Vitamin D
Vitamin D is inactive at first. The liver and then the kidneys each convert it once, giving the form that helps the intestine absorb calcium.
Full ranking Dose tool Products (5,334)
Key facts
Sources: https://ods.od.nih.gov/factsheets/VitaminD-HealthProfessional/ · FDA DV 20 mcg (https://www.fda.gov/food/nutrition-facts-label/daily-value-nutrition-and-supplement-facts-labels); pre-2016 DV [10] (https://www.federalregister.gov/documents/2016/05/27/2016-11867/food-labeling-revision-of-the-nutrition-and-supplement-facts-labels); adult UL 100 mcg
How it works: What happens to vitamin D after you take it?
- Skin makes vitamin D under UVB light, or it is absorbed from food and supplements. At this point it is not yet biologically active.
- The liver converts it to 25(OH)D. This is the marker that blood tests measure.
- The kidneys convert 25(OH)D to the active form, 1,25(OH)₂D (calcitriol).
- The active form promotes calcium and phosphorus absorption in the small intestine.
- Blood calcium and phosphate stay in the normal range, which bone needs to mineralise normally.
Schematic only; positions and scale are not anatomical.
Sources: NIH ODS: VitaminD Fact Sheet for Health Professionals
Daily dose across products (mcg/day)
Label data from official national databases and brand websites, as declared; not lab-verified.
Common forms
| Form | Products | Median | P5–P95 | Elemental fraction |
|---|---|---|---|---|
| Vitamin D3 (cholecalciferol) | 4939 | 15 mcg | 2.5 – 75 | — |
| Vitamin D2 (ergocalciferol) | 298 | 10 mcg | 1.25 – 25 | — |
Common questions
What is the Daily Value for Vitamin D?
The US FDA Daily Value for adults and children aged 4 and over is 20 mcg. It is a labelling reference, not a personal recommendation. [source]
Is there an upper limit for Vitamin D?
The adult Tolerable Upper Intake Level (UL) is 100 mcg per day. Going above it long term raises the risk of adverse effects. See the linked source. [source]
How much Vitamin D do products usually contain per day?
As of 2026-11-01, 5,334 products list a comparable daily dose (5,828 dose records; one product can have several). The median is 12.5 mcg per day, and 90% of records fall between 2.5 and 64 mcg. Figures come from labels and are not lab-tested. [source]
What happens to vitamin D after you take it?
Vitamin D is inactive at first. The liver and then the kidneys each convert it once, giving the form that helps the intestine absorb calcium. Adult Tolerable Upper Intake Level (UL): 100 mcg (4,000 IU) per day. Long-term excess can cause high blood calcium. [source]
What are the side effects of Vitamin D?
At recommended amounts it is generally fine. Very high blood levels (above 375 nmol/L or 150 ng/mL) can cause nausea, vomiting, muscle weakness, confusion, pain, loss of appetite, dehydration, excessive urination and thirst, and kidney stones. (Source: NIH ODS) [source]
What happens if you take too much Vitamin D?
The adult UL is 100 mcg (4,000 IU) a day from all sources. Extremely high levels can cause kidney failure, irregular heartbeat and even death, almost always from taking too much in supplements; sunshine cannot cause it. A doctor may use higher doses for a time to treat deficiency. (Source: NIH ODS) [source]
Is Vitamin D safe during pregnancy and breastfeeding?
The recommended amount in pregnancy and breastfeeding is 15 mcg (600 IU) a day, and the UL is 100 mcg (4,000 IU). Breastfed infants should get a 10 mcg (400 IU) supplement each day. (Source: NIH ODS) [source]
Does Vitamin D interact with medications or other supplements?
Orlistat reduces vitamin D absorption. Statins (atorvastatin, lovastatin, simvastatin) may work less well with high-dose vitamin D. Steroids such as prednisone lower blood vitamin D. Thiazide diuretics plus vitamin D supplements could raise blood calcium too high. (Source: NIH ODS) [source]
How and when should you take Vitamin D?
Vitamin D is fat-soluble and is best absorbed with a meal or snack that has some fat. Both D2 and D3 raise blood levels, but D3 may raise them higher and for longer. (Source: NIH ODS) [source]
Top ranked
| Rank | Brand | Product | Per day | Score |
|---|---|---|---|---|
| 1 | Nordic Naturals | Plant-Based Vitamin D3 Liquid | 25 mcg | 100.0 |
| 1 | The Vitamin Shoppe | Vitamin D3 | 25 mcg | 100.0 |
| 1 | Nordic Naturals | Vitamin D3 1000 | 25 mcg | 100.0 |
| 4 | Vitamin World | Sunvite Chewable Vitamin D3 1000 IU | 25 mcg | 97.8 |
| 4 | Vitamin World | Sunvite Vitamin D3 2000 IU | 100 mcg | 97.8 |