For most adults, a normal level of vitamin D in the blood is 20 nanograms per milliliter or above. The amount of vitamin D a person needs per day depends on their age.

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

In this article, we look at:

  • normal vitamin D levels by age
  • why vitamin D is important
  • signs of a deficiency
  • how to increase vitamin D
  • if too much is possible

a man sitting in the sun and topping up on normal vitamin D levelsShare on Pinterest
Exposure to sunlight can help a person get enough vitamin D.

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

AgeAmount
0–12 months10 micrograms (mcg) or 400 international units (IU)
1–70 years15 mcg or 600 IU
71+ years20 mcg or 800 IU

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.

LevelBlood test result
Low30 nmol/l or 12 ng/ml or below
Adequate50 nmol/l or 20 ng/ml or above
High125 nmol/l or 50 ng/ml or above

A person can talk to 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 the body absorb calcium and phosphorus, both vital minerals for building strong bones.

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.

Evidence suggests vitamin D may help to prevent some medical conditions, including some types of cancer.

However, scientists are still trying to understand how vitamin D may influence specific conditions. Research into its ability to influence diseases, such as diabetes, hypertension, and multiple sclerosis, is ongoing.

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 be subtle, but the classic symptoms are bone aches and muscle weakness.

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:

  • breastfed infants, as human milk has limited vitamin D
  • older adults, who do not absorb vitamin D, plus younger adults
  • people with darker skin, who absorb less vitamin D from sunlight
  • people who stay indoors for prolonged periods
  • people with obesity, as fat cells bind to vitamin D and stop it entering the bloodstream

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

People can also get some of their vitamin D from food. According to the Office of Dietary Supplements, food sources of vitamin D include:

  • oily fish, such as mackerel, tuna, and trout
  • beef liver
  • portobello mushrooms
  • chicken breasts
  • dairy products
  • fortified cereals

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

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.

According to one study, vitamin D toxicity can produce symptoms that include:

  • recurrent vomiting
  • polyuria, or increased daily urine output
  • confusion
  • polydipsia, or an abnormal increase in thirst
  • apathy
  • abdominal pain
  • dehydration

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

AgeMaximum
0–6 months25 mcg or 1,000 IU
7–12 months38 mcg or 1,500 IU
1–3 years63 mcg or 2,500 IU
4–8 years75 mcg or 3,000 IU
9+ years100 mcg or 4,000 IU

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

Normal 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 or at risk for a deficiency may require more.

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.