Where Is Vitamin D3 Found — and Why Most Children in Northern Europe Don’t Get Enough

Last November, my daughter’s paediatrician asked how much time she spent outdoors. Honestly — not much. Belgium in November. The doctor nodded and suggested a vitamin D test. The result wasn’t surprising, but seeing the number made it real.

Vitamin D3 is found primarily in fatty fish such as salmon, mackerel and trout, in egg yolks, beef liver, and full-fat dairy products. It is also produced in the skin when exposed to UVB sunlight — the body’s main natural source. In Northern Europe, however, the sun angle is too low for effective UVB synthesis from approximately October to April, which means diet and supplementation carry almost the entire load for around half the year.

Quick reference: Vitamin D3 for children at a glance

Topic

Key fact

Main food sources

Fatty fish (salmon, trout, mackerel), egg yolks, beef liver, full-fat dairy

Sunlight

Primary natural source — unreliable in Northern Europe from October to April

D3 (cholecalciferol)

Animal-derived form; more effective at raising blood vitamin D levels

D2 (ergocalciferol)

Found in UV-exposed mushrooms — the plant-based alternative

Vegan D3

Derived from lichen — check supplement labels

EFSA daily adequate intake

15 mcg (600 IU) for children aged 1–17 (EFSA 2016)

D3 vs D2 — What’s the Difference and Why It Matters

Not all vitamin D is the same form, and the distinction matters for children.

Vitamin D3 — cholecalciferol — is the form produced in human skin on UVB exposure and found in animal foods: fatty fish, egg yolks, liver, full-fat dairy. It’s also the form most widely used in food supplements. Research consistently shows that D3 is more effective than D2 at raising and sustaining blood 25-hydroxyvitamin D levels, which is the standard measure of vitamin D status. A 2012 meta-analysis in the American Journal of Clinical Nutrition by Tripkovic et al. concluded that D3 was approximately 87% more effective at raising serum 25(OH)D than D2.

Vitamin D2 — ergocalciferol — is found in fungi, specifically mushrooms that have been exposed to UV light. Some fortified foods use D2; others use D3. For children’s supplementation, D3 is generally preferred based on current evidence.

If your family follows a plant-based diet, there is a vegan D3 option: lichen-derived D3. Lichen is one of the only plant-based organisms that produces cholecalciferol, and supplements derived from it are nutritionally equivalent to animal-derived D3. Worth checking the label of any supplement you choose.

The Food Sources of Vitamin D3 — the Honest Picture

The honest picture is that food alone rarely covers what children need. But it’s worth knowing which foods contribute most.

Fatty fish

Salmon, trout, mackerel, herring and sardines are the most concentrated food sources of D3. A 100g serving of farmed salmon provides roughly 8–10 mcg (320–400 IU) of vitamin D — a meaningful contribution toward the 15 mcg daily adequate intake, but not all of it, and only if eaten that day. Wild salmon tends to be higher. Herring and mackerel are also high and underused in children’s meals.

Egg yolks

Each egg yolk provides roughly 1–2 mcg (40–80 IU) of vitamin D, with amounts varying depending on the hen’s diet and exposure to light. Outdoor-reared hens with access to sunlight tend to produce eggs with higher D3 content. Modest, but a consistent daily contributor if eggs feature regularly at breakfast.

Beef liver

Beef liver is relatively high in vitamin D3 but also extremely high in vitamin A — the same reason to limit it to occasional servings. The vitamin A content in liver makes daily feeding a genuine risk for children. Once a week is the standard guidance.

Full-fat dairy

Milk, butter and full-fat yoghurt contain modest amounts. In Belgium and the Netherlands, most fluid milk is not mandatorily fortified with vitamin D — unlike in the United States or Scandinavia. Check individual product labels; some brands do voluntarily fortify. Skimmed milk contains less because vitamin D is fat-soluble and is largely removed with the fat.

Fortified foods

Fortification policies differ meaningfully across markets. In Belgium, mandatory vitamin D fortification is limited. In the Netherlands, margarine is fortified; some dairy products and breakfast cereals add D3 voluntarily. In Germany, there is no mandatory fortification policy, and voluntary fortification is limited. The practical upshot: you cannot assume your child’s food supply is compensating for low sun exposure in the way US or Finnish children’s diets might. Check labels specifically.

