Vitamin D2 vs D3: What the New Research Means for Your Winter Supplement
Vitamin D3 raises blood vitamin D more reliably than D2, and a 2025 Nutrition Reviews meta-analysis found that D2 lowered people's own 25(OH)D3 by about 9–18 nmol/L versus no supplement. D2 still works, but D3, including vegan lichen-derived D3, is the better default for autumn and winter. Most healthy adults need 600–800 IU a day and no routine blood test.
Is vitamin D3 better than D2?
For most adults, yes. D3 (cholecalciferol) raises blood vitamin D more reliably than D2 (ergocalciferol). A 2025 meta-analysis also found that taking D2 lowered people's own D3 levels. D2 still works, but D3 is the better default.
600–800 IU (15–20 mcg) of D3 daily from October to March
Choose lichen-derived D3 rather than D2
Keep taking it and ask whether D3 is an option, don't switch on your own
Switch to the same daily dose of D3 at your next refill
Ask your doctor about a 25(OH)D blood test before you take high doses
Talk to your doctor before taking any vitamin D
In October 2026, ScienceDaily re-ran a University of Surrey report with an unsettling headline: a popular vitamin D supplement “may have a hidden downside.” The supplement is vitamin D2. The research behind the story is a systematic review and meta-analysis of randomized controlled trials, published online in Nutrition Reviews on September 18, 2025. It found that people who took D2 ended up with lower levels of vitamin D3 in their blood than people who took nothing.
The timing matters. North of about 40° latitude, the sun from roughly November to February is too weak for your skin to make vitamin D3. In that season, your supplement does most of the work. This guide explains what the new research found, where the evidence is less certain, how the two forms differ in dose and source, what to know about testing your blood level, and which form makes sense for you.
What's New: Vitamin D2 May Lower Your D3 Levels
In a 2025 meta-analysis of 11 trials, people taking D2 had 9–18 nmol/L less of their own D3 than people taking nothing. Total vitamin D still rose, and harm hasn't been shown.
The study. The paper is by Emily Brown, Andrea Darling, Susan Lanham-New, Ruan Elliott, and colleagues. They are from the University of Surrey, the John Innes Centre, and the Quadram Institute in the UK. The team searched PubMed for trials published from 1975 to February 2023. They found 202 articles and included 20 in the review, 11 of which had data suitable for meta-analysis. Every included trial was a randomized controlled trial that measured 25-hydroxyvitamin D3, written 25(OH)D3, before and after supplementation.
The finding. Compared with control groups that took no vitamin D, people who took D2 had lower 25(OH)D3 levels:
To put that in context, 50 nmol/L (20 ng/mL) is the level the US National Academies consider adequate for most people. A drop of 9–18 nmol/L in one form of the vitamin is noticeable, though not dramatic.
What the authors say and don't say. D2 still raises total vitamin D. It adds 25(OH)D2 to the blood while 25(OH)D3 falls. The authors suggest one cause: the body may clear 25(OH)D faster once total vitamin D levels go up. They also say plainly that more research is needed before anyone can tell whether D2 and D3 lead to different health outcomes. In the university's press release, lead author Emily Brown said that “vitamin D3 supplements may be more beneficial for most individuals over vitamin D2.” She also stressed that supplements matter most “between October and March.”
Vitamin D3 supplements may be more beneficial for most individuals over vitamin D2.
Why the immune angle came up. Co-author Colin Smith pointed to his team's earlier work. In a 12-week winter trial, women took 15 mcg of D2 or D3 a day. Researchers then measured gene activity in their blood. Many changes were specific to one form or the other. Only D3 increased the activity of type I and type II interferon genes, which help the body make its first response to viruses and bacteria. That study measured gene activity, not infections, so it shows a possible mechanism, not a clinical benefit.
A second 2026 paper. The March 2026 issue of Nutrition Reviews printed a separate meta-analysis of 26 trials of D2 alone. It found that D2 lowered parathyroid hormone by 12.77 pg/mL and raised serum calcium by 0.15 mg/dL. Those are the expected effects of a working vitamin D. The takeaway is that D2 is not inert. The question is whether it is the best choice, not whether it does anything.
The evidence has limits. This is one meta-analysis of 11 trials with different doses, lengths, and lab methods. An earlier, well-known 2008 trial gave adults 1,000 IU of D2 a day for 11 weeks at the end of winter, and their 25(OH)D3 levels did not fall. The overall picture favors D3, but this effect has not been proven to cause harm.
