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Vitamins

Your vitamin D levels after six months indoors

Your vitamin D level shows how much vitamin D you have in store, and in the Netherlands that mostly reflects the sun of the past few months. If you train indoors, work indoors and commute in the dark, a low result in February is no sign that you are doing something wrong: the number follows your exposure rather than your discipline. The laboratory also prints its own range, which differs from the Dutch Health Council floor, so read your result against both.

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 the laboratory measures is 25-hydroxyvitamin D, or 25-OH-D, reported in nmol/l. That is the storage form, and the figure describes your reserve rather than your day. Its half-life is two to three weeks, so the result lags months behind your behaviour: a sunny weekend barely moves it, half a year indoors moves it a lot.

The active form, 1,25-dihydroxyvitamin D, is deliberately not measured here. It shifts within hours and is kept in check by parathyroid hormone, the hormone from the parathyroid glands that keeps your calcium steady. It can read normal or even high while your reserve is empty, so do not measure the active form when you suspect a shortage: you measure the wrong thing and get a reassuring number back.

Ask for total 25-OH-D, meaning D2 and D3 together. That counts if you use a plant-based D2 product, because not every immunoassay recovers D2 fully and your result then comes out below your actual status.

Your report carries the laboratory's reference range, 50 to 150 nmol/l. The Dutch Health Council uses no range but a floor that must be met all year round: 30 nmol/l until your seventieth birthday and 50 nmol/l after it. Between 30 and 50 the lab therefore flags you as low while the Health Council regards you as sufficient under seventy. What that means for you is a conversation with your doctor.

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

If you lift, you will meet the testosterone question sooner or later, and the link is thinner than it looks. Observational studies do find low vitamin D status and lower testosterone together. That observation is real, but it does not show that one causes the other: men with a low value also tend to carry more fat mass, get outdoors less and are more often in poorer health, and those three lower testosterone on their own, while the season moves all of them at once. In controlled trials where men are given vitamin D, the effect on testosterone is inconsistent and usually absent. So learn your status because a shortage matters in itself, and expect no hormonal lever from it.

What the value does govern directly is calcium and bone. Too little vitamin D means less calcium absorbed from your food; parathyroid hormone rises and the skeleton is used as a buffer.

For that the Dutch Health Council uses a floor rather than a laboratory reference: until your seventieth birthday at least 30 nmol/l, all year round, and from seventy at least 50 nmol/l. Below it the term is deficiency; the Farmacotherapeutisch Kompas calls anything below 35 nmol/l from seventy a severe deficiency. The Health Council names no target above that floor, so stacking higher is no goal.

The laboratory also prints its own range of 50 to 150 nmol/l, and below 50 the two yardsticks diverge. So read the result against both and alongside calcium and parathyroid hormone: a low reserve with a rising PTH weighs more than the vitamin D number 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,- · Tiredness · €196,- · Extended Health Checkup · €259,-
Where
650+ draw sites run by independent laboratories across the Netherlands. Draw sites

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

Measure at the end of winter rather than in August. August shows your summer peak, and that says nothing about the rest of the year. If you train indoors, work indoors and commute in the dark, February or March is when your value sits lowest.

Test too if strength or recovery slips while your programming stayed the same. Vitamin D is then one thing you can tick off, alongside sleep, nutrition and iron. 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

Most of the time you notice nothing. A reserve can sit low for months without anything feeling different, so the number turns up before the complaint does. When something does show, it sits in the muscles closest to the trunk: heavy legs coming out of a deep squat, stairs that feel harder than they should and a dull ache in bones and muscles. A deep, long-standing shortage leaves new bone poorly mineralised, which in adults is called osteomalacia.

A lifter puts exactly these things down to volume or sleep, and usually that is right. They point at vitamin D and at dozens of other causes, so the blood result decides here rather than how you feel.

High Levels

A high result almost always comes out of a bottle and rarely out of the sun, because once the skin has made enough, it shuts its own production down. Plenty of men stack several sources without noticing: vitamin D on its own, a multivitamin, a fish oil blend with D in it and a sports formula. Real toxicity with a raised calcium is seen in the literature only well above 250 nmol/l, after prolonged very high intake; the laboratory prints 150 nmol/l as its upper limit.

The exception matters more. In granulomatous disease such as sarcoidosis and tuberculosis, and in some lymphomas, macrophages make the active form themselves, outside the normal control. Calcium can then climb at a perfectly ordinary 25-OH-D. If your calcium is climbing too, ask your GP.

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

Male

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

From October through March the sun sits too low here. The UVB your skin needs, 290 to 315 nanometres, barely reaches the ground, so you make almost none of your own in those months and live off the summer reserve. A gym full of daylight does not help, because glass blocks UVB.

So write the month of the draw next to every result. Put March beside September without that date and you see a drop that is only the season.

Expect a lower value with indoor work and night shifts, with darker skin, because melanin soaks up UVB, with covering clothing, with a higher fat mass, because vitamin D accumulates in fat tissue and less stays in the blood, with older age, because the skin holds less of the precursor, with impaired fat absorption, and with anticonvulsants, rifampicin and glucocorticoids, which speed up breakdown.

The Dutch Health Council names groups who are advised to supplement, including people who spend little time outdoors and people with darker skin. How much that means is a question for your GP or the Voedingscentrum. If you take high-dose biotin, say so at the blood draw, because it can falsely raise some 25-OH-D assays.

Vitamin D (25-OH): frequently asked questions

Does vitamin D raise my testosterone?

There is an observed association between vitamin D status and testosterone, but an association is no cause. The studies are confounded by season, body fat and general health, and in controlled trials the effect is usually absent. There is no evidence that raising your vitamin D raises your testosterone.

I have trained hard for six months and my value is low. How?

Training barely matters here. Your skin makes vitamin D under UVB, and if you train indoors and commute in the dark, you never get that UVB. The number follows your exposure. The Dutch Health Council floor is 30 nmol/l until you turn seventy; the laboratory prints 50 to 150 nmol/l.

When should I measure?

At the end of winter. February or March shows your lowest point, while a test in August flatters you and says little about the rest of the year. Note the month with every result, or a difference between two values cannot be read.

Can my value get too high?

Not from the sun, because your skin shuts production down once there is enough. From stacking, yes: a multivitamin, an omega-3 with vitamin D and a separate D3 all add up. Real toxicity generally sits above roughly 250 nmol/l in the literature; the laboratory prints 150 nmol/l as its upper limit.

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)

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