Short answer. Most children and adults need 15 mcg (600 IU) of vitamin D a day, and adults over 70 need 20 mcg (800 IU), according to the NIH Office of Dietary Supplements. The upper limit from age 9 is 100 mcg (4,000 IU). Vitamin D3 raises blood levels more than D2, and routine blood testing is not advised for healthy people.
Vitamin D3 and D2 at a glance
| Vitamin D3 (cholecalciferol) | Vitamin D2 (ergocalciferol) | |
|---|---|---|
| Where it comes from | Skin exposed to sunlight; supplements use lanolin (sheep wool) or lichen for a vegan version | UV-irradiated yeast; also UV-exposed mushrooms |
| Effect on blood 25(OH)D | Raises it more and keeps it higher for longer | Raises it less, especially as large infrequent doses |
| Head-to-head evidence | Meta-analysis favors D3 (Tripkovic 2012); about 87% more potent at 50,000 IU a week (Heaney 2011) | Works; the gap closes with small daily doses |
Source: NIH Office of Dietary Supplements; PubMed records under Sources.
What does vitamin D do in the body?
Vitamin D from sunlight, food or a supplement is inactive when it arrives. The liver converts it to 25-hydroxyvitamin D, written 25(OH)D, the form a blood test measures, and the kidneys then make the active hormone 1,25(OH)2D, or calcitriol. Its best-established job is to help the gut absorb calcium and to keep blood calcium and phosphate where normal bone mineralization needs them (NIH Office of Dietary Supplements).
Many tissues carry vitamin D receptors, but the bone role has the strongest evidence. Long deficiency leaves bones thin, brittle or misshapen: rickets in children, osteomalacia in adults. Those are reasons to get tested, not to start high doses on your own.
How much vitamin D do children and adults need?
The US amounts below are published by the NIH Office of Dietary Supplements. Infants have an Adequate Intake; everyone from age 1 has a Recommended Dietary Allowance (RDA). The Tolerable Upper Intake Level (UL) is the most that should be taken daily without a clinician watching. Labels show micrograms or international units: 1 mcg equals 40 IU, and the US Daily Value is 20 mcg (800 IU).
| Age | Recommended daily amount | Upper limit (UL) |
|---|---|---|
| 0–6 months | 10 mcg (400 IU), Adequate Intake | 25 mcg (1,000 IU) |
| 7–12 months | 10 mcg (400 IU), Adequate Intake | 38 mcg (1,500 IU) |
| 1–3 years | 15 mcg (600 IU) | 63 mcg (2,500 IU) |
| 4–8 years | 15 mcg (600 IU) | 75 mcg (3,000 IU) |
| 9–13 years | 15 mcg (600 IU) | 100 mcg (4,000 IU) |
| 14–18 years | 15 mcg (600 IU) | 100 mcg (4,000 IU) |
| 19–70 years | 15 mcg (600 IU) | 100 mcg (4,000 IU) |
| Over 70 years | 20 mcg (800 IU) | 100 mcg (4,000 IU) |
| Pregnancy and lactation | 15 mcg (600 IU) | 100 mcg (4,000 IU) |
Source: NIH Office of Dietary Supplements.
For babies, the American Academy of Pediatrics advises 400 IU a day from shortly after birth for every infant who is breastfed or drinks less than 1,000 mL of fortified formula a day, because human milk carries only about 25 to 78 IU per liter (NIH Office of Dietary Supplements; Wagner 2008). A randomized trial in 132 healthy breastfed infants compared 400, 800, 1,200 and 1,600 IU a day: every dose kept blood 25(OH)D at 50 nmol/L or above in 97% of babies at 3 months, and the 1,600 IU arm was stopped early because levels climbed too high (Gallo 2013). A child's dose belongs with the pediatrician.
Should you get a 25(OH)D blood test?
Blood 25(OH)D sums up what skin, food and supplements contributed, so it is the test for vitamin D status. Results come in ng/mL or nmol/L; 1 ng/mL equals 2.5 nmol/L.
| Blood 25(OH)D | What the Food and Nutrition Board says it means |
|---|---|
| Below 12 ng/mL (30 nmol/L) | Deficiency; can lead to rickets in children and osteomalacia in adults |
| 12 to under 20 ng/mL (30 to under 50 nmol/L) | Generally inadequate for bone and overall health |
| 20 ng/mL (50 nmol/L) or more | Generally adequate for most healthy people |
| Above 50 ng/mL (125 nmol/L) | Linked to potential adverse effects, particularly above 60 ng/mL (150 nmol/L) |
Source: NIH Office of Dietary Supplements.
Who should be tested is a separate question. In its 2024 guideline the Endocrine Society reviewed 14 clinical questions and suggested against routine 25(OH)D testing in every population it studied, because the panel could not find a blood level above which healthy people gain a benefit (Demay 2024). It did suggest supplementing above the RDA without a test for children and adolescents aged 1 to 18, adults 75 and older, and people who are pregnant, while healthy adults under 75 stay at the RDA.
A test makes sense when there is a risk factor, such as very little sun, dark skin, a condition that limits fat absorption, obesity, or a medicine that interferes with vitamin D, and before anyone takes more than the UL for long. Muscle weakness and aching bones are the early, nonspecific signs that justify one.
Is vitamin D3 better than D2?
Both forms raise blood 25(OH)D and both are well absorbed. The difference is in how far and for how long. A 2012 meta-analysis of randomized trials that compared the two directly found that D3 raised 25(OH)D significantly more than D2; the gap was large with big, infrequent doses and faded with small daily doses (Tripkovic 2012). In a 12-week trial of 33 adults taking 50,000 IU a week, the steady-state rise in 25(OH)D was 45 ng/mL with D3 against 24 ng/mL with D2, about 87% more potent (Heaney 2011).
In practice almost every over-the-counter product is D3; D2 remains reasonable for people who avoid animal products, although lichen-sourced vegan D3 now exists. Format matters less than concentration. Oil drops and softgels suit most people, and micellized drops, where the oil is broken into tiny particles in water, are marketed to people who absorb fat poorly. With any drop, read the label: one drop may carry 400 IU or 1,000 IU, and four drops of a 1,000 IU product already equal the adult UL.
Can you get enough vitamin D from sun and food?
Skin makes vitamin D3 when UVB light strikes it, and in summer that is the main source for most people. Latitude and season decide how much: in a classic experiment, skin exposed to sunlight in Boston (42.2 degrees north) made no previtamin D3 from November through February, and in Edmonton (52 degrees north) the dead period ran from October through March (Webb 1988). UVB does not pass through window glass, sunscreen of SPF 8 or more blocks the useful rays when applied properly, and older and darker skin make less (NIH Office of Dietary Supplements). The American Academy of Pediatrics advises keeping infants under 6 months out of direct sun.
Food rarely closes the gap. In the 2015 to 2016 national survey, US men averaged 5.1 mcg (204 IU) a day from food and drink, women 4.2 mcg (168 IU) and children aged 2 to 19 4.9 mcg (196 IU); 92% of men and more than 97% of women ate less than the 10 mcg (400 IU) estimated average requirement (NIH Office of Dietary Supplements).
| Food and serving | Vitamin D, mcg (IU) |
|---|---|
| Cod liver oil, 1 tablespoon | 34.0 (1,360) |
| Rainbow trout, farmed, cooked, 3 ounces | 16.2 (645) |
| Sockeye salmon, cooked, 3 ounces | 14.2 (570) |
| White mushrooms exposed to UV light, 1/2 cup | 9.2 (366) |
| Milk, 2%, vitamin D fortified, 1 cup | 2.9 (120) |
| Egg, 1 large | 1.1 (44) |
Source: NIH Office of Dietary Supplements. Cod liver oil also carries a lot of vitamin A, which has its own upper limit.
How much vitamin D is too much?
Vitamin D toxicity is almost always caused by supplements: manufacturing errors, products taken in excess, or doses prescribed incorrectly. Sun exposure does not cause it, because extra previtamin D3 in skin breaks down into inactive forms. The harm comes through calcium. Too much vitamin D pushes blood calcium above the normal range, with 25(OH)D typically above 150 ng/mL (375 nmol/L), bringing nausea, vomiting, weakness, thirst, frequent urination and sometimes kidney stones. The Food and Nutrition Board prefers blood 25(OH)D below roughly 50 to 60 ng/mL even though obvious toxicity is unlikely below 10,000 IU a day (NIH Office of Dietary Supplements).
Large doses taken rarely are a separate problem. In a trial of 2,256 women aged 70 and older, a single 500,000 IU dose each autumn or winter produced 171 fractures against 135 on placebo and 15% more falls, with the excess concentrated in the first 3 months after each dose (Sanders 2010). The Endocrine Society now suggests that people over 50 who take vitamin D use a modest daily dose rather than intermittent high doses (Demay 2024). Calcium adds to the risk: among 36,282 postmenopausal women taking 1,000 mg of calcium with 400 IU of vitamin D daily, kidney stones were 17% more common over 7 years (NIH Office of Dietary Supplements). If you combine the two, count calcium from food as well; see our calcium page.
What do the large trials show?
The biggest test of everyday supplementation is VITAL, which randomized 25,871 US adults (men 50 and older, women 55 and older) to 2,000 IU of vitamin D3 a day or placebo for a median of 5.3 years. Neither primary outcome was less frequent in the vitamin D group (hazard ratios 0.96 and 0.97), death from any cause was unchanged, and no excess of high blood calcium appeared (Manson 2019). A follow-up analysis of the same participants counted 1,991 fractures and found no difference either: hazard ratio 0.98 for total fractures and 1.01 for hip fractures (LeBoff 2022).
Participants were not selected for low vitamin D, so the trial says little about people who start out deficient.
Does vitamin D interact with medicines?
The NIH Office of Dietary Supplements lists four groups to mention to a prescriber.
- Orlistat with a low-fat diet reduces vitamin D absorption and lowers 25(OH)D.
- Statins. High vitamin D intakes, especially from supplements, might reduce the potency of atorvastatin, lovastatin and simvastatin, which share a metabolizing enzyme with vitamin D.
- Corticosteroids such as prednisone reduce calcium absorption and impair vitamin D metabolism; in a national survey, 25(OH)D below 10 ng/mL was found in 11% of oral steroid users against 5% of nonusers.
- Thiazide diuretics reduce calcium loss in urine; with vitamin D they can push blood calcium too high, especially in older adults and people with reduced kidney function.
Vitamin D is often paired with vitamin K2; the evidence behind that pairing is on our vitamin K page.
Which ASDHelp products contain vitamin D?
Doses are copied from each label; all are vitamin D3. Softgels are adult formats; for a child, use drops at the dose the pediatrician sets.
- Vitamin D3 Micellized: 10 mcg (400 IU) per drop (approx. 0.05 mL), 50% DV. Water-based micellized drops, orange mango flavor; one drop matches the infant Adequate Intake.
- Vitamin D3 + K2 Liquid: 25 mcg (1,000 IU) per drop (0.025 mL), 125% DV, plus 10 mcg of vitamin K2 (MK-7) in a medium chain triglyceride base. Four drops reach the adult UL.
- ADEK Mini: 25 mcg (1,000 IU) per softgel, 125% DV, with vitamins A, E and K in a bovine gelatin softgel.
- ADEK-Formula: 125 mcg (5,000 IU) per softgel, 625% DV, with vitamin A, 1,050 mcg of vitamin K and tocotrienols. One softgel exceeds the UL of 100 mcg (4,000 IU) for every age group, so this is an adult product for use with a clinician who checks 25(OH)D and calcium.
- Spectrum Formula Advance: 25 mcg (1,000 IU) per scoop (approximately 5.2 g), 125% DV, inside a multivitamin powder.
- Spectrum Formula Chewable + Iron: 12.5 mcg (500 IU) per 4 chewable tablets, inside a multivitamin with iron.
Questions to take to your doctor
- Does my child or I have a risk factor that makes a 25(OH)D test worthwhile?
- What daily dose fits my child's age and weight, and for how many months of the year?
- How much vitamin D is already in the multivitamin, the protein powder and the fortified foods we use?
- Do any of our medicines, including steroids, diuretics or statins, change the plan?
Sources
- NIH Office of Dietary Supplements. Vitamin D fact sheet for health professionals, updated June 27, 2025. ods.od.nih.gov
- National Academies. Dietary Reference Intakes tables (NCBI Bookshelf). ncbi.nlm.nih.gov/books/NBK545442
- Demay MB et al. Vitamin D for the Prevention of Disease: An Endocrine Society Clinical Practice Guideline. J Clin Endocrinol Metab 2024. PMID 38828931
- Manson JE et al. Vitamin D Supplements and Prevention of Cancer and Cardiovascular Disease (VITAL). N Engl J Med 2019. PMID 30415629
- LeBoff MS et al. Supplemental Vitamin D and Incident Fractures in Midlife and Older Adults. N Engl J Med 2022. PMID 35939577
- Sanders KM et al. Annual high-dose oral vitamin D and falls and fractures in older women: a randomized controlled trial. JAMA 2010. PMID 20460620
- Tripkovic L et al. Comparison of vitamin D2 and vitamin D3 supplementation in raising serum 25-hydroxyvitamin D status: a systematic review and meta-analysis. Am J Clin Nutr 2012. PMID 22552031
- Heaney RP et al. Vitamin D3 is more potent than vitamin D2 in humans. J Clin Endocrinol Metab 2011. PMID 21177785
- Webb AR, Kline L, Holick MF. Influence of season and latitude on the cutaneous synthesis of vitamin D3. J Clin Endocrinol Metab 1988. PMID 2839537
- Gallo S et al. Effect of different dosages of oral vitamin D supplementation on vitamin D status in healthy, breastfed infants: a randomized trial. JAMA 2013. PMID 23632722
- Wagner CL, Greer FR. Prevention of rickets and vitamin D deficiency in infants, children, and adolescents. Pediatrics 2008. PMID 18977996
These statements have not been evaluated by the Food and Drug Administration. These products are not intended to diagnose, treat, cure or prevent any disease. This article is educational and is not medical advice.