Vitamin D is more than just one vitamin. It’s a family of nutrients that shares similarities in chemical structure.
In your diet, the most commonly found members are vitamin D2 and D3. While both types help you meet your vitamin D requirements, they differ in a few important ways.
Research even suggests that vitamin D2 is less effective than vitamin D3 at raising blood levels of vitamin D.
This article sums up the main differences between vitamin D2 and D3.
Vitamin D is a fat-soluble vitamin that promotes the absorption of calcium, regulates bone growth and plays a role in immune function.
Your skin produces vitamin D when it’s exposed to sunlight. However, if you spend most of your time indoors or live at a high latitude, you’ll need to get this vitamin from your diet.
Good dietary sources include fatty fish, fish oils, egg yolk, butter and liver.
However, it may be difficult to get adequate amounts of this vitamin from your diet alone, as rich natural sources are rare. For these reasons, it’s common for people to not get enough.
Luckily, many food manufacturers add it to their products, especially milk, margarine and breakfast cereals. Supplements are also popular.
To prevent deficiency symptoms, make sure to eat vitamin D-rich foods regularly, get some sunlight or take supplements.
Since vitamin D is fat-soluble, it is better to choose oil-based supplements or take them with food that contains some fat (1).
The vitamin comes in two main forms:
- Vitamin D2 (ergocalciferol)
- Vitamin D3 (cholecalciferol)
Their differences are discussed in detail below.
Summary Vitamin D is a fat-soluble vitamin that exists in two main forms: vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol).
The two forms of vitamin D differ depending on their food sources.
Vitamin D3 is only found in animal-sourced foods, whereas D2 mainly comes from plant sources and fortified foods.
Sources of Vitamin D3
- Oily fish and fish oil
- Egg yolk
- Dietary supplements
Sources of Vitamin D2
- Mushrooms (grown in UV light)
- Fortified foods
- Dietary supplements
Since vitamin D2 is cheaper to produce, it’s the most common form in fortified foods.
Summary Vitamin D3 is only found in animals, while vitamin D2 comes from plant-sourced foods.
Your skin makes vitamin D3 when it’s exposed to sunlight.
Specifically, ultraviolet B (UVB) radiation from sunlight triggers the formation of vitamin D3 from the compound 7-dehydrocholesterol in skin (2).
A similar process takes place in plants and mushrooms, where UVB light leads to the formation of vitamin D2 from ergosterol, a compound found in plant oils (3).
If you regularly spend time outdoors, lightly clad and without sunscreen, you may be getting all the vitamin D you need.
In Indian people, an estimated half an hour of midday sun twice a week provides the adequate amount (4).
Just keep in mind that this duration of exposure does not apply in countries farther away from the equator. In these countries, you may need more time to achieve the same results.
Nevertheless, be careful not to spend too much time in the sun without sunscreen. This is especially important if you have light-colored skin. Sunburns are a major risk factor for skin cancer (5).
Unlike dietary vitamin D, you cannot overdose on vitamin D3 produced in your skin. If your body already has enough, your skin simply produces less.
That said, many people get very little sun. They either work indoors or live in a country that doesn’t get much sunlight during the winter. If this applies to you, make sure to regularly eat plenty of food rich in vitamin D.
Summary Your skin produces vitamin D3 when you spend time in the sun. In contrast, vitamin D2 is produced by plants and mushrooms exposed to sunlight.
Vitamin D2 and D3 are not equal when it comes to raising your vitamin D status.
Both are effectively absorbed into the bloodstream. However, the liver metabolizes them differently.
The liver metabolizes vitamin D2 into 25-hydroxyvitamin D2 and vitamin D3 into 25-hydroxyvitamin D3. These two compounds are collectively known as calcifediol.
Calcifediol is the main circulating form of vitamin D, and its blood levels reflect your body’s stores of this nutrient.
For this reason, your health care provider can estimate your vitamin D status by measuring your levels of calcifediol (6).
However, vitamin D2 seems to yield less calcifediol than an equal amount of vitamin D3.
For example, one study in 32 older women found that a single dose of vitamin D3 was nearly twice as effective as vitamin D2 at raising calcifediol levels (9).
If you are taking vitamin D supplements, consider choosing vitamin D3.
Summary Vitamin D3 appears to be better than D2 at improving vitamin D status.
Scientists have raised concerns that vitamin D2 supplements might be lower quality than D3 supplements.
In fact, studies suggest vitamin D2 is more sensitive to humidity and fluctuations in temperature. For this reason, vitamin D2 supplements may be more likely to degrade over time (10).
However, whether this is relevant to human health is unknown. Also, no studies have compared the stability of vitamin D2 and D3 dissolved in oil.
Until new research proves otherwise, you shouldn’t worry about the quality of your vitamin D2 supplements. Simply make sure to store your supplements in a closed container, at room temperature, in a dry place and out of direct sunlight.
Summary Vitamin D2 supplements may be more likely to degrade during storage. However, it’s unknown whether the same applies to oil-based vitamin D2. More studies are needed to examine the relevance of this to human health.
Fortunately, there are many ways you can improve your vitamin D status.
Below are a few ideas:
- Select mushrooms that have been exposed to ultraviolet light (11)
- Take fish oil supplements such as cod liver oil
- Eat fatty fish twice a week (12)
- Choose milk or orange juice that’s been fortified with vitamin D
- Eat some eggs and butter (13)
- Spend at least half an hour in the sun daily, if possible
If you take vitamin D supplements, make sure not to exceed the safe upper intake level, which is 4,000 IU (100 micrograms) per day for adults (14).
According to the US Institute of Medicine, the recommended daily allowance is 400–800 IU (10–20 micrograms), but common supplemental doses range from 1,000–2,000 IU (25–50 micrograms) per day.
For detailed information on the optimal dosage of vitamin D, read this article.
Summary You can increase your vitamin D levels by regularly eating foods rich in vitamin D and spending time in the sun.
Vitamin D is not a single compound but a family of related nutrients. The most common dietary forms are vitamins D2 and D3.
The D3 form is found in fatty animal-sourced foods, such as fish oil and egg yolk. Your skin also produces it in response to sunlight or ultraviolet light. In contrast, vitamin D2 comes from plants.
Interestingly, vitamin D3 appears to be more effective at increasing levels of vitamin D in the blood. Although, scientists debate the relevance of this to human health.
To maintain adequate vitamin D levels, make sure to regularly eat plenty of foods rich in vitamin D or spend some time in the sun. If you take supplements, vitamin D3 is probably your best choice.