For adults, a level of vitamin D in the blood of 20 nanograms per milliliter (ng/mL) or above is generally considered adequate. Levels below 20 ng/mL are generally too low for adequate bone health and overall health.

Levels above 50 ng/mL may be too high. Levels in a range that is too high or too low may affect a person’s health.

The body depends on vitamin D for a variety of reasons, but it is especially important for bone health.

This article looks at vitamin D levels by age and why vitamin D is important. It also discusses signs of a deficiency, how to increase vitamin D, and if too much is possible.

According to the Office of Dietary Supplements, the following are the average recommended amounts of vitamin D a person needs per day:

People who are pregnant or breastfeeding also need 15 mcg or 600 IU of vitamin D per day.

Doctors use blood tests to determine if someone has adequate levels of vitamin D. They measure vitamin D using one of two measurements: nanomoles per liter (nmol/l) or nanograms per milliliter (ng/ml).

The following table provides rough ranges for low, normal, and high vitamin D levels for the average adult in nmol/ml and ng/ml.

It is also important to note that medical professionals generally consider a range of 30–50 nmol/L inadequate for a person’s bone health and overall health.

However, this may vary for different people, and research is still underway about the serum concentration linked to deficiency, bone health, and overall health.

A person can talk with their doctor to get a better understanding of what their blood test results mean.

According to the U.S. Department of Agriculture, vitamin D helps to promote and improve bone health.

Without adequate vitamin D, a person may develop soft, weak, or brittle bones. This can cause conditions such as rickets in children, or osteomalacia and osteoporosis in adults.

Vitamin D also contributes to the health of muscles, nerves, the brain, and the immune system.

Vitamin D may help to prevent some medical conditions, including some types of cancer. However, evidence from observational studies and clinical trials is mixed.

However, scientists are still trying to understand how vitamin D may influence specific conditions.

Learn more about the health benefits of vitamin D.

People can get vitamin D from exposure to sunlight or, to a lesser extent, from food. If someone does not get enough vitamin D from these sources, they may develop a deficiency.

The symptoms of a vitamin D deficiency can include bone and muscle weakness and pain. Symptoms may differ for osteoporosis and osteomalacia.

Vitamin D deficiency can happen when a person does not get enough vitamin D, either from sunlight or food.

According to the U.S. Department of Health and Human Services, some people are more at risk of developing vitamin D deficiency than others. This includes:

Some health conditions and medications can also make it more difficult for someone to absorb vitamin D, including:

People can get at least some of their daily vitamin D from exposure to sunlight.However, as light levels vary, depending on location and the time of year, a person may not be able to get all the vitamin D they need from sunlight.

A 2019 study in Switzerland found that only 10–15 minutes of sun exposure per day was enough to provide 1,000 IU of vitamin D in spring and summer. However, getting this amount in fall and winter was unrealistic, requiring someone to spend over 6 hours a day outdoors.

This suggests that people who live in colder climates, or who spend most of their time indoors, may benefit from vitamin D supplements. However, a person should talk with their doctor before taking vitamin D, as it can interact with some medications.

Sunlight can also cause skin damage and sunburn, so it is essential to use sunscreen when spending time outside.

A 2019 study on Australian office workers found that applying sunscreen meant people could spend more time outdoors, leading to higher vitamin D levels overall.

The study found that fish consumption, in particular, had a positive effect on vitamin D levels during winter.

According to the Office of Dietary Supplements, other food sources of vitamin D include:

Learn more about food sources of vitamin D.

A person can take too much vitamin D. Since vitamin D occurs naturally in only a few food sources, the most likely way a person can get too much vitamin D is through taking a high strength supplement.

The upper limits for how much vitamin D a person should take per day by age, are as follows:

Vitamin D toxicity refers to toxic levels of vitamin D in the body. According to a 2018 study, vitamin D toxicity can produce symptoms that include:

To help reduce the risk of vitamin D toxicity, it is important to contact a doctor for advice before taking vitamin D supplements.

Learn more about getting too much vitamin D.

A person should contact a doctor if they notice the symptoms of vitamin D toxicity. They can bring a list of any supplements they are taking to the appointment to help with the doctor’s diagnosis.

A person should also contact their doctor if they notice symptoms of a lack of vitamin D. A doctor may do a physical examination, ask questions, and perform a blood test to see if the person has a deficiency.

It is also best to contact a doctor before taking any supplements. Some supplements may interact with current medications or affect certain medical conditions.

Generally adequate vitamin D levels in the blood are 20 ng/ml or above for adults. People aged 1–70 years should aim to get at least 15 mcg or 600 IU of vitamin D per day. Those who are older may require more.

It is important to note that a person can also get too much vitamin D, so it is best to contact a doctor for advice.

Vitamin D is an essential nutrient for a variety of reasons, particularly for bone health. A person will often get enough vitamin D from sunlight, but if they are at risk for a deficiency they may benefit from taking a supplement.

It is important to contact a doctor before taking vitamin D supplements to reduce the risk of vitamin D toxicity.