How the evidence stacked up
- 2008 · Trial
1,000 IU of D2 daily for 11 weeks: D3 levels did not fall.
- 2012 · Meta-analysis
D3 raised total 25(OH)D more, clearest with bolus doses.
- 2017 · Trial, 335 UK women
600 IU a day in winter: D3 raised levels 15–17 nmol/L more.
- 2022 · Gene-activity study
Only D3 boosted interferon genes — a mechanism, not proof.
- 2025 · Meta-analysis, 11 trials
D2 lowered people's own D3 versus no supplement.
- 2026 · Meta-analysis, 26 trials
D2 lowered PTH and raised calcium, as a working vitamin D should.
How Vitamin D2 and D3 Work in the Body
Both forms are inactive “prohormones.” They follow the same two-step route:
Vitamin D2 or D3 becomes 25(OH)D2 or 25(OH)D3. Together these make up the “total 25(OH)D” that blood tests measure.
25(OH)D becomes the active hormone 1,25-dihydroxyvitamin D. It controls how much calcium you absorb and acts on immune cells and many other tissues.
The two molecules differ only slightly, in the side chain. D2 comes from ergosterol, a sterol found in fungi and yeast. D3 comes from 7-dehydrocholesterol, the same compound your skin turns into vitamin D3 under UVB light. That small difference seems to matter for how long each form lasts in the blood.
A 2012 meta-analysis of head-to-head trials found that D3 raised total 25(OH)D significantly more than D2 (P = 0.001). The gap was clearest with large, infrequent “bolus” doses, and it disappeared when both forms were taken daily. A 2017 trial in 335 UK women filled in the daily-dose picture. Women took 15 mcg (600 IU) a day of D2 or D3 in juice or biscuits for 12 weeks in winter. D3 raised total 25(OH)D about 15–17 nmol/L more than D2.
So D3 holds up better with large weekly or monthly doses, and it also did better at modest daily doses in the 2017 trial. The new meta-analysis adds a possible reason: some of the 25(OH)D2 gained from D2 is offset by lost 25(OH)D3.
Vitamin D2 vs D3: Sources, Forms, and Doses
- Made by
- Your skin under UVB light, and animals.
- Food sources
- Oily fish, egg yolks, liver, and fortified foods.
- Supplement sources
- Most D3 is made from lanolin, the fat in sheep's wool, so it is not vegan. Vegan D3 made from lichen is widely sold. It is the same cholecalciferol molecule. We found no head-to-head trials of lichen versus lanolin D3, and there is no chemical reason to expect them to differ.
- Typical forms
- Softgels, tablets, liquid drops, sprays, and combined D3 + K2 products.
- Common strengths
- 400 IU (10 mcg), 1,000 IU (25 mcg), 2,000 IU (50 mcg).
- Made by
- Fungi and yeast exposed to UV light.
- Food sources
- UV-exposed mushrooms. A 2018 review found they usually still hold more than 10 mcg of D2 per 100 g before their best-before date. That is close to a full day's recommended intake in one serving. Some plant milks and cereals are also fortified with D2.
- Supplement sources
- Plant-derived, so D2 has long been the vegan default.
- Typical forms
- Tablets and capsules. In the US, high-dose prescription capsules (often 50,000 IU taken weekly) are commonly D2.
How much do you need?
The US National Academies set these daily reference intakes:
| Group | Recommended daily intake | Tolerable upper limit |
|---|---|---|
| Ages 1–70 | 600 IU (15 mcg) | 4,000 IU (100 mcg) for ages 9+ |
| Ages 71+ | 800 IU (20 mcg) | 4,000 IU (100 mcg) |
| Pregnant or breastfeeding | 600 IU (15 mcg) | 4,000 IU (100 mcg) |
The UK advises 10 mcg (400 IU) a day for everyone in autumn and winter. To convert units: 1 mcg = 40 IU.
The UK’s daily advice for everyone in autumn and winter (10 mcg). Also a common supplement strength.
The US reference intake for ages 1–70, and in pregnancy or breastfeeding (15 mcg).
The US reference intake for ages 71+ (20 mcg).
A common supplement strength (25 mcg). Count multivitamins and fortified foods on top.
A common supplement strength (50 mcg). Healthy adults under 75 don’t need doses above the reference intakes.
The tolerable upper limit for ages 9+ (100 mcg), from all sources combined, unless a doctor has told you otherwise.
The Endocrine Society's 2024 guideline adds three practical points:
Healthy adults under 75 don't need doses above the reference intakes to prevent disease.
