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Medical Disclaimer: This information is for educational purposes only and is not a substitute for professional medical advice.
Vitamin C [EPC]
Vitamin D is a fat-soluble secosteroid essential for calcium homeostasis and bone mineralization. It belongs to a class of nutritional agents and prohormones that facilitate the intestinal absorption of calcium, magnesium, and phosphate.
Name
Vitamin D
Raw Name
VITAMIN D
Category
Vitamin C [EPC]
Drug Count
15
Variant Count
31
Last Verified
February 17, 2026
RxCUI
1365980, 1720258, 2569082, 2569088, 1364855, 1365984, 2671090, 2671097, 1119569, 1119573
UNII
PQ6CK8PD0R, 8ZYQ1474W7, 81G40H8B0T, 9VU1KI44GP, 935E97BOY8, WR1WPI7EW8, P6YC3EG204, 2679MF687A, KV2JZ1BI6Z, TLM2976OFR, 8K0I04919X, CE3G3J56LR, 4162LZ0N4O, Y882YXF34X, 95OX15I8ZU, M4I0D6VV5M, O3B55K4YKI, 2NVP93XVQ3, CUI83R2732, 8EKI9QEE2H, 4PP86KK527, 53D441QVT8, E934B3V59H, 1MBW07J51Q, 18E7415PXQ, 97C5T2UQ7J, M9VVZ08EKQ, T7S323PKJS, 2E32821G6I, ETJ7Z6XBU4, L6L8KA2AA0, 2KBE35NE8S, 91D9GV0Z28, IHN2NQ5OF9, 9E8X80D2L0, SY7Q814VUP, 789U1901C5, R5L488RY0Q, 68Y4CF58BV, X66NSO3N35, J41CSQ7QDS, 9P9W8GGU78, L11K75P92J, 5HOC10FSIC, W8N8R55022, 02WM57RXZJ, TRS31EO6ZN, 08X0K2M57P, 00GG7UT6PL, Q95C157M3I, W1D68QW48M, 1DP6Y6B65Z, VS041H42XC, 5PO6NN3RRJ, 0RBV727H71, I38ZP9992A, 42Z2K6ZL8P, 7OV03QG267, 49OY13BE7Z, 0B4FDL9I6P, MLM29U2X85, V1XJQ704R4, F05Q2T2JA0, U1B11I423Z, E1UOL152H7, 25X51I8RD4, 1C4QK22F9J, SOI2LOH54Z, A9R10K3F2F, H4N855PNZ1, 9679TC07X4, 71M78END5S
About Vitamin D
Vitamin D is a fat-soluble secosteroid essential for calcium homeostasis and bone mineralization. It belongs to a class of nutritional agents and prohormones that facilitate the intestinal absorption of calcium, magnesium, and phosphate.
Detailed information about Vitamin D
References used for this content
This page is for informational purposes only and does not replace medical advice. Consult a qualified healthcare professional before using any medication containing Vitamin D.
Historically, the importance of Vitamin D was recognized during the industrial revolution when rickets (a softening and weakening of bones in children) became a public health crisis due to lack of sunlight in smog-filled cities. The FDA has a long history of regulating Vitamin D, primarily through the fortification of milk and other foods, which began in the 1930s. Today, Vitamin D is recognized not just as a nutrient but as a critical hormone precursor that influences over 200 genes in the human body. Healthcare providers typically categorize Vitamin D as a therapeutic agent for bone health, endocrine function, and immune modulation.
At the molecular level, Vitamin D functions as a prohormone. Once it is converted into its active form, 1,25-dihydroxyvitamin D [1,25(OH)2D], also known as calcitriol, it acts as a ligand for the Vitamin D Receptor (VDR). The VDR is a member of the nuclear receptor superfamily of ligand-activated transcription factors. When calcitriol binds to the VDR, the receptor forms a complex with the Retinoid X Receptor (RXR). This complex then enters the cell nucleus and binds to Vitamin D Response Elements (VDREs) in the promoter regions of target genes.