Mushrooms exposed to UV light

Mushrooms that have been exposed to UV light — sunlight or artificial UV — produce D2, not D3. The amounts vary widely depending on exposure. Some supermarkets in Belgium and the Netherlands now stock UV-exposed mushrooms specifically. A relevant source for plant-based families, though D2 is less potent than D3 at equivalent doses.

The honest summary: even a diet that includes fish once or twice a week, eggs regularly, and some dairy will probably reach somewhere between 5 and 10 mcg of vitamin D per day — short of the 15 mcg adequate intake. In the Northern European context, food alone is rarely sufficient. 

The Sunlight Problem — Especially in Northern Europe

Sunlight is supposed to be the main source of vitamin D3 for humans. The problem is the sun.

Vitamin D3 is synthesised in the skin when UVB radiation — wavelengths between 290–315 nm — reaches skin cells and converts 7-dehydrocholesterol into pre-vitamin D3. This process is efficient in the right conditions. Those conditions are not reliably present in Northern Europe for roughly half the year.

Belgium, the Netherlands and Germany all sit above 50 degrees north latitude. At this latitude, from approximately October through March or April, the sun angle is too low for meaningful UVB to reach the Earth’s surface — the UVB is absorbed by the atmosphere before it arrives. No UVB means no cutaneous vitamin D3 synthesis, regardless of how much time your child spends outdoors. (Worth internalising: standing in the sun in Brussels in January does nothing for vitamin D.) Both the Belgian Royal Academy of Medicine and the Health Council of the Netherlands have formally acknowledged this seasonal gap and recommend year-round vitamin D supplementation for young children.

Even in summer — May through September — getting adequate UVB requires specific conditions. Skin not covered by clothing. No high-SPF sunscreen on exposed areas. Midday sun, between roughly 10am and 3pm, when UVB intensity is highest. At least 15–30 minutes, depending on skin tone. For children who are appropriately and responsibly sun-protected, this is harder to achieve consistently than it sounds.

Skin tone matters, and this point deserves clarity. Melanin — the pigment that gives skin its colour — also filters UVB. Darker skin tones require significantly longer sun exposure to synthesise the same amount of vitamin D3 as lighter skin tones. For families from Africa, South Asia, the Middle East or Latin America who have settled in Belgium or Germany, children with darker skin have a substantially higher risk of vitamin D deficiency year-round — not just in winter. This is a documented public health issue, not a speculation, and it warrants specific attention when assessing a child’s vitamin D needs.

The practical conclusion is clear and not controversial: for most children in Belgium and the Netherlands, sunlight alone cannot maintain adequate vitamin D status throughout the year. This is the position of national health authorities, not a fringe concern.

What Vitamin D3 Does for Children — the Approved Science

Bones. Teeth. Immune system. Muscles. Calcium absorption. Vitamin D is doing a lot, and each of these roles is specifically recognised at EU level.

The most important claim for the children’s context starts here. There’s a specific, EU-regulated recognition that vitamin D contributes to normal growth and development of bone in children — not a generic ‘good for bones’ message, but a children-specific, evidence-based acknowledgement of what adequate vitamin D does during the years when bone mineral density is being established. A child’s skeleton is not fully formed; the vitamin D that flows through childhood years is doing structural work that cannot be easily caught up later.

Here’s the connection that most parents haven’t made: vitamin D contributes to the normal absorption and utilisation of calcium and phosphorus. The calcium in your child’s diet — the dairy, the fortified plant milk, the leafy greens — only reaches the bloodstream and then the bones if vitamin D is adequate. Without it, calcium passes through largely unabsorbed. Giving a child plenty of dairy and assuming their bone nutrition is covered misses this dependency.

The related recognition: vitamin D contributes to normal blood calcium levels — the body’s ability to regulate calcium in the bloodstream, which underpins both bone health and muscle function.

On the skeleton specifically: vitamin D contributes to the maintenance of normal bones. This is broader than the children’s development claim — it applies across life — and it underlines that the bones built during childhood need ongoing vitamin D to maintain their structure.

Separately, vitamin D contributes to the maintenance of normal teeth. Less discussed, but relevant for a population of children eating sugar and relying on enamel density.

Immune function: there’s a formal recognition that vitamin D contributes to the normal function of the immune system. The association between low vitamin D and increased respiratory infection rates in children has been studied extensively. One sentence won’t do it justice, but the direction of evidence is consistent.

