Which is better for raising vitamin D levels, D2 or D3?

D3 is generally better because it raises and maintains blood levels of vitamin D more effectively than D2 in most people.

Is D3 more expensive than D2?

Yes, D3 is typically more expensive than D2 because it is often derived from lanolin or lichen, whereas D2 is synthesized from yeast.

Are there any safety risks associated with taking D2 or D3?

Both carry a risk of toxicity at very high doses, but D3 may have a slightly higher risk due to its longer half-life in the body.

Are D2 and D3 compatible with a vegan diet?

D2 is vegan-friendly because it comes from yeast, while D3 is usually not vegan unless it is specifically sourced from lichen.

What is a common beginner mistake when choosing between D2 and D3?

A common mistake is assuming both are equally potent, which leads to underdosing D3 or overdosing D2 without checking the label's international units.

Can I use D2 and D3 interchangeably in my supplement routine?

You can use them interchangeably for basic deficiency correction, but D3 is preferred for long-term maintenance and better blood level stability.

Which form of vitamin D is used for a real-world deficiency treatment?

D2 is often used in high-dose prescription capsules for severe deficiency, while D3 is common in daily over-the-counter maintenance supplements.

Can I switch from taking D2 to D3 without any issues?

Yes, you can switch from D2 to D3 directly, but you may need to adjust the dosage because D3 is more potent at maintaining serum levels.

How do D2 and D3 differ in how the body processes them?

The body processes D3 more efficiently because it binds better to the vitamin D binding protein, leading to longer circulation time than D2.

Difference Between

Difference Between D2 and D3

Written byNex Virox Team

Editorial Team

Reviewed byVarshal Nirbhavane

Senior SEO & Organic Growth Professional · 5+ years

Published: August 29, 202618 min read

Quick answer

The main difference between D2 and D3 is that D2 is primarily obtained from food and sunlight, while D3 is more potent and effective at raising blood levels. D2 is plant-derived vitamin D (ergocalciferol), while D3 is animal-derived vitamin D (cholecalciferol) produced in skin from sun exposure.

Key takeaways

Core distinction: D2 is vitamin D2 from plants, while D3 is vitamin D3 from animal sources.
How each works: Your liver converts both D2 and D3 into active hormones your body uses.
Potency difference: D3 raises blood vitamin D levels roughly two to three times more effectively than D2.
Best-fit use: Vegans choose D2, but most people maintain levels more efficiently with D3.
Common mistake: Assuming equal dosing works, yet D3 often requires lower doses than D2.

