Vitamin D deficiency is easy to miss, because mild cases often cause no symptoms. When it’s severe or goes on for a long time, it weakens bones. It’s also one of the easier nutrient problems to fix.

The short version

  • What it does: vitamin D helps your body absorb calcium, which keeps bones strong, according to MedlinePlus.
  • What goes wrong: without enough vitamin D, bones can become soft and weak. The condition is called osteomalacia in adults and rickets in children.
  • Who’s at risk: people who get little sun, have darker skin, have obesity, have had gastric bypass surgery, or have a condition that makes it hard to absorb nutrients.
  • Testing: a blood test for 25-hydroxyvitamin D. A level below 12 ng/mL is considered deficient.
  • Treatment: vitamin D supplements, usually with calcium, and sometimes other minerals. Most people improve within weeks, and bones heal within about 6 months, according to MedlinePlus.
  • How much you need: 600 IU a day for most adults, and 800 IU for people 71 and older. The upper limit is 4,000 IU a day unless a provider prescribes more.

Symptoms

Many people with low vitamin D have no symptoms. When the deficiency is severe enough to soften the bones, the condition is osteomalacia, and its symptoms can include bone pain and muscle weakness, according to MedlinePlus. Low calcium can add its own symptoms. Because these signs look like many other problems, a blood test is the way to know.

In children, severe deficiency causes rickets, which causes weak or deformed bones. See Vitamin D Drops for Breastfed Babies for how to prevent it in infants.

What causes it

Your body gets vitamin D from food and from sunlight on your skin. Deficiency happens when you don’t get enough of either, or when your body can’t absorb it. MedlinePlus lists these causes:

  • Living in a climate with little sun, or having to stay indoors
  • Not being able to absorb vitamin D in the intestines, such as after gastric bypass surgery or because of a digestive condition
  • Side effects of medicines used to treat seizures

The NIH also notes that people with obesity may need more vitamin D than others, and darker skin makes less vitamin D from the same amount of sun, according to MedlinePlus. Keep using sunscreen, because sun exposure raises the risk of skin cancer. Food and supplements matter more than sunlight for most people.

Testing

The best measure of your vitamin D status is a blood test for 25-hydroxyvitamin D, also written 25(OH)D, according to MedlinePlus. Labs report it in ng/mL or nmol/L. The NIH uses these ranges:

Level ng/mL nmol/L
Deficient Below 12 Below 30
Inadequate 12 to 20 30 to 50
Adequate 20 or higher 50 or higher
Possibly too high Above 50 Above 125

Routine screening of adults who have no symptoms isn’t recommended. The U.S. Preventive Services Task Force found there isn’t enough evidence to say whether screening helps. Testing makes the most sense if you have a risk factor or symptoms. If you’re pregnant, see Vitamin D Deficiency in Pregnancy.

Treatment

Treatment usually means vitamin D supplements taken by mouth. When bones are soft, calcium and phosphorus may be added too. Some people with a vitamin deficiency get better within a few weeks, and with treatment, healing should happen within 6 months, according to MedlinePlus. Symptoms can come back, so follow-up matters.

Your provider chooses the dose based on how low your level is and why, and a higher dose may be prescribed for a time. Don’t go above 4,000 IU a day on your own, because too much vitamin D can make your body absorb too much calcium, which can cause nausea, vomiting, constipation, weakness, and kidney problems.

If the cause is a medicine, such as a seizure medicine, or trouble absorbing nutrients, treat that with your provider too. Don’t stop a medicine on your own.

Prevention

Eating a diet rich in vitamin D and calcium and getting enough sunlight can help prevent deficiency, according to MedlinePlus.

  • Food. Fatty fish such as salmon, fortified milk, and fortified cereals are the main sources. See Vitamin D in Pregnancy for amounts.
  • A supplement. If you get little sun or eat few vitamin D foods, ask your provider whether to take one, and how much.
  • Calcium. It works together with vitamin D. See Calcium in Pregnancy for food sources.

What to do now

  • Check whether you have a risk factor: little sun, darker skin, obesity, gastric bypass, or a digestive condition.
  • If you do, or you have bone pain or muscle weakness, ask about a vitamin D blood test.
  • If you’re low, take the dose your provider recommends and ask when to retest.
  • Keep your total under 4,000 IU a day unless your provider says otherwise.

Related reading

Sources

Updated November 2026. This article is for general information and is not a substitute for advice from your health care provider.