Vitamin D3 vs D2: Which Form Raises Your Levels Better?

Sunrise over an open field

Photo: Morning sun over an open field. Sunlight helps your skin make vitamin D, but in a Canadian winter it is rarely enough on its own. (Photo: Unsplash)

Two bottles, two forms, one vitamin — and a label that rarely explains the difference.

Version française : Vitamine D3 ou D2 : laquelle augmente le mieux votre taux ?

You are standing in the supplement aisle, again

If you have ever picked up a vitamin D bottle, turned it over, and paused at the small print, you are not alone. One bottle says vitamin D3, or cholecalciferol. The next says vitamin D2, or ergocalciferol. The doses look the same, the prices are close, and neither label explains which one your body actually uses better. It is the kind of small decision that feels like it should be simple, and yet the shelf gives you almost nothing to decide with.

That confusion is understandable, because the two forms really are close cousins. Both are vitamin D, both are measured in the same units, and both can raise the vitamin D level in your blood. The difference is in where they come from, how long they tend to stay active in the body, and which one fits your diet and your values. None of that is printed in large letters, so most people end up choosing by price, by habit, or by whichever bottle they happened to grab first.

This guide compares vitamin D3 and vitamin D2 the way you would actually use them: what each form is, how they differ in the body, how much you need, what food and sunlight can and cannot do in Canada, and which one makes sense in which situation. The numbers below come from the U.S. National Institutes of Health (NIH) Office of Dietary Supplements and Health Canada, and the aim is a calm, practical choice — not a race to the highest dose.

The short answer first

For most people, vitamin D3 is the better default choice. The NIH notes that vitamin D3 may raise the level of vitamin D in your blood higher, and keep it there longer, than the same dose of vitamin D2 does. Both forms do raise blood levels, and a D2 supplement is still a reasonable choice if it is the one that fits your diet — for example, if you eat a fully plant-based diet — but when the two are otherwise equal, D3 usually wins on effectiveness.

That said, the form is only one part of the picture. Taking the right amount consistently matters more than the letters on the bottle, and food, sunlight, your age and your health conditions all shape how much vitamin D you need. In Canada, Health Canada advises that adults over 50 take a daily vitamin D supplement of 400 IU (10 mcg), and that people aged 2 to 50 either eat foods that contain vitamin D every day or take a 400 IU supplement. The official recommended dietary allowance (RDA) for adults aged 19 to 70 is 600 IU (15 mcg) per day, rising to 800 IU (20 mcg) per day after age 71. The tolerable upper intake level — the most the NIH considers safe for most adults to take every day — is 4,000 IU (100 mcg) per day. More is not better, and high doses should only be used when a clinician has checked your level and recommended them.

Vitamin D3 vs D2 at a glance

Full name: Vitamin D3 is cholecalciferol; vitamin D2 is ergocalciferol.
Where it comes from: D3 is made in your skin from sunlight and is found in animal foods such as fatty fish, fish liver oils and egg yolk; D2 comes from fungi and yeast, for example mushrooms exposed to ultraviolet light, and from fortified foods.
How it raises blood levels: Both raise the blood marker 25-hydroxyvitamin D, but D3 may raise it higher and keep it raised longer; with larger or longer-term doses, that gap tends to shrink.
Typical dose on the label: Both are sold in 400 IU, 1,000 IU and higher strengths, measured in the same units, so the dose comparison is like for like.
Diet fit: D2 is naturally plant-based; most D3 comes from lanolin (from sheep's wool) or fish, although a vegan D3 made from lichen is now widely sold.
What it is used for in the body: Both forms are converted in the liver and kidney to the active form, and both support calcium absorption and bone health.
Price and availability: In Canada and the U.S., D3 is the form in most single-ingredient vitamin D products; D2 is more common in some multivitamins and in medicines prescribed in some countries.
The one number to remember: Adults should not routinely go above 4,000 IU (100 mcg) a day without a clinician's advice.

What is vitamin D3?

Vitamin D3 is the form your skin makes when sunlight touches it. Ultraviolet B rays convert a cholesterol-like compound in the skin into vitamin D3, and over the next few days your liver and kidneys convert it into the active form your body uses. It is also the form found in oily fish: a 3-ounce (85 g) serving of cooked salmon provides about 570 IU (14 mcg), and smaller amounts are found in egg yolk and fortified milk — roughly 120 IU (3 mcg) per cup of fortified milk, according to the NIH.

In supplements, most D3 is made from lanolin, the oil found in sheep's wool, which is cleaned and processed into cholecalciferol. A smaller number of products use lichen, a slow-growing plant-like organism, which is the usual vegan source of D3. If you are vegan and want D3, look for the word "lichen" on the label or for a product that states it is vegan.

A bottle of vitamin D3 gummies

Photo: A vitamin D3 supplement bottle. D3 is the form in most single-ingredient vitamin D products sold in Canada. (Photo: Unsplash)

Who D3 suits best

D3 suits most people who simply want a vitamin D supplement that raises their blood level efficiently, including people who rarely get sun in winter, people who cover their skin outdoors, and people whose blood test has come back low. If you eat fish and eggs, or you are comfortable with a lanolin-based product, D3 is the straightforward choice. If you are vegan, lichen-based D3 gives you the same form without animal ingredients.

