Published on 24 May 2026 · Last updated on 24 May 2026.
Fingernails grow about 3 millimetres per month, which means they store several months of signals from your body. Ridges, white spots or a spoon-shaped curve can point to a shortage of iron, vitamin B12, zinc or thyroid hormone. Read them as a reason to test, not as a diagnosis.
I grew up thinking nails were mostly a beauty thing. That is a missed opportunity. Nails are one of the few places where blood values from months ago are literally visible. Below is the decoder I use to map a sign to a sensible blood test.
What do healthy nails look like?
A healthy nail is evenly pink, smooth, firm without being brittle, and grows about three millimetres per month. Faint vertical lines increase with age and are usually harmless. Sudden changes in colour, shape or thickness deserve attention, especially when they show up on both hands at the same time.
The anatomy of a nail
Underneath the cuticle sits the nail matrix, the tissue where your nail is actually made. What happens there in week 1 becomes visible at the tip about three to four months later. A horizontal groove (Beau line) therefore works as a time stamp: count back from where the groove sits now.
The nail decoder: seven signs and the blood test that fits
One nail sign never proves one deficiency. But two or three signs together plus complaints like fatigue or hair loss shifts the probability considerably. The table below summarises seven common changes, the most likely blood value, and the Vitalcheck panel that fits.
| What you see | Term | Likely blood value | Evidence | Vitalcheck panel |
|---|---|---|---|---|
| Spoon-shaped nails | Koilonychia | Ferritin, Hb | Strong | prime-iron-studies |
| Vertical ridges | Onychorrhexis | Usually age; sometimes ferritin or B12 | Weak to moderate | b-vitamins-panel |
| Horizontal groove | Beau line | Prior systemic stress: fever, infection, chemo, malnutrition | Strong | basic-health-checkup |
| Small white dots | Punctate leukonychia | Usually trauma; sometimes zinc | Weak | b-vitamins-panel (zinc) |
| Wide white bands | Mees lines | Possible metal toxicity, chemo, kidney failure (red flag) | Strong | See your GP |
| Brittle, splitting nails | Onychoschizia | Thyroid (TSH), ferritin, sometimes biotin | Moderate | prime-thyroid-function |
| Pale nail beds | Pallor | Anaemia: Hb, ferritin, B12 | Strong | anemia-panel |
What do ridges in your nails mean?
Vertical ridges from cuticle to tip are usually a harmless sign of aging, similar to wrinkles. Horizontal ridges (Beau lines) are different: they form after a short period when your nail matrix briefly stopped producing properly. Think a week of high fever, surgery or heavy medication. Count back three to four months from where the groove is now.
Which vitamin deficiency can you recognise from your nails?
The four deficiencies your nails reveal most clearly are iron, vitamin B12, zinc and thyroid hormone. Biotin is often mentioned, but the evidence for biotin as a cause of brittle nails is limited and mostly based on small, older studies. Honest hedging belongs here.
Iron and ferritin: koilonychia
Spoon-shaped nails, where the centre dips and the edges curl up, are a classic sign of long-term iron deficiency. The phenomenon can appear before your haemoglobin drops below the official threshold. Ask for ferritin, not just a full blood count.
Vitamin B12: ridges and discolouration
B12 deficiency is linked in the literature to bluish-grey nail discolouration and longitudinal streaks. Vegetarians, older adults and users of acid suppressants carry a higher risk. See our B12 explainer.
Zinc: slow growth and white marks
Prolonged zinc deficiency can slow nail growth and produce white spots or bands. Most white spots are simply trauma, though. Zinc becomes a serious hypothesis only when multiple signs cluster.
Biotin (B7): the honest take
Biotin is sold as a miracle cure for brittle nails. The scientific support is thin. Deficiency is rare in the Netherlands, and high biotin doses can interfere with thyroid blood tests. Do not start biotin shortly before a blood draw.
What do white spots on your nails mean?
White spots are caused by tiny trauma to the nail matrix in 80 to 90% of cases, becoming visible only weeks later. Zinc deficiency is a less common cause. Wide white bands across the whole nail (Mees lines) are a different matter and point to a serious signal.
What does the colour of your nail say?
Colour is perhaps the fastest signal. A uniformly pink nail is good news. Pale beds on both hands can point to anaemia. Yellow or bluish nails and a sudden brown or black streak each require a different next step.
