<p>Your vitamin D levels depend heavily on the month your blood was drawn. September is your yearly high, late March your yearly low. Nothing about your health has changed in between.</p><p>From October to March the sun sits too low over the Netherlands for skin production. You live off what you built up in summer. One result on its own says less than you would think. Two results say something only if you know both months.</p>
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| Result | Value (nmol/l) |
|---|---|
| Deficiency | < 30 |
| Sufficient | ≥ 30 |
| Result | Value (nmol/l) |
|---|---|
| Severe deficiency | < 35 |
| Deficiency | 35–50 |
| Sufficient | ≥ 50 |
Nederlandse richtlijnen zijn het niet eens over deze grens. Het Zorginstituut stelt vast: "Er ontbreekt een eenduidige grens voor vitamine D-deficiëntie" (2022). Wij volgen de Gezondheidsraad, het NHG en het Farmacotherapeutisch Kompas. De NVKC hanteert 50 nmol/l voor iedereen; de osteoporoserichtlijn hanteert 50 nmol/l bij verhoogd fractuurrisico.
Source: Gezondheidsraad Reference population: Nederlandse bevolking (Gezondheidsraad 2012)
Source: Zorginstituut Nederland Reference population: Nederlandse bevolking (Gezondheidsraad 2012)
Reference ranges may vary between laboratories. When you order a test, a BIG-registered doctor assesses your personal results in context. For treatment decisions, discuss your results with your GP.
What you are measuring is 25-hydroxyvitamin D (25-OH-D), reported in nmol/l. Think of it as the level in your storage tank, not what you took in yesterday. Its half-life is two to three weeks.
The result therefore covers roughly the past few months. It lags behind your summer and behind your winter.
There is also an active form, 1,25-dihydroxyvitamin D. It is deliberately not measured here. It clears from your blood within hours. Parathyroid hormone (PTH) keeps it tightly regulated.
Your body steps up the conversion when the tank is nearly empty. A normal or even raised active value therefore does not rule out a shortage. That is why it is the wrong test when a shortage is suspected.
Your report should give total 25-OH-D, meaning D2 and D3 together. If you use a plant-based D2 supplement, say so. Not every immunoassay picks up D2 fully.
What vitamin D does explains the rest. It lets you absorb calcium and phosphate from your food. Once your stores run down, you take up less calcium.
Parathyroid hormone rises and your body pulls calcium out of your bones. That covers the shortfall in your blood. So the reading is judged against your skeleton, not against how you feel.
The Dutch Health Council works with decision thresholds rather than a single normal value:
| What your result says | What it is called |
|---|---|
| Below 30 nmol/l | Deficiency |
| 30 to 50 nmol/l | Too little, but not a deficiency |
| 50 nmol/l or above | Enough for your bones |
From the age of seventy that first line moves up to 50 nmol/l. Above 75 nmol/l no added benefit has been shown. Higher is not something to aim for.
Reference values also differ between laboratories. Always read the thresholds printed next to your own result.
On its own the number says little. Calcium, phosphate and PTH finish the picture. A raised PTH alongside a low 25-OH-D counts for more. That pattern is called secondary hyperparathyroidism, and it outweighs the vitamin D figure alone.
Test when you have complaints that fit a deficiency. Think of heavy thighs, difficulty standing up, or bone pain.
Test too if you get outdoors little, have darker skin, or wear covering clothing. The odds of a low value are higher then.
Above all, watch the month. In September you sit at your highest point of the year. In February and March, your lowest.
Want to put two results side by side? Pick the same month, or you are comparing seasons.
<p>The awkward part is that low stores usually do not feel like anything. When you do notice something, it is rarely recognisable:</p><ul><li>strength draining out of your thighs and hips</li><li>a struggle to get up from a low chair</li><li>stairs that start to feel heavier</li><li>nagging bone and muscle pain</li><li>a slightly unsteady walk</li></ul><p>If a deep shortage lasts, new bone tissue mineralises poorly. In adults that is called osteomalacia, in children rickets. Both bring bone pain and deformity.</p><p>In older people a low value often goes with weak muscles and more falls. That raises the chance of a fracture.</p><p>All of these fit dozens of other explanations. The number starts the conversation, not the feeling.</p>
<p>The sun will not give you a high value. Your skin stops making vitamin D once it has enough. So a high result almost always comes out of a supplement.</p><p>Real toxicity, with calcium climbing too high, is generally seen only around 250 nmol/l. And then after months of taking far too much.</p><p>A second route matters more. In some lymphomas and in granulomatous conditions, macrophages make the active form themselves. Sarcoidosis and tuberculosis are the usual examples.</p><p>The normal brake does not apply there. <strong>Your calcium can then run high while your 25-OH-D looks perfectly ordinary. </strong></p><p>Are calcium and vitamin D both on the high side? Then call your doctor before you change anything about your supplements.</p>
Low vitamin D may cause fatigue, muscle weakness, and bone pain. Consider 2000-5000 IU daily supplementation and increase sun exposure.
High vitamin D may indicate excessive supplementation. Reduce supplement dose and retest in 3 months.
Low vitamin D may cause fatigue, muscle weakness, and bone pain. Consider 2000-5000 IU daily supplementation and increase sun exposure.
High vitamin D may indicate excessive supplementation. Reduce supplement dose and retest in 3 months.
We sit at about 52 degrees north here. Between early October and late March too little UVB (290 to 315 nm) gets through. Your skin cannot get to work.
You live off what you built up between June and August. Your level peaks around September and bottoms out in March.
Only compare two results if you know both months. Going from 78 nmol/l in September to 44 nmol/l in March is the ordinary annual swing. That is not a decline.
The same 44 nmol/l in August stands out. August is when you should be at your peak.
You run lower with darker skin. Melanin soaks up UVB, so you need more time outdoors. A lower result also fits with:
The Dutch Health Council advises several groups to supplement. These include pregnant women, people with darker skin, those rarely outdoors and everyone over seventy. How much is a question for your doctor or the Voedingscentrum.
If you take high-dose biotin, say so when your blood is drawn. It can falsely raise some 25-OH-D assays.
This marker is included in the following test panels.
Measure your vitamin D, important for your bones, muscles and immune system. No referral needed, results within a few working days.
Key health markers: CBC, lipids, and Vitamin D.
A 5-biomarker inflammation panel inspired by InsideTracker's Inflammation category — hs-CRP, a complete blood count with differential, vitamin D and ferritin behind your inflammation score.
Key nutrients at risk on a plant-based diet: Ferritin, CBC, B12, Vitamin D, Zinc, Magnesium.
Articles that explain this value in context.
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Every result includes a professional assessment from a BIG-registered doctor. For treatment decisions, discuss your results with your GP.
Vitamin D (25-OH)
€35,-