This genetic signaling leads to the production of proteins that facilitate calcium transport. In the small intestine, Vitamin D increases the expression of calbindin, a protein that shuttles calcium across the intestinal epithelial cells. In the bones, Vitamin D works in tandem with parathyroid hormone (PTH) to regulate the activity of osteoblasts (bone-forming cells) and osteoclasts (bone-resorbing cells), ensuring that serum calcium levels remain within a very narrow physiological range. Without sufficient Vitamin D, only about 10% to 15% of dietary calcium and about 60% of phosphorus are absorbed.
Vitamin D is absorbed in the small intestine via passive diffusion and a mechanism involving intestinal membrane proteins. Because it is fat-soluble, its absorption is significantly enhanced when taken with a meal containing dietary fats. Studies have shown that taking Vitamin D with the largest meal of the day can increase blood levels by approximately 50%. In patients with malabsorption syndromes (such as Celiac disease or Crohn's disease), bioavailability is markedly reduced.
Once absorbed, Vitamin D is incorporated into chylomicrons and transported via the lymphatic system into the venous circulation. In the blood, it is primarily bound to Vitamin D-binding protein (DBP) (approximately 85-90%) and albumin (10-15%). It is stored in adipose (fat) tissue and muscle, which acts as a reservoir, releasing the vitamin slowly into the circulation. It does not readily cross the blood-brain barrier in large amounts, though VDRs are present in the central nervous system.
Vitamin D undergoes two hydroxylation steps for activation. The first occurs in the liver, mediated by the enzyme CYP2R1 (25-hydroxylase), converting Vitamin D into 25-hydroxyvitamin D [25(OH)D], the primary circulating form used to measure a patient's status. The second step occurs primarily in the kidneys, mediated by the enzyme CYP27B1 (1-alpha-hydroxylase), which converts 25(OH)D into the biologically active calcitriol. This renal step is tightly regulated by parathyroid hormone (PTH) and serum phosphorus levels.
Vitamin D and its metabolites are excreted primarily through the bile into the feces. Only a very small percentage (less than 5%) is excreted in the urine. The biological half-life of the circulating form, 25(OH)D, is approximately 2 to 3 weeks, whereas the active form, calcitriol, has a much shorter half-life of about 5 to 8 hours.
Vitamin D is FDA-approved and clinically indicated for several conditions:
Off-label uses often discussed by healthcare providers include immune system support, management of certain autoimmune conditions, and adjunctive therapy in mood disorders, though clinical evidence for these uses is still evolving.
Vitamin D is available in several formulations to accommodate different patient needs:
> Important: Only your healthcare provider can determine if Vitamin D is right for your specific condition.
The dosage of Vitamin D varies significantly based on the patient's baseline blood levels and the condition being treated.
In patients with stage 3-5 chronic kidney disease (CKD), the conversion of 25(OH)D to active calcitriol is impaired. These patients may require 'active' Vitamin D analogs (e.g., calcitriol, paricalcitol) rather than cholecalciferol or ergocalciferol. Monitoring of serum calcium and phosphorus is mandatory.
Severe liver disease can impair the first hydroxylation step. While standard doses may work for mild impairment, severe cirrhosis may require higher doses or monitoring of 25(OH)D levels to ensure adequate absorption and conversion.
Older adults have a reduced capacity to synthesize Vitamin D in the skin and often have lower dietary intake. They are at higher risk for falls and fractures, necessitating a target serum level of at least 30 ng/mL. Doses of 800-2,000 IU are common in this population.
If you miss a dose, take it as soon as you remember. However, if it is almost time for your next scheduled dose, skip the missed dose and resume your regular schedule. Do not 'double up' on doses to catch up, as Vitamin D is stored in the body and excessive intake over a short period can lead to toxicity.
