Where Do Humans Get Vitamin D3 From? The Complete Guide

November 25, 2025 •

4 min read

Approximately one billion people worldwide have vitamin D deficiency. Vitamin D3 can be obtained through sunlight, foods, and supplements. Each of these sources plays a crucial role in maintaining healthy vitamin D levels.

Quick Summary

Humans obtain vitamin D3 from sun exposure, certain foods, and supplements. Sunlight triggers skin synthesis, while fatty fish and fortified products offer dietary sources. Supplements provide a reliable alternative.

Key Points

Sunlight is the main natural source: UVB rays convert a cholesterol derivative in the skin into vitamin D3, but this is affected by multiple factors.
Fatty fish are a rich dietary source: Oily fish like salmon, sardines, and mackerel are natural sources of vitamin D3.
Fortified foods boost intake: Many common foods, including milk, cereals, and orange juice, are fortified with vitamin D3.
Supplements provide consistent intake: Vitamin D3 supplements offer a reliable, controlled way to ensure adequate intake, particularly during winter or for at-risk groups.
Vitamin D3 is more effective than D2: Vitamin D3, from animal sources or lichen, is generally more efficient at raising and sustaining blood vitamin D levels compared to D2, from plants.
Combining sources is often needed: A combination of sensible sun exposure, a varied diet, and, if necessary, supplements is the most effective method for maintaining healthy vitamin D3 levels.

Sunlight Exposure: The Body's Natural Production

Sunlight is a primary natural source for vitamin D3, also known as cholecalciferol. Ultraviolet B (UVB) rays from the sun react with a cholesterol derivative (7-dehydrocholesterol) in the skin. This initiates a process that converts it into pre-vitamin D3, which body heat then changes into the usable form of vitamin D3.

Factors Influencing Vitamin D3 Synthesis from the Sun

Several factors affect how much vitamin D3 a person synthesizes from sun exposure:

Season and Latitude: During autumn and winter, the sun's angle is lower, especially far from the equator. This limits the penetration of UVB rays and reduces vitamin D3 production.
Skin Pigmentation: Melanin in the skin acts as a natural sunscreen. Darker skin requires more sun exposure than lighter skin to produce similar amounts of vitamin D3.
Age: The skin's ability to produce vitamin D3 decreases with age.
Sunscreen Use: Sunscreen with an SPF of 15 or higher blocks UVB rays, reducing vitamin D3 production. Despite this, sunscreen is still recommended for sun protection to reduce skin cancer risk.
Clothing and Indoor Time: Covered skin cannot produce vitamin D3. Individuals who spend most of their time indoors or wear clothing that covers their skin, cannot rely on sun exposure.

Dietary Sources: Finding Vitamin D3 in Food

Few foods naturally contain significant levels of vitamin D3, which can make it challenging to meet daily needs through diet alone. Nevertheless, some options are available, mainly from animal sources.

Naturally Occurring Sources

Fatty Fish: Fatty fish such as salmon, sardines, mackerel, and trout are among the best natural dietary sources of vitamin D3.
Fish Liver Oils: Cod liver oil is a well-known source of vitamin D3, providing a concentrated dose.
Egg Yolks: Vitamin D in eggs is found in the yolk. Eggs from free-range chickens exposed to sunlight may have higher vitamin D content.
Beef Liver and Cheese: These contain smaller amounts of vitamin D3.

Fortified Foods

Food fortification programs, where manufacturers add vitamin D to products, are a significant source of vitamin D3 for many people. Common fortified foods include:

Milk: Most cow's milk in the U.S. is fortified with vitamin D3.
Plant-Based Milks: Soy, almond, and oat milks are often fortified to match the nutritional profile of dairy milk.
Cereals and Orange Juice: Many breakfast cereals and orange juice brands have added vitamin D.
Margarine and Yogurt: Some brands of margarine and yogurt are also fortified.

Dietary Supplements: A Consistent Option

For individuals with limited sun exposure, dietary restrictions, or concerns about insufficiency, supplements provide a reliable means to get vitamin D3.

Vitamin D2 vs. Vitamin D3

Vitamin D2 (Ergocalciferol): Derived from plants and fungi (like UV-exposed mushrooms), D2 is also available in some supplements.
Vitamin D3 (Cholecalciferol): Derived from animal sources, such as lanolin from sheep's wool, or lichen for vegan options.
Efficacy: Most evidence indicates that vitamin D3 supplements are more effective at raising and maintaining blood levels of vitamin D than D2 supplements.

How Supplements Work

Vitamin D from supplements, similar to that from food, is absorbed in the small intestine. It then goes through hydroxylation in the liver and kidneys to become its active form, calcitriol, which the body utilizes. A healthcare provider can determine the appropriate dosage based on individual needs.

Comparison of Vitamin D Sources


Source	Pros	Cons	Best For
Sunlight	Free and natural. Skin synthesizes D3.	Varies by season, latitude, skin tone. Risk of skin cancer with overexposure.	Individuals with moderate, consistent sun access and appropriate skin type
Fatty Fish	Excellent source of D3 and omega-3s.	Not an option for vegetarians/vegans. May contain mercury.	Those who eat seafood regularly and in moderation
Fortified Foods	Convenient and accessible. Integrates into the diet.	Content can vary between brands. May not provide sufficient amounts for everyone.	Individuals seeking an easy way to boost intake via common foods
Supplements	Consistent and measurable dosage. Year-round reliability.	Not regulated equally. Can lead to toxicity if dosage is too high without medical guidance.	At-risk groups, those with deficiency, or limited sun exposure

Conclusion: A Balanced Approach to Vitamin D3

Adequate vitamin D3 intake is crucial for overall health, primarily because it helps with calcium absorption for strong bones and supports the immune system. While sunlight is a strong trigger for synthesis, depending solely on it can be impractical or unsafe due to environmental factors and the risk of skin cancer. Dietary sources, especially fatty fish and fortified products, contribute significantly but are often insufficient for daily needs.

Therefore, a balanced strategy that combines sensible sun exposure, a diet rich in natural and fortified sources, and potentially a daily supplement is the most effective approach for most people. Anyone concerned about their vitamin D status should consult a healthcare provider for a blood test to determine if a supplement is needed and what dosage is appropriate. This ensures adequate intake and safety from vitamin D toxicity.

For more detailed nutritional information on vitamin D, consult the NIH Office of Dietary Supplements website.

Frequently Asked Questions

Relying on sun exposure alone for vitamin D3 is often insufficient, especially during certain times of the year and depending on individual factors. Skin color, age, sunscreen use, and geographic location impact vitamin D3 production.

Excellent food sources of vitamin D3 include fatty fish like salmon, sardines, and mackerel. Smaller amounts can be found in egg yolks and beef liver.

Fortified foods have vitamin D3 added by manufacturers. Milk, cereals, orange juice, and plant-based milks are common examples. They are a beneficial way to boost intake, but they may not be enough for those with significant deficiency.

Vitamin D2 (ergocalciferol) comes from plant sources, whereas vitamin D3 (cholecalciferol) comes from animal sources or lichen. Research indicates D3 is more effective at increasing and maintaining blood vitamin D levels.

The body regulates vitamin D3 production from the sun by converting excess precursors into inactive compounds, making toxicity from the sun alone unlikely. However, excessive sun exposure increases the risk of skin cancer.

Those at higher risk include breastfed infants, older adults, people with dark skin, those with limited sun exposure, and individuals with medical conditions affecting fat absorption.

Supplements offer a consistent, measured dose of vitamin D3 and are a reliable option when sun exposure or diet is inadequate. Unlike the sun, supplements can lead to toxicity if taken in high doses without medical supervision.