Vitamin D

What is Vitamin D?

Vitamin D is a fat-soluble vitamin. The skin makes it when it is exposed to sunlight (UVB rays), and it is also found in a small number of foods and in supplements.^[1]

The body has to change vitamin D in the liver and then the kidneys before it becomes active.^[1]

Its role in the body

• Helps the gut absorb calcium and keeps calcium and phosphate levels right for healthy bones.^[1]
• Is needed for bones to grow and stay strong; very low levels can lead to soft bones (rickets in children, osteomalacia in adults).^[1]
• Also plays a part in muscles, nerves and the immune system.^[1]

Important food sources

• Fatty fish such as salmon, mackerel and sardinesAmong the best natural food sources.
• Egg yolkContains small amounts.
• Fortified milk, fortified edible oil or other fortified foodsOnly if the label says "fortified with vitamin D"; amounts vary by brand.
• Mushrooms exposed to UV lightVitamin D content varies a lot.
• Sunlight on skinA major source for many people, but it varies with season, time of day, skin colour, clothing and pollution.

Recommended dietary intake

Signs sometimes associated with low levels

• In adults, long-term low vitamin D can cause osteomalacia, with bone pain and muscle weakness.^[1]
• In children, it can cause rickets, with soft, bent bones.^[1]
• Many people with low levels have no obvious signs at all.^[1]

Why symptoms alone cannot confirm a deficiency

Signs like tiredness, weakness, hair fall or low mood are very common and have many possible causes, such as poor sleep, stress, infections, thyroid problems or other illnesses.

The same sign can come from several different nutrients, or from no nutrient problem at all.

Only a qualified clinician, using your history, an examination and, when needed, lab tests, can say whether a deficiency is present. This app cannot diagnose a deficiency from symptoms or from BMI.

Bone and muscle aches are common and are much more often caused by other things than by low vitamin D.

Tests a clinician might consider

• A blood test for 25-hydroxyvitamin D [25(OH)D] is the usual measure of vitamin D status. Results can differ between laboratories and test methods.^[1]
• A clinician may also check blood calcium, phosphate, parathyroid hormone or kidney function, depending on the situation.^[1]
• The Endocrine Society does not recommend routine testing of healthy people, and the US Preventive Services Task Force found insufficient evidence for screening adults without symptoms. Your clinician decides whether a test is useful.^[1]

Who is more likely to have low intake

• People who get little sun, for example those who stay indoors most of the day or cover most of their skin.^[1]
• People with darker skin, because more melanin reduces how much vitamin D the skin makes.^[1]
• Older adults, whose skin makes less vitamin D.^[1]
• Breastfed infants (paediatric guidance applies).^[1]
• People with conditions that reduce fat absorption (such as some liver diseases, celiac disease, Crohn’s disease) and people with obesity or after gastric bypass surgery.^[1]

Potential benefits and quality of evidence

• Getting enough vitamin D, together with calcium, is needed for normal bone health.^[1] Established
• Vitamin D plus calcium supplements can give small increases in bone density in older adults and reduce fractures in people living in care homes; results for people living at home are inconsistent.^[1] Moderate evidence
• Supplements have generally not been shown to lower the chance of getting cancer, though some studies suggest a possible effect on cancer deaths.^[1] Limited evidence
• Clinical trials have not shown that vitamin D supplements prevent heart disease, depression or type 2 diabetes, or help weight loss.^[1] Not enough evidence

Side effects

• At usual intakes from food and sun, side effects are not expected. Problems come mainly from taking too much in supplements.^[1]

Risks of too much

• Too much vitamin D raises blood calcium. This can cause nausea, vomiting, muscle weakness, confusion, pain, loss of appetite, dehydration, frequent urination, thirst and kidney stones.^[1]
• In extreme cases it can lead to kidney failure, irregular heartbeat and even death. Toxicity is almost always caused by supplements, not by sunlight.^[1]
• Taking calcium supplements together with vitamin D may raise the risk of some side effects, such as kidney stones.^[1]

Medicine and supplement interactions

• Orlistat (weight-loss medicine): Can reduce absorption of vitamin D.^[1]
• Statins (some cholesterol medicines): May reduce vitamin D made by the body; high vitamin D intakes might reduce how well some statins work.^[1]
• Corticosteroids such as prednisone: Can reduce calcium absorption and affect vitamin D metabolism.^[1]
• Thiazide diuretics (some blood-pressure medicines): Together with vitamin D supplements, may raise blood calcium too much, especially in older adults or people with kidney problems.^[1]

Never start, stop or change a prescribed medicine because of this list — talk to your doctor or pharmacist.

Pregnancy and breastfeeding

• Needs in pregnancy are the same as for other adults in the US reference values. Upper limits still apply in pregnancy. Use supplements in pregnancy only as advised by your doctor.^[1]

Kidney and liver cautions

• The liver and kidneys activate vitamin D, so kidney or liver disease can change how the body handles it. Combining vitamin D supplements with thiazide diuretics can raise blood calcium, especially in people with reduced kidney function. People with kidney or liver disease should have vitamin D managed by their doctor.^[1]

Upper intake limits

When to talk to a professional

Talk to a doctor or registered dietitian before starting a supplement, especially if you are pregnant or breastfeeding, have a long-term illness, or take any regular medicines.

Do not start, stop or change a prescribed medicine because of anything you read here.

Supplements sold without a prescription are not automatically safe. Doses, quality and interactions still matter.

Seek medical care promptly if you have severe, sudden or worsening symptoms.

High-dose vitamin D should only be used under medical supervision.

Still being verified

• ICMR-NIN 2020 values for pregnancy/lactation and Tolerable Upper Limit not verified; not stated.

References

1. NIH Office of Dietary Supplements. Vitamin D — Fact Sheet for Health Professionals (opens in a new tab) (2025-06-27). Accessed 9 Oct 2026.
2. ICMR-National Institute of Nutrition (India). A Brief Note on Nutrient Requirements for Indians, the Recommended Dietary Allowances (RDA) and the Estimated Average Requirements (EAR), ICMR-NIN, 2020 (opens in a new tab). Accessed 9 Oct 2026.

Sources checked: 9 Oct 2026