Vitamin deficiency: recognising symptoms and which vitamins to test

You have been tired for weeks, your hair seems to be thinning and sometimes your fingers tingle. Online, within five minutes you find a list that says you almost certainly have a vitamin deficiency. But is that true? Fatigue and hair loss can point to a deficiency, but just as easily to your thyroid, your sleep or simply a busy spell.

My advice up front: do not take supplements on a hunch. Measure first, then know. A targeted blood value says more than any symptom list.

What is a vitamin deficiency?

A vitamin deficiency means your body structurally takes in or absorbs too little of a certain vitamin to function well. Vitamins and minerals drive countless processes, from your energy balance to your blood production and your nerves. A deficiency usually builds up slowly, so you easily miss the first symptoms.

The difference from minerals is small in practice. Vitamins are organic substances (such as vitamin D and B12), minerals are inorganic (such as magnesium and iron). For both: too little causes complaints, and you often notice it only once the deficiency has existed for a while.

What are the symptoms of a vitamin deficiency?

The symptoms depend on which vitamin you lack. Common complaints are persistent fatigue, hair loss, pale skin, tingling in hands or feet, muscle cramps, mouth ulcers and low moods. Because these complaints are broad, they do not automatically point to a specific cause.

What makes it tricky: fatigue can just as well come from your thyroid, your iron or your sleep. That is why the pattern matters. Tingling together with fatigue and concentration problems, for example, fits a vitamin B12 deficiency better than fatigue alone.

• Fatigue and low energy: can be linked to vitamin B12, vitamin D or iron
• Tingling or numbness: fit a vitamin B12 deficiency
• Muscle cramps and tremors: can point to too little magnesium
• Hair loss and brittle nails: often linked to iron, vitamin D or folate
• Pale skin and shortness of breath: can fit anaemia from iron, B12 or folate
• Bone pain and muscle weakness: are classic signs of a vitamin D deficiency

Which vitamin deficiencies are most common?

In the Netherlands, four deficiencies are by far the most common: vitamin D, vitamin B12, folate and iron (measured via ferritin). Magnesium follows at some distance. These substances come from food and, for vitamin D, mainly from sunlight, which makes the risk groups clearly identifiable.

• Vitamin D: at the end of winter, according to the RIVM, a considerable share of people in the Netherlands has too low a level. You make it mainly in your skin under the influence of sunlight. Read more about vitamin D deficiency and the symptoms and how serious a deficiency is.
• Vitamin B12: a risk for vegans, vegetarians and older adults, and with stomach or bowel problems. See the risk groups for a B12 deficiency.
• Folate (vitamin B11): important when trying to conceive and in the first weeks of pregnancy. The Voedingscentrum then advises 400 micrograms per day. Read more about folate deficiency and pregnancy.
• Iron: women with heavy menstruation are particularly at risk. You assess iron via your ferritin.
• Magnesium: a deficiency can be linked to muscle cramps, fatigue and a restless feeling.

How do you know which vitamin you are short of?

From your symptoms alone you cannot tell which vitamin you lack, because many symptoms overlap. A targeted blood value gives clarity. The table below links common complaints to the vitamin or mineral that may be behind them, and to the value you should have checked.

An abnormal value is not a diagnosis. It shows where something may be going on, so you and your GP can look further in a targeted way.

Vitamins versus minerals: what do you test for?

The words vitamin deficiency and mineral deficiency are often mixed up, but the distinction helps you choose a test. Vitamins are organic compounds your body largely cannot make itself, with vitamin D as the well-known exception because you produce it in your skin under the influence of sunlight. Minerals such as iron, magnesium and calcium are inorganic building blocks you must get entirely from food.

In practice this means that with vague complaints you rarely need to measure everything at once. If fatigue goes with a plant-based diet, vitamin B12 and iron (via ferritin) come first. If there are muscle cramps, magnesium is more logical. If it concerns bone complaints or a lack of sun, you look at vitamin D and possibly calcium. By choosing the logical combination that fits your situation, you get a usable answer without unnecessary measurements.

What does a result say and not say?

A blood value is a snapshot. Some values, such as folate, fluctuate with what you ate over the past few days, while others, such as ferritin, also rise with inflammation and can then mask a deficiency. That is why a doctor never looks at a single number, but at the pattern of several values together with your symptoms. A vitamin B12 just within range in someone with tingling calls for a different conclusion than the same value in someone without symptoms.

That is also why at Vitalcheck every result is accompanied by a professional assessment from a BIG-registered doctor. A number next to a reference value says little on its own: the interpretation in your context makes it usable. If your values deviate, the logical next step is a conversation with your GP, who can connect the picture to your history and, if needed, arrange follow-up tests.

Can you test a vitamin deficiency with a blood test?

