What are the main sources of vitamin D?

What counts as a vitamin D source?

Four practical source categories

The main sources are vitamin D made in skin after UVB sunlight exposure, vitamin D naturally present in food, vitamin D added to fortified foods, and vitamin D taken as supplements. The NIH Office of Dietary Supplements notes that sunlight, food, fortified foods and supplements all contribute, but the mix varies with season, location and habits, and no single source works reliably for everyone.

D2 and D3 are both vitamin D, but they are not the same

Vitamin D3 (cholecalciferol) is made in human skin and occurs in fish and other animal foods. Vitamin D2 (ergocalciferol) occurs in mushrooms exposed to ultraviolet light and can be made by irradiating yeast. Supplements and fortified foods may contain either form, and the form cannot reliably be inferred from a food’s name alone. The same ODS fact sheet says both forms are absorbed and raise blood 25-hydroxyvitamin D, but D3 generally raises it more, and for longer, at comparable doses.

Why Europe cannot rely on sunlight alone

Sunlight can be a major source when conditions allow, but it is seasonal and unpredictable. The NHS says that in the UK most people can make enough vitamin D from sunlight from about late March or early April to the end of September, while between October and early March sunlight is not strong enough for that route to work well. The Nordic Nutrition Recommendations 2023 similarly notes that at Nordic and Baltic latitudes sunlight is insufficient for part of the year. For that reason, diet and fortified foods matter when sun exposure is limited.

For European readers, the practical takeaway is simple: use the label to see whether a food is truly fortified, and do not assume that a mushroom, milk or plant drink contains vitamin D unless the package says so. Fortification practices differ between countries, and an ordinary product is not automatically a useful source.

How does sunlight make vitamin D?

The skin pathway

When UVB light, roughly 290–320 nm, reaches uncovered skin, it converts 7-dehydrocholesterol to previtamin D₃, which then becomes vitamin D₃. The liver and then mainly the kidneys turn vitamin D into its measured and active metabolites. NIH ODS explains the UVB skin pathway.

That is why sunlight behind ordinary window glass does not count for this route: UVB does not pass through window glass. Sitting by a bright window is not the same as having uncovered skin outdoors. NIH ODS on window glass and UVB

What reduces production

Vitamin D production falls when too little UVB reaches the skin. The main reasons listed in the evidence are season, time of day, cloud or smog, being indoors, and clothing that covers the skin. NIH ODS on UVB limits

Latitude alone does not tell you a person’s vitamin D status; behavior and local conditions matter. A systematic review found that dose-response results were largely applicable to lighter-skinned participants, not a universal exposure schedule, and another review found reduced UV-induced production in darker skin in 7 of 12 experimental studies, but not all of them. NIH ODS on study limits

Why there is no universal safe time

Sunscreen can substantially block vitamin-D-producing UV under controlled conditions, but the review evidence is mixed in everyday use: it identified four experimental studies, three field trials, and 69 observational studies, and the two randomized field trials using about SPF 16 found no reduction in vitamin D status with daily use. The reviewers also noted the lack of comparable trials of modern high-SPF sunscreens. PubMed review of sunscreen and vitamin D

There is no well-supported, universally safe number of minutes in the sun that guarantees adequate vitamin D for everyone. PubMed review

For that reason, tanning beds are not a reliable strategy for vitamin D planning, and any approach that aims to supply vitamin D must be balanced against skin protection. NHS vitamin D guidance

Which foods are richest in vitamin D?

Among foods that occur naturally, the highest values in the evidence are in fish and fish-liver oil. The NIH Office of Dietary Supplements lists cod-liver oil at 34 µg per tablespoon, while cooked fish examples are lower but still substantial: 16.2 µg in 85 g of cooked farmed rainbow trout and 14.2 µg in 85 g of cooked sockeye salmon. The NHS also lists oily fish such as salmon, sardines, trout, herring and mackerel among food sources of vitamin D. NHS vitamin D advice

No single fish or mushroom has one fixed vitamin D value for every shop, season or preparation.

