How much vitamin D per day and why sunlight is not enough

A vitamin D supplement can say "2,000 % NRV" on the label without containing twenty times what you need. What it means is that the reference value used by European labelling is 5 micrograms, that EFSA — the European Food Safety Authority, the scientific body that advises the European Union on food — recommends 15, that the safe ceiling is 100, and that the percentage on the label is calculated using the first of those four. It is the vitamin with the most official numbers in circulation and the one that is worst understood.

This article sorts those numbers out, explains why December sunlight in Barcelona makes almost no vitamin D even on a clear day, and says with data what you can expect from a supplement and what you cannot. The uncomfortable part first: the largest trial ever run, on 25,871 people, found no evidence that supplementing prevents cancer or heart attacks. And the most convenient regimen — one high-dose capsule a month — is precisely the one that does not work in the meta-analyses.

In short

• The %NRV on the label is misleading. It is calculated on 5 µg (Regulation 1169/2011), not on the 15 µg EFSA considers an adequate intake. Divide the percentage by 20 to get the actual micrograms.
• EFSA's adequate intake is 15 µg/day (600 IU) for adults and children aged 1 to 17, aiming at a blood level of 50 nmol/L.
• The tolerable upper limit is 100 µg/day (4,000 IU) in adults, and 50 µg in children aged 1 to 10.
• In winter and spring, above latitude 35 ºN skin synthesis is poor. Barcelona sits at 41 ºN: from November to March the city's sun contributes little, however clear the day.
• If you take it, take it daily. In the 2025 meta-analysis the effect on respiratory infections appears only with daily dosing, not monthly.
• Tinned oily fish is the cheapest food route, and cod liver oil the most concentrated food there is.
• Mushrooms provide vitamin D2, not D3, and far less than people think: an untreated portobello has 0.1 µg per half cup.

The four official numbers for vitamin D, and why they disagree

Almost all the confusion around this vitamin comes from the fact that there are four legitimate figures, published by different bodies, measuring different things. It helps to keep them apart, because the one printed on the label is the least useful of the four.

The nutrient reference value (NRV) is 5 µg. It is set by Annex XIII of Regulation (EU) 1169/2011 and it is the figure the law requires for calculating the percentage you see on the label. It is a labelling value, not a nutritional recommendation, and it sits well below what is considered adequate today.

The adequate intake is 15 µg/day. EFSA set it in 2016 for adults and for children aged 1 to 17, and 10 µg/day for infants aged 7 to 11 months. It was derived by targeting a blood 25-hydroxyvitamin D concentration of 50 nmol/L, under one important assumption: that skin synthesis is minimal. Where there is effective sun exposure the dietary requirement falls, and may be zero.

The tolerable upper intake level is 100 µg/day. EFSA reviewed it in 2023 and kept it at 100 µg for adults and adolescents aged 11 to 17, lowering it to 50 µg for children aged 1 to 10 because of their smaller body size. It is not a recommended dose: it is the ceiling above which long-term safety cannot be assumed.

The US Daily Value is 20 µg. This matters because half the tables circulating online are American. If you read "50 % of the Daily Value" on a US source, the maths is done on 20 µg; on a Spanish label, on 5. It is the same trap as with iron, where the US value is 18 mg and the European one 14.

The practical rule: to turn the label percentage into micrograms, divide by 20. A "1,000 % NRV" is 50 µg. And to judge whether that suits you, compare it with the 15 µg reference and the 100 µg ceiling, not with the percentage.

Why Barcelona's sun is not enough in winter

Vitamin D is not strictly a vitamin: the skin makes it when short-wavelength ultraviolet B radiation reaches it. The catch is that this radiation enters the atmosphere at an angle that depends on latitude and season, and below a certain angle it is filtered out almost entirely. The standard Spanish review puts it plainly: most of Spain lies above latitude 35 ºN, where skin synthesis is poor in winter and spring.

Barcelona is at 41 ºN, north of Rome and almost level with New York. In December the midday sun does not climb high enough for UVB to arrive in useful amounts, and what little arrives meets the fact that in winter we are covered up: face and hands are a small fraction of body surface. Add that ultraviolet does not pass through glass, so a bright office or a drive in the car does not count.

This explains the Spanish paradox, one of the most counter-intuitive facts in nutrition: a very sunny country with frequent deficiency. In Spanish osteoporosis clinics, 76 % of postmenopausal women with untreated osteoporosis had 25-hydroxyvitamin D below 30 ng/mL, and 44 % below 40. It is not that there is no sun: it is that between November and March it does not work, that we avoid it when it does, and that the Spanish diet supplies little.