Yes, a blood test is the most reliable way to establish a vitamin deficiency. In the laboratory, the amount of a vitamin or mineral in your blood is measured. For vitamin D, vitamin B12, folate, iron and magnesium there are clear, validated assays.

Important to know: both GPs via the NHG and the Gezondheidsraad point out that randomly testing many vitamins often yields little. Testing is mainly useful if you have symptoms or belong to a risk group, think of a plant-based diet, little sunlight, older age, a wish to conceive or stomach and bowel complaints. Less useful is having your whole vitamin panel measured without symptoms or risk factors. A targeted test based on your situation gives more value than a broad screen.

If you want to decide what to test, a custom test lets you choose exactly the values that fit your complaints, or you choose the ready-made B-vitamins panel. If fatigue is among your complaints, the tiredness panel looks more broadly, and the basic health checkup gives a broad picture of your key values. If you are unsure which vitamins make sense in your case, work through the vitamin check.

Which blood values are involved?

The four most commonly measured values when a vitamin deficiency is suspected are:

• Vitamin D (25-OH), the most common deficiency in the Netherlands
• Vitamin B12, relevant with fatigue plus tingling
• Folate, especially around a wish to conceive
• Ferritin and iron, for your iron stores

With muscle cramps or a restless feeling, magnesium can also be relevant. If you want a broader health picture that goes beyond vitamins alone, look at the annual blood test.

When is testing useful and when not?

The difference between a useful and a redundant test lies in the reason for it. A specific reason makes the result usable, while measuring without a reason often only raises questions. These rules of thumb help you choose:

• Useful: you have complaints that fit a deficiency, such as persistent fatigue, tingling or hair loss that cannot be otherwise explained.
• Useful: you belong to a risk group, for example through a plant-based diet, little sunlight, older age or a wish to conceive.
• Useful: you already take a supplement and want to know whether your dose is enough.
• Less useful: you have no complaints and no risk factors, but want everything measured just in case.

If you doubt whether your situation gives a reason to test, discuss it with your GP. They can judge whether a targeted measurement adds something or whether you should first rule out other causes. This prevents you from starting to take supplements based on an incidentally abnormal value without it being necessary.

What can you do about a vitamin deficiency?

With a proven deficiency you usually start at the cause: your diet, your lifestyle and possibly a supplement. Which approach fits depends on which vitamin is too low and how large the deficiency is. Discuss this with your GP, certainly if the deficiency is large.

• Diet: oily fish, eggs, meat, dairy, legumes and green leafy vegetables provide most vitamins and minerals.
• Sunlight: for vitamin D, being outdoors is the main source. In the Dutch winter that is often not enough.
• Supplements: the Health Council advises some groups (such as women over 50 and men over 70) to take vitamin D. Read how much vitamin D you need per day. For other deficiencies a supplement may be needed on your doctor's advice.
• Follow-up: after a while you can have your value measured again to see whether the approach is working.

Prevention is better: how do you keep your values up?

The best way to prevent a deficiency is a varied diet, with enough vegetables, legumes, wholegrain products and, if you eat them, fish, meat, eggs and dairy. For most vitamins and minerals such a pattern provides more than enough. Vitamin D is the big exception: even with a perfect plate you cannot manage in the Dutch winter without sun or a supplement, which is exactly why the Gezondheidsraad and the Voedingscentrum advise certain groups to supplement year-round.

If you belong to a risk group, it is smart to adjust your lifestyle accordingly rather than wait until complaints appear. A vegan who takes B12 as standard, a woman with a wish to conceive who starts folic acid in time, or an older person who takes vitamin D year-round: these are not excessive precautions, but targeted measures that get ahead of a deficiency. A periodic check of the values that matter to you helps you see whether your approach is working and gives peace of mind when all is well.

Frequently asked questions

How quickly do you notice a vitamin deficiency?

That differs per vitamin. A deficiency usually builds up over weeks to months. As a result the first complaints are often vague, such as a little more fatigue than normal.

Which vitamin most often causes fatigue?

Fatigue fits several deficiencies. Vitamin B12, vitamin D and iron are the most common culprits. A blood value shows which of the three is at play.

Do I need to fast for a vitamin test?

For most vitamin assays you do not need to fast. If your iron or glucose is measured alongside, fasting blood may be requested. Follow the advice with your test.

My closing advice: do not let yourself be driven mad by symptom lists online. Fatigue or hair loss says little on its own. If you have symptoms or belong to a risk group, have the values that matter for your situation measured in a targeted way. 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.

Further reading

• Zinc, selenium and copper in your blood
• Which B vitamins there are and what they do
• When measuring vitamin C makes sense

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 B12: what if you have too little? Accessed 2026.
• Voedingscentrum. Folic acid and pregnancy. Accessed 2026.