Nails grow about 3 millimetres a month and therefore store months of signals from your body. Ridges, white spots or a spoon-shaped curve can point to a deficiency of iron, vitamin B12, zinc or thyroid hormone. Read them as a reason to test in a targeted way, not as a diagnosis.
My stance up front: a nail is no oracle. A single sign never proves a deficiency, but two or three signs together with complaints like fatigue or hair loss shift the probability seriously. That is exactly the moment to look in a targeted way instead of guessing.
What do healthy nails look like?
A healthy nail is evenly pink, smooth, firm without being brittle, and grows about three millimetres a month. Faint vertical lines increase with age and are usually harmless. Sudden changes in colour, shape or thickness do deserve attention, especially when they affect both hands. Under the cuticle lies the nail matrix, where your nail is actually made. What happens there, you only read three to four months later at the tip of your nail.
The nail decoder: seven signals and the matching blood value
Below are the seven changes that come up most often, linked to the most likely blood value, the level of evidence and the matching Vitalcheck panel. A nail sign never proves a deficiency: use the table as a line of reasoning to discuss with your doctor.
| What you see | Term | Likely blood value | Evidence | Matching test |
|---|---|---|---|---|
| Spoon-shaped nails (dip in the middle) | Koilonychia | Ferritin, Hb | Strong | Iron studies |
| Vertical ridges | Onychorrhexis | Often ageing; sometimes ferritin or B12 | Weak to moderate | B vitamins |
| Horizontal groove across the nail | Beau's line | Past systemic stress: fever, infection, chemo | Strong | Basic health checkup |
| Small white spots | Leukonychia punctata | Usually trauma; sometimes zinc | Weak | B vitamins |
| Broad white bands across the whole nail | Mees' lines | Possible metal poisoning, chemo, kidney failure (red flag) | Strong | Straight to your GP |
| Brittle, splitting nails | Onychoschizia | Thyroid (TSH), ferritin | Moderate | Thyroid function |
| Pale nail beds | Pallor | Anaemia: Hb, ferritin, B12 | Strong | Anaemia panel |
What do ridges in your nails mean?
Vertical ridges (from cuticle to tip) are usually a harmless sign of ageing, comparable to wrinkles. Horizontal ridges, the so-called Beau's lines, are different: they form after a short period in which your nail matrix briefly faltered, such as a week with high fever or heavy medication. A Beau's line 3 mm from the cuticle roughly means an event a month ago; at 9 mm you are around three months back. If vertical ridges go together with hair loss, fatigue or a red tongue, it is wise to test vitamin B12 and ferritin.
Which vitamin deficiency can you recognise in your nails?
The four deficiencies your nails can reveal most clearly are iron, vitamin B12, zinc and thyroid hormone. Biotin is often mentioned, but the evidence for it is limited and largely from small, old studies. Honest hedging belongs here.
Iron and ferritin: koilonychia
Spoon-shaped nails, where the middle dips and the edges rise, are a classic sign of prolonged iron deficiency. It can occur before your haemoglobin officially drops below the threshold. When in doubt, ask for ferritin, not just the blood count.
Vitamin B12: ridges and colour change
B12 deficiency is associated with blue-grey discolouration and longitudinal streaks. Vegetarians, older people and users of stomach acid inhibitors are at higher risk. The RIVM names these groups in the vitamin status of the Dutch population.
Zinc: slow growth and white spots
With prolonged zinc deficiency, nails grow more slowly and white spots can appear. Note: most white dots come from a knock, not from zinc. Only when several signs converge does zinc become a serious hypothesis.
Biotin (B7): honest about the evidence
Biotin is presented in supplement advertising as a miracle cure, but the support is thin. A deficiency is rare in the Netherlands, and high doses can disrupt thyroid test results. Do not start biotin just before having blood drawn.
What does the colour of your nail say?
Colour is perhaps the fastest signal. An evenly pink nail is good news. A pale nail bed on both hands can point to anaemia: press the tip for a second, the pink colour should return within two seconds. Yellowed nails come most often from fungus or smoking. A bluish discolouration can indicate a lack of oxygen or a circulation problem; sudden blueness with shortness of breath is a reason to seek medical help immediately. A new, dark vertical streak under a nail that is widening can be a melanoma. That is not a vitamin issue: have it assessed within a few weeks by a GP or dermatologist.
When to see your GP or have a blood test?
Three questions help you choose between waiting, a blood test or a GP visit: since when has the change existed, on how many fingers do you see it, and which other complaints are present. Shorter than four weeks on one finger? Often just wait for it to grow out. On both hands plus fatigue or hair loss? Time for a targeted blood test.
- Spoon-shaped, pale or brittle plus fatigue: iron and ferritin testing or the anaemia panel.
- Ridges plus tingling or memory complaints: test B vitamins.
- Brittle plus feeling cold or weight gain: measure thyroid function.
- Several signals, no idea where to start: basic health checkup.
Red flags that are not a vitamin issue and call for a GP the same week: a new dark streak under a nail, broad white Mees' lines on several nails, sudden clubbing, or sudden blueness with shortness of breath.
Frequently asked questions
How fast do changes grow out again?
A fingernail replaces itself in about six months, a toenail in twelve to eighteen months. With a Beau's line, count back three to four months for the moment the nail matrix briefly faltered.
Do I need to fast for a nail-related blood test?
For ferritin, B12, TSH and zinc, fasting is not strictly needed. For glucose and cholesterol it is. The instructions with your order tell you exactly what to do.
Does biotin really help for brittle nails?
The evidence is thin and based on small, older studies. High doses can also disrupt thyroid and troponin tests. Practically: test first, then supplement under guidance if needed.
Can stress alone cause nail changes?
Yes. A week with high fever or heavy stress can briefly disrupt the nail matrix and produce a Beau's line. With chronic stress you often see combinations with hair loss and poor sleep.
Sources
- NHG (Dutch College of General Practitioners). NHG anaemia guideline. Accessed 2026.
- RIVM (National Institute for Public Health). Vitamin and mineral status of the Dutch population. Accessed 2026.
Every blood test result at Vitalcheck includes a professional assessment by a BIG-registered doctor. A blood test is a tool to make decisions together with your doctor, not a final diagnosis.
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