What Vitamin D Dosage Is Best?

What is vitamin D and why is it important?

Vitamin D belongs to the family of fat-soluble vitamins, which include vitamins A, D, E, and K. These vitamins are absorbed well with fat and are stored in the liver and fatty tissues (6).

There are two main forms of vitamin D in the diet:

• Vitamin D2 (ergocalciferol): found in plant foods like mushrooms
• Vitamin D3 (cholecalciferol): found in animal foods like salmon, cod, and egg yolks

However, sunlight is the best natural source of vitamin D3. The ultraviolet (UV) rays from sunlight convert cholesterol in your skin into vitamin D3 (1).

Before your body can use dietary vitamin D, it must be “activated” through a series of steps (1).

First, the liver converts dietary vitamin D into the storage form of vitamin D. This is the form that is measured in blood tests. Later, the storage form is converted by the kidneys to the active form of vitamin D that’s used by the body (1).

Though both vitamin D2 and vitamin D3 can increase blood levels of vitamin D, some research suggests that vitamin D3 is more effective (7).

The main role of vitamin D in the body is to manage blood levels of calcium and phosphorus. These minerals are important for healthy bones (6).

Research also shows that vitamin D aids your immune system and may reduce your risk of heart disease and certain cancers (2).

A low blood level of vitamin D is linked to a greater risk of fractures and falls, heart disease, multiple sclerosis, several cancers, and even death (8, 9, 10, 11, 12, 13).

summary

There are two main forms of vitamin D in the diet, including vitamin D2 and vitamin D3. Vitamin D3 is more effective at raising blood levels of vitamin D, which is linked to a variety of health benefits.

How much vitamin D do you need for optimal health?

In the United States, current guidelines suggest that consuming 400–800 International Units (IU), or 10–20 micrograms (mcg), of vitamin D should meet the needs of 97%–98% of all healthy people (14).

However, many experts believe the guidelines are far too low and point out that there may have been a statistical error in the data originally used to estimate the recommended dietary allowance (RDA) (15, 16).

Your vitamin D needs depend on a variety of factors. These include your age, skin color, current blood vitamin D levels, location, sun exposure, and more (17).

To reach blood levels linked to better health outcomes, many studies have shown that you need to consume more vitamin D than the guidelines recommend.

For instance, one review of 17 studies found that vitamin D deficiency was associated with a significantly higher risk of developing colorectal cancer (18).

Another study found that taking 1,000 IU (25 mcg) of vitamin D3 daily was more effective at increasing vitamin D blood levels in people with a “normal” body mass index (BMI) compared to those with a higher BMI (19).

What’s more, a recent analysis found that having lower blood levels of vitamin D was associated with an increased risk of heart disease (20).

However, note that another analysis of 21 studies found that vitamin D supplementation was not linked to a reduced risk of heart attack, stroke, or death (21).

Though more research is needed, it seems that consuming 1,000–4,000 IU (25–100 mcg) of vitamin D daily should be ideal for most people to reach healthy vitamin D blood levels (14).

Keep in mind that it’s important not to consume more than 4,000 IU of vitamin D without a doctor’s permission, as it exceeds the safe upper limits of intake and is not linked to additional health benefits (14).

summary

Consuming 400–800 IU (10–20 mcg) of vitamin D should meet the needs of 97%–98% of healthy people. However, several studies show that taking more than this is linked to greater health benefits.

Supplements 101: Vitamin D

How do you know if you have a vitamin D deficiency?

A vitamin D deficiency can only be discovered through blood tests that measure levels of storage vitamin D, known as 25(OH)D.

According to the Institute of Medicine (IOM), the following values determine your vitamin D status (22):

• Deficient: levels less than 12 nanograms per milliliter (ng/mL), or 30 nanomoles per liter (nmol/L)
• Insufficient: levels between 12–20 ng/mL (30–50 nmol/L)
• Sufficient: levels between 20–50 ng/mL (50–125 nmol/L)
• High: levels greater than 50 ng/mL (125 nmol/L)

However, several older studies have found that a blood level of 30 ng/mL (75 nmol/L) could be even better for preventing fractures, falls, and certain cancers (23, 24, 25).

Additionally, some other organizations, such as the Endocrine Society, define blood levels of vitamin D lower than 30 ng/mL (75 nmol/L) as a vitamin D deficiency (1).

summary

Blood tests are the only way to know if you are deficient in vitamin D. Most people should aim for blood levels over 20 ng/mL (50 nmol/L). Some studies find that a blood level over 30 ng/mL is better for preventing falls, fractures, and certain types of cancers.

Sources of vitamin D

Getting plenty of sunlight is the best way to increase your blood vitamin D levels.

That’s because your body makes dietary vitamin D3 out of the cholesterol in the skin when it is exposed to the sun’s UV rays (1).

However, people who don’t live in sunny countries need to consume more vitamin D through foods and supplements (26).

