The most reliable ways to get more vitamin D are sunlight exposure, food sources rich in the vitamin, and supplements. Most adults need 600 to 800 IU per day, though many experts argue that number should be higher. Since vitamin D deficiency is remarkably common, especially during winter months, understanding all three routes gives you the best chance of keeping your levels where they should be.
Sunlight Is the Most Efficient Source
Your skin manufactures vitamin D when ultraviolet B rays hit a cholesterol compound sitting in your skin cells. That raw material then travels to your liver, where it’s converted into the form your doctor measures on a blood test. From there, your kidneys activate it into the hormone your body actually uses for calcium absorption, immune function, and dozens of other processes.
For most people with lighter skin, exposing your arms and legs to midday sun (between 10 a.m. and 3 p.m.) for 5 to 30 minutes, twice a week, can produce enough vitamin D to meet basic needs. That window matters because UVB rays are strongest when the sun is high in the sky. Early morning and late afternoon sun won’t do much for your vitamin D levels no matter how long you stay outside.
Skin tone significantly changes the math. Melanin, the pigment that darkens skin, competes with the cholesterol compound in your skin for UV absorption. It acts as a natural sunscreen. People with dark skin can require up to ten times as long in the sun to produce the same amount of vitamin D as someone with very fair skin. This is one reason vitamin D deficiency rates are disproportionately high in Black and Hispanic populations.
When Sunlight Won’t Work
If you live north of the 37th parallel (roughly a line from Richmond, Virginia to San Francisco), the sun sits too low in the sky from late October through late April to trigger meaningful vitamin D production in your skin. It doesn’t matter how long you spend outside during those months. Cities like New York, Chicago, Seattle, Boston, and the entire United Kingdom fall well within this zone. During winter, you’re essentially dependent on food and supplements.
Sunscreen with SPF 15 or higher blocks most UVB-driven vitamin D synthesis. That doesn’t mean you should skip sun protection. A few minutes of unprotected exposure before applying sunscreen is enough to start the process. Glass also blocks UVB rays completely, so sitting by a sunny window doesn’t count.
Foods That Contain Vitamin D
Very few foods naturally contain significant vitamin D, which is part of why deficiency is so widespread. The richest natural sources are fatty fish. A 3-ounce serving of cooked salmon provides roughly 400 to 600 IU, depending on whether it’s wild-caught or farmed. Wild salmon tends to have substantially more. Swordfish, tuna, mackerel, and sardines are also good options, typically delivering 150 to 550 IU per serving.
Cod liver oil is the single most concentrated food source. One tablespoon provides around 1,360 IU, more than twice the daily recommendation for most adults. It’s not for everyone taste-wise, but it’s effective.
Beyond fish, your options thin out quickly. Egg yolks contain about 40 IU each. Beef liver offers a small amount. UV-exposed mushrooms (look for labels that specifically say “UV-treated” or “high in vitamin D”) can provide 400 IU or more per serving, making them one of the few plant-based sources.
Fortified foods fill some of the gap. Most milk in the U.S. is fortified with about 100 IU per cup. Many orange juices, cereals, and plant-based milks are also fortified, though amounts vary by brand. Check the nutrition label, where vitamin D is listed in micrograms (mcg) or IU. One mcg equals 40 IU.
Choosing the Right Supplement
If you can’t get enough from sun and food, a supplement is the most straightforward fix. Vitamin D supplements come in two forms: D2 and D3. Research consistently shows that D3 is 1.7 to 3 times more effective than D2 at raising your blood levels, and its effects last longer. Most over-the-counter supplements now use D3, but check the label. If you follow a strict vegan diet, note that most D3 is derived from sheep’s wool lanolin, though lichen-based vegan D3 supplements exist.
Vitamin D is fat-soluble, meaning your body absorbs it better when fat is present in your gut. Taking your supplement with a meal that includes some fat, even a small amount like avocado on toast or eggs, improves absorption. That said, some vitamin D is absorbed even without dietary fat, so taking it on an empty stomach is better than skipping it entirely.
For most adults under 70, the official recommendation is 600 IU daily. Adults over 70 are advised to get 800 IU. The tolerable upper intake level is set at 4,000 IU per day for adults, though many clinicians recommend doses in the 1,000 to 2,000 IU range for people who are already deficient. Higher therapeutic doses should be guided by blood test results.
How to Know If You’re Deficient
The only way to know your vitamin D status is a blood test measuring 25-hydroxyvitamin D, the form circulating in your blood. Most experts consider a level between 20 and 40 ng/mL (50 to 100 nmol/L) adequate, though some recommend a higher target of 30 to 50 ng/mL. Levels below 20 ng/mL are generally considered deficient.
Symptoms of low vitamin D are frustratingly nonspecific: fatigue, muscle weakness, bone pain, and getting sick frequently. Many people with deficiency feel nothing unusual at all, which is why testing matters if you have risk factors. Those include spending most of your time indoors, living at northern latitudes, having darker skin, being over 65 (your skin becomes less efficient at making vitamin D with age), or carrying significant excess weight. Fat tissue absorbs and holds onto vitamin D, reducing the amount available in your bloodstream.
Combining Strategies for Consistent Levels
Relying on a single source rarely works year-round. The most practical approach layers all three methods based on the season and your circumstances. During summer months, regular brief sun exposure can supply most of what you need, topped off by fatty fish or fortified foods a few times a week. During winter, or if you work indoors during daylight hours, a daily D3 supplement in the 1,000 to 2,000 IU range alongside vitamin D-rich foods keeps levels steady.
If you’ve been tested and found deficient, it typically takes 2 to 3 months of consistent supplementation to bring levels back into a healthy range. Retesting after that period confirms whether your dose is working. Because vitamin D is fat-soluble and stored in body tissue, toxicity is possible at very high doses sustained over time, but it’s extremely rare at intakes below 10,000 IU per day. Sticking under 4,000 IU daily without medical guidance keeps you well within safe territory.