Clarifying How to Increase Vitamin D4: The Facts About D2 and D3

November 18, 2025 •

3 min read

While there are several forms of vitamin D, the one known as vitamin D4 is not a standard dietary recommendation for human health. Rather than focusing on how to increase vitamin D4, the effective strategy involves understanding and prioritizing the clinically relevant forms: vitamin D2 and vitamin D3.

Quick Summary

Vitamin D4 is a fungal metabolite with unconfirmed human health benefits, unlike D2 and D3. This guide explains how to effectively boost your body's usable vitamin D levels through diet, safe sun exposure, and supplementation.

Key Points

Focus on D2 and D3: The clinically relevant forms of vitamin D are D2 (ergocalciferol) and D3 (cholecalciferol), not D4.
D4 is a Fungal Form: Vitamin D4 is primarily found in certain mushrooms and its human health benefits are not well-studied or confirmed.
Sunlight is Key for D3: Safe, controlled exposure to sunlight is a major way for your body to produce vitamin D3.
Boost D2/D3 with Diet: Incorporate fatty fish, fortified dairy, and UV-exposed mushrooms into your diet to increase your intake.
Supplements are an Option: D2 and D3 supplements, especially D3, are an effective way to address deficiency, particularly with a doctor's guidance.
Consult a Professional: Always talk to a healthcare provider before starting a supplement regimen to determine your correct vitamin D needs.

What is Vitamin D4 and Why Isn't it the Focus?

Vitamin D is a group of fat-soluble secosteroids responsible for enhancing intestinal absorption of calcium, magnesium, and phosphate, and numerous other biological effects. The term 'vitamin D' often refers to either vitamin D2 (ergocalciferol) or vitamin D3 (cholecalciferol). In contrast, vitamin D4 (22-dihydroergocalciferol) is a less-common form found primarily in certain mushroom species.

The Fungal Origin of Vitamin D4

Unlike vitamin D3, which humans produce in their skin from sun exposure, vitamin D4 is created by fungi from a precursor called 22,23-dihydroergosterol. While its presence in certain foods like mushrooms is noted, its function in human physiology is largely unstudied and not considered clinically significant. The vast body of research and clinical practice focuses on the more prevalent and well-understood D2 and D3 forms, which are critical for bone health and immune function. For this reason, attempting to specifically increase vitamin D4 is not a recognized health strategy and can be misleading.

The Scientifically Proven Ways to Increase Vitamin D (D2 and D3)

Instead of searching for how to increase vitamin D4, a far more productive approach is to concentrate on proven ways to boost your levels of D2 and D3. These methods include safe sun exposure, dietary changes, and targeted supplementation.

Maximize Safe Sunlight Exposure

Your body produces vitamin D3 when your bare skin is exposed to UVB radiation from the sun. A few minutes of sun exposure daily to your arms, legs, and face can be sufficient for many people, depending on factors like skin tone, location, and time of year. However, remember to balance sun exposure with skin cancer risks and wear sunscreen after the initial few minutes of sun, or if you plan to be out for longer periods.

Consume Vitamin D-Rich Foods

Dietary intake is another vital source of vitamin D, especially for those with limited sun exposure. While naturally occurring sources can be limited, many foods are now fortified with vitamin D. To increase your intake, consider incorporating these options into your diet:

Fatty Fish: Excellent natural sources include salmon, mackerel, tuna, sardines, and trout.
Fortified Dairy and Alternatives: Almost all milk in the U.S. is fortified with vitamin D. Many plant-based milks, including almond, soy, and oat milk, are also fortified.
Fortified Cereals and Juices: Check the nutrition label on breakfast cereals and orange juice, as many brands add vitamin D.
Mushrooms: Some mushrooms contain vitamin D2, and their content can be significantly increased by exposing them to UV light.
Other Sources: Smaller amounts can be found in egg yolks, beef liver, and cheese.

Take Dietary Supplements

For many, especially those with limited sun exposure or dietary restrictions, supplements are the most effective way to maintain adequate vitamin D levels. Supplements typically come in the form of D2 (ergocalciferol) or D3 (cholecalciferol). Clinical evidence suggests that D3 supplements may be more effective at raising blood levels for a more sustained period than D2. Always consult with a healthcare provider before starting any new supplement regimen to determine the appropriate dosage for your needs.

Comparing the Different Forms of Vitamin D


Feature	Vitamin D2 (Ergocalciferol)	Vitamin D3 (Cholecalciferol)	Vitamin D4 (22-Dihydroergocalciferol)
Source	UV-irradiated fungi (e.g., mushrooms) and fortified foods.	Sunlight on skin, fatty fish, egg yolks, fortified foods.	Primarily certain fungi and mushrooms.
Significance in Humans	Clinically relevant and well-studied; raises blood vitamin D levels.	Most biologically active form in humans; crucial for calcium absorption and bone health.	Minimal, unconfirmed relevance; not a standard target for supplementation.
Bioavailability	Well absorbed in the small intestine.	Well absorbed and potentially more effective at raising blood levels than D2.	Bioavailability and clinical effect are not well established.
Supplement Availability	Available, sometimes requires a prescription.	Widely available over-the-counter.	Not available as a mainstream supplement.

Conclusion: Prioritize the Right Vitamin D

In summary, while the question of how to increase vitamin D4 may arise, it is not a practical or beneficial goal for human health. The medical community and nutritional guidelines focus on vitamins D2 and D3 due to their proven roles in supporting bone density, immune function, and overall wellness. By prioritizing safe sun exposure, incorporating D-rich and fortified foods, and considering a D3 supplement, you can confidently and effectively increase your usable vitamin D levels. For more information on dietary needs and supplements, refer to reputable health sources such as the NIH Office of Dietary Supplements.

Frequently Asked Questions

Vitamins D2 and D3 are the two primary forms that impact human health, supporting calcium absorption and bone density. Vitamin D4 is a less-common form found in fungi, with minimal confirmed relevance to human health.

The human health benefits of vitamin D4 have not been well-studied or confirmed. Most clinical recommendations and nutritional science focus on the benefits and requirements for vitamins D2 and D3.

Vitamin D4 is found naturally in certain mushroom species, such as some varieties of button and shiitake mushrooms, particularly those exposed to UV light.

No. Vitamin D4 supplements are not widely available and are not recommended for supplementing vitamin D levels. The focus should be on D2 or D3 supplements, with a healthcare provider's consultation.

You can increase your overall vitamin D levels by getting safe sun exposure, eating foods naturally rich in vitamin D like fatty fish, or consuming fortified foods. Supplements are also an effective option.

Yes, some mushrooms contain vitamin D2, and their content can be significantly increased by exposure to UV light. However, the most reliable and potent sources for humans are fatty fish, fortified dairy, and supplements.

Many people prefer vitamin D3 (cholecalciferol) supplements, as some studies suggest they may be more effective at raising and maintaining blood levels than D2. The best choice for you depends on your specific needs and a healthcare provider's advice.