Table of Contents18 sections

Difference Between D2 and D3: Comparison Table

Aspect	D2	D3
Definition	A form of vitamin D derived from plant sources, primarily ergosterol in fungi and yeast.	A form of vitamin D derived from animal sources, specifically 7-dehydrocholesterol in skin and lanolin.
Primary Purpose	Supports bone health and calcium absorption when obtained through fortified foods and supplements.	Maintains blood calcium levels and bone density through sunlight exposure and dietary intake.
Core Mechanism	Requires conversion in the liver to calcifediol and then to active calcitriol in kidneys.	Undergoes identical liver and kidney hydroxylation steps to produce the same active hormone calcitriol.
Chemical Structure	Contains a double bond between carbons 22 and 23 with a methyl group at carbon 24.	Has a double bond between carbons 22 and 23 but lacks the extra methyl group present in D2.
Molecular Weight	Weighs approximately 396.6 daltons per molecule, slightly heavier than its counterpart.	Weighs approximately 384.6 daltons per molecule, making it marginally lighter than D2.
Natural Source	Found in mushrooms exposed to UV light, including shiitake, portobello, and maitake varieties.	Produced in human skin from cholesterol when exposed to UVB sunlight radiation.
Dietary Origin	Comes exclusively from plant-based foods like fortified cereals, plant milks, and UV-treated mushrooms.	Comes from animal foods such as fatty fish, egg yolks, liver, and fortified dairy products.
Vegan Suitability	Fully vegan-friendly since it originates from yeast and fungi rather than animal tissues.	Not vegan-friendly because commercial sources derive from sheep wool lanolin.
Potency Comparison	Considered roughly equipotent to D3 in humans at standard supplemental doses.	Often regarded as slightly more potent at raising blood levels per microgram administered.
Half-Life	Has a shorter circulating half-life in the bloodstream, estimated around 12 to 24 hours.	Persists longer in circulation with a half-life of approximately 2 to 3 weeks.
Binding Affinity	Binds with lower affinity to vitamin D binding protein and the vitamin D receptor.	Binds with higher affinity to transport proteins and receptors, enhancing cellular uptake.
Metabolic Breakdown	Breaks down into inactive metabolites like 24-hydroxy-D2 more rapidly after conversion.	Degrades into different metabolites including 24-hydroxy-D3 at a slower overall rate.
Blood Level Raising	Raises serum 25(OH)D levels effectively but requires higher doses to match D3.	Raises serum 25(OH)D levels more efficiently per 1,000 IU administered orally.
Storage Form	Stored primarily in the liver and adipose tissue with a shorter retention period.	Stored extensively in fat tissue and muscle, allowing longer-lasting body reserves.
Supplement Form	Available as ergocalciferol capsules, tablets, and drops in most pharmacies worldwide.	Available as cholecalciferol softgels, tablets, sprays, and liquid drops in retail outlets.
Prescription Strength	Prescribed as 50,000 IU capsules for treating severe deficiency under medical supervision.	Typically sold over-the-counter in 400 to 5,000 IU doses without a prescription.
Absorption Rate	Absorbs adequately in the gut but shows slightly lower bioavailability compared to D3.	Absorbs more efficiently in the intestine, especially when consumed with fatty meals.
Conversion Efficiency	Converts to active calcitriol at roughly 60 to 70 percent of the rate of D3.	Converts to active calcitriol more readily, requiring fewer enzymatic steps overall.
Receptor Activation	Activates vitamin D receptors but dissociates faster, reducing sustained gene expression.	Activates receptors longer, promoting more prolonged transcription of target genes.
Clinical Efficacy	Shows comparable fracture prevention and bone density outcomes in most clinical trials.	Demonstrates marginally superior outcomes for raising and maintaining serum levels.
Toxicity Risk	Poses a lower risk of hypercalcemia at equivalent high doses due to faster clearance.	Carries a slightly higher toxicity risk at very high doses because of longer retention.
Cost Comparison	Generally cheaper to manufacture, making budget-friendly supplement options widely available.	Costs slightly more to produce, though prices remain comparable at retail level.
Stability Profile	Shows greater sensitivity to heat, light, and humidity during long-term storage periods.	Exhibits better chemical stability and a longer shelf life in typical packaging.
Fortification Use	Used to fortify plant-based milks, orange juice, and breakfast cereals in many countries.	Used to fortify cow's milk, yogurt, cheese, and other conventional dairy products.
Research Volume	Has fewer recent clinical studies compared to D3 in the current scientific literature.	Dominates modern vitamin D research with thousands of published clinical trials.
Regulatory Status	Approved as a dietary supplement and pharmaceutical in the US, EU, and most nations.	Approved similarly as a supplement and drug across global regulatory agencies.
Typical Users	Chosen by vegans, vegetarians, and individuals with plant-based dietary preferences.	Preferred by omnivores, older adults, and those seeking maximal blood level increases.
Common Example	Ergocalciferol capsules like Drisdol represent the standard pharmaceutical D2 product.	Cholecalciferol products like Nature Made and Carlson Labs represent common D3 brands.
Key Limitation	Shows reduced effectiveness in maintaining long-term serum levels between dosing intervals.	May cause allergic reactions in individuals sensitive to lanolin-derived ingredients.
Best-Fit Scenario	Ideal for strict plant-based diets or when a vegan-certified vitamin D source is required.	Best for general population supplementation and correcting deficiency with fewer units.

What Is D2?

D2 is vitamin D2, also called ergocalciferol. It is a fat-soluble vitamin that helps the body absorb calcium and phosphorus. D2 comes from plant sources and is commonly used in fortified foods and supplements.

Definition of D2

D2, or ergocalciferol, is a secosteroid formed by ultraviolet irradiation of ergosterol, a fungal sterol. It functions as a prohormone that the liver converts to calcifediol and the kidneys to calcitriol, the active form regulating calcium homeostasis.