Vitamin D toxicity (hypervitaminosis D) is rare but serious. It usually occurs from long-term over-supplementation rather than diet or sun exposure.
> Important: Follow your healthcare provider's dosing instructions. Do not adjust your dose without medical guidance.
When taken at recommended doses (RDA levels), Vitamin D typically does not cause side effects. However, when starting therapeutic doses for deficiency, some patients may experience:
As doses increase toward the upper tolerable limit (4,000 IU daily for most adults), some individuals may report:
Rarely, individuals may experience hypersensitivity or idiosyncratic reactions:
Serious side effects are almost exclusively associated with Vitamin D toxicity, leading to hypercalcemia (high calcium levels in the blood).
> Warning: Stop taking Vitamin D and call your doctor immediately if you experience any of these.
No FDA black box warnings for Vitamin D. It is generally recognized as safe (GRAS) when used within established upper limits. However, the FDA warns against the use of extremely high doses (e.g., 50,000 IU) without strict medical supervision and regular blood monitoring.
Report any unusual symptoms to your healthcare provider. Monitoring of serum calcium, phosphorus, and 25(OH)D levels is the standard of care for patients on high-dose therapy.
Vitamin D is a potent hormone precursor. While essential for health, it must be managed carefully, especially in patients with underlying metabolic or renal conditions. The primary risk associated with Vitamin D is the development of hypercalcemia (excessive blood calcium), which can have systemic consequences on the heart, kidneys, and central nervous system.
No FDA black box warnings for Vitamin D. Unlike some pharmaceutical agents, Vitamin D does not carry the highest level of FDA warning, but its safety profile is dependent on maintaining blood levels within the therapeutic range (typically 30–60 ng/mL).
Patients on therapeutic doses of Vitamin D (above the RDA) should undergo regular laboratory testing:
Vitamin D at standard doses does not typically affect the ability to drive or operate machinery. However, if a patient develops hypercalcemia, symptoms like confusion, dizziness, or somnolence may occur, making these activities unsafe.
Chronic, excessive alcohol consumption can interfere with the liver's ability to process Vitamin D and can also impair the absorption of the vitamin from the gut. While there is no direct 'toxic' interaction between Vitamin D and a single drink, long-term alcohol use contributes to Vitamin D deficiency and osteoporosis.
Vitamin D does not require a tapering period and does not cause a withdrawal syndrome. However, stopping Vitamin D suddenly in a patient with a known deficiency will likely result in a return to deficient blood levels within weeks, potentially worsening bone density or increasing the risk of fractures.
> Important: Discuss all your medical conditions with your healthcare provider before starting Vitamin D.
There are few absolute contraindications for Vitamin D, but it should not be used with:
> Important: Tell your doctor about ALL medications, supplements, and herbal products you are taking.
Vitamin D must NEVER be used in the following circumstances:
These conditions require a careful risk-benefit analysis by a healthcare provider:
There is no known cross-sensitivity between Vitamin D and other vitamin classes (like Vitamin C or B12). However, patients sensitive to specific 'carriers' (like lanolin-derived D3 or fungal-derived D2) should choose the alternative form. Patients with yeast allergies should use caution with certain D2 preparations derived from irradiated yeast.
> Important: Your healthcare provider will evaluate your complete medical history before prescribing Vitamin D.
Vitamin D is critical during pregnancy for the development of the fetal skeleton and the maintenance of maternal bone health.
Vitamin D passes into breast milk, but the concentration is typically low (about 20 to 60 IU per liter), which is insufficient to meet the needs of a nursing infant.
Vitamin D is approved for use in children from birth. It is essential for preventing rickets and ensuring peak bone mass attainment during adolescence.
Older adults (over 65) are a primary target for Vitamin D therapy.
In patients with a GFR (Glomerular Filtration Rate) below 30 mL/min, the kidneys' ability to produce the active form of Vitamin D is severely compromised. These patients often develop Secondary Hyperparathyroidism. Treatment usually involves calcitriol or calcimimetics rather than standard Vitamin D3.
