Vitamin D

Pronunciation: VY-tuh-min D.

Generic name: vitamin D
Drug class: Fat-soluble vitamin
Form: Tablets, capsules, softgels, drops, or other oral dosage forms
Route: Oral
Legal status: Dietary supplement available over-the-counter in standard doses; higher-dose prescription forms also exist

Availability and supply rules vary by country

Trade names by country: Canada

What vitamin D is and how it works

Vitamin D is an essential fat-soluble vitamin that can be obtained from sun exposure, food, and dietary supplements. It exists in two main forms: cholecalciferol (vitamin D3) and ergocalciferol (vitamin D2). (1) (2)

It is used to prevent or correct vitamin D insufficiency (serum 25-hydroxyvitamin D below 30 ng/mL) and to meet recommended daily intakes. Toxicity is possible with excessive supplement intake.

Mechanism of action: how vitamin D works

No detailed pharmacological mechanism was reviewed in this research pass. (2)

What vitamin D is used for

Prevention and treatment of vitamin D insufficiency

Vitamin D supplements are taken to maintain adequate serum 25-hydroxyvitamin D levels (generally at or above 30 ng/mL) and to meet recommended dietary allowances. Individual requirements vary by age and health status. (1)

Before taking vitamin D

Do not take / not appropriate for

Do not take more than the recommended daily intake unless directed by a clinician. (all products) (2)
Do not take if you have hypercalcemia (high blood calcium) or a condition that predisposes to high calcium, unless under medical supervision. (all products) (2)

Tell your clinician about

All supplements and medications you are taking, especially other vitamin D or calcium products.
Any history of kidney stones, kidney disease, hypercalcemia, or parathyroid disorders.

(2)

How to take vitamin D

Take vitamin D exactly as directed on the product label or by your healthcare provider.
Standard supplement doses are taken orally, usually once daily.
Do not exceed the Tolerable Upper Intake Level (UL) without medical supervision.

(1) (2)

Procedures and treatment changes

Tell the treating team before surgery, procedures, or any medicine change. Do not alter treatment without the responsible clinician. (2)

Missed dose

If you miss a dose, skip it and take the next dose at the usual time. Do not take an extra dose to make up for a missed one unless advised by a clinician.

Overdose

Taking more than 10,000 IU per day can lead to vitamin D toxicity, which causes hypercalcemia (high blood calcium). Symptoms include nausea, vomiting, muscle weakness, neuropsychiatric disturbances, pain, loss of appetite, dehydration, excessive urination/thirst, and kidney stones. In severe cases, renal failure, calcification of soft tissues, cardiac arrhythmias, and death can occur. If you suspect an overdose or experience symptoms, seek medical attention promptly. A clinician will advise on discontinuing supplements and may administer treatments such as intravenous fluids, calcitonin, or bisphosphonates. (1) (2)

Side effects

Vitamin D is generally well tolerated at recommended doses. Adverse effects are primarily related to toxicity from excessive intake, leading to hypercalcemia.

Gastrointestinal symptoms (rare at standard doses)

What to notice: Mild nausea, loss of appetite, or constipation may occur, particularly with higher intakes.

What to do: Discuss with your clinician if symptoms persist or are bothersome. (2)

Hypercalcemia symptoms

What to notice: Nausea, vomiting, weakness, fatigue, bone pain, confusion, apathy, agitation, irritability, ataxia, stupor, abdominal pain, constipation, excessive urination, excessive thirst, or kidney stones.

What to do: Seek medical attention promptly for assessment of calcium levels and possible toxicity. (1) (2)

Serious warnings

Vitamin D Toxicity (Hypercalcemia) — seek_medical_attention

Symptoms: Severe nausea, vomiting, profound weakness, confusion, loss of coordination, stupor, coma, cardiac arrhythmias, or signs of kidney failure (e.g., decreased urine output).

Action: Seek medical attention immediately. A clinician will evaluate and may discontinue supplements, provide isotonic saline, calcitonin, or intravenous bisphosphonates as needed. (1) (2)

Interactions

Medicine or test	Effect	Action
Other vitamin D or calcium supplements	Combined intake increases the risk of hypercalcemia.	Monitor total daily vitamin D and calcium intake from all sources. Inform your clinician of all supplements you use. (2)
Prescription medications	Specific drug interaction data was not reviewed in this research pass.	Consult a clinician or pharmacist for a full interaction check.

Pregnancy, breastfeeding, kidney/liver function, age

Children and adolescents

Recommended Dietary Allowance (RDA) varies by age. The research sources reviewed cite ranges from 400 to 800 IU/day for children, depending on age group. Individual needs should be assessed by a paediatrician. (1)

Older adults

For adults aged 50–70, an RDA of at least 600 IU/day is cited; for those over 70, at least 800 IU/day. Requirements should be personalized. (1) (2)

Pregnancy and breastfeeding

The research notes mention RDA figures that include pregnancy, but no specific pregnancy/lactation dosing guidance was reviewed in this pass. Consult a clinician. (1)

People with kidney disorders

No specific guidance on vitamin D supplementation in renal impairment was reviewed in this research pass. Caution is warranted, and clinician advice is essential.

Monitoring

Before starting

Consider measuring serum 25-hydroxyvitamin D if deficiency is suspected (typically below 30 ng/mL).

During treatment

Monitor for symptoms of hypercalcemia, especially when taking doses above the UL.
In cases of high-dose therapy or suspected toxicity, periodic monitoring of serum calcium and 25(OH)D levels may be performed by a clinician.

(1) (2)

Storage

Store at room temperature away from moisture and light, as per product label. Keep out of reach of children.

Professional information

Clinician-facing context only. This draft is based on limited research notes and does not replace full product information or clinical guidelines.

All regions

Indication: Prevention and treatment of vitamin D insufficiency

Dose summary: Recommended Dietary Allowance (RDA) varies: typical adult range 600–800 IU/day; Tolerable Upper Intake Level (UL) 1,000–4,000 IU/day depending on age. Toxicity associated with intakes above 10,000 IU/day. Exact age-by-age table not confirmed identically across sources reviewed.

Renal context: No specific renal dosing guidance was reviewed in this research pass. Individual assessment required. (1) (2)

Mechanism of action

Hepatic guidance

Not reviewed.

Overdose note

Management includes discontinuing vitamin D and calcium, intravenous isotonic saline, and in severe cases, calcitonin (4 units/kg IM) or intravenous bisphosphonates (pamidronate 90 mg or zoledronic acid 4 mg). All treatments must be administered under medical supervision. (2)

Frequently asked questions

How much vitamin D do I need daily?

Recommendations vary by age. For most adults, the range cited is 600–800 IU per day. Children and older adults may have different requirements. Consult a healthcare provider for a personalized intake. (1) (2)

Can I get too much vitamin D from sun exposure?

No. The skin's production of vitamin D is metabolically self-regulated, so excessive sun exposure does not cause vitamin D toxicity. (2)

What are the symptoms of vitamin D toxicity?

Toxicity causes hypercalcemia, leading to nausea, vomiting, weakness, confusion, excessive thirst/urination, kidney stones, and in severe cases cardiac arrhythmias or renal failure. Seek medical attention if you experience these after taking high doses. (1) (2)

What is the mechanism of action of vitamin D?