Key Characteristics of D2

Characteristic	What It Means in Practice
Plant-derived source	Comes from yeast, mushrooms, and other fungi, making it suitable for vegan diets.
Ergosterol precursor	Requires UV light exposure to convert ergosterol into usable vitamin D2.
Shorter half-life	Clears from the bloodstream faster than D3, requiring more frequent dosing.
Fortification staple	Widely added to milk, cereals, and plant-based milks because it is inexpensive.
Prescription strength	Available in high-dose capsules like 50,000 IU for treating severe deficiency.
Liver hydroxylation	Metabolised in the liver to calcifediol before the kidneys activate it fully.
Lower potency	Raises blood vitamin D levels less effectively per IU compared to D3.
UVB dependent	Naturally produced in mushrooms only when exposed to ultraviolet B light.
Overdose risk	Accumulates in fat tissue, so excessive intake can cause hypercalcemia.
Storage stability	Remains potent for years in sealed containers away from light and heat.

Common Examples of D2

Mushrooms – Portobello and shiitake exposed to UV light naturally produce significant D2.
Fortified milk – Most commercial cow's milk in the US is supplemented with D2.
Breakfast cereals – Many bran and corn flakes list ergocalciferol in their ingredient labels.
Orange juice – Several major juice brands add D2 to boost nutritional value.
Plant-based milks – Almond, soy, and oat milks commonly use D2 for fortification.
Ergocalciferol capsules – Prescription 50,000 IU capsules treat rickets and deficiency.
Over-the-counter drops – Liquid D2 supplements for infants and elderly patients.
Nutritional yeast – Fortified varieties provide D2 alongside B vitamins.
Yogurt products – Some single-serve yogurts are fortified with ergocalciferol.
Tofu and soy products – Certain brands fortify their products with D2 for vegans.

Advantages and Limitations of D2

Advantages	Limitations
Suitable for vegans and vegetarians who avoid animal-derived D3 from lanolin.	Less effective at raising and maintaining blood vitamin D levels than D3.
Available in high-dose prescription forms for rapid correction of severe deficiency.	Has a shorter half-life in circulation, so levels drop faster between doses.
Inexpensive to produce, keeping fortified foods and supplements affordable for consumers.	Requires higher IU doses to achieve the same clinical effect as D3.
Naturally present in edible mushrooms, offering a whole-food source for plant-based diets.	Conversion to active calcitriol is less efficient in the liver and kidneys.
Widely used in food fortification programs, reducing deficiency rates in the general population.	Some studies suggest D2 degrades faster during storage than D3 supplements.
Effective for treating rickets and osteomalacia when taken at prescribed therapeutic doses.	Can cause hypercalcemia if taken excessively, leading to kidney stones and calcification.
Does not rely on animal farming, reducing environmental impact compared to lanolin-based D3.	May not bind as strongly to vitamin D binding proteins in the bloodstream.
Available without prescription in low doses, making it accessible for self-managed supplementation.	Intermittent high doses are less effective than daily dosing due to rapid clearance.
Stable in fortified foods, maintaining potency through typical shelf-life periods.	Most multivitamins now use D3 instead, making D2 options less common in retail.
Well-studied in clinical trials for deficiency correction, with established dosing protocols.	Does not raise calcifediol levels as predictably as D3 in obese individuals.

What Is D3?

D3 is a fat-soluble vitamin and hormone precursor essential for calcium absorption, immune function, and bone health. The body synthesizes it from sunlight exposure, and it also comes from animal foods and supplements. It exists to regulate phosphorus and calcium levels in the bloodstream.

Definition of D3

D3, chemically named cholecalciferol, is a secosteroid produced in human skin from 7-dehydrocholesterol upon ultraviolet B radiation exposure. It undergoes hepatic hydroxylation to calcifediol and renal conversion to calcitriol, the active hormone that binds vitamin D receptors to control gene transcription for mineral homeostasis.

Key Characteristics of D3

Characteristic	What It Means in Practice
Fat-soluble storage	Excess D3 stores in adipose tissue and liver, so overdosing accumulates over weeks.
Sunlight synthesis	Skin produces roughly 10,000 to 25,000 IU after 20 minutes of midday summer exposure.
Animal-derived source	Found naturally in fatty fish, egg yolks, and liver, unlike plant-based D2.
Two-step activation	Liver converts D3 to calcifediol, then kidneys make calcitriol, the active hormone.
Nuclear receptor binding	Calcitriol activates vitamin D receptors in over 30 tissues, not just bone.
Longer half-life	Circulates for roughly 15 to 25 days, roughly double the duration of D2.
Potency equivalence	Roughly 1.7 times more effective than D2 at raising blood calcifediol levels.
Seasonal dependency	Winter sunlight at high latitudes produces zero cutaneous vitamin D synthesis.
Hormone precursor	Acts as a prohormone, not a true vitamin, because the body manufactures it.
Thermal stability	Withstands normal cooking and baking temperatures without significant degradation.

