What is Vitamin D?

Vitamin D is a fat-soluble vitamin that primarily aids calcium absorption, promoting growth and mineralization of your bones. It's also involved in various functions of your immune, digestive, circulatory, and nervous systems (1).

Emerging research suggests that vitamin D may help prevent a variety of illnesses, such as depression, diabetes, cancer, and heart disease. However, vitamin D's relationship to these conditions is still poorly understood (1).

How Much Do You Need?

There is significant debate within the scientific community about how much vitamin D your body needs.

While the U.S. National Academy of Medicine considers 600–800 IU of daily vitamin D to be sufficient for the majority of the population, the U.S. Endocrine Society recommends 1,500–2,000 IU per day (2, 3).

The Reference Daily Intake (RDI) is currently set at 600-800 IU of vitamin D for adults, based on the U.S. National Academy of Medicine's recommendations (2).

The optimal blood level of vitamin D is not concretely established but likely falls between 20 and 50 ng/ml (4, 5, 6).

The U.S. National Academy of Medicine further suggests that a daily intake up to 4,000 IU of vitamin D per day is safe for most people, although much higher doses may be temporarily necessary in order to raise blood levels in some individuals (4).

Although toxicity is rare, it is best to avoid long-term vitamin D doses in excess of 4,000 IU without supervision from a qualified healthcare professional.

Summary

Vitamin D is necessary for calcium absorption and bone health. While there is no set guidance, dosage recommendations range from 600–2,000 IU per day — but some people may need heavier doses to reach and maintain healthy blood levels.

1. Spend Time in Sunlight

Vitamin D is often referred to as "the sunshine vitamin" because the sun is one of the best sources of this nutrient.

Your skin hosts a type of cholesterol that functions as a precursor to vitamin D. When this compound is exposed to UV-B radiation from the sun, it becomes vitamin D.

In fact, sun-derived vitamin D may circulate for twice as long as vitamin D from food or supplements (1).

However, the amount of vitamin D your body can make depends on several variables.

Skin Tone and Age

People with darker skin need to spend more time in the sun to produce vitamin D than those with lighter skin. That's because darker skin has more melanin, a compound that can inhibit vitamin D production (7).

Age can have an impact as well. As you get older, vitamin D production in your skin becomes less efficient (8).

Geographical Location and Season

The closer you live to the equator, the more vitamin D you'll be able to produce year-round because of your physical proximity to the sun's rays.

Conversely, your opportunities for adequate sun exposure decreases proportionally the farther away from the equator you live (9).

Sunscreen and Clothing

Certain types of clothing and sunscreen can hinder — if not completely block — vitamin D production (1).

While it's vital to protect yourself from skin cancer by avoiding overexposure to sunlight, it takes very little unprotected sun exposure for your body to start producing vitamin D.

Although there's no official recommendation, sources suggest that as few as 8–15 minutes of exposure is enough to make plenty of vitamin D for lighter-skinned individuals. Those with darker skin may need more time (10).

Summary

Your skin can produce large quantities of vitamin D on its own when exposed to the sun's UV-B rays. However, many factors affect this process.

2. Consume Fatty Fish and Seafood

Fatty fish and seafood are among the richest natural food sources of vitamin D.

In fact, a 3.5-ounce (100-gram) serving of canned salmon can provide up to 386 IU of vitamin D — about 50% of the RDI (11).

The exact vitamin D content of seafoods may vary depending on the type and species in question. For example, some research suggests that farmed salmon may contain only 25% of the amount of wild-caught salmon (12).

Other kinds of fish and seafood rich in vitamin D include:

• tuna
• mackerel
• oysters
• shrimp
• sardines
• anchovies

Many of these foods are also rich in heart-healthy omega-3 fatty acids (13).

Summary

Fatty fish and seafood are among the foods highest in vitamin D, though exact vitamin content may vary depending on the type and source of the food in question.

3. Eat More Mushrooms

Mushrooms are the only completely plant-based source of vitamin D.

Like humans, mushrooms can make their own vitamin D upon exposure to UV light. Humans produce a form of vitamin D known as D3 or cholecalciferol, whereas mushrooms produce D2 or ergocalciferol(14).

Both forms of this vitamin can raise circulating vitamin D levels, though research suggests that D3 may raise levels more effectively and efficiently than D2 (15).

While vitamin D content depends on the type of mushroom, certain varieties — such as wild maitake mushrooms — provide as much as 2,348 IU per 3.5-ounce (100-gram) serving. That's almost 300% of the RDI (11, 16).

Due to their exposure to sunlight, wild mushrooms usually have more vitamin D than commercially grown types. However, you can also purchase mushrooms treated with UV light.