Patients with Child-Pugh Class B or C cirrhosis may have impaired 25-hydroxylation and fat malabsorption. They may require higher oral doses or parenteral (injection) administration to achieve therapeutic blood levels.
> Important: Special populations require individualized medical assessment.
Vitamin D (as calcitriol) acts by binding to the Vitamin D Receptor (VDR), a nuclear transcription factor. This binding triggers the heterodimerization of the VDR with the Retinoid X Receptor (RXR). The VDR-RXR complex binds to Vitamin D Response Elements (VDREs) in the genome. This primarily increases the expression of the TRPV6 (calcium channel) and Calbindin-D9k in the intestinal mucosa, which facilitates the active transport of calcium from the gut lumen into the bloodstream. It also regulates the RANKL/OPG pathway in bone, which controls the maturation of osteoclasts.
| Parameter | Value |
|---|---|
| Bioavailability | 50% to 80% (enhanced by dietary fat) |
| Protein Binding | 99% (primarily to Vitamin D-Binding Protein) |
| Half-life | 15 to 25 days (for 25(OH)D) |
| Tmax | 24 hours (for 25(OH)D) |
| Metabolism | Hepatic (CYP2R1) and Renal (CYP27B1) |
| Excretion | Fecal (>95%), Renal (<5%) |
Vitamin D is classified as a Vitamin / Nutraceutical and a Prohormone. Within the EPC (Established Pharmacologic Class) framework provided, it is associated with Provitamin D2 Compounds and nutritional agents. It is chemically related to other steroids but lacks the hormonal effects of glucocorticoids or sex hormones.
Common questions about Vitamin D
Vitamin D is primarily used to maintain healthy bones by aiding the absorption of calcium and phosphorus from the diet. Healthcare providers prescribe it to treat or prevent conditions like rickets in children and osteomalacia or osteoporosis in adults. It is also essential for treating Vitamin D deficiency, which can cause muscle weakness and bone pain. Beyond bone health, it is used to manage low calcium levels caused by hypoparathyroidism. Some evidence suggests it may also play a role in supporting the immune system and regulating mood, although these are often considered secondary or off-label uses. Always consult your doctor to determine if you need Vitamin D based on your specific blood levels.
At standard recommended doses, Vitamin D rarely causes side effects in most healthy individuals. However, if doses are excessively high, patients may experience gastrointestinal symptoms such as nausea, vomiting, or constipation. A metallic taste in the mouth and a loss of appetite are also occasionally reported. More serious side effects, such as confusion or heart rhythm changes, only occur if Vitamin D levels become toxic, leading to high calcium in the blood. Most people taking 400 IU to 2,000 IU daily will not experience any adverse effects. If you notice unusual symptoms after starting a supplement, it is important to contact your healthcare provider for a blood test.
There is no direct, acute interaction between Vitamin D and alcohol that would cause an immediate toxic reaction. However, chronic and excessive alcohol consumption is a major risk factor for Vitamin D deficiency and bone loss. Alcohol interferes with the liver's ability to process Vitamin D into its circulating form and can damage the lining of the gut, reducing the absorption of fat-soluble vitamins. Furthermore, alcohol can increase the risk of falls, which is particularly dangerous for individuals with weakened bones due to low Vitamin D. For the best results in improving bone health, it is recommended to limit alcohol intake while taking Vitamin D supplements. Discuss your alcohol consumption habits with your doctor to ensure your treatment plan is effective.
Vitamin D is not only safe but essential during pregnancy for both the mother and the developing fetus. It helps the baby develop a strong skeleton and may reduce the risk of pregnancy complications like preeclampsia and low birth weight. Most prenatal vitamins contain a standard dose of 400 IU to 600 IU, which is considered safe for almost all pregnant women. However, pregnant women should avoid taking very high doses (such as 50,000 IU) unless specifically directed and monitored by their obstetrician. Extremely high levels of Vitamin D can potentially lead to hypercalcemia, which may affect the baby's heart development. Your doctor will likely check your Vitamin D levels as part of your routine prenatal care to ensure you are in the optimal range.