Common Examples of D3

Cod liver oil – a traditional teaspoon delivers roughly 450 IU per serving from fish liver.
Salmon – wild-caught fillets provide about 600 to 1000 IU per 100 grams.
Fortified milk – standard commercial milk adds 100 IU per cup in many countries.
Egg yolk – one large yolk contains roughly 40 IU from the hen's diet.
Cholecalciferol supplements – over-the-counter capsules commonly sold in 1000, 2000, or 5000 IU.
Beef liver – a cooked 100-gram portion supplies about 50 IU of natural D3.
UV-exposed mushrooms – treated with ultraviolet light to convert ergosterol into vitamin D.
Fortified orange juice – some brands add cholecalciferol at 100 IU per 240 ml serving.
Herring – pickled or fresh, this fatty fish delivers roughly 200 to 300 IU per fillet.
Sardines – canned in oil, two fish provide about 50 IU of natural D3.

Advantages and Limitations of D3

Advantages	Limitations
Raises blood calcifediol levels nearly twice as efficiently as equal D2 doses.	Excess intake causes hypercalcemia, leading to kidney stones and vascular calcification.
Sustains stable circulating levels for weeks due to its longer biological half-life.	Obese individuals store D3 in fat tissue, making it less bioavailable for circulation.
Supports calcium absorption for bone density maintenance across all adult ages.	Requires adequate magnesium to activate, so deficiency in magnesium blocks its function.
Modulates innate immune responses against respiratory pathogens in clinical trials.	Sunlight synthesis carries skin cancer risk, limiting safe natural production.
Reduces fracture risk in elderly populations when combined with calcium supplementation.	Fat-soluble nature means toxicity symptoms appear only after months of silent accumulation.
Available widely as low-cost generic supplements in pharmacies worldwide.	Does not correct deficiency if liver or kidney disease prevents activation to calcitriol.
Resists degradation during food processing and long-term storage.	Dietary sources alone rarely meet the 600 to 800 IU daily requirement.
Plays a role in muscle strength, reducing fall risk in older adults.	High-dose bolus protocols show no fracture benefit and may increase fall rates.
Measurable via standard 25-hydroxyvitamin D blood tests in clinical practice.	Individual sun exposure needs vary wildly with latitude, skin tone, and sunscreen use.
Supports parathyroid hormone regulation, preventing secondary hyperparathyroidism.	No universal optimal blood level exists; ranges from 20 to 50 ng/mL remain debated.

Similarities Between D2 and D3

Shared Aspect	How D2 and D3 Are Alike
Core Purpose	Both D2 and D3 are designed to convert raw data into structured, actionable information for decision-makers.
Primary Category	D2 and D3 both belong to the same functional class of analytical tools used for processing and reporting.
Input Format	D2 and D3 accept identical raw data file types, including CSV and JSON, from source systems.
Output Structure	Both D2 and D3 generate tabular output that is compatible with standard spreadsheet software.
Target Users	Data analysts and business intelligence professionals are the primary users of both D2 and D3.
Learning Curve	D2 and D3 require roughly the same onboarding time for a new user to achieve basic proficiency.
Deployment Model	Both D2 and D3 are available as on-premise installations or as cloud-hosted services.
Operating System	D2 and D3 run natively on Windows, macOS, and Linux without requiring emulation layers.
Data Volume	D2 and D3 both handle datasets up to 10 gigabytes in size before performance degrades.
Processing Speed	Both D2 and D3 complete identical batch jobs in comparable timeframes under normal load.
Error Handling	D2 and D3 both log malformed records to a separate error file instead of stopping execution.
Data Security	Both D2 and D3 encrypt data at rest using AES-256 and in transit using TLS 1.2.
Access Control	D2 and D3 both support role-based permissions to restrict access to sensitive fields.
Audit Trail	Both D2 and D3 maintain a timestamped log of every user action and data modification.
Workflow Steps	D2 and D3 follow the same extract, transform, and load sequence for each processing cycle.
Automation Support	Both D2 and D3 can be scheduled to run unattended at predefined intervals via cron jobs.
API Availability	D2 and D3 both expose a RESTful API for integrating with external applications.
Scripting Language	Both D2 and D3 use a Python-based scripting interface for advanced custom transformations.
Configuration Files	D2 and D3 both store their settings in human-readable YAML configuration files.
Documentation Quality	Both D2 and D3 ship with comprehensive official documentation and API reference guides.
Community Support	D2 and D3 both have active user forums where common issues are resolved by peers.
Licensing Cost	Both D2 and D3 are priced in the same mid-tier range for a standard commercial license.
Hardware Needs	D2 and D3 both require a minimum of 8 GB RAM and 4 CPU cores for optimal operation.
Failure Risk	Both D2 and D3 carry a similar risk of data corruption if the system loses power mid-write.
Performance Metric	D2 and D3 both measure success by throughput in records processed per second.
Quality Checks	Both D2 and D3 validate incoming data against the same schema rules before loading.
Patch Cycle	D2 and D3 both receive security patches and bug fixes on a monthly release schedule.
Backup Method	Both D2 and D3 rely on full database snapshots taken nightly for disaster recovery.
Maintenance Task	D2 and D3 both require periodic index rebuilding to maintain query performance over time.
Long-Term Outcome	Both D2 and D3 deliver consistent, repeatable reporting that reduces manual spreadsheet work.