Finally: vitamin D contributes to the maintenance of normal muscle function. For younger children developing coordination and strength, this is a quieter but real role.

One practical note on combinations: if you’re thinking about vitamin D and bone health together, it’s worth knowing that vitamin K2 works alongside vitamin D. Vitamin D increases calcium absorption from the gut; vitamin K2 helps direct that calcium into bone rather than soft tissue. They’re not the same supplement, but they work as a pair. Worth discussing with a healthcare professional if bone health is a specific concern.

How Much Vitamin D3 Does a Child Need?

The EFSA Dietary Reference Values for vitamin D, published in 2016, set the adequate intake at 15 mcg (600 IU) per day for children aged 1–17. This figure assumes minimal sun exposure — which, as discussed, is a reasonable assumption for Northern European children across much of the year.

The tolerable upper intake level — the maximum daily amount considered safe for ongoing use — is 50 mcg (2,000 IU) per day for children. Above this level, vitamin D toxicity becomes a risk. This is for reference; food supplement products are formulated well below this threshold. If you are considering doses higher than what’s on your supplement label, discuss it with a GP first.

The Belgian Health Council recommends daily vitamin D supplementation for all children in Belgium, with specific higher doses for infants and for children with dark skin or limited sun exposure. The Health Council of the Netherlands (Gezondheidsraad) recommends daily supplementation for children under 4 and for older children with limited sun exposure or darker skin. These national guidelines are more specific than the EFSA adequate intake figure and reflect the Northern European reality.

How much can diet realistically provide? For most children eating a broadly healthy diet in Belgium or the Netherlands — some fish occasionally, eggs, some dairy — dietary vitamin D intake likely falls in the 3–7 mcg range per day. That’s 20–47% of the EFSA adequate intake. The rest needs to come from sunlight in summer and supplementation in winter.

Signs a Child May Not Be Getting Enough Vitamin D

The tricky thing about vitamin D deficiency is that it’s often quiet. The early signs are nonspecific and easy to attribute to other things.

Fatigue and persistently low energy are common and have many possible causes — but they appear frequently in studies of vitamin D-deficient children and are worth noting alongside other signs. 

Muscle weakness or aches — a child who tires quickly during physical activity, complains of leg aches that aren’t growth pains, or seems less strong than expected for their age — can sometimes reflect poor vitamin D status. It’s not diagnostic on its own, but it’s more specific than fatigue alone.

Bone pain or tenderness is a more specific signal. At the extreme end of long-term, severe deficiency — particularly in young children — vitamin D deficiency causes rickets, with visible bowing of weight-bearing bones and deformities of the legs, wrists and ribcage. Rickets is rare in Belgium and the Netherlands but not unknown, particularly in children with very dark skin and no supplementation. It represents the clinical endpoint of sustained, severe deficiency and is mentioned here as context for why catching lower-level deficiency matters.

Frequent respiratory infections — colds, chest infections, ear infections that seem to come one after another — have been associated with low vitamin D status in multiple studies. The immune function connection is real, even if the individual child’s pattern is hard to attribute definitively.

If you’re concerned, the test to ask for is a 25-hydroxyvitamin D blood test — specifically 25(OH)D. Results below 30 nmol/L are generally considered deficient; 50–75 nmol/L is adequate in most guidelines; above 75 nmol/L is considered optimal. Ask for the number, not just a ‘normal’ or ‘abnormal’ result, because the clinical reference ranges vary between labs. Symptoms alone are not a diagnosis. The blood test is the only reliable confirmation.

Vegetarian and Vegan Children — a Specific Note

If your child follows a vegetarian or vegan diet, the vitamin D situation is more constrained.

Almost all dietary D3 comes from animal sources. A vegetarian child who eats eggs and full-fat dairy has some D3 intake; a vegan child eating no animal products has essentially none from food. Plant-based diets provide D2 from UV-exposed mushrooms — inconsistent, lower potency than D3, and dependent on whether mushrooms were actually UV-exposed before purchase.

Fortified plant milks are the practical fortification route for many vegan families. Check what form they use (D2 or D3) and how much — amounts vary widely by brand. Some use lichen-derived D3; others use D2. Neither is harmful, but D3 is more effective.

