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Vitamin D
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Food Nutrition

Vitamin D

Vitamin D is essential for bone health and immune function, and can be obtained through sunlight, diet, or supplementation.

Why do I need vitamin D?

Vitamins are substances that your body needs to grow and develop normally. Vitamin D is important to your body because:

  • It helps your body absorb calcium. Calcium is one of the main building blocks of bone. A lack of vitamin D can lead to bone diseases such as osteoporosis or rickets.
  • It also has a role in your nerve, muscle, and immune systems:
    • Your muscles need it to move
    • Your nerves need it to carry messages between your brain and your body
    • Your immune system needs vitamin D to fight off bacteria and viruses

How do I get vitamin D?

You can get vitamin D in three ways: through your skin, from your diet, and from supplements. Your body forms vitamin D naturally after exposure to sunlight. However, too much sun exposure can lead to skin aging and skin cancer. So many people try to get their vitamin D from other sources.

Very few foods naturally contain vitamin D. Most people get vitamin D in their diet from foods that are fortified. This means that vitamin D is added to the food. These foods may include milk, cereal, and yogurt. Foods that naturally have vitamin D include egg yolks, saltwater fish, and liver.

Vitamin D is available in supplements. It is also included in many multivitamins. The two forms of vitamin D in supplements are D2 and D3. Both types increase vitamin D in your blood, but D3 might raise it higher and for longer than D2. Vitamin D is fat soluble. You can absorb it better when you take your supplements with a meal or snack that includes some fat.

How much vitamin D do I need?

The amount of vitamin D you need each day depends on your age. The recommended amounts, in international units (IU), are:

  • Birth to 12 months: 400 IU
  • Children 1-13 years: 600 IU
  • Teens 14-18 years: 600 IU
  • Adults 19-70 years: 600 IU
  • Adults 71 years and older: 800 IU
  • If you are pregnant or breastfeeding: 600 IU

Risk Factors and Supplementation

Certain people may need extra vitamin D, such as:

  • Older adults
  • Breastfed infants
  • People with dark skin
  • People with certain conditions that limit the absorption of fat, such as Crohn's disease, celiac disease, and ulcerative colitis
  • People who have obesity or have had gastric bypass surgery

Check with your health care provider to see if you need to take vitamin D supplements, and if so, how much you should take. Your provider may want to first do a vitamin D test to see if you are getting enough of it.

Frequently Asked Questions

Many symptoms of vitamin D deficiency are non-specific and frequently misdiagnosed as general fatigue, depression, or aging. Common signs include persistent bone pain or tenderness, particularly in the lower back, hips, or legs, along with muscle weakness that makes climbing stairs or rising from a chair difficult. Some patients also report frequent fractures from minor falls, hair loss, or slow wound healing. Because these symptoms overlap with many other conditions, a simple blood test is the only way to confirm a deficiency.
Taking high-dose vitamin D without medical supervision is generally not recommended because vitamin D is fat-soluble and can accumulate in the body, leading to toxicity. Symptoms of toxicity, known as hypervitaminosis D, include nausea, vomiting, weakness, and frequent urination, and can lead to dangerous calcium buildup in the blood that affects the heart and kidneys. It is best to get a baseline blood test to determine your current level and allow a clinician to prescribe a dosage that is safe and effective for your specific needs.
It typically takes four to eight weeks of consistent daily supplementation to see a significant increase in serum 25-hydroxyvitamin D levels. The exact timeline depends on your starting level, the dosage prescribed, and your body weight. If you have severe deficiency, your healthcare provider may recommend a higher loading dose initially, followed by a maintenance dose, with a follow-up blood test in three months to ensure levels have stabilized.
Sunscreen with an SPF of 30 or higher blocks more than 95% of UVB rays, which are the specific rays needed for vitamin D synthesis in the skin. While this protection is crucial for preventing skin cancer and premature aging, it effectively prevents your body from producing vitamin D during that time. Therefore, if you use sunscreen consistently, you should rely on dietary sources or supplements to meet your daily vitamin D requirements rather than expecting to generate enough through sun exposure.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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