The thresholds used to read a blood test, in case you have had one: below 30 nmol/L (12 ng/mL) counts as deficiency; 30 to 50 nmol/L is generally inadequate for bone; and from 50 nmol/L (20 ng/mL) upwards is considered adequate for most healthy people. One nanomole per litre is 0.4 nanograms per millilitre, and since Spanish laboratories usually report ng/mL, it is worth checking the unit before worrying.

What a vitamin D product may legally say, and what it may not

Vitamin D is one of the nutrients with the most authorised health claims in the European Union: seven, listed in Regulation (EU) 432/2012. These are the official wordings:

• "Vitamin D contributes to normal absorption/utilisation of calcium and phosphorus"
• "Vitamin D contributes to normal blood calcium levels"
• "Vitamin D contributes to the maintenance of normal bones"
• "Vitamin D contributes to the maintenance of normal muscle function"
• "Vitamin D contributes to the maintenance of normal teeth"
• "Vitamin D contributes to the normal function of the immune system"
• "Vitamin D has a role in the process of cell division"

All seven share exactly the same condition of use, and it is the part nobody reads: "The claim may be used only for food which is at least a source of vitamin D as listed in the Annex to Regulation (EC) No 1924/2006".

Translated: "source of vitamin D" requires 15 % of the NRV, and the NRV is 5 µg. That is 0.75 µg per 100 grams. With that amount — one fifteenth of the adequate intake — a product may already print "contributes to the normal function of the immune system" on the pack. The claim is true and the threshold is tiny. That is why the sentence on the pack does not separate a good product from an irrelevant one, and the only figure that does is the micrograms per dose.

And there is one claim that does not exist, which matters as much as the ones that do: cardiovascular function. EFSA assessed it in 2010 alongside the immune system and muscle function claims, and only those last two made it onto the 432/2012 list. If you see a vitamin D product hinting at anything about the heart, it is outside the regulation.

How to cover your vitamin D, step by step

1. Read the %NRV and divide it by 20

It is the only sum worth doing in the aisle. "400 % NRV" is 20 µg; "2,000 %" is 100 µg, which is exactly EFSA's safety ceiling for an adult. A four-figure percentage is neither a virtue nor a hazard: it is the result of dividing by 5. In our vitamins and minerals section, doses from 10 to 100 µg per capsule sit side by side — a formula such as D3 with K2 at 4,000 IU is declaring 100 µg, that is, EFSA's ceiling for an adult — and the label presents them as different worlds when the only thing that changes is a number.

2. If you take it, take it every day

This is the most useful finding of recent years and it runs against habit. The 2025 meta-analysis on acute respiratory infections, covering 40 studies and 61,589 participants, found no statistically significant protection overall: OR 0.94, interval 0.88 to 1.00, p = 0.057. But split by regimen, daily dosing did show an effect — OR 0.84 (0.73-0.97) — and monthly or three-monthly dosing did not: 0.98 (0.93-1.03). The best-performing dose range was the most modest one: 400 to 1,000 IU a day, OR 0.70 (0.55-0.89).

Put another way: the high-dose ampoule every thirty days, the most convenient regimen and the best-selling one, is the one that does not show up as working. If you are going to take vitamin D, a small daily dose has better support than a large spaced-out one. Liquid drops, such as the organic liquid D3 forte, make that easier because they let you adjust the dose without splitting capsules.

3. Start with oily fish, the cheap route

A supermarket has an advantage here over a capsule shop: the vitamin D in oily fish arrives with protein, iodine, selenium and omega 3 in the same mouthful. Cooked salmon runs at about 14.2 µg per 85 grams and trout at 16.2: one portion covers the day's reference with room to spare. In tins we carry the same wild Alaskan salmon in water and in extra virgin olive oil, which is a good place to check that the oil in the tin changes the taste and the calories, not the vitamin D. Tinned fish is more modest — two tinned sardines give 1.2 µg and light tuna in water 1.0 µg per 85 g — but it is cheap and keeps in the cupboard; melva in olive oil plays the same role (melva is a small tuna from the Spanish coast, close to mackerel). And for the opposite extreme, cod liver oil in pearls is the most concentrated food there is: around 34 µg per tablespoon. We have 33 lines in tinned fish, and the rest of the tinned goods round out the cupboard.

4. Eggs and dairy add little, but they add it daily

One yolk provides about 1.1 µg and a glass of fortified milk 2.9 µg. These are small amounts, and that is exactly why they count: they come in every day without anyone having to remember. With eleven lines of organic eggs, including loose ones sold singly and the fresh km 0 boxes, plus the refrigerated section for dairy, the baseline comes from the ordinary shop rather than from a jar.

