The Netherlands lies at 52 degrees north latitude. That sounds like a quiz fact, but it has a direct effect on your blood: between October and March the sun here is too low to deliver enough UVB radiation for vitamin D production in your skin. However much you are outdoors, in those months your body makes almost none.
My view: do not panic over a low number, but do not ignore it either. A large or prolonged deficiency really is worth addressing.
Is a vitamin D deficiency dangerous?
A mild and short-lived deficiency is usually not dangerous and often causes no symptoms. A large or prolonged one does: it can weaken your bones, reduce your muscle strength and make you more vulnerable to infections. The effects build up slowly, so you notice them late.
| Effect | What happens? | Who is at extra risk? |
|---|---|---|
| Bone loss | Osteomalacia in adults, rickets in children | Older adults, young children |
| Increased fall risk | Reduced muscle strength, more chance of fractures | Older adults (70+) |
| Reduced resistance | Associated with more susceptibility to infections | Anyone with a large deficiency |
| Low mood | Possible link with low mood and low energy | Mainly in autumn and winter |
For the symptoms and testing, read vitamin D deficiency: symptoms, causes and how to test it.
Vitamin D deficiency and mental complaints
There is increasing evidence that vitamin D plays a role in regulating your mood. A deficiency can be associated with low mood, irritability and low energy, especially in autumn and winter. Vitamin D is rarely the only cause, so see it as one of the possible factors. Complaints such as persistent low mood belong with your GP. A vitamin D value can help to rule out or confirm one possible factor, but does not replace a conversation about your mental health.
Why is the Netherlands at extra risk?
The combination of factors makes a deficiency almost inevitable without conscious measures:
- Geography: at 52 degrees north, UVB radiation from October to March is insufficient, even on a sunny day.
- Indoor lifestyle: the average person here spends most of the day indoors, and glass blocks UVB radiation completely.
- Sunscreen: correct use of SPF 30+ blocks most UVB radiation. Necessary for skin cancer prevention, but it inhibits production.
- Diet: there are few natural food sources of vitamin D.
- Ageing: the efficiency of production in the skin declines with age.
According to the RIVM, a considerable part of the Dutch population has too low a vitamin D level at the end of winter, with higher percentages in the risk groups.
Risk groups
- People with dark skin, because melanin blocks part of the UVB radiation
- Older adults (70+), due to reduced skin production, less time outdoors and lower food intake
- People who wear covering clothing
- People who mainly work or live indoors
- Pregnant and breastfeeding women
- People with obesity, because vitamin D is stored in fat tissue
Supplementation: the Health Council advice
The Gezondheidsraad advises children aged 0 to 4 to take 10 ug per day, adults up to 70 with light skin 10 ug if they are outdoors too little, women from 50 and men from 70 to take 20 ug, and people with dark skin or covering clothing 10 to 25 ug per day. Choose vitamin D3 over D2 and take it with a meal containing fat. Also read exactly how much vitamin D you need per day.
The relationship with calcium
Vitamin D and calcium work closely together. Vitamin D is needed to absorb calcium from your food. With a deficiency, calcium absorption drops, so your body draws calcium from your bones. That is why, if a deficiency is suspected, it is useful to also have your calcium level measured.
A myth unravelled: summer as a buffer
A persistent idea is that a sunny summer builds up your vitamin D store so well that you are safe all winter. That is not quite right. Your body does store vitamin D, but for most people that buffer is not large enough to bridge five to six months without production. In practice levels decline gradually through winter, to be lowest at the end of it. A tanned summer skin is therefore no guarantee of a healthy value in February, which is exactly why year-round supplementation for the risk groups makes more sense than only starting in winter.
When does testing make sense?
The Health Council does not advise screening the whole population for vitamin D. Testing is useful if you have symptoms that fit a deficiency, belong to a risk group, have osteoporosis, or want to know whether your current supplementation is enough. The blood test measures 25-hydroxyvitamin D. View your vitamin D value or place it in a broader picture with the basic health checkup. This article is part of our vitamin deficiency overview.
Every blood test result at Vitalcheck includes a professional assessment by a BIG-registered doctor. A blood value is not a diagnosis: always discuss symptoms and treatment decisions with your GP.
Sources
- Gezondheidsraad. Dietary reference values for vitamins and minerals. 2018.
- RIVM. Vitamin D deficiency in winter among the Dutch population. 2023.
- Thuisarts.nl / NHG. Vitamin D. Accessed 2026.
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