You've seen the list. Here's what the list doesn't say: what studies have measured, and why you're still missing out even when eating "well".

1. 1
   Chapped lipsB2, B3, B6, ironThe little cracks at the corners of the mouth have a name, angular cheilitis, and it's a classic sign of iron and B2 deficiency in internal medicine. Balm soothes, it doesn't fix anything: it's solved from within.
2. 2
   Dandruffzinc, B6, omega 3The active ