Most adults need 600 IU (15 mcg) of vitamin D per day, rising to 800 IU (20 mcg) after age 70. Those are the official recommended amounts set by the National Academies of Sciences, Engineering, and Medicine. But the right amount for you depends on your age, body weight, skin tone, and whether you’re pregnant or managing a specific health condition.
Daily Recommendations by Age
The standard recommendations break down simply. Adults aged 19 to 70 need 600 IU daily. Adults over 70 need 800 IU. Children and teenagers from age 1 through 18 also need 600 IU. Infants under 12 months need 400 IU, which is typically given as liquid drops since breast milk alone doesn’t provide enough.
These numbers represent the Recommended Dietary Allowance, meaning they’re designed to meet the needs of about 97.5% of healthy people. They’re a baseline, not a ceiling, and some people need considerably more.
When You Might Need More
Body weight and skin color are two of the biggest factors that shift your personal requirement. Melanin in darker skin reduces the amount of vitamin D your body produces from sunlight, and fat tissue absorbs and holds onto vitamin D so that less of it reaches your bloodstream. Research on children and adolescents found that heavier individuals and those with dark skin may need up to 2,000 IU daily just to reach the same blood levels that lighter-skinned, leaner individuals achieve on 600 IU.
The Endocrine Society’s 2024 guidelines suggest higher amounts for certain groups based on clinical trial data. For adults 75 and older, the weighted average dose used in trials showing mortality benefits was about 900 IU daily. For pregnant women, trial doses averaged around 2,500 IU. For adults with prediabetes, trial doses averaged roughly 3,500 IU. These aren’t formal upper limits; they reflect what was actually tested and shown to help in studies.
Pregnant and lactating women have a baseline recommendation of 600 IU. If a deficiency is identified, the American College of Obstetricians and Gynecologists considers 1,000 to 2,000 IU daily safe, with most experts agreeing that up to 4,000 IU is acceptable during pregnancy or breastfeeding.
What Your Blood Levels Mean
A simple blood test measuring 25-hydroxyvitamin D tells you where you stand. Results are reported in ng/mL (or nmol/L), and the ranges break down like this:
- Below 12 ng/mL (30 nmol/L): Deficient. This level is associated with weakened bones, and in severe cases, rickets in children or soft, painful bones in adults.
- 12 to 19 ng/mL (30 to 49 nmol/L): Inadequate for bone and overall health.
- 20 ng/mL or above (50 nmol/L): Adequate for most healthy people.
- Above 50 ng/mL (125 nmol/L): Potentially harmful, especially above 60 ng/mL.
The target for most people is getting to and staying at or above 20 ng/mL. That said, the U.S. Preventive Services Task Force says there isn’t enough evidence to recommend routine vitamin D screening for adults who have no symptoms, so this test is typically ordered when you have risk factors or signs of deficiency like bone pain, muscle weakness, or frequent fractures.
D3 vs. D2: Which Supplement Works Better
Vitamin D supplements come in two forms: D2 (ergocalciferol, from plants) and D3 (cholecalciferol, from animal sources or lichen). D3 is significantly more effective at raising blood levels. In one comparative study, D3 was roughly twice as effective as D2 when given by injection alone, and a separate study found D3 had about 87% greater potency than D2 at the same dose taken orally. If you’re choosing a supplement, D3 is the better option for most people.
Nutrients That Help Vitamin D Work
Vitamin D doesn’t work in isolation. It relies on other nutrients to do its job properly, particularly vitamin K and magnesium.
Vitamin D increases your body’s production of proteins that manage where calcium ends up in your body. Two key proteins, one active in bones and one in blood vessel walls, both need vitamin K to switch on. Without enough vitamin K, these proteins remain inactive. The result is a scenario where calcium is more likely to deposit in your arteries instead of your bones. Taking vitamin D without adequate vitamin K can promote this imbalance.
Magnesium plays a role in activating vitamin D in the body. If your magnesium intake is low, your body may not efficiently convert vitamin D into its usable form. Green leafy vegetables, nuts, seeds, and whole grains are good dietary sources of magnesium. Vitamin K2 is found in fermented foods, egg yolks, and certain cheeses.
Upper Limits and Signs of Too Much
The tolerable upper intake level for adults is 4,000 IU per day. Going above this consistently without medical supervision raises the risk of toxicity, though harmful effects are more closely tied to blood levels than to a specific pill count. Blood levels above 50 ng/mL enter a zone where problems can develop, and levels above 60 ng/mL carry clearer risk.
Vitamin D toxicity causes too much calcium to build up in your blood. Early symptoms are vague: fatigue, weakness, loss of appetite, and bone pain. As it progresses, you may experience nausea, vomiting, constipation, abdominal pain, excessive thirst, and frequent urination. In severe cases, it can cause confusion, irregular heartbeat, kidney stones, and even kidney damage. Toxicity doesn’t happen from sun exposure or normal food intake. It comes from supplements, usually from taking very high doses (well above 4,000 IU) over extended periods.
Practical Starting Points
If you’re a healthy adult under 70 with lighter skin and a moderate body weight who gets some sun exposure, 600 IU daily from food and supplements combined is a reasonable baseline. If you’re over 70, aim for at least 800 IU. If you have darker skin, carry extra body weight, spend very little time outdoors, or live at a northern latitude where winter sunlight is weak, you likely need more, and 1,000 to 2,000 IU daily is a common and safe range for most adults.
Fatty fish like salmon and mackerel, fortified milk and orange juice, egg yolks, and fortified cereals all contribute dietary vitamin D, but it’s difficult to get enough from food alone. Most people who are serious about maintaining adequate levels use a supplement. Taking it with a meal that contains some fat improves absorption, since vitamin D is fat-soluble.