Adults over 50 who need vitamin D should take it daily rather than in big intermittent doses.
Extra vitamin D is suggested for children and teens, adults over 75, pregnant people, and people with high-risk prediabetes.
Vitamin D2 vs D3 Comparison Table
| Criterion | Vitamin D3 (lanolin) | Vitamin D3 (lichen, vegan) | Vitamin D2 (supplement) | UV-exposed mushrooms (D2) |
|---|---|---|---|---|
| Raises total 25(OH)D | Strongest, most consistent | Same molecule as lanolin D3 | Weaker, especially with weekly or monthly doses | Adds D2, but amounts vary with storage and cooking |
| Effect on your own 25(OH)D3 | Raises it | Raises it | May lower it by 9–18 nmol/L | Can lower it too; seen in UV-mushroom trials, while total vitamin D still rises |
| Suitable for vegans | No | Yes | Yes | Yes |
| Best dosing pattern | Daily or weekly | Daily | Daily (bolus doses work less well) | As food |
| Price and availability | Cheapest, everywhere | Slightly higher, widely sold | Cheap, widely sold | Seasonal, varies by store |
| Shows up on standard tests | Yes | Yes | Yes on LC-MS/MS, some immunoassays may underread it | Yes |
| Evidence base | Large | Relies on D3 data | Large but mixed | Small |
For daily winter use, vitamin D3 is our default pick.
Lanolin D3 is the cheapest option. Lichen D3 is the vegan choice and gives up nothing in effect. D2 is not dangerous and does correct deficiency, but the 2025 meta-analysis gives one more reason to prefer D3 when you can choose. If a doctor has prescribed D2, ask them about switching. Don't stop on your own. Mushrooms are a good food source, not a replacement for a winter supplement.
Testing Your Vitamin D Level: The 25(OH)D Test
The blood test for vitamin D measures serum 25-hydroxyvitamin D, or 25(OH)D. The lab may report it in nmol/L or ng/mL. To convert, divide nmol/L by 2.5 to get ng/mL. The National Academies use these cut-offs:
| Level | nmol/L | ng/mL |
|---|---|---|
| Deficient | Under 30 | Under 12 |
| Possibly inadequate for some people | 30–50 | 12–20 |
| Adequate for most people | 50 or higher | 20 or higher |
| Possible adverse effects | Over 125 | Over 50 |
Who should be tested? Not everyone. The Endocrine Society found no trial evidence to support routine screening in healthy people, including people with obesity or darker skin. Testing makes sense when a doctor suspects deficiency or plans treatment. Examples include osteoporosis, malabsorption (such as celiac disease, Crohn's disease, or after bariatric surgery), chronic kidney or liver disease, and medicines that affect vitamin D.
D2-specific tips if you are tested
Ask whether the lab uses LC-MS/MS. This method, used in the main D2 and D3 trials, reports 25(OH)D2 and 25(OH)D3 separately. Some automated immunoassays may detect 25(OH)D2 less fully than 25(OH)D3. If you take D2, that could make your result look lower than it really is. Results can also vary between labs and test methods.
Look at total 25(OH)D for decisions about adequacy. A low D3 fraction on its own, while you take D2, is the pattern the new study describes. It has not been shown to cause harm.
Retest after about 3 months, not 3 weeks. Blood levels take that long to settle after a dose change.
Which Vitamin D Is Right for You?
Healthy adult in a northern city with little winter sun.
Take D3 at 600–800 IU (15–20 mcg) daily from October to March. You don't need a test. Take it with a meal that contains some fat. If you already take a multivitamin, check the label first so you don't double up.
Our guide on combining supplements safely explains how.Vegan or strict vegetarian.
Switch from D2 to lichen-derived D3 at the same dose. Check the label: “vegan D3” or “from lichen” means cholecalciferol. If it lists “ergocalciferol,” it is D2. Eating UV-exposed mushrooms on a regular basis is a useful extra, not a replacement. Vegans should also review vitamin B12 status, which is more likely to be low than vitamin D.
Adult over 75, or anyone with limited mobility or time outdoors.
The Endocrine Society suggests supplementing at this age. Daily D3 at or above 800 IU, as your clinician advises, is a sensible baseline. Daily doses are better than large monthly ones. Ask about calcium intake and fall-prevention at the same visit.
Diagnosed deficiency, on prescription D2.
High-dose D2 has corrected deficiency in clinical use for decades, and it lowers parathyroid hormone as expected. Finish the course your doctor prescribed. Then ask whether a daily D3 maintenance dose would hold your level better. Retest as your doctor advises.
Pregnant or planning pregnancy.
Supplementation is suggested in pregnancy. Most prenatal vitamins contain D3, so check how much yours has before you add more, and talk to your obstetric provider.
You want vitamin D “for immunity” this winter.
Keep expectations modest. A 2021 meta-analysis found a small reduction in acute respiratory infections (OR 0.92). A 2025 update with more trials found a similar estimate, but it was no longer statistically significant (OR 0.94, 95% CI 0.88–1.00). Correcting a deficiency is reasonable. Taking megadoses to “boost” immunity is not supported.
For broader strategies, see how to boost your immune system naturally.Practical Tips for Autumn and Winter
Start in October.
In northern regions, skin makes little or no vitamin D from roughly November to February, and even longer at higher latitudes. Starting early keeps your level from dropping through the season.
Read the active ingredient, not the front of the label.
“Vitamin D” alone is not enough. Look for “cholecalciferol” (D3) or “ergocalciferol” (D2).
Take it with food.
Vitamin D is fat-soluble. Taking it with your largest meal is a simple habit.
Prefer daily to monthly.
Both the D2 vs D3 evidence and the Endocrine Society guidance for adults over 50 favor regular daily doses over large, infrequent ones.
Count every source.
Multivitamins, fortified milk, cereals, and plant milks all add up. Stay under 4,000 IU a day from all sources unless a doctor has told you otherwise.
Choose third-party-tested products.
Seals from USP, NSF, or similar groups confirm that the label dose matches what is inside. Our guide to choosing supplements safely explains what to look for.
Get daylight anyway.
Winter sun won't make much vitamin D, but morning light still supports sleep and mood. A morning routine built around light is worth keeping.
In Boston (42°N), winter sunlight on clear days made no previtamin D3 in skin from November through February.
In Edmonton (52°N), that period ran from October through March. Winter light helps your body clock, not your vitamin D.
Common Misconceptions About Vitamin D2 and D3
D2 is useless.
True or not? Tap to find outHere’s what the evidence says
Not true. D2 raises total 25(OH)D, lowers parathyroid hormone, and slightly raises calcium. It is less efficient than D3, and the new study suggests it may lower D3 levels. That makes it a weaker choice, not a useless one.
The new study proves D2 is harmful.
True or not? Tap to find outHere’s what the evidence says
It doesn't. It measured blood levels, not health outcomes. The authors say longer-term studies are needed.
Vegans have to use D2.
True or not? Tap to find outHere’s what the evidence says
That was mostly true before about 2012. Now lichen-derived D3 is widely sold.
More is better.
True or not? Tap to find outHere’s what the evidence says
Levels above 125 nmol/L (50 ng/mL) are linked to possible harm. Very high intakes can raise blood calcium. The Endocrine Society advises against doses above the reference intakes for healthy adults under 75.
A sunny winter walk tops up my vitamin D.
True or not? Tap to find outHere’s what the evidence says
In Boston (42°N), winter sunlight on clear days made no previtamin D3 in skin from November through February. In Edmonton (52°N), that period ran from October through March. Winter light helps your body clock, not your vitamin D.
If I feel tired, it must be low vitamin D.
True or not? Tap to find outHere’s what the evidence says
Fatigue has many causes, including iron deficiency, poor sleep, thyroid problems, and depression. See why you might always be tired before you blame vitamin D.
When to See a Doctor
See a clinician promptly if you have:
- Signs of high calcium or vitamin D toxicity: nausea, vomiting, constipation, strong thirst, frequent urination, confusion, or irregular heartbeat, especially if you take high doses.
- Bone pain, muscle weakness, or a fracture from a minor fall. These can point to osteomalacia or osteoporosis.
- Conditions that change how your body handles vitamin D: chronic kidney or liver disease, sarcoidosis or other granulomatous diseases, hyperparathyroidism, or kidney stones.
- Malabsorption: celiac disease, inflammatory bowel disease, pancreatic insufficiency, or a history of bariatric surgery.
- Medicines that interact with vitamin D: thiazide diuretics, digoxin, long-term glucocorticoids, some anti-seizure drugs, orlistat, or cholestyramine.
- A prescription for high-dose D2 or D3 that you are thinking of changing or stopping.
- Pregnancy, or a child who needs vitamin D, so the dose is right for their age and situation.