What is the difference between vitamin D and D3?

According to the National Institutes of Health, nearly 50% of the global population is affected by vitamin D insufficiency, a nutrient vital for bone health and immune function. Much of the confusion surrounding this nutrient stems from the different forms available, specifically differentiating the general term "vitamin D" from the more specific "vitamin D3".

Quick Summary

The term "vitamin D" encompasses different forms, primarily D2 and D3. D3 is synthesized in the skin from sun exposure and found in animal-sourced foods, while D2 is plant-derived. D3 is often more effective at raising and maintaining blood levels.

Key Points

• Umbrella Term: The term "vitamin D" is a general name for several related compounds, primarily D2 and D3.

• Source Difference: D3 is synthesized in the skin from sunlight and found in animal products, while D2 is plant-based and found in fungi.

• Potency Distinction: Research suggests vitamin D3 is more effective than D2 at increasing and sustaining blood vitamin D levels over time.

• Supplement Choice: D3 is recommended for most people, while vegans can use D2 or D3 from lichen sources, with supplements showing equal or better efficacy depending on the individual.

• Metabolic Process: Both D2 and D3 are inactive until the body converts them in the liver and kidneys into calcitriol, the active form of vitamin D.

• Health Impact: Vitamin D, in either form, is vital for calcium absorption, bone mineralization, immune function, and can help prevent long-term health issues associated with deficiency.

Vitamin D is a fat-soluble vitamin crucial for various bodily functions, including promoting calcium absorption and regulating cell growth. However, when people refer to "vitamin D," they are often using it as a blanket term for a family of compounds, the most common being vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol). While both play a role in maintaining health, they differ significantly in their source and how effectively the body utilizes them.

Understanding the Two Forms: D2 vs. D3

Vitamin D3 (Cholecalciferol)

Often called the “sunshine vitamin,” vitamin D3 is the form naturally produced in human and animal skin upon exposure to ultraviolet B (UVB) radiation from sunlight. This makes sun exposure the primary source for most people, though many rely on food and supplements to maintain adequate levels, especially in regions with limited sunlight.

• Sources: Animal-sourced foods are the natural dietary providers of vitamin D3, including oily fish (salmon, trout, mackerel), fish oil, egg yolks, and liver.
• Production: In the skin, a cholesterol precursor called 7-dehydrocholesterol is converted to pre-vitamin D3 by UVB radiation, which then spontaneously converts to cholecalciferol.

Vitamin D2 (Ergocalciferol)

Vitamin D2 is the plant-based variant of the vitamin, produced when fungi, like mushrooms, are exposed to UV light. This form is also commonly used to fortify foods, such as cereals, plant-based milks, and orange juice, making it a key source for those on vegetarian or vegan diets.

• Sources: Naturally found in UV-exposed mushrooms and yeasts. It is also the form added to many fortified food products due to its lower production cost.
• Production: Ergosterol, a compound in plants and fungi, is irradiated to produce ergocalciferol.

The Body's Processing of Vitamin D

Both vitamin D2 and D3 are biologically inactive when ingested or produced. For the body to use them, they must undergo two hydroxylation steps. First, the liver converts both forms into 25-hydroxyvitamin D (calcifediol). This is the main circulating form measured in blood tests to determine vitamin D status. The kidneys then perform a second conversion to produce the active form, calcitriol (1,25-dihydroxyvitamin D), which binds to vitamin D receptors to regulate bodily functions.

Comparison of Vitamin D2 and D3

Feature	Vitamin D3 (Cholecalciferol)	Vitamin D2 (Ergocalciferol)
Primary Source	Sunlight exposure and animal-based foods	Plant-based foods (mushrooms) and fortified products
Effectiveness	Shown to be more effective at increasing and maintaining serum vitamin D levels	Raises vitamin D levels but is generally considered less potent and has a shorter half-life
Chemical Stability	More stable than D2	More sensitive to humidity and temperature fluctuations, which may affect shelf life
Suitability for Diet	Naturally found in animal products, so not suitable for strict vegans unless derived from lichen	Suitable for vegetarians and vegans
Production Cost	Generally more expensive to produce in supplement form compared to D2	Cheaper to produce, making it common in fortified foods and some supplements

Which Form Is Superior: D3 vs. D2?

