Vitamin D in autumn and winter: how much you need and which foods have it

On Sunday 25 October the clocks go back and the evenings close in. The clocks don’t move the sun, but they mark the season well: from now until late winter the midday sun sits so low that your skin struggles to make vitamin D, and blood levels keep falling until winter ends. That is why what you eat matters more in these months than it does in summer. Here is how much vitamin D the European reference recommends, why winter changes the picture, which foods actually contain it, and how to follow it with vitaloop.

What vitamin D does

Its main job is helping your gut absorb calcium and phosphorus from food, the raw material your bones are mineralised with. It also plays a part in normal muscle function.

The vitamin D your skin makes or your food supplies isn’t active yet. The liver turns it into 25-hydroxyvitamin D, or 25(OH)D, the form that circulates in the blood and the one a blood test measures; the kidney then converts it into the active form as the body needs it.

How much vitamin D do you need a day?

For vitamin D, EFSA gives no average requirement or population reference intake, as it does for iron: it judges that the data can’t support them. It sets an adequate intake instead, the amount at which most people reach a blood 25(OH)D of 50 nmol/L, the level it takes as the target.

The most important part of the table is the part you can’t see. EFSA derived those 15 µg from data on people whose skin was making very little vitamin D, and it notes that when the skin does make it, the amount needed from the diet is lower, possibly zero. In other words, 15 µg is a reference for the worst case, and in Spain the worst case looks a lot like winter.

The other column is the tolerable upper intake level: 100 µg a day for adults, pregnancy and breastfeeding included. EFSA considers it very hard to get near that from food; the people who can exceed it are those taking high-dose supplements every day.

Which reference does vitaloop use?

The same one: 15 µg a day for every adult, men and women alike, with no change by age, and the upper level of 100 µg. vitaloop is for over-18s and doesn’t model pregnancy. If a doctor or dietitian has given you a different figure, you can change the target in the app.

The sun: the main source, and not much use in winter

Most vitamin D isn’t eaten; it’s made. Ultraviolet B (UVB) light converts a cholesterol-related molecule in the skin, 7-dehydrocholesterol, into previtamin D3, which the skin’s own warmth then turns into vitamin D3. But the ozone layer filters out much of the UVB, and the lower the sun, the more atmosphere its light crosses and the less UVB reaches the ground.

This is what’s known as the “vitamin D winter”. The classic study, from 1988, exposed skin samples to sunlight on clear days: in Boston, at 42° north, no previtamin D3 formed at all from November to February; in Edmonton, Canada, at 52°, from October to March (Webb et al., 1988). Boston sits on the same latitude as Burgos; Santiago de Compostela and Bilbao are slightly further north.

Further south, production doesn’t stop entirely, but it drops sharply. A team at the Universitat Politècnica de València used eight years of the city’s UV measurements to work out how much midday sun it takes to get the daily dose they used as a reference: 7 minutes in July, 31 in October and more than two hours in January, when people are also almost fully covered up (Serrano et al., 2017). In a later paper, the same author estimated that in winter, schoolchildren, outdoor workers and athletes get roughly a quarter of that dose from the sun (Serrano, 2018).

It shows up in the blood. A study of 206 blood donors in Burgos and Valencia measured it at two points in 2018:

In both cities vitamin D was significantly lower after winter than after summer, and the gap was larger in Burgos, which lies further north.

So does what I eat matter?

In summer, next to the sun, not much. In winter, a good deal more, because it’s the part that doesn’t depend on latitude. That doesn’t mean you have to hit 15 µg every day from food alone (EFSA’s figure already assumes no sun), but these are the months when it’s worth knowing how much vitamin D you eat and where it comes from.

The foods with the most vitamin D

Few foods carry useful amounts of vitamin D, and nearly all of them are fish. These are the figures vitaloop uses per 100 g, as they stand in our food database on 10 October 2026. Each row links to its source: the US Department of Agriculture (USDA) table or the European ANSES-CIQUAL table.

What the table shows:

• Oily fish is far ahead. A 120 g portion of grilled salmon gives about 16.7 µg, a little more than a day’s adequate intake. Trout and sardines are in the same league.
• White fish has much less. Hake has roughly a quarter of what salmon has.
• Tinned fish counts, though not all equally. Tinned mackerel has far more than tinned tuna.
• In eggs, the vitamin D is in the yolk. Two boiled eggs (100 g) give about 2.5 µg.

Two cases the table leaves out:

• Mushrooms. Like our skin, mushrooms make vitamin D (D2, in their case) when ultraviolet light hits them. Wild ones can carry a fair amount, but button and other cultivated mushrooms, grown in the dark, have very little unless they’ve been treated with UV light, which the pack will say.
• Fortified foods. Some milks, plant drinks, breakfast cereals and margarines have vitamin D added. When a product does, the label has to declare it, so the figure is there (why the label is usually silent on the rest).

Who falls short in Spain?

From food, almost everyone. In the ANIBES study, 2,009 people representative of Spain’s population recorded everything they ate and drank for three days (Olza et al., Nutrients, 2017):

• Mean vitamin D intake was 4.4 µg a day.
• 93% reported eating less than 80% of the European recommendation.
• Fish was the main source.

Three important caveats before drawing conclusions:

• This is what people say they eat, not blood tests.
• Most vitamin D comes from the sun, which ANIBES doesn’t measure. Eating less than 15 µg doesn’t mean you are short of vitamin D, especially from spring to autumn.
• ANIBES was funded by a grant from Coca-Cola Iberia through the Spanish Nutrition Foundation (FEN); the authors state the company had no role in the design, analysis or writing.

What about vitamin D supplements?

They are among the most common supplements in autumn and winter. If you take one, or a multivitamin that contains it, you can log it in vitaloop from the supplement catalogue, and its vitamin D is added to your food’s in the same daily total. A practical detail: many packs state it in international units (IU), and 1 µg is 40 IU, so EFSA’s 15 µg is 600 IU.

How much to take, and for how long, depends on your blood test and your circumstances, and is for a doctor or other qualified professional to decide. What’s worth keeping in mind is that vitamin D builds up in the body, so more isn’t better: the 100 µg upper level exists precisely because of supplements.

How to follow your vitamin D with vitaloop

You log what you eat (by searching, scanning the barcode or telling the AI chat) and vitaloop works out the vitamin D in every food, along with the other vitamins and minerals. In Analytics you see your vitamin D for today or the last 7 days against your 15 µg reference. Tap it and its detail opens:

• Which meals gave you it. The three meals (or supplements) that gave you the most vitamin D in the period, with the micrograms from each.
• Which foods contain it, such as salmon, sardines or eggs, with a usual portion and its vitamin D.
• A note on the figure. Every time, not only when it reads low, vitaloop reminds you that the number counts what you’ve eaten and taken, not what your skin makes, which depends on latitude, season, time of day, skin tone, clothing and sunscreen. It’s a floor on your total, not the total.

For the same reason, vitaloop’s weekly report draws no conclusions from your vitamin D: we won’t build a recommendation on a number that only tells part of the story. Nor will vitaloop tell you how much sun to get: that’s a question of UV exposure, not nutrition.

vitaloop is a nutrition app made in Barcelona that works in English, Spanish and Catalan: the app, the chat, the food names and the weekly report. Your data is stored on EU servers, under the GDPR.

Is vitaloop for you?

If you’re looking for an app that tells you how much vitamin D you’re eating this winter, compares it with the European reference and shows which meals and supplements it comes from, vitaloop is for you.

It’s a free download on the App Store and Google Play. To keep going with the series, read how much iron you need a day or which app calculates the vitamins and minerals in what you eat.