You can get vitamin D without any sun exposure through food, fortified products, supplements, and even special UVB lamps. Most people who live in northern climates, work indoors, or avoid sun for skin-health reasons rely on a combination of these strategies. The recommended daily intake for most adults is 600 IU (15 mcg), rising to 800 IU for adults over 70.
How Your Body Uses Vitamin D Without Sun
When you eat or swallow vitamin D instead of making it through your skin, the same activation process kicks in. Your liver converts it into a storage form, and then your kidneys convert that into the active hormone your body actually uses. This two-step process works identically whether the vitamin D came from salmon, a supplement capsule, or sunlight hitting your forearm. The key difference is quantity: your skin can produce thousands of IU in a single session of sun exposure, so replacing that through diet alone takes deliberate effort.
Best Food Sources of Vitamin D
Very few foods contain vitamin D naturally, and the list is dominated by fatty fish and fish oils. Here’s what delivers the most per serving, based on NIH data:
- Cod liver oil (1 tablespoon): 1,360 IU. This single spoonful exceeds the full daily recommendation and is the most concentrated natural source available.
- Rainbow trout, farmed and cooked (3 oz): 645 IU
- Sockeye salmon, cooked (3 oz): 570 IU
- Canned tuna, light, in water (3 oz): 40 IU
- Sardines, canned in oil (2 sardines): 46 IU
- One large egg, scrambled: 44 IU (all of it in the yolk)
- Beef liver, braised (3 oz): 42 IU
The gap between the top-tier sources and everything else is striking. A serving of salmon or trout gets you close to a full day’s worth. An egg gives you less than 10% of it. If you’re building a sun-free vitamin D strategy around food, fatty fish needs to show up on your plate several times a week, or you’ll need to fill the gap with fortified foods or supplements.
Fortified Foods Fill the Gap
Because so few foods contain vitamin D naturally, many countries require or encourage fortification. In the U.S., nearly all cow’s milk is fortified to provide roughly 120 IU per cup. Many plant-based milks (soy, almond, oat) are fortified to similar levels, though this varies by brand, so check the label. Orange juice, breakfast cereals, and some yogurts are also commonly fortified, typically providing 80 to 140 IU per serving.
Fortified foods are useful as a baseline, but they rarely get you to 600 IU on their own unless you’re consuming multiple servings across different products each day. Think of them as a reliable floor, not a ceiling.
Mushrooms: The Plant-Based Option
Mushrooms are the only plant-based food that can produce meaningful vitamin D, and they do it through the same UV mechanism your skin uses. When mushrooms are exposed to ultraviolet light, either from sunlight or commercial UV lamps, their vitamin D2 content skyrockets. USDA data shows that UV-treated portabella mushrooms contain 140 to 752 IU per 100 grams, compared to just 10 IU per 100 grams without UV exposure. Maitake mushrooms treated with a proprietary UV method reached as high as 2,242 IU per 100 grams.
You can try this at home by placing sliced mushrooms gill-side up in direct sunlight for 15 to 30 minutes before eating them. The vitamin D2 they produce is less potent than D3 (the form in animal foods and most supplements), but it still raises blood levels. Look for packages labeled “UV-treated” or “high in vitamin D” at the grocery store if you want a reliable dose.
Supplements: D3 vs. D2
For most people avoiding sun, a daily vitamin D supplement is the simplest and most reliable strategy. Supplements come in two forms: D3 (cholecalciferol, from animal sources or lichen) and D2 (ergocalciferol, from fungi). D3 is the better choice for raising and maintaining your blood levels. A meta-analysis of randomized controlled trials found that D3 raises serum vitamin D concentrations significantly more than D2, especially when taken in larger, less frequent doses. When taken daily in smaller amounts, the difference between D2 and D3 narrows, but D3 still has the edge.
The reason comes down to biology: D3 binds more effectively to the vitamin D receptor and resists being broken down as quickly as D2. If you follow a vegan diet and prefer D2, you can still reach adequate levels, but you may need a slightly higher dose. Lichen-derived D3 supplements are also available as a vegan-friendly D3 option.
Vitamin D is fat-soluble, so taking your supplement with a meal that contains some fat (eggs, avocado, nuts, olive oil) improves absorption. Taking it on an empty stomach means a portion passes through without being used.
UVB Lamps as an Indoor Alternative
Your skin produces vitamin D3 when it absorbs UVB radiation in the 295 to 315 nanometer wavelength range, with peak production around 296 nm. Some people use narrowband UVB lamps designed to mimic this specific range. These devices trigger the same chemical reaction that sunlight does: converting a cholesterol compound in your skin into previtamin D3.
UVB lamps are particularly popular in Scandinavian countries and among people with conditions that prevent them from absorbing oral vitamin D well. They require careful use because the same wavelengths that produce vitamin D also cause sunburn. Most protocols involve very short exposure times, starting at just a few minutes. This is a niche option, not a first-line strategy for most people, but it works for those who can’t get enough through food and supplements alone.
How to Know If You’re Getting Enough
The standard blood test measures 25-hydroxyvitamin D, the storage form your liver produces. Most experts consider 20 to 40 ng/mL adequate, while some recommend 30 to 50 ng/mL as optimal. Below 20 ng/mL is generally considered deficient, and below 12 ng/mL is severely deficient.
If you get minimal sun exposure and don’t regularly eat fatty fish, there’s a reasonable chance your levels are below optimal. A simple blood test can tell you exactly where you stand and whether your current diet-and-supplement routine is working. Testing is especially worthwhile if you have darker skin, are over 65, have obesity, or have a condition affecting fat absorption, since all of these factors make deficiency more likely.
Putting It Together
The most practical approach combines two or three of these strategies. A daily D3 supplement of 600 to 1,000 IU covers your baseline. Adding fatty fish two to three times per week and choosing fortified milk or plant milk builds a buffer. Mushrooms, especially UV-treated varieties, offer a useful boost for plant-based eaters. Most adults can safely take up to 4,000 IU per day, which is the tolerable upper limit set by the NIH, though the majority of people do fine with 1,000 to 2,000 IU daily when they’re getting no sun at all.