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Vitamins

Your vitamin D levels: skin, season and pregnancy

Your vitamin D level says how much vitamin D your body has in store, and in the Netherlands that store depends almost entirely on the UVB your skin caught last summer. Two groups come out low unusually often: women who are pregnant or breastfeeding, and women who cover their skin or have darker skin. So the month of the blood draw belongs with the result, and any advice about supplementing runs through your midwife or GP.

Doctor's Assessment Included

When is this value abnormal?

See the value that applies to you:

Choose male or female — this range differs by sex.

Enter your age — this range changes with age.

This range also depends on context such as cycle phase or sample material; the highlighted rows apply to your group.

up to 69 years Your group

Decision limits per result, in nmol/l
Result Value (nmol/l)
Deficiency < 30
Sufficient ≥ 30

70 years and older Your group

Decision limits per result, in nmol/l
Result Value (nmol/l)
Severe deficiency < 35
Deficiency 35–50
Sufficient ≥ 50

Dutch guidelines disagree on this limit. The Dutch National Health Care Institute (Zorginstituut) concluded in 2022 that there is no single agreed limit for vitamin D deficiency. We follow the Health Council of the Netherlands (Gezondheidsraad), the NHG and the Farmacotherapeutisch Kompas. The NVKC uses 50 nmol/l for everyone; the osteoporosis guideline uses 50 nmol/l when fracture risk is raised.

Source: Gezondheidsraad Reference population: Dutch population (Health Council of the Netherlands 2012)

Source: Zorginstituut Nederland Reference population: Dutch population (Health Council of the Netherlands 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.

Vitamin D (25-OH): what this test measures

What goes into the tube is 25-hydroxyvitamin D, 25-OH-D for short, reported in nmol/l. It is the form your body stores vitamin D in, and the only form that says anything about the size of that store. The store shifts slowly: half of the 25-OH-D in your blood is still there two to three weeks later, so the result describes the past few months rather than yesterday. A sunny week just before the draw will not pull the number straight.

The active hormone, 1,25-dihydroxyvitamin D, is deliberately left out. It survives only hours, and parathyroid hormone, the hormone from the parathyroid glands that regulates your calcium, keeps it on a tight rein. When the store runs down, your body converts harder, so you can have a perfectly normal active level with an empty shelf behind it.

Ask for total 25-OH-D, D2 and D3 together. If you take a plant-based D2 supplement, that is no detail, because some immunoassays recover D2 incompletely.

The laboratory prints a reference range of 50 to 150 nmol/l on your report. The Dutch Health Council looks at it differently and uses a floor that must be met all year round: 30 nmol/l until your seventieth birthday and 50 nmol/l after it. A value between 30 and 50 is therefore flagged as low by the lab while the Health Council regards it as sufficient under seventy. What that means for you, and certainly during a pregnancy, is a conversation with your midwife or GP.

Vitamin D (25-OH): why this value matters

Vitamin D decides how much calcium and phosphate your gut takes out of your food, and that is why a low store shows up in your bones rather than in your blood calcium. When the store empties, your gut absorbs less calcium, parathyroid hormone rises and it pulls calcium out of your bones to keep blood calcium steady.

Pregnancy and breastfeeding ask more of that system. Your baby's skeleton is built through your calcium balance, and the vitamin D your child is born with comes out of your store. That is why the Dutch Health Council lists pregnant women among the groups advised to supplement; how much that advice involves is a question for your midwife or GP.

The Health Council works with a floor rather than a laboratory reference. Until your seventieth birthday that is at least 30 nmol/l, all year round; below it the term is deficiency. From seventy that line sits at 50 nmol/l, and the Farmacotherapeutisch Kompas calls a value below 35 nmol/l at that age a severe deficiency. The Health Council names no target above that floor, so a higher number is no target to chase.

The laboratory also applies its own range of 50 to 150 nmol/l, and the two yardsticks diverge below 50. Read your number against both, and never apart from calcium and parathyroid hormone: a low 25-OH-D with a raised PTH tells you more than the vitamin D figure alone.

Vitamin D (25-OH): how the blood test works

Referral
No GP referral needed. After the order we arrange the referral through ZorgDomein, within one business day; orders after 17:00 or at the weekend start on the next business day. ZorgDomein emails a barcode, and that barcode is what the draw site needs.
The draw
A blood draw from a vein in the arm, at a partner laboratory's draw site. No home kit, no finger prick.
Which test
Basic Health Checkup · €104,- · Vegetarian · €161,- · Prenatal Essentials · €199,- · Tiredness · €196,-
Where
650+ draw sites run by independent laboratories across the Netherlands. Draw sites

Vitamin D (25-OH): when is testing worthwhile?

If you are pregnant or breastfeeding, discuss testing with your midwife or GP; the Dutch Health Council names pregnant women as a group that supplements. Test too if you cover your skin or have darker skin, because both shrink your summer reserve, and that reserve has to carry you through winter.