5. Mushrooms do not count for what you have been told

This is the most widespread myth among people trying to cover vitamin D without animal products, and it deserves a plain answer. Mushrooms supply vitamin D2 (ergocalciferol), not D3, and the meta-analysis comparing them — 22 studies and 1,277 participants — found that D3 raises blood 25-hydroxyvitamin D by 15.69 nmol/L more than D2, with an interval of 9.46 to 21.93. On top of that, the amount depends entirely on whether they have been exposed to ultraviolet light: a UV-treated white mushroom reaches 9.2 µg per half cup, while an untreated portobello stops at 0.1 µg, which is next to nothing. If you buy mushrooms in vegetables, buy them for the flavour; as a vitamin D strategy they do not work.

6. Get the blood test before raising the dose

The figure almost nobody uses in their own favour: in the 2025 meta-analysis, when results were split by baseline 25-hydroxyvitamin D, no subgroup showed a significant effect — not even those starting below 25 nmol/L. That does not mean correcting a real deficiency is pointless — it is not, and for bone it is beyond dispute — but that benefit cannot be predicted from a single number, and that moving to high doses is a clinical decision. If you suspect deficiency, the test costs less than a year of capsules and is the only way to know. It is the same reasoning as in iron and tiredness: without a number in front of you, raising the dose is guesswork.

What to take home, depending on your case

The shopping list

To cover vitamin D from food, the basket fills up in four places: tinned fish, eggs, cheeses and dairy from the refrigerated section. If what you want is the supplement, it is in vitamins and minerals: D3 with K2 in pearls, the D3, K2 and magnesium formula, the 60-capsule format and, if it is the whole package you are after, biotin with zinc, selenium and D3. Cod liver oil lives in fatty acids, next to the omega 3.

Around that, what usually goes with a winter shop: immune system for zinc and vitamin C, bones and joints if bone is the reason, nervous system, plants and extracts, superfoods and hair, skin and nails. For the base of the diet, seasonal vegetables, the whole pantry, the oils and vinegars you cook the fish in, and fortified plant drinks. And if you would rather not think about it, the organic baskets and the week's offers.

Do you need vitamin D supplements?

In winter, in Barcelona, many people do. This is one of the few vitamins where the honest answer is not "a varied diet has you covered", because the Spanish diet supplies little and December sun at this latitude supplies less. That said, what a supplement does needs separating from what it gets credited with.

What it does: correct and maintain an adequate blood concentration, with the effects on bone, muscle, teeth, calcium and the immune system covered by the seven authorised claims. That is recognised by the regulator and it is not trivial.

What it does not do: prevent cancer and cardiovascular disease in the general population. The data here is blunt, because it comes from the largest trial ever run. The VITAL study assigned 25,871 people to 2,000 IU of vitamin D3 daily or to placebo and followed them for a median of 5.3 years. For invasive cancer the hazard ratio was 0.96 (95 % confidence interval 0.88-1.06), with 793 cases against 824. For major cardiovascular events, 0.97 (0.85-1.12), with 396 against 409. Neither reached statistical significance: both intervals cross 1 comfortably.

On respiratory infections the story is even more instructive. In 2021 a meta-analysis by the same research group, covering 43 trials and 48,488 participants, found small but significant protection: OR 0.92 (0.86-0.99). In 2025, after adding six new trials and reaching 61,589 participants, the same group published that the interval now included 1 and that significant protection had gone. This is not one source contradicting another: it is the same team correcting itself as more data arrived, which is exactly how this is supposed to work and almost never how it gets told.

Our position, which goes against selling the most profitable formats: if you are healthy and it is summer, eat fish and skip the capsule. If it is winter and you decide to take it, a small daily dose has better support than a big monthly one. And if what worries you is your heart or cancer, vitamin D is not the answer and no European claim says otherwise.

What vitamin D does not do

• It does not prevent cancer or heart attacks in the general population. VITAL, 25,871 participants, five years, no effect on either primary endpoint.
• There is no European claim about cardiovascular function. EFSA assessed it in 2010 and it is not among the seven authorised ones.
• A monthly high-dose capsule is not the same as taking it daily. In the 2025 meta-analysis the effect appears with daily dosing (OR 0.84) and not with monthly (0.98).
• "Source of vitamin D" on the pack does not mean much: 0.75 µg per 100 g is enough, 15 % of an NRV of 5 µg.
• Mushrooms are not a serious source of vitamin D unless they have been UV-treated, and the D2 they supply is less effective than D3.
• More is not better. EFSA's ceiling is 100 µg/day in adults, and 50 in children aged 1 to 10.

