Vitamins, minerals and amino acids · Blood

Vitamin D (25-OH)

The storage form of vitamin D; shows whether there is a deficiency, but in healthy people the result usually does not change the advice.

At a glance

Measured in blood
In 12 test panels
Check the preparation

Explanation

Vitamin D (25-OH): what is measured?

Vitamin D is mainly made in the skin under the influence of sunlight and comes for a small part from food (oily fish, margarine, eggs). The liver converts it into 25-hydroxyvitamin D, the storage form that this analysis measures; the kidneys turn that into the active form. Vitamin D is needed for the absorption of calcium and phosphate and thus for strong bones and muscles. The value is lowest at the end of winter and highest in late summer.

What can it detect?

Vitamin D deficiency, which with a long-term severe deficiency can cause softening of the bones (osteomalacia), muscle weakness and, in children, rickets
Too much vitamin D from high-dose supplements (rare)
An explanation for an abnormal calcium or parathyroid hormone (PTH)

Result

What does the result mean?

Vitamin D (25-OH) too high

A raised 25-OH vitamin D is caused almost only by high-dose supplements. Only at very high values, far above the target value, can the calcium in the blood rise, with nausea, thirst, frequent urination, confusion and, in the long run, kidney damage. Sunlight alone does not cause too high a value, because the skin limits production itself.

Vitamin D (25-OH) too low

A low 25-OH vitamin D is very common at the end of winter, in people who rarely go outside or who cover their skin, with dark skin, at older age and with overweight. According to the Health Council of the Netherlands, in adults up to 70 years a value below 30 nmol/L counts as a deficiency, and above 70 years a value below 50 nmol/L. A slightly low value usually causes no symptoms; a long-term severe deficiency can lead to bone pain, muscle weakness, falling more often and fractures. Symptoms such as tiredness are often attributed to vitamin D, but the evidence that a supplement improves those symptoms is weak. A deficiency due to poor absorption occurs with bowel diseases such as celiac disease and Crohn's disease, after bariatric surgery and with some antiepileptic drugs.

After an abnormal result

With a deficiency, the GP usually advises a vitamin D supplement and a follow-up measurement is usually not needed; with a severe deficiency or a condition causing poor absorption, a check after a few months sometimes follows, along with tests of calcium, phosphate and PTH. With a strongly raised value, supplement use is checked and calcium is measured.

Reliability

How reliable is the test?

Measuring 25-OH vitamin D is the recognized measure of vitamin D status, but the result differs between laboratories and measurement methods and varies with the season. According to the Dutch GP association's position statement (NHG) on diagnosing vitamin D deficiency, the result does not change the advice in healthy people without symptoms, and for the risk groups of the Health Council of the Netherlands a supplement advice applies regardless of the result. The result says the most with symptoms that fit a severe deficiency, with conditions causing poor absorption and with an abnormal calcium.

What can affect the result?

Season: the value is lowest at the end of winter and highest in late summer; a measurement in March and one in September are not comparable.
Laboratories and measurement methods differ; shortly after a high dose of a supplement, the value is temporarily higher than the true stores.
With a raised or lowered protein level (pregnancy, liver disease, kidney disease), the total value says less about the available vitamin D.
Antiepileptic drugs, some HIV medicines and fat-binding agents lower the value; biotin supplements can disturb the measurement.

Preparation

Do you take biotin (vitamin B8, often in hair and nail supplements)? Stop at least 2 days before the sample is taken, or 4 days for a high dose.

Who it is for

Who is the test useful for?

Useful for

Useful with symptoms that fit a severe deficiency (bone pain, muscle weakness, frequent falls), with osteoporosis or a fracture, with conditions causing poor absorption (celiac disease, Crohn's disease, after bariatric surgery), with an abnormal calcium and for monitoring treatment with high doses. For the risk groups of the Health Council of the Netherlands (children up to 4 years, pregnant women, women over 50, everyone over 70, people with dark skin or who rarely go outside), a supplement advice of 10 to 20 micrograms per day applies, regardless of the result. In healthy adults without symptoms or risk factors the result says little, partly because a slightly low value at the end of winter is very common.

How common is it?

At the end of winter, about 7 to 26 in 100 Dutch adults have a vitamin D deficiency, depending on the cut-off used; in summer this drops to 0 to 5 in 100. Men have a deficiency more often than women, and people with dark skin, older people in care homes and people who rarely go outside much more often. A severe deficiency with bone symptoms is rare.

RIVM (Lifelines study 2023, published 2025) and Health Council of the Netherlands (2012)

Drawbacks and risks

With a slightly low value in winter, a normal seasonal effect is easily read as a 'deficiency'; in healthy people without symptoms the result does not change the advice (whether or not to take a supplement).
Taking high-dose supplements on your own initiative after a low result can lead to too much calcium.

Get tested

Vitamin D (25-OH): test panels

Vitamin D (25-OH) is part of these test panels. You order online and have your blood drawn at a collection point or collect the sample at home.

Blood draw
Vitamin D3
25-OH-D3; bone and immune system.
€ 32,00
Blood draw
Vegan Test
Panel for vegetarian or vegan diet; B12 D iron and more.
€ 116,00
Blood draw
General Health Checkup
With this General Health Check-up, you gain detailed insight into your overall health and well-being.
€ 125,00
Fingerstick
Vitamin D3
25‑OH‑vitamin D; bone and immune system.
€ 32,00
Blood draw
InsideTracker
InsideTracker Blood Analysis: analyze 48 biomarkers for complete health optimization and personalized recommendations.
€ 335,00
Blood draw
Vegetarian Basic
Iron, vitamin B12, vitamin D, and ferritin. For vegetarians and vegans who want to check key nutrients.
€ 125,00
Blood draw
Vegetarian Extensive
Iron, ferritin, B12 total and active, vitamin D, folic acid, zinc, magnesium, hemoglobin, and hematocrit. Complete nutritional status check.
€ 269,00
Blood draw
Fatigue Basic
Vitamin D, B12, TSH, fT4, glucose, hemoglobin, MCV, iron, and magnesium. Tests most common causes of fatigue.
€ 116,00
Blood draw
Comprehensive Fatigue Test
Vitamin D, B12, TSH, fT4, glucose, MCV, ferritin, ESR and complete blood count. For persistent fatigue with inflammation check.
€ 152,00

How reliable is the test?

Vitamin D (25-OH)