Pale: think anaemia
Press the tip of the nail for a second. The pink colour should return within two seconds. If it returns slowly, or if the nail stays structurally pale, a Hb, ferritin and B12 test is a logical next step.
Yellow: fungus, sometimes thyroid or liver
Yellow nails most often come from fungus or nicotine use. Combined with cough, oedema or fatigue, a thyroid or liver assessment can make sense.
Bluish: oxygen or circulation
Bluish discolouration can indicate low blood oxygen or a circulation problem. Sudden blue with breathlessness is a reason to seek medical help right away.
Brown or black streak: red flag
A new dark vertical streak under a single nail, especially if it widens or spreads into the skin, can be melanoma. This is not a vitamin issue. See your GP or a dermatologist within a few weeks.
Red flags: this is not a vitamin issue
- New dark streak under one nail (possible melanoma)
- Wide white Mees lines on multiple nails
- Sudden clubbing (nails curving over fingertips)
- Splinter haemorrhages with fever
- Sudden bluish nails with breathlessness
In these cases, do not order a blood test, contact your GP the same week.
When should you see a GP or order a blood test?
Three questions guide the choice between watchful waiting, blood testing and a GP visit: how long the change has existed, how many fingers show it, and which other complaints co-occur. Less than four weeks on one finger? Often fine to wait it out. Both hands plus fatigue or hair loss? Time for a targeted blood test.
A simple three-step decision aid
- Photograph one hand. Date it and compare again in four weeks.
- Tally other signals. Fatigue, hair loss, cold hands, concentration issues, racing or sluggish heart rate. More than two of those together increases the value of a blood test.
- Pick the right test. One signal? Test narrowly. Multiple signals plus fatigue? Test broadly. See the panel guide below.
Which Vitalcheck test fits which signal?
- Spoon-shape, pale or brittle plus fatigue: iron and ferritin or anemia panel.
- Ridges plus tingling or memory issues: B-vitamins panel.
- Brittle plus cold, weight gain or slow digestion: thyroid function.
- Multiple signals, no idea where to start: basic health checkup.
The practical rule we use
A single nail sign never proves a diagnosis. But two different changes on both hands, together with persistent fatigue, is a clear moment for us to check ferritin, B12 and TSH. Three values, one blood draw, three to five working days of waiting.
What to do this week
Keep one hand in a notes app for a week. Photo on day 1, photo on day 7, a short line on how you feel. Multiple signals clustering? A targeted basic health checkup via Vitalcheck is drawn and interpreted within three working days. Always discuss the result with your own GP: a blood test is a starting point, not a final diagnosis.
Frequently asked questions
How fast do nail changes grow out?
A fingernail replaces itself in about six months, a toenail in twelve to eighteen months. With a Beau line, count back three to four months to estimate when the matrix briefly faltered.
Does insurance cover a blood test for nail-related complaints?
Blood tests ordered by your GP are usually covered under basic Dutch health insurance (after deductible). Tests you order yourself without a referral are paid out of pocket. Some supplementary plans partially reimburse preventive testing.
Can stress alone cause nail changes?
Yes. A week of high fever or significant psychological stress can briefly disturb the nail matrix and produce a Beau line. Chronic stress often creates clusters: thinner nails, hair loss, poor sleep. A broad panel can help rule out nutritional and hormonal deficiencies.
Does biotin really help brittle nails?
The evidence is thin and based on small, older studies. High biotin doses can also interfere with thyroid and troponin blood tests. Practical advice: test first, then supplement with guidance if needed.
References
- Cashman MW, Sloan SB. Nutrition and nail disease. Clinics in Dermatology. 2010;28(4):420-425. PMID: 20620759.
- Iorizzo M, Pazzaglia M, Piraccini BM, et al. Brittle nails. Journal of Cosmetic Dermatology. 2004;3(3):138-144. PMID: 17163964.
- Lipner SR, Scher RK. Biotin for the treatment of nail disease: what is the evidence? Journal of Dermatological Treatment. 2018;29(4):411-414. PMID: 28954540.
- NHG-Standaard Anemie (M76). Dutch College of General Practitioners. 2024 version.
- RIVM. Vitamin and mineral status of the Dutch population. 2023.
About this article
Written with AI assistance by the Vitalcheck editorial team and fact-checked against the primary sources listed above. Last updated 24 May 2026.
Disclaimer: this article is general information and does not replace medical advice, diagnosis or treatment. If you have health concerns, contact your GP. A blood test is a tool to make decisions with your doctor, not a final diagnosis.
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