While both forms can effectively treat and prevent vitamin D deficiency, a growing body of evidence indicates that D3 is superior for raising and sustaining vitamin D levels in the blood. A 2012 meta-analysis, for example, found that D3 was significantly more effective than D2 at increasing serum 25-hydroxyvitamin D concentrations. This is because D3 has a greater affinity for the vitamin D binding proteins in the bloodstream and a longer half-life, leading to more stable and higher circulating levels.

For most people who are not on a strictly plant-based diet, vitamin D3 is the recommended supplement choice due to its higher potency. However, for vegans and some vegetarians, vitamin D2 remains a viable option, though they should be aware of its potential lower effectiveness. For plant-based individuals seeking the benefits of D3, supplements derived from lichen are now widely available. Regardless of the form, it is always best to consult a healthcare provider to determine the appropriate dosage for your needs.

Key Roles of Vitamin D in the Body

As a crucial fat-soluble nutrient, vitamin D performs many roles beyond bone health, including:

• Calcium Absorption: Vitamin D's primary function is to regulate calcium and phosphorus levels. It enhances the intestinal absorption of calcium and promotes the mineralization of bones.
• Bone Health: Adequate vitamin D prevents bone disorders such as rickets in children and osteomalacia and osteoporosis in adults.
• Immune System Modulation: Vitamin D helps modulate immune responses, supporting the body's defense against infections by regulating immune cell activity and reducing inflammation.
• Muscle Function: It contributes to muscle strength and function, with deficiency often linked to muscle weakness and fatigue.
• Mental Health: Studies have shown a link between low vitamin D levels and an increased risk of depression and anxiety.
• Chronic Disease Prevention: Vitamin D insufficiency is associated with a higher risk of chronic conditions, including cardiovascular disease, diabetes, and some cancers.

How to Choose Your Vitamin D Supplement

1. D3 or D2: Unless you are vegan, D3 is generally the superior choice for supplementation due to its higher effectiveness. Vegans can opt for D2 or D3 sourced from lichen.
2. Dosage: The recommended daily allowance varies by age, but a healthcare provider can help determine the correct dose based on your individual needs and current levels.
3. Form: Supplements come in various forms, including capsules, tablets, and liquid drops. Liquid drops may be beneficial for those with swallowing or digestive issues and often have better absorption.
4. Third-Party Testing: To ensure a product's quality and accuracy, look for third-party certifications from organizations like U.S. Pharmacopeia (USP) or National Sanitation Foundation (NSF).
5. Storage: Since vitamin D is fat-soluble, it's best absorbed when taken with a meal containing some healthy fat.

Conclusion

In summary, while both D2 and D3 are forms of vitamin D, they have distinct origins, and D3 is generally more effective at raising and maintaining the body's vitamin D levels. Vitamin D is an essential nutrient with profound effects on bone health, immune function, and overall well-being. Selecting the right supplement requires understanding the differences between these forms, considering dietary needs, and consulting a healthcare professional to ensure appropriate dosing. For further information on the broader effects of this nutrient, explore resources from the Office of Dietary Supplements at the National Institutes of Health.

Frequently Asked Questions

What is the primary difference between vitamin D2 and vitamin D3?

The main difference lies in their source. Vitamin D3 is naturally produced in the skin from sun exposure and found in animal products, while Vitamin D2 is plant-derived, often from mushrooms exposed to UV light.

Which form of vitamin D is more potent?

Many studies show that vitamin D3 is more effective than vitamin D2 at increasing and sustaining overall vitamin D levels in the blood.

Can vegans take vitamin D3?

Yes, vegans can take vitamin D3 from specific plant sources, as some supplements use D3 derived from lichen rather than animal-based lanolin.

How does the body use vitamin D?

After absorption or synthesis, the liver and kidneys convert vitamin D (D2 or D3) into its active form, calcitriol, which helps absorb calcium and phosphorus for healthy bones.

What are the health risks of low vitamin D?

Long-term vitamin D deficiency can lead to bone disorders like rickets in children and osteomalacia in adults, and is linked to chronic illnesses such as cardiovascular disease, diabetes, and certain cancers.

How can I choose a quality vitamin D supplement?

To choose a high-quality supplement, look for third-party testing certifications (like USP or NSF), check the label for the specific form (D3 is often preferred), and consider liquid or gel-cap formulations for better absorption.

Do fortified foods contain vitamin D3 or D2?

Fortified foods, such as cereals and milk, most often contain the plant-based vitamin D2 (ergocalciferol) because it is cheaper to produce.