D2 or D3: Which Should You Choose?

The deciding variable is your budget. D2 delivers adequate performance at a lower cost, while D3 demands a higher investment for superior speed and efficiency. If you cannot justify the premium, D2 is the practical choice. If performance is non-negotiable, D3 is the clear winner.

When to Use D2

Choose D2 when cost is your primary constraint. It fits tight budgets, small-scale projects, or short-term deployments. D2 also suits tasks where maximum speed is not critical, such as standard data processing or basic archival work. It is the sensible default for users who prioritize affordability over top-tier output.

When to Use D3

Choose D3 when performance directly impacts your revenue. It is essential for high-frequency operations, large datasets, or real-time applications where latency is unacceptable. D3 also wins for long-term investments, as its efficiency reduces energy and maintenance costs. If downtime or delay costs money, D3 is the only option.

Common Misconceptions About D2 and D3

Common Myth	The Reality
D2 and D3 are the exact same vitamin with different names.	D2 and D3 are distinct chemical forms of vitamin D with different side chains and slightly different metabolic pathways.
Both D2 and D3 come from the same natural food sources.	D2 comes from yeast and mushrooms exposed to UV light, while D3 comes from animal sources like fish liver and lanolin.
Your skin produces both D2 and D3 when exposed to sunlight.	Human skin synthesizes only D3 from cholesterol precursors; D2 is never produced by the human body.
D2 and D3 have identical potency milligram for milligram.	D3 raises blood levels of calcidiol roughly 2 to 3 times more effectively than an equal dose of D2.
Vegan supplements always contain D3, not D2.	Most vegan vitamin D supplements use D2 from mushrooms, though lichen-derived D3 is also available.
D2 is completely useless and provides no health benefit at all.	D2 still effectively treats deficiency and prevents rickets when taken at appropriate therapeutic doses.
D3 is a synthetic chemical, while D2 is the natural form.	Both D2 and D3 occur naturally; D3 is the form humans naturally produce from sun exposure.
Taking D2 and D3 together causes dangerous vitamin D toxicity.	Combined D2 and D3 use is safe at normal doses; toxicity only occurs from excessive prolonged intake.
D2 is better for bone health because it is plant-based.	D3 is more effective at maintaining bone density because it sustains higher active vitamin D levels.
Your body cannot convert D2 into the active hormone calcitriol.	D2 converts to active calcitriol through the same liver and kidney hydroxylation steps as D3.
D3 requires a prescription, but D2 is available over the counter.	Both D2 and D3 are sold over the counter; prescription forms of each also exist for high-dose therapy.
D2 and D3 have completely different functions in the human body.	Both D2 and D3 perform the same core functions of calcium absorption and immune regulation.
D3 is only found in supplements, never in natural food.	D3 occurs naturally in fatty fish like salmon, mackerel, sardines, and egg yolks.
D2 is the stronger form because it is used in prescription megadoses.	Prescription D2 uses higher doses because D3 is more efficient, not because D2 is stronger.
Switching from D2 to D3 requires a completely different dosage regimen.	Most guidelines suggest reducing the D3 dose slightly because D3 is more potent than D2.
D2 and D3 both have identical half-lives in your bloodstream.	D3 has a longer half-life in circulation, so D2 levels drop faster after supplementation stops.
Mushrooms contain D3, not D2, when sold in grocery stores.	Typical grocery mushrooms contain D2; only UV-exposed varieties contain meaningful amounts of D2.
D2 is a hormone, while D3 is just a vitamin.	Both D2 and D3 are prohormones that require activation before they act as hormones.
D3 causes more side effects than D2 in normal daily doses.	Both D2 and D3 are well tolerated at standard doses; side effects are rare and dose-dependent.
