Most adults need 600 IU (15 mcg) of vitamin D per day, while adults over 70 need 800 IU (20 mcg). These are the Recommended Dietary Allowances set by the National Academies of Sciences, Engineering, and Medicine, designed to maintain bone health and normal calcium metabolism. But the right amount for you depends on your age, body weight, and specific health conditions.
Daily Recommendations by Age
Vitamin D is measured in International Units (IU) or micrograms (mcg), with 1 mcg equaling 40 IU. Here’s what each age group needs:
- Infants 0 to 12 months: 400 IU (10 mcg)
- Children and teens 1 to 18 years: 600 IU (15 mcg)
- Adults 19 to 70 years: 600 IU (15 mcg)
- Adults over 70: 800 IU (20 mcg)
The infant recommendation is technically an “Adequate Intake” rather than an RDA, since there isn’t enough data to set a formal RDA for babies. In practice, this means 400 IU is considered sufficient for infants, and most pediatricians recommend a liquid vitamin D supplement for breastfed babies since breast milk contains very little.
What the 2024 Endocrine Society Guidelines Changed
The Endocrine Society released updated guidelines in 2024 that shifted the conversation around vitamin D supplementation. For healthy adults under 75, the society now recommends against taking extra vitamin D beyond the standard RDA. In other words, 600 IU daily is enough for most people, and there’s no strong evidence that megadoses provide additional disease prevention benefits.
The notable exception is adults 75 and older. For this group, the society recommends daily vitamin D supplementation because of a potential reduction in mortality risk. In the clinical trials reviewed, doses ranged from 400 to 3,333 IU daily, with a weighted average of about 900 IU per day. The guidelines also emphasize that daily, lower-dose supplementation is preferred over taking large weekly or monthly doses.
For adults with high-risk prediabetes, the guidelines suggest vitamin D supplementation alongside lifestyle changes to help reduce the risk of progressing to type 2 diabetes.
During Pregnancy and Breastfeeding
The official RDA for pregnant and breastfeeding women is the same 600 IU as other adults, but many experts consider this insufficient. The Endocrine Society recommends 1,500 to 2,000 IU daily during pregnancy, and clinical trials have shown that 600 IU per day often fails to bring maternal blood levels into the sufficient range. Doses of 2,000 to 4,000 IU daily consistently achieved blood levels above 30 ng/mL in pregnant women.
For breastfeeding mothers, the recommendation is 1,500 to 2,000 IU daily to meet their own needs. If the baby isn’t receiving a separate vitamin D supplement, mothers may need 4,000 to 6,000 IU daily so that enough vitamin D passes through breast milk to cover the infant’s requirements as well.
When Higher Doses May Be Needed
Certain conditions make it harder for your body to absorb or process vitamin D, which means the standard 600 to 800 IU may not be enough. People with obesity often need two to three times the usual dose to reach the same blood levels as someone at a normal weight. This is because vitamin D is fat-soluble and gets sequestered in fat tissue, leaving less available in the bloodstream. For older adults with obesity, this can mean 7,000 to 10,000 IU daily.
People with digestive conditions that impair fat absorption, such as Crohn’s disease, celiac disease, or chronic liver disease, face a similar challenge. Their bodies simply don’t pull as much vitamin D from food or supplements. Clinical recommendations for these groups start at 7,000 IU daily for prevention, with higher doses used short-term to correct an existing deficiency.
Blood Levels and What They Mean
If you do get your vitamin D level tested, the result is reported as 25-hydroxyvitamin D in nanograms per milliliter (ng/mL). Most experts consider 20 to 40 ng/mL a normal range, though some recommend aiming for 30 to 50 ng/mL. The 2024 Endocrine Society guidelines actually recommend against routine vitamin D blood testing for healthy adults, including those with darker skin or obesity, since the test results rarely change clinical management for people without symptoms.
Testing makes more sense when there’s a specific reason to suspect deficiency: unexplained bone pain, frequent fractures, muscle weakness, or a condition known to impair vitamin D metabolism.
Upper Limits and Toxicity Risk
Vitamin D toxicity is rare but real, and it comes exclusively from supplements, not from sun exposure or food. Toxicity generally requires sustained daily intake above 10,000 IU, pushing blood levels past 150 ng/mL. At that point, the body accumulates too much calcium in the blood, which can cause a cascade of problems.
Early symptoms of vitamin D toxicity include nausea, vomiting, abdominal pain, excessive thirst, and frequent urination. As it progresses, it can cause confusion, drowsiness, depression, kidney damage, and in severe cases, heart rhythm disturbances. The earliest detectable sign is excess calcium spilling into the urine, which typically shows up before any noticeable symptoms.
For context, the tolerable upper intake level, the maximum considered safe for long-term daily use in healthy adults, is 4,000 IU. This doesn’t mean 4,000 IU is harmful; it means doses above that level haven’t been studied well enough in the general population to guarantee safety without medical supervision. People with obesity or malabsorption conditions may safely take higher doses under guidance, but for most healthy adults, staying at or below 4,000 IU daily is a reasonable ceiling.
Supplements vs. Sunlight and Food
Your body produces vitamin D when ultraviolet B rays from sunlight hit exposed skin. Brief midday sun exposure on the arms and face, roughly 10 to 30 minutes depending on skin tone and latitude, can generate a meaningful amount of vitamin D. Darker skin requires more time because melanin reduces UVB absorption. During winter months at higher latitudes, the sun’s angle is too low to trigger meaningful production, which is one reason deficiency is more common in northern climates.
Few foods are naturally rich in vitamin D. Fatty fish like salmon, mackerel, and sardines are the best dietary sources, with a 3-ounce serving of salmon providing roughly 400 to 600 IU. Egg yolks contain small amounts (around 40 IU each), and fortified milk, orange juice, and cereals typically add 100 to 150 IU per serving. For most people, especially those with limited sun exposure, food alone won’t cover the full daily recommendation, which is where a supplement fills the gap.
Standard over-the-counter vitamin D supplements come in two forms: D2 and D3. Vitamin D3 is generally preferred because it raises blood levels more effectively and sustains them longer. Most daily supplements range from 1,000 to 2,000 IU, which comfortably covers the RDA for adults without approaching toxicity levels.