What is vitamin D2?

Vitamin D2 comes from a different starting material. When fungi and yeast are exposed to ultraviolet light, they produce ergocalciferol — vitamin D2. That makes D2 the form that appears naturally in mushrooms exposed to sunlight or ultraviolet lamps, and it is the form added to some fortified foods and used in some prescribed high-dose vitamin D products, particularly in the United States.

D2 goes through the same conversion steps as D3, and at ordinary doses it does raise blood vitamin D levels. The practical concern is that it is cleared from the body a little faster, so its effect on blood levels may be somewhat smaller and shorter-lived than the same dose of D3. That does not make D2 a poor supplement — a dose of D2 every day still adds up — but it is the reason most guidance quietly favours D3 when either would do.

Who D2 suits best

D2 suits people who eat a fully plant-based diet and prefer a supplement that has always been plant-derived, as well as people whose clinician has specifically prescribed D2. It also suits anyone who finds a good-quality D2 product at a fair price and takes it regularly: a supplement you take every day beats a supposedly better one that sits unopened in the cupboard. If your blood level is already in the range your clinician wants and you are maintaining it, there is no need to switch forms for its own sake.

Food, sun and the Canadian winter

Food helps, but it is hard to rely on food alone. Oily fish is the richest source, with salmon, mackerel, sardines and arctic char at the top of the list. Fortified milk, fortified plant-based beverages, fortified cereals, margarine and egg yolk add smaller amounts, and ultraviolet-exposed mushrooms are the main food source of D2. A varied diet with fortified foods every day is exactly what Health Canada recommends for people aged 2 to 50, with a 400 IU supplement as the alternative when food alone is not dependable.

Sunlight is the other natural source, and this is where Canada is at a disadvantage. Your skin makes vitamin D when it is exposed to UVB rays, but from late autumn to early spring most of Canada is too far north for the sun to be strong enough, and in summer, clothing, shade and sunscreen all reduce how much your skin makes. The NIH warns that too much sun without protection raises the risk of skin cancer, and that sunscreen of SPF 15 or higher reduces how much vitamin D your skin produces — there is no safe way to sunbathe your way to a guaranteed level.

A cooked salmon dish, a rich food source of vitamin D

Photo: Cooked salmon is one of the richest food sources of vitamin D. Fortified milk, egg yolk and UV-exposed mushrooms add smaller amounts. (Photo: Unsplash)

The only way to know your own level for certain is a blood test for 25-hydroxyvitamin D, which your clinician can order. The NIH describes a level of 50 nmol/L (20 ng/mL) or higher as adequate for most people, a level below 30 nmol/L (12 ng/mL) as too low, and levels above 125 nmol/L (50 ng/mL) as potentially too high. If you feel tired, get frequent infections or worry that your diet and sunlight are not enough, a test is more useful than guessing from symptoms, because low vitamin D often has no obvious symptoms at all.

How to choose, and how much is enough?

Start with the official numbers, then adjust with your clinician. For most healthy adults, that means 600 IU (15 mcg) per day from all sources — food plus supplements — and 800 IU (20 mcg) after age 71, within an upper limit of 4,000 IU (100 mcg) a day. In practice, many Canadians take a single 1,000 IU tablet a day, which is a common strength in pharmacies and sits comfortably below the upper limit, or follow Health Canada's advice of a 400 IU daily supplement, especially after age 50.

A few practical tips make the choice easier. Take any vitamin D supplement with food that contains some fat, because vitamin D is fat-soluble and is absorbed better that way. Pick one form and one dose and take it every day rather than taking a large dose once in a while. Check the label for the total vitamin D and the form (D2 or D3), and count vitamin D from a multivitamin as well so you do not add the two together by accident. And tell your clinician or pharmacist about it before you start, especially if you take other medicines or supplements — high doses, or a long period above the upper limit, can raise blood calcium and cause problems that a blood test would have caught early.

The bottom line, by situation

You want the simplest, most effective supplement: Choose vitamin D3, in a dose your clinician agrees with, and take it daily with food.
You eat a fully plant-based diet: Choose vegan D3 from lichen if you can find it, or D2 if you prefer a plant-derived form — and take it every day.
You were prescribed D2: Keep taking the dose your clinician prescribed, and do not switch or add another form without asking.
Your blood level came back low: Ask your clinician what dose to use and when to retest; do not decide the dose and the retest date from the label alone.
You already take a vitamin D supplement and your level is fine: There is no benefit in changing forms, raising the dose, or adding a second vitamin D product.

Frequently asked question

Can I take both D2 and D3? There is no reason to take both — they both contribute to the same total vitamin D intake, and taking both only makes it harder to know how much you are getting. Choose one form, count every source of vitamin D you take, and stay within the daily upper limit of 4,000 IU unless a clinician has advised a higher dose. If you are already taking a multivitamin or a calcium and vitamin D combination, read those labels first.

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