Lichen-derived D3 supplements give vegan children access to the same D3 form as animal-derived supplements, at equivalent potency. If your child follows a strict plant-based diet and lives in Northern Europe, regular monitoring of vitamin D status is particularly important. A seasonal blood test — one in late winter (February or March, when levels are at their lowest) and one in late summer — is a reasonable approach to discuss with your GP.

Three Practical Steps for Parents

Starting from what’s already in place, not from a supplement shelf.

Step one: assess sun exposure honestly by season. In October through April in Belgium or the Netherlands, assume your child’s vitamin D synthesis from sunlight is effectively zero. That’s not pessimism — it’s the geographic and atmospheric reality at above 50 degrees north. Plan the winter months with that assumption. In summer, 15–30 minutes of midday sun on arms and legs without high-SPF sunscreen is a reasonable target — achievable on holidays or weekend outdoor time, but not always consistent enough to rely on alone.

Step two: identify one dietary D3 source to add per week. Salmon or trout once a week. Eggs at breakfast three or four days a week. These won’t close the full gap on their own, but they shift the starting point meaningfully. A child eating eggs regularly is at 3–4 mcg from eggs alone — that’s 20–27% of the adequate intake from a single uncomplicated food.

Step three: keep a seasonal vitamin D log. Note when the dark months begin, when supplementation starts (if applicable), and how your child’s energy levels and illness frequency track through winter. A useful log entry: ‘October 15 — started daily vitamin D, given with dinner. Energy: normal.’ A vague one: ‘Gave it sometimes.’ The specific log makes it easier to see patterns and have an informed conversation with a GP if needed.

When to Contact Your Doctor

Most situations call for a routine GP conversation rather than urgency. But some trigger points are worth acting on promptly. Contact your healthcare provider if your child shows muscle weakness, persistent bone pain or tenderness, or unexplained ongoing fatigue. If your child follows a vegan or strict vegetarian diet with no fortified foods and no supplementation, a conversation and probably a blood test is overdue. If your child has a fat malabsorption condition — coeliac disease, Crohn’s disease, cystic fibrosis, liver conditions — vitamin D is fat-soluble and absorption is significantly impaired; standard dosing may not be sufficient. If your child has darker skin and lives in Northern Europe, their vitamin D need is substantially higher than light-skinned peers and should be discussed with a GP specifically. If a blood test has shown 25(OH)D below 30 nmol/L, follow up with a clinician rather than self-managing the dose.

If you are considering supplementing at doses higher than what’s on the label of a standard food supplement, talk to a GP first. Vitamin D toxicity from over-supplementation is real, and the upper tolerable intake of 50 mcg (2,000 IU) per day for children exists for a reason. If your child is taking medications that affect vitamin D metabolism — certain anticonvulsants or corticosteroids — discuss supplementation with the prescribing clinician.

A Word on Safety

Vitamin D is fat-soluble. Unlike vitamin C or B vitamins, excess doesn’t leave the body in urine. It accumulates — primarily in the liver and fatty tissue — and at sufficiently high intakes, it causes toxicity.

Vitamin D toxicity from food or sunlight alone is essentially impossible under normal circumstances. The risk is from over-supplementation — taking doses significantly above the tolerable upper intake of 50 mcg (2,000 IU) per day for children, over an extended period. Standard food supplement products for children are formulated well below this level.

Symptoms of vitamin D toxicity include nausea, vomiting, weakness, frequent urination and loss of appetite. In severe cases, calcium can accumulate in soft tissues and kidneys. These symptoms are uncommon at standard supplement doses and are mentioned as context for why dose limits exist.

Never combine multiple supplements containing vitamin D without checking the total daily intake across all products. Never exceed the dose on the label without medical guidance.

Store all supplements out of reach of children. If accidental ingestion of a large amount is suspected, do not wait for symptoms. Contact Poison Control immediately: Belgium: 070 245 245 | Netherlands: 030 274 88 88.

Vitamin D deficiency in Northern European children is common, well-documented, and — this is the important part — entirely addressable. The combination of understanding the seasonal gap, adding one or two consistent dietary sources, and bridging the winter deficit is straightforward once you know what you’re actually managing. Most families are already halfway there without realising it. The other half is knowing which months to take it seriously.

Food supplements are not a substitute for a varied and balanced diet and a healthy lifestyle. Always consult a qualified healthcare professional before starting any supplement.

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