk are frequently fortified.
Cereals and juices: Many breakfast cereals and some orange juice brands have added vitamin D.
Other products: Margarine and certain yogurts are also fortified with the vitamin.

The Role of Supplements

For many, especially those at higher latitudes, older adults, or those with darker skin, diet and sun exposure alone may not be enough. In these cases, dietary supplements can be a vital source. Supplements are available in two forms: vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol). While both are effective, some evidence suggests that vitamin D3 supplements may raise blood levels more efficiently and for a longer duration than D2. As always, it is recommended to consult a healthcare provider to determine if supplementation is right for you and what dosage is appropriate.

Comparison of Vitamin D Sources


Feature	Sunlight	Diet (Natural)	Diet (Fortified)	Supplements
Availability	Dependent on season, latitude, time of day, skin tone.	Variable; few foods are naturally rich in vitamin D.	Widespread, especially in milk and cereals.	Widely available in various forms (pills, liquids).
Form	Primarily Vitamin D3.	Primarily Vitamin D3 (in animal products) or D2 (in UV-exposed mushrooms).	Often D3 (milk, some cereals) or D2 (some plant-based milks).	Both D2 and D3 are available.
Risks	Excessive exposure can cause skin cancer.	High consumption of some sources (beef liver, eggs) can increase cholesterol.	Risk of excessive intake is low through fortified foods alone.	Excessive intake can lead to toxicity (hypercalcemia).
Reliability	Unreliable due to environmental and individual factors.	Requires consistent consumption of specific foods.	Varies by brand and product; requires checking labels.	Highly reliable, offering precise, consistent dosing.
Absorption	Can be less efficient with age or darker skin.	Dependent on digestion and fat absorption.	Good absorption, especially with fatty foods.	Better absorbed with meals containing fat.

The Synthesis Pathway of Vitamin D

Regardless of its source, vitamin D goes through a specific activation process in the body. Once produced in the skin or absorbed from food and supplements, vitamin D is biologically inactive. It is first transported to the liver, where it is converted into 25-hydroxyvitamin D (calcifediol). This is the major circulating form of vitamin D, and a blood test measuring its levels (25(OH)D) is the best way to assess your vitamin D status. Finally, in the kidneys, the calcifediol is converted into calcitriol, the active hormonal form of vitamin D that plays a crucial role in calcium regulation and overall health. This multi-step process ensures the body's vitamin D levels are carefully regulated. Learn more about its function at the NIH Office of Dietary Supplements fact sheet.

Conclusion

To answer the question of where did we get vitamin D from, the human body has evolved multiple pathways to acquire this vital nutrient. While sunlight is the most natural method, its effectiveness is highly dependent on individual and environmental factors. Dietary sources, both naturally occurring and fortified, provide a consistent intake but may not be sufficient for everyone. Supplements offer a reliable and controlled way to maintain adequate levels, especially for those at higher risk of deficiency. A balanced approach, combining sensible sun exposure, a vitamin D-rich diet, and targeted supplementation as needed, is the best strategy for most people to ensure their bodies have enough of the "sunshine vitamin" for optimal health.

Frequently Asked Questions

While the sun is an excellent source, it is not reliable for everyone. Factors like skin pigmentation, latitude, season, age, and sunscreen use can limit production. Experts recommend a combination of sources to ensure adequate intake.

Both forms can effectively raise blood vitamin D levels. However, some evidence suggests that D3 (cholecalciferol) may be more effective at increasing and maintaining vitamin D concentrations in the blood than D2 (ergocalciferol).

The best natural sources are fatty fish like salmon, trout, and sardines, as well as fish liver oils. Fortified foods, such as milk, cereals, and orange juice, also provide a significant amount.

Yes, fortified foods are a great way to increase your vitamin D intake, especially if you have limited sun exposure or dietary restrictions. Fortification has helped reduce deficiency-related diseases like rickets.

Groups at higher risk include older adults, people with darker skin, individuals with limited sun exposure, those with certain medical conditions affecting fat absorption (like Crohn's disease), and exclusively breastfed infants.

After intake from the skin, food, or supplements, vitamin D is first processed by the liver and then the kidneys to become its active form, calcitriol. This process is crucial for regulating calcium absorption.

You cannot get toxic levels of vitamin D from sun exposure because the body's synthesis process self-regulates. However, over-supplementation can be dangerous and lead to excessively high calcium levels (hypercalcemia).