However, you should always take care to meticulously identify wild mushrooms or purchase them from a trusted supplier — such as a grocery store or farmers market — to avoid exposure to poisonous varieties.

Summary

Much like humans, mushrooms produce vitamin D when exposed to UV light. Wild mushrooms — or commercially grown ones treated with UV light — have the greatest vitamin D levels.

4. Include Egg Yolks in Your Diet

Egg yolks are another source of vitamin D that you can easily add to your routine.

Like many other natural food sources, yolks have variable vitamin D content.

Conventionally raised chickens that don't have access to the outdoors typically only produce eggs harboring 2–5% of the RDI (17).

However, some research indicates that eggs from pasture-raised or free-range chickens offer up to 4 times more — or up to 20% of the RDI — depending on how much time the fowl spend outside (17).

Chicken feed can also affect the vitamin D content of eggs. Those fed vitamin-D-enriched grain may produce yolks that boast well over 100% of the RDI (18).

Summary

Free-range and pastured eggs are a great source of vitamin D, as chickens with access to sunlight produce more vitamin D in their eggs than those that remain indoors.

5. Eat Fortified Foods

Because few foods naturally contain high levels of vitamin D, this nutrient is often added to staple goods in a process known as fortification.

Still, you should keep in mind that the availability of vitamin-D-fortified foods varies by country, and the amount added to foods may differ by brand and type.

Some commonly fortified goods include:

• cow's milk
• plant-based milk alternatives like soy, almond, and hemp milk
• orange juice
• ready-to-eat cereals
• certain types of yogurt
• tofu

If you're unsure whether a particular food has been fortified with vitamin D, check its ingredients list.

Summary

Vitamin D is often added to food staples — such as milk and breakfast cereals — to increase intake of this nutrient.

6. Take a Supplement

For many people, taking a vitamin D supplement may be the best way to ensure adequate intake.

Vitamin D exists in two main biological forms — D2 (ergocalciferol) and D3 (cholecalciferol). Typically, D2 comes from plants and D3 from animals (15).

Research suggests that D3 may be significantly more effective at raising and maintaining overall vitamin D levels than D2, so look for a supplement with this form (15).

Additionally, it's important to purchase high-quality supplements that have been independently tested. Some countries — such as the United States — don't regulate nutritional supplements, which can negatively impact supplement quality.

It's best to choose supplements tested for purity and quality by a third party, such as the U.S. Pharmacopeia (USP), Informed-Choice, ConsumerLab.com, or the Banned Substances Control Group (BSCG).

Dosage

Vitamin D supplements vary in dosage. That said, the amount you need depends on your current vitamin D levels.

For most people, 1,000–4,000 IU is considered a safe daily dose for maintaining healthy levels (4).

However, you may need a much larger dose in certain circumstances — and especially if your current levels are very low or you have limited exposure to sunshine (4).

For this reason, it's ideal to have your vitamin D levels tested by your medical professional to ensure you're taking the most appropriate dose.

Vegan Supplement Options

The majority of vitamin D supplements are derived from animal sources — and thus inappropriate for vegans. However, a few vegan D supplement options exist.

Because vitamin D2 is plant-derived, D2 supplements are typically vegan-friendly and widely available.

Vegan D3 is significantly less common than D2 but can be made from lichens. You're most likely to find them in specialty health stores or online.

Summary

Supplements are often needed if you don't obtain enough vitamin D from food or sunlight. Having your vitamin D levels checked before supplementing is the best way to pick the appropriate dose.

7. Try a UV Lamp

Lamps that emit UV-B radiation may also boost your vitamin D levels, though these lamps can be costly.

When your skin is exposed to UV-B radiation from the sun, it's able to produce its own vitamin D. UV lamps mimic the action of the sun and can be especially helpful if your sun exposure is limited due to geography or time indoors.

UV radiation has been used therapeutically for various skin conditions for decades, but only recently has it been marketed as a way to improve vitamin D levels (19).

Safety is an important concern with these devices, as too much exposure could burn your skin. You're typically recommended to limit your exposure to no more than 15 minutes at a time.

Summary

You can purchase lamps that emit UV-B radiation to stimulate vitamin D production. However, they can be expensive and dangerous if used for more than 15 minutes at a time.

The Bottom Line

Vitamin D is an essential nutrient that many people around the world don't get enough of.

That said, you can boost your vitamin D levels by getting more sun exposure, eating foods rich in vitamin D, and/or taking supplements.

If you suspect you're low in this essential nutrient, consult with a health professional to get your levels checked.