Animal foods: fish lead, eggs and liver trail far behind

The same NIH table shows how sharply amounts fall after fish and fish-liver oil: 1.1 µg in one large scrambled egg and 1.0 µg in 3 oz of braised beef liver. For readers comparing salmon, a PubMed analysis found wild Atlantic salmon fillets averaging 9.4 ± 1.9 µg/100 g in North Sea samples and 18.5 ± 4.6 µg/100 g in Baltic Sea samples, while farmed fillets measured 2.9–9.5 µg/100 g. That spread shows why species, farming method and capture area matter. PubMed salmon study

Vegan sources: UV-exposed mushrooms

UV-exposed mushrooms can be a vegan source of vitamin D₂, but the amount depends on species and treatment. In retail samples analysed without reported UV treatment, morel, chanterelle and maitake mushrooms ranged from 5.2 to 28.1 µg/100 g, while white button, crimini and portabella samples had only 0.1–0.3 µg/100 g. The EU listing for UV-treated Agaricus bisporus allows up to 20 µg vitamin D₂ per 100 g fresh weight, but that is a regulatory maximum, not a guarantee on any package. PubMed mushroom study EU UV-treated mushroom rule

Read the serving, not just the species

The NIH warns not to compare a cooked-food figure with a raw-food figure as if cooking had no effect. That matters because vitamin D values are measured in the specific edible portion described, not in every version of the food. For fish, egg and mushroom shoppers, the safest rule is to treat each number as a snapshot of one product, one preparation and one analysis, not as a permanent value for the whole category. NIH vitamin D fact sheet

Which fortified foods and supplements work?

In Europe, the practical fortified foods to check are milk and other liquid dairy products, fortified plant-based alternatives, and fat spreads, plus breakfast cereals and any juice whose label confirms added vitamin D. Finland’s fortification recommendation, for example, specifies 1 µg vitamin D3 per 100 ml for listed milk and liquid dairy products and 20 µg per 100 g for listed spreads; that is a fortification recommendation, not a measured amount in every product. The practical rule is simple: check the package, because the vitamin D content depends on the exact product, not the food category alone.

Which supplement forms are used?

Labels may name D2 or D3. Vitamin D2 (ergocalciferol) occurs in mushrooms exposed to ultraviolet light and can be made by irradiating yeast; vitamin D3 (cholecalciferol) is the form made in human skin and occurs in fish and other animal foods. Supplements and fortified foods may contain either form, so vegan shoppers need to check the ingredient source rather than assuming it from the product category. Both forms raise blood 25-hydroxyvitamin D, though D3 generally raises it more and for longer at comparable doses.

1 µg vitamin D = 40 IU, so the number in micrograms and the serving size matter. The FDA uses 20 µg as 100% Daily Value on US labels, while the EU food-label nutrient reference value is 5 µg; percentages are therefore jurisdiction-specific and should not be compared blindly. Read the amount in the serving you will actually eat or drink, and check whether the vitamin D is naturally present or has been added through fortification. FDA label guidance and EU labelling rules both treat the declared amount as the key number.

What can EU claims say?

The claim is allowed only when the food qualifies as at least a source of vitamin D.

How much vitamin D do you need?

Vitamin D recommendations are usually given in micrograms per day and are set for generally healthy people, not for treating deficiency. EFSA says its dietary reference values assume minimal sun exposure; the Nordic recommendations allow for some ordinary summer exposure, which is one reason the figures differ. EFSA dietary reference values for vitamin D Nordic Nutrition Recommendations 2023

How the main European figures compare

The practical recommendation is the 10 µg/day intake for adults under 75, rising to 20 µg/day at 75 or older or when sun exposure is little or absent. Nordic vitamin D chapter Finnish sustainable health from food guidance

What the authorised EU claims actually cover

In the retrieved EU material, vitamin D claims are tied to foods that qualify as at least a source of vitamin D. The authorised wording is limited to vitamin D contributing to normal calcium and phosphorus absorption, maintenance of normal bones and muscle function, and normal immune-system function. Those are the supported functions to use; they are not a basis for broader promises. EU vitamin D health claims

For label reading, remember that 1 µg equals 40 IU, so the same number can look different across countries or packages even when the underlying amount is the same. NHS vitamin D guidance

Who needs extra care with vitamin D?

Upper limits are ceilings, not goals.