Generally speaking, very few foods are great sources of vitamin D. However, the following foods are exceptions (27, 28, 29, 30, 31, 32, 33):

• Cod liver oil: 1 tablespoon, or 14 grams (g), contains 170% of the Daily Value (DV)
• Swordfish, cooked: 3 ounces (oz), or 85 g, contain 71% of the DV
• Salmon, cooked: 3 oz (85 g) contain 56% of the DV
• Canned tuna, drained: 3 oz (85 g) contain 29% of the DV
• Beef liver, cooked: 3 oz (85 g) contain 5% of the DV
• Egg yolks, large: 1 yolk contains 5% of the DV

Mushrooms also produce a significant amount of vitamin D2 when exposed to sunlight or UV light (34).

In fact, 1 cup (70 g) of raw white mushrooms provides less than 1% of the DV for vitamin D. Meanwhile, the same amount of UV-exposed raw white mushrooms contains nearly 92% of the DV (35, 36).

If you’re choosing a vitamin D supplement, be sure to find one that contains D3 (cholecalciferol), as it may be more effective at raising your blood levels of vitamin D (7).

summary

Sunlight is the best source of vitamin D, but many people can’t get enough for various reasons. Foods and supplements that are high in vitamin D can help and include cod liver oil, fatty fish, egg yolks, and mushrooms.

Some people need more vitamin D

There are certain groups of people who need more dietary vitamin D than others.

These include older people, those with darker skin, people who live far from the equator and those with certain medical conditions.

Older adults

There are many reasons why people need to consume more vitamin D with age.

For starters, your skin gets thinner as you grow older. This makes it harder for your skin to make vitamin D3 when it is exposed to sunlight (37).

Older people also often spend more time indoors. This means they get less exposure to sunlight, which is the best way to naturally boost vitamin D levels.

Additionally, your bones become more fragile with age. Maintaining adequate blood levels of vitamin D can help preserve bone mass with age and may protect against fractures (8, 38).

People with darker skin

Research shows that people with darker skin are more prone to vitamin D deficiency (39, 40).

This is because they have more melanin in their skin — a pigment that helps determine skin color. Melanin helps protect the skin from the sun’s UV rays (41).

However, it also reduces the body’s ability to make vitamin D3 from the skin, which can make you prone to deficiency (42).

If you have a vitamin D deficiency, a doctor can recommend an appropriate dosage for supplementation based on your vitamin D blood levels.

Those who live farther away from the equator

Countries close to the equator get plenty of sunlight all year round. Conversely, countries farther away from the equator get less sunlight all year round.

This can cause low blood vitamin D levels, especially during winter months when there is even less sunlight.

For instance, a 2007 study of Norwegians discovered that they don’t produce much vitamin D3 from their skin during the winter months of October to March (43).

If you live far from the equator, then you need to get more vitamin D from your diet and supplements. According to one older review, many experts agree that at least 1,000 IU (25 mcg) of vitamin D3 daily is needed in situations where there is no exposure to sunlight (44).

People with medical conditions that reduce fat absorption

Because vitamin D is fat-soluble, it relies on the gut’s ability to absorb fat from the diet.

Thus, people who have medical conditions that reduce fat absorption are prone to vitamin D deficiencies. These include inflammatory bowel disease (Crohn’s disease and ulcerative colitis), liver disease, and people who have had bariatric surgery (14, 45).

People with the above conditions are often advised to take vitamin D supplements in an amount prescribed by a doctor.

summary

Those who need the most vitamin D are older adults, people with darker skin, those who live farther from the equator, and people who can’t absorb fat properly.

Can you take too much vitamin D?

While it is possible to take too much vitamin D, toxicity is very rare.

In fact, you would need to take extremely high doses of 50,000 IU (1,250 mcg) or more for a long period of time (46).

It’s also worth noting that it is impossible to overdose on vitamin D from sunlight (47).

Although 4,000 IU (100 mcg) is set as the maximum amount of vitamin D you can take safely, several studies have shown that taking up to 10,000 IU (250 mcg) daily is not more likely to cause side effects than lower doses (48, 49).

However, it’s best to consult with a doctor or dietitian for personalized recommendations on how much vitamin D you should take, depending on your needs.

summary

Although it is possible to take too much vitamin D, toxicity is rare, even above the safe upper limit of 4,000 IU. That said, it’s best to talk to a doctor or dietitian for personalized dosing recommendations.

The bottom line

Getting enough vitamin D from sunlight and foods is necessary for optimal health.

It helps maintain healthy bones, aids your immune system, and may reduce the risk of many harmful diseases. Yet despite its importance, many people don’t get enough vitamin D.

In addition, older people, people with darker skin, those who live farther away from the equator, and people who can’t absorb fat properly have higher dietary vitamin D needs.

The current recommendations suggest consuming 400–800 IU (10–20 mcg) of vitamin D per day.

However, people who need more vitamin D can safely consume 1,000–4,000 IU (25–100 mcg) daily. Consuming more than this is not advised unless prescribed by a healthcare professional.