The month of your draw decides what you see. September is your highest point and March your lowest, so only compare two results if they come from the same month. Fasting is not needed and the time of day does not matter; the result is back within about 72 hours.

Vitamin D (25-OH): symptoms of a high or low value

Low Levels

An empty store is quiet for a long time. Plenty of women with a value below 30 nmol/l feel fine, and the number usually surfaces through a blood test rather than a complaint. When symptoms do appear, they are vague: weakness in your thighs, trouble getting up out of a low chair or a squat, aching bones and muscles and a less steady walk. During pregnancy and the months after birth they barely stand out, because they get filed under tiredness or recovery.

A long, deep shortage leaves new bone tissue poorly mineralised. That is osteomalacia in adults and rickets in children. Because such complaints fit dozens of other causes, the number is the starting point and the symptom is not.

High Levels

A high 25-OH-D almost always comes out of a jar and rarely out of the sun, because your skin stops making more once it has enough. In pregnancy there is a practical wrinkle: a pregnancy multivitamin usually contains vitamin D already, and if you take a separate preparation alongside it, two sources quietly add up. Bring a list of everything you take to your midwife or GP. Poisoning with a raised calcium is generally seen in the literature only above roughly 250 nmol/l; the laboratory prints 150 nmol/l as its upper limit.

There is one exception that weighs more clinically. In granulomatous disease such as sarcoidosis and tuberculosis, and in some lymphomas, macrophages convert 25-OH-D to the active form without regulation. Calcium can then run high at a completely ordinary 25-OH-D, so a raised calcium alongside vitamin D is a question for your GP.

Vitamin D (25-OH): what to do about an abnormal value

Female

If Low

Low vitamin D may cause fatigue, muscle weakness, and bone pain. Consider 2000-5000 IU daily supplementation and increase sun exposure.

If High

High vitamin D may indicate excessive supplementation. Reduce supplement dose and retest in 3 months.

Vitamin D (25-OH): lifestyle and this value

At about 52 degrees north, the Dutch sun stands too low from October through March and almost no UVB of 290 to 315 nanometres reaches the ground, so your skin makes next to nothing in those months and you live off what you built up in summer.

How large that summer store gets varies a lot. Melanin absorbs UVB, so darker skin needs more time in the same sun for the same synthesis, and covering clothing works the same way: where no UVB reaches skin, nothing happens. This is physics at a latitude where the sun is too weak for half the year, and nothing you are doing wrong. That is why low values are measured more often here in women with darker skin and in women who cover their skin; they go into the winter with a smaller reserve.

Other reasons for a low result are being indoors most of the day or working nights, obesity, because vitamin D is sequestered in fat tissue, fat malabsorption, and drugs that speed up its breakdown, such as anticonvulsants, rifampicin and glucocorticoids.

The Dutch Health Council advises several groups to supplement. Pregnant women are on that list, as are people with darker skin and people who are rarely outdoors. The amount is a question for your midwife, GP or the Voedingscentrum. If you take high-dose biotin, mention it at the draw, because it can falsely raise some 25-OH-D assays.

Vitamin D (25-OH): frequently asked questions

Does vitamin D matter during pregnancy?

The Dutch Health Council names pregnant women as a group that supplements, because your baby's skeleton is built through your calcium balance and your child receives its first store from yours. What amount goes with that is a conversation with your midwife or GP; we deliberately give no figure for it.

Why is my value lower than a friend's?

Skin and clothing explain a lot. Melanin absorbs UVB, so darker skin needs more exposure for the same synthesis, and covering clothing works the same way. That is physics at a latitude where the sun is too weak for half the year, and it says nothing about what you are doing right or wrong.

Does the month of my blood draw count?

Strongly. From October through March the sun sits too low for synthesis and you live off your summer reserve. A March result should sit lower than a September one, so only compare results from the same month.

My value is high. Is that my pregnancy vitamins?

Often yes. A prenatal multivitamin usually contains vitamin D, and if you also take a separate product, the two add up. The laboratory prints 150 nmol/l as its upper limit. Talk to your midwife or GP before changing anything.

Vitamin D (25-OH): sources

  1. Gezondheidsraad. Evaluatie van de voedingsnormen voor vitamine D. Den Haag: Gezondheidsraad, 2012; publicatienr. 2012/15. Overgenomen in NHG LESA Laboratoriumdiagnostiek Vitamine D-deficiëntie (2018). (retrieved 2026) gezondheidsraad.nl
  2. Zorginstituut Nederland. Farmacotherapeutisch Kompas: vitamine D-deficiëntie bij ouderen. Geraadpleegd 14 juli 2026. (retrieved 2026) farmacotherapeutischkompas.nl

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Vitamin D (25-OH)

€35,-