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The verdict
Take vitamin D3. Comparative human studies consistently show that D3 raises 25-hydroxyvitamin D, the blood marker your clinician actually measures, more effectively than an equal dose of D2, and holds it higher for longer. D3 is the form your skin makes from sunlight and the form found in fatty fish and egg yolks, and supplements source it from lanolin or, for plant-based buyers, from lichen. D2 comes from yeast and fungi exposed to UV light, and it persists for three reasons that have nothing to do with superiority: it is cheap, it is what large prescription doses in the United States are made of, and it is used in a lot of food fortification. The practical protocol is 2,000-5,000 IU of D3 taken with your fattiest meal, paired with vitamin K2, which is how we use it. Test your level after about three months and dose to sufficiency rather than to the biggest number on the shelf.
Vitamin D is the most common deficiency correction in modern supplementing, mostly because indoor work, sunscreen, latitude, and darker skin tones all reduce how much your skin makes. It is also one of the few supplements where a cheap blood test tells you whether you need it and how much is enough, which puts it in rare company.
The D3 versus D2 question usually comes up in one of two ways: someone reading a label that just says vitamin D and wondering which they got, or someone handed a 50,000 IU weekly prescription and wondering why it is a different molecule from the bottle in their cabinet. Both are worth answering precisely, because the difference shows up in your blood work.
Vitamin D3 (Cholecalciferol) vs Vitamin D2 (Ergocalciferol), side by side
| Criterion | Vitamin D3 (Cholecalciferol) | Vitamin D2 (Ergocalciferol) |
|---|---|---|
| Best for | Everyday supplementing and maintaining vitamin D status year-round | Prescription high-dose protocols and food fortification, as directed by your clinician |
| Source | Lanolin from sheep wool, or lichen for a vegan D3 | Yeast and fungi exposed to UV light, which is why it dominates vegan fortification |
| Effect on blood levels | Raises 25-hydroxyvitamin D more per IU and sustains it longer | Raises it less per IU and falls off faster between doses |
| Evidence base | Strong. Repeated head-to-head comparisons favor D3 for raising and maintaining status | Adequate but consistently second place in those same comparisons |
| Typical dose | 2,000-5,000 IU daily with a fat-containing meal | Commonly 50,000 IU weekly by prescription, or small amounts in fortified foods |
| Stability | Good shelf stability in oil-based softgels | Less stable, more sensitive to heat, humidity, and time on the shelf |
| Onset | Blood levels move over 8-12 weeks. Retest at about three months | Similar timeline, with more variability between doses |
| Cost per month | Roughly $4-10, one of the cheapest interventions in supplementing | Prescription-dependent, or effectively free in fortified foods |
| Form we use | Yes, vitamin D3 paired with K2 | No |
Which one to choose
Choose Vitamin D3 (Cholecalciferol) if…
- You are supplementing on your own to correct or maintain vitamin D status, which is nearly everyone.
- You work indoors, live at a northern latitude, use sunscreen consistently, or have darker skin, all of which reduce skin synthesis.
- You want the form that pairs cleanly with K2 and with the fat-containing meal you are already eating.
- You are plant-based and want D3 specifically, in which case look for lichen-sourced D3 rather than settling for D2.
Choose Vitamin D2 (Ergocalciferol) if…
- Your clinician prescribed high-dose ergocalciferol to correct a documented low level, in which case follow that protocol.
- You get meaningful vitamin D from fortified foods and are not adding a supplement at all.
- A strict formulation constraint makes D2 the only option available to you, in which case expect to need more of it.
Relevant stacks
Frequently asked questions
Is vitamin D3 better than D2?
For raising and holding 25-hydroxyvitamin D, yes. Head-to-head studies repeatedly show a bigger and more durable rise from D3 at the same IU, which is why almost every over-the-counter product uses it. D2 still raises levels, just less efficiently, and it degrades faster on the shelf.
How much vitamin D3 should I take daily?
Most adults do well on 2,000-5,000 IU daily with a fat-containing meal, then testing after about three months and adjusting. The goal is sufficiency, not a maximum. Very high open-ended dosing without testing is where people run into trouble, since D is fat-soluble and accumulates.
Why do prescriptions use vitamin D2?
Largely history, cost, and regulatory approval: high-dose 50,000 IU ergocalciferol capsules have long been the available prescription product in the United States. Weekly high doses can work for correcting a documented low level. It reflects what is on the formulary rather than which molecule performs better per IU.
Do I need vitamin K2 with D3?
Pairing them is the sensible default and is how we use D3. Vitamin D increases calcium absorption while K2 supports the proteins that direct calcium into bone, so the two work as a pair for bone and cardiovascular health. Look for 90-180 mcg of K2 as MK-7. If you take a prescribed anticoagulant, ask your clinician before adding K2.
Is vegan vitamin D3 as good as regular D3?
Lichen-sourced D3 is the same cholecalciferol molecule as lanolin-derived D3, so it performs the same way in your blood work. It typically costs a few dollars more per month. For plant-based buyers it is a much better choice than defaulting to D2.
Written for adults aged 18 and over. This content is for education only and is not medical advice. Supplements are not intended to diagnose, treat, cure, or prevent any disease. Talk with your clinician before starting any supplement, especially if you are pregnant, nursing, taking medication, or managing a health condition. Supplements for children are a pediatric clinician's decision — keep all supplements out of reach of children.
Our medical advisor is Dr. Garrett Wdowin, NMD, ABAAHP, FAARM, naturopathic doctor. This page has not been medically reviewed.