Cod liver oil provides D2, not D3, as its main vitamin.	Cod liver oil naturally contains D3, not D2, along with vitamin A and omega-3 fatty acids.
D2 and D3 bind to completely different receptors in your body.	Both D2 and D3 bind to the same vitamin D receptor after conversion to active forms.
D2 is more water-soluble, so it works faster than D3.	Both D2 and D3 are fat-soluble vitamins; neither dissolves readily in water for faster action.
Fortified milk contains D3, but fortified plant milks always contain D2.	Fortified plant milks may use either D2 or D3; check labels because D3 can be lichen-derived.
D2 is the only form suitable for people with liver disease.	Both D2 and D3 require liver hydroxylation, so neither is inherently safer for liver disease.
D3 is a newer discovery, while D2 has been used for centuries.	Both D2 and D3 were identified in the 1930s; D3 was recognized as the natural human form later.
D2 and D3 have identical effects on your immune system function.	D3 appears more effective at supporting immune responses due to better receptor binding affinity.
You can get enough D2 from sunlight if you eat mushrooms daily.	Sunlight produces D3 only; mushrooms provide D2, which is less efficient at raising blood levels.
D2 is the standard choice in hospitals because D3 is untested.	Hospitals historically used D2 for availability, but D3 is equally tested and now preferred in many settings.
D2 and D3 are interchangeable in every clinical situation without adjustment.	Clinical guidelines often recommend D3 for maintenance therapy because it sustains levels more reliably.
D3 is only for adults, while D2 is safer for children and infants.	Both D2 and D3 are safe for children at appropriate doses; D3 is commonly used in pediatric drops.

Conclusion

Difference Between D2 and D3 comes down to source and synthesis: D2 comes from plants and fortified foods, while D3 comes from animals and sunlight. Choose D2 for vegan diets or fortified products. Choose D3 for superior absorption and maintaining blood levels effectively.

FAQs on Difference Between D2 and D3

What is the main difference between D2 and D3?: The main difference is the source: D2 comes from plants and fortified foods, while D3 comes from animal products and sunlight exposure.
Which is better for raising vitamin D levels, D2 or D3?: D3 is generally better because it raises and maintains blood levels of vitamin D more effectively than D2 in most people.
Is D3 more expensive than D2?: Yes, D3 is typically more expensive than D2 because it is often derived from lanolin or lichen, whereas D2 is synthesized from yeast.
Are there any safety risks associated with taking D2 or D3?: Both carry a risk of toxicity at very high doses, but D3 may have a slightly higher risk due to its longer half-life in the body.
Are D2 and D3 compatible with a vegan diet?: D2 is vegan-friendly because it comes from yeast, while D3 is usually not vegan unless it is specifically sourced from lichen.
What is a common beginner mistake when choosing between D2 and D3?: A common mistake is assuming both are equally potent, which leads to underdosing D3 or overdosing D2 without checking the label's international units.
Can I use D2 and D3 interchangeably in my supplement routine?: You can use them interchangeably for basic deficiency correction, but D3 is preferred for long-term maintenance and better blood level stability.
Which form of vitamin D is used for a real-world deficiency treatment?: D2 is often used in high-dose prescription capsules for severe deficiency, while D3 is common in daily over-the-counter maintenance supplements.
Can I switch from taking D2 to D3 without any issues?: Yes, you can switch from D2 to D3 directly, but you may need to adjust the dosage because D3 is more potent at maintaining serum levels.
How do D2 and D3 differ in how the body processes them?: The body processes D3 more efficiently because it binds better to the vitamin D binding protein, leading to longer circulation time than D2.