Where to buy vitamin D in Barcelona and Sant Cugat

At Linverd Market we stock the catalogue's six vitamin D lines and all 33 tinned fish lines in our three shops — which are in Spain, in Barcelona and Sant Cugat del Vallès — and this is where a physical shop beats any screen: putting two jars on the counter and doing the division by 20 with someone in front of you. In ten seconds you can see that the bottle advertising "2,000 % NRV" holds 100 µg and sits at the safety ceiling, and that the one saying "400 %" holds 20 µg and matches EFSA's reference. An Amazon listing will not do that sum for you, and it is the difference between buying a number and buying a dose.

The second argument is free and cannot be copied either: if what you need is to get through the winter, fish will cost you less. With a tin of sardines, an egg a day and a portion of salmon a week, plenty of healthy people do not need the jar. We say so even though the jar carries a better margin than the tin.

• Provença 242, 08008 Barcelona (Eixample district).
• Còrsega 78, 08029 Barcelona (Eixample, near Sants).
• Antoni Bell 2, 08174 Sant Cugat del Vallès (Volpelleres).

Phone +34 683 118 961 and email linverd@linverd.com. If you bring a recent blood test, better still: the regimen is decided with the number, not with the packaging.

Frequently asked questions

How much vitamin D should you take per day?

EFSA's adequate intake is 15 µg a day (600 IU) for adults and children aged 1 to 17, aiming at 50 nmol/L in blood. The tolerable upper limit is 100 µg a day in adults. The percentage printed on the label is calculated on a different reference value, of 5 µg.

Why does my supplement say 2,000 % NRV?

Because the European labelling reference value is 5 µg and the regulation requires the percentage to be calculated on that figure. A 2,000 % works out at 100 µg, which matches EFSA's safety ceiling for adults. To convert a percentage into micrograms, divide by 20.

Is Barcelona's sunshine enough for vitamin D?

In summer, with real exposure, it can be. In winter and spring it is not: above latitude 35 ºN skin synthesis is poor, and Barcelona sits at 41 ºN. Ultraviolet also does not pass through glass, so light through a window or in the car does not count.

Is daily vitamin D better than one high monthly dose?

Daily. In the 2025 meta-analysis on respiratory infections, the effect showed up with daily dosing (OR 0.84) and not with monthly or three-monthly dosing (0.98). The best-performing range was 400 to 1,000 IU a day, the most modest one rather than the highest.

Does vitamin D prevent cancer or heart attacks?

Not according to the best available evidence. The VITAL trial followed 25,871 people for a median of 5.3 years on 2,000 IU daily and found no reduction in invasive cancer (HR 0.96) or major cardiovascular events (HR 0.97). There is also no authorised European claim on cardiovascular function.

Which foods are highest in vitamin D?

Cod liver oil, at roughly 34 µg per tablespoon, and oily fish: trout runs at about 16.2 µg per 85 g and salmon at 14.2. Further down come tinned fish, egg yolk (1.1 µg) and fortified dairy. Mushrooms supply vitamin D2, which is less effective than D3.

What is the difference between vitamin D2 and D3?

D3, or cholecalciferol, is the form the skin makes and the one that raises blood levels best. In the meta-analysis comparing them, with 22 studies and 1,277 participants, D3 raised 25-hydroxyvitamin D by 15.69 nmol/L more than D2. D2, or ergocalciferol, is the form found in mushrooms and other fungal products.

To finish

Vitamin D is the clearest case of a regulatory figure that is no use for deciding anything. The label percentage is calculated on 5 µg, the real reference is 15 and the ceiling is 100: three numbers sharing the same pack with nobody putting them in order. Putting them in order takes one division and saves a fair amount of money.

You can see the lines in vitamins and minerals and the fish in tinned fish, or drop into any of the three shops and we will look at it together. If the subject interests you, the blog has one on omega 3 and how much EPA and DHA per day, one on zinc or vitamin C for immunity and one on which magnesium to take, the mineral that comes alongside almost every D3 formula. And if the idea of a regulation measuring something other than what you are after rang true, the one on how much olive oil per day is exactly about that. It is all on the health blog.

This information is for general guidance and does not replace advice from a healthcare professional. If you suspect a vitamin D deficiency, are pregnant, take medication or have kidney, liver or calcium-metabolism disease, consult your doctor or pharmacist before supplementing. Do not exceed the product's recommended daily dose.