You get vitamin D three ways: sunlight, food, and supplements. For most adults, a combination of brief regular sun exposure and either dietary sources or a supplement is the most reliable approach. The recommended daily intake is 600 IU for adults up to age 70 and 800 IU for those older.
Sunlight Is the Most Efficient Source
Your skin produces vitamin D when ultraviolet B (UVB) rays hit a cholesterol compound sitting in skin cells. That compound gets converted first in the liver, then in the kidneys, into the active hormone your body actually uses. This process is remarkably efficient. Exposing your face, hands, and arms to sunlight for about 12 minutes on a day with a UV index of 7 (a typical clear summer afternoon), two to three times per week, produces enough vitamin D for most people with light-to-medium skin. The general rule: aim for roughly half the time it would take your unprotected skin to turn pink.
Darker skin contains more melanin, which filters UVB, so people with deeper skin tones need longer exposure to produce the same amount. The same goes for older adults, whose skin synthesizes vitamin D less efficiently.
Where You Live Matters
Latitude plays a major role. During November through February, the sun sits too low in the sky at higher latitudes for UVB rays to reach the ground at full strength. The farther north (or south) you live, the more dramatically vitamin D production drops in winter months. If you live above roughly 37°N latitude (think San Francisco, Seoul, Athens, or anywhere farther north), your skin may produce little to no vitamin D during winter regardless of how much time you spend outside.
Sunscreen and Vitamin D
Sunscreen does reduce vitamin D production, but the real-world effect is smaller than you might expect. In lab testing, SPF 30 sunscreen applied at a typical thickness still allowed about 22% of the vitamin D precursor to form compared to bare skin. People rarely apply sunscreen as thickly or as evenly as lab conditions assume, so in practice some UVB still gets through. The practical takeaway: brief unprotected sun exposure a few times a week handles vitamin D needs, and you can apply sunscreen afterward or for longer outings without worrying about blocking production entirely.
Foods That Contain Vitamin D
Very few foods are naturally rich in vitamin D, which is one reason deficiency is so common. The best natural sources are fatty fish and fish liver oils. Here are the most practical options:
- Salmon (sockeye, cooked): roughly 450–570 IU per 3-ounce serving
- Trout (rainbow, cooked): about 645 IU per 3-ounce serving
- Sardines (canned): around 165 IU per 3.75-ounce can
- Cod liver oil: about 1,360 IU per tablespoon
- Egg yolks: roughly 44 IU per large egg
- UV-exposed mushrooms: variable, but some commercially treated varieties provide 400+ IU per serving
Fortified foods fill in the gap for most people. Milk, orange juice, breakfast cereals, and some yogurts in the U.S. are commonly fortified with 100 to 150 IU per serving. These add up over the course of a day but rarely cover the full 600 IU recommendation on their own.
Vitamin D is fat-soluble, meaning your body absorbs it better when you eat it alongside some dietary fat. Taking a supplement with your largest meal of the day, or eating vitamin D-rich fish with olive oil or avocado, improves absorption compared to taking it on an empty stomach.
Choosing a Supplement
Supplements come in two forms: D2 (ergocalciferol, derived from plants and fungi) and D3 (cholecalciferol, the same form your skin makes). They were once considered interchangeable, but more recent evidence shows D3 is meaningfully more effective at raising and sustaining blood levels, particularly if you’re starting from a deficient state. A 2025 meta-analysis in Nutrition Reviews found that D2 supplementation actually lowered D3 levels in the blood, likely because D2 triggers an enzyme that speeds up the breakdown of existing D3. If you’re choosing between the two, D3 is the better option. Vegans can find D3 supplements sourced from lichen rather than animal products.
For most adults, a daily supplement of 600 to 1,000 IU of D3 is enough to maintain adequate levels, especially when combined with some sun exposure and food sources. People who are deficient may need higher doses temporarily, but this is best guided by a blood test.
How Much You Need by Age
The recommended daily amounts set by the National Institutes of Health break down simply:
- Infants (0–12 months): 400 IU
- Children and adults (1–70 years): 600 IU
- Adults over 70: 800 IU
The safe upper limit for adults is 4,000 IU per day. You can’t overdose from sunlight (your skin self-regulates production), and it’s nearly impossible to get toxic amounts from food alone. Toxicity comes from supplements. Blood levels above 150 ng/mL are associated with dangerously high calcium, which can cause nausea, weakness, excessive thirst, and in severe cases kidney damage. Staying under 4,000 IU daily from supplements keeps virtually everyone well within safe territory.
Who’s Most Likely To Be Low
Several factors make deficiency more likely, and many of them overlap in the same person:
- Limited sun exposure: office workers, people who cover most of their skin, and anyone living at high latitudes during winter
- Darker skin: higher melanin levels slow UVB-driven production
- Older age: skin produces less vitamin D with age, and the kidneys become less efficient at converting it to its active form
- Higher body fat: vitamin D gets sequestered in fat tissue, reducing the amount circulating in blood
- Digestive conditions: Crohn’s disease, celiac disease, and other conditions affecting fat absorption reduce how much vitamin D you take up from food and supplements
If several of these apply to you, a simple blood test measuring your 25-hydroxyvitamin D level gives a clear picture. Levels below 20 ng/mL are generally considered deficient, and 20 to 30 ng/mL is sometimes classified as insufficient. Most experts consider 30 ng/mL and above adequate for bone health and overall function. The test is widely available and often covered by insurance when deficiency is suspected.