The time it takes for Vitamin D to 'work' depends on what you are measuring. If you are taking a supplement to correct a deficiency, it typically takes 3 to 6 weeks of consistent daily dosing to see a significant rise in your blood levels of 25(OH)D. However, the physical benefits, such as improved bone density or reduced muscle pain, may take 3 to 6 months to become apparent. For acute conditions like hypocalcemia (low blood calcium), active forms of Vitamin D can begin working within hours. Because Vitamin D is fat-soluble and stored in the body, it is a slow-acting nutrient that requires long-term consistency rather than immediate results. Your doctor will usually re-test your blood levels after 8 to 12 weeks of therapy.
Yes, you can stop taking Vitamin D suddenly without experiencing withdrawal symptoms or immediate physical distress. Unlike some medications like antidepressants or steroids, Vitamin D does not require a tapering period because it is a nutrient the body naturally stores. However, if you were prescribed Vitamin D to treat a deficiency or osteoporosis, stopping it will cause your blood levels to gradually decline over several weeks. This could lead to a return of symptoms like bone pain or an increased risk of fractures over time. It is always best to discuss stopping any supplement with your healthcare provider, especially if it was prescribed to manage a specific medical condition. They can help you determine if you can maintain your levels through diet and sunlight instead.
If you miss a dose of Vitamin D, you should take it as soon as you remember. Vitamin D has a very long half-life, meaning it stays in your system for several weeks, so missing a single day will not significantly impact your overall health. If it is almost time for your next dose, simply skip the missed one and continue with your regular schedule. You should not take two doses at once to make up for a missed one, as this could slightly increase the risk of stomach upset. Consistency is more important than the exact timing of the dose. If you frequently forget your doses, consider using a pill organizer or a daily reminder app to stay on track.
There is no clinical evidence to suggest that Vitamin D causes weight gain. In fact, some observational studies have found a correlation between Vitamin D deficiency and obesity, leading researchers to investigate if Vitamin D might actually assist with weight management. Because Vitamin D is stored in body fat, individuals with more adipose tissue often require higher doses of the supplement to achieve the same blood levels as thinner individuals. Some patients may feel better and have more energy once their deficiency is corrected, which can lead to increased physical activity. If you experience unexpected weight gain while taking Vitamin D, it is likely due to other factors and should be discussed with your doctor. Overall, Vitamin D is considered weight-neutral.
Vitamin D can be taken with many medications, but there are several important exceptions that require caution. It can interact with certain heart medications like digoxin, potentially causing dangerous heart rhythms if calcium levels get too high. Weight-loss drugs like Orlistat and cholesterol medications like Cholestyramine can block the absorption of Vitamin D, so these should be taken at different times of the day. Additionally, certain anti-seizure medications can cause the body to break down Vitamin D more quickly, necessitating a higher dose. Because of these potential interactions, it is crucial to provide your healthcare provider with a complete list of all prescriptions, over-the-counter drugs, and herbal supplements you are using. They can help you schedule your doses to avoid interference.
Vitamin D is widely available as a generic supplement and is often very affordable. It is sold over-the-counter in two main forms: Vitamin D2 (ergocalciferol) and Vitamin D3 (cholecalciferol). While both are effective, most clinical research suggests that Vitamin D3 is slightly better at raising and maintaining blood levels over the long term. Generic versions are just as effective as expensive 'name brand' supplements, provided they are manufactured by a reputable company that follows Good Manufacturing Practices (GMP). Some high-dose versions (like 50,000 IU capsules) may require a prescription depending on your country's regulations. When buying generic Vitamin D, check the label to ensure it does not contain any allergens or fillers that you may be sensitive to.