The NIH ODS says excess vitamin D is usually linked to too much supplement use rather than ordinary sun exposure or food, and that it can raise blood and urinary calcium and harm the kidneys. EFSA vitamin D reference values NIH ODS vitamin D fact sheet

When blood testing or individual advice is sensible

A blood test for 25-hydroxyvitamin D [25(OH)D] reflects vitamin D from both diet and skin production, but does not show how much came from either source. If excess is suspected, the right response is clinical assessment, not more self-dosing. NIH ODS vitamin D fact sheet

Common mistake: treating every label as a green light

One missed detail can matter: EFSA’s upper limits, the NHS supplement advice, and label amounts are not the same thing. The NHS recommends 10 µg/day for adults and children over 4 during autumn and winter, and year-round for some higher-risk groups, but that is not a licence to stack multiple products without checking the total. NHS vitamin D guidance EFSA

How do you choose the best source for your diet?

The practical answer depends on where you live, the season, and how predictable your food routine is. UK public guidance says most people can make enough vitamin D from sunlight only from about late March or early April to the end of September, and that everyone should consider a 10 microgram daily supplement in autumn and winter. The Nordic recommendations also raise the suggested intake to 20 micrograms daily when sun exposure is little or absent.

Match the source to your routine

If you want a food-first approach, use it only when your usual pattern is realistic. The NHS lists oily fish, egg yolks, fat spreads, breakfast cereals and fortified foods as sources, and says cow’s milk in the UK is generally not a good source because it is not fortified there. In Finland, by contrast, fortification recommendations include milk, liquid dairy products, plant-based alternatives and some fat spreads, so the package matters.

Read the label, not the front-of-pack claim

Compare the amount per serving, not just the %DV; the FDA explains that Daily Value is a label reference, not a personal target. In the EU, the vitamin D nutrient reference value is 5 micrograms, so percentages can be misleading if you do not check the actual micrograms. For fortified foods, confirm that vitamin D is actually added. For supplements, check whether the form is D2 or D3; mushrooms usually provide D2, while animal foods and some supplements provide D3, and supplements may also use animal-free D3.

Best rule: if your sun exposure is seasonal or limited, choose the source you can verify on the label and repeat reliably.

That usually means food-first in brighter months if you eat fish and fortified foods consistently, and fortified foods or a supplement when your routine, latitude, diet, or pill preference makes daily intake less certain.

How does vitamin D fit with B12 and other vitamins?

Foods that can cover more than one nutrient

In mixed diets, the easiest overlap is with animal foods and fortified dairy. The NIH food table gives 2.9 µg vitamin D and about 1.3 µg vitamin B12 per cup of fortified 2%-fat milk, while cooked sockeye salmon is listed at 14.2 µg vitamin D per 3 oz and cooked farmed rainbow trout at 16.2 µg per 3 oz. The same ODS material also lists 1.1 µg vitamin D in one large scrambled egg, 1.0 µg in 3 oz of beef liver, and 1.0 µg in 3 oz of drained canned light tuna. These are specific foods and servings, not a guarantee for every brand or recipe. NIH ODS vitamin D food table

Why one food rarely covers vitamins A, C, E and K

For the other letters, the evidence points to different food groups. Vitamin C is shown by raw sweet red pepper at 95 mg per 1/2 cup and orange juice at 93 mg per 3/4 cup; vitamin E by dry-roasted almonds at 6.8 mg per ounce; and vitamin K by raw spinach at 145 µg per cup. That makes it unrealistic to expect one “all-in-one” food to cover the whole vitamin spread. NIH ODS vitamin C fact sheet

Vitamin A is mainly a label check in this context: the FDA says vitamin A must be listed on Nutrition Facts and Supplement Facts labels when it is added to foods or supplements, and the ODS notes that cereals and plant drinks supply vitamin D, B12, A or E only when those nutrients have been added and declared. For vegan or low-fish diets, that means fortified foods are the practical bridge for vitamin D and any added B12, while fruit, vegetables, nuts, seeds and oils usually fill in the other vitamins. FDA Daily Value label guide NIH ODS vitamin D fact sheet

One food can help, but the label decides whether a plant drink or cereal actually contains the vitamin mix you want.

If you are comparing products, check the package for the exact nutrients added, then compare the amount in the serving you will actually eat or drink. That avoids the common mistake of assuming every milk alternative, cereal or mushroom product contains vitamin D, B12, A or E just because the category sometimes does. EU food label reference value rules