Many of my patients who come into the office for their physical exams ask to have their vitamin D levels checked. They may have a family member with osteoporosis, or perhaps they have had bone thinning themselves. Mostly, they want to know that they're doing everything they can to keep their bones strong. Vitamin D is critical for healthy bones. But when we check that blood level, how to act on the result is the subject of great controversy in medical-research land.

What Is a Healthy Vitamin D Level?

Pinpointing a "healthy" vitamin D level is tricky

So, what is the current cutoff value at which people are considered "low," and thus at risk for developing bone thinning and having fractures? (We are talking about the blood level of 25-hydroxy-vitamin D, which is usually measured in nanograms per milliliter.) Ah. This is where there is a lot of argument.

In 2010, the venerable Institute of Medicine (IOM) issued a report based on lengthy examination of data by a group of experts. To sum up, they estimated that a vitamin D level of 20 ng/mL or higher was adequate for good bone health, and subsequently a level below 20 was considered a vitamin D deficiency.

In my practice, and in most, it is not uncommon to see a vitamin D level less than 20. When that happens, we tell the patient that they are deficient and recommend fairly aggressive replenishment, as well as ongoing supplementation. The majority of folks have a level between 20 and 40, in my experience, and this is corroborated by the IOM's findings in that 2010 report.

But in 2011, the respected Endocrine Society issued a report urging a much, much higher minimum blood level of vitamin D. At that time, their experts concluded: "Based on all the evidence, at a minimum, we recommend vitamin D levels of 30 ng/mL, and because of the vagaries of some of the assays, to guarantee sufficiency, we recommend between 40 and 60 ng/mL for both children and adults."

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.

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 method of obtaining vitamin D3. The ultraviolet (UV) rays from sunlight convert cholesterol in your skin into vitamin D3.

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

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.

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

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.

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

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.

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.

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).

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.

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.

Another study found that taking people who have obesity have a greater risk of having vitamin D deficiency, so the dose should be adjusted according to size.

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

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.

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:

• 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.

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.

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.

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

Generally speaking, very few foods are great sources of vitamin D. However, the following foods are exceptions:

1. Cod liver oil: 1 tablespoon, or 14 grams (g), contains 170% of the Daily Value (DV)
2. Swordfish, cooked: 3 ounces (oz), or 85 g, contain 71% of the DV
3. Salmon, cooked: 3 oz (85 g) contain 56% of the DV
4. Canned tuna, drained: 3 oz (85 g) contain 29% of the DV
5. Beef liver, cooked: 3 oz (85 g) contain 5% of the DV
6. 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.

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%Trusted Source of the DV.

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.

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.

FAQS 

1. What is vitamin D?

Vitamin D is a nutrient that helps your body:

build strong bones and teeth

absorb calcium

Support muscles and immune system

Your body makes it from sunlight, and you can also get it from food and supplements.

2. What is a healthy vitamin D level?

Vitamin D is measured with a blood test called 25-hydroxyvitamin D.

Healthy/adequate: 20–50 ng/mL (50–125 nmol/L)

Low (inadequate): 12-19 ng/mL

Deficiency: below 12 ng/ml

Very high (potential toxicity): above 100 ng/ml

Most doctors aim for at least 20 ng/ml for general health.

3. Why is vitamin D important?

Vitamin D helps:

Prevent weak or brittle bones

Assisted development in adolescence

keep the muscles in order

Help the immune system fight disease

4. How can I get vitamin D naturally?

You can get vitamin D from:

Sunlight (your skin makes it)

Foods, for example:

fatty fish (salmon, tuna)

egg yolk

fortified milk, cereal or plant milk

5. Who is more likely to have low vitamin D?

People who may have low levels include:

those that receive less sunlight

people who spend a lot of time indoors

dark skin

People who do not eat vitamin D-rich foods

6. Can you get too much vitamin D?

Yes. Too high levels (usually from too much supplementation) can cause problems such as:

Nausea

weakness

high calcium levels

Therefore, dietary supplements should only be taken in amounts recommended by healthcare professionals.

7. Should teenagers take vitamin D supplements?

Some teenagers may need supplements, especially in winter or if levels are low - but this should be decided by a doctor or healthcare professional.

8. How can I know my vitamin D level?

The only way to know for sure is to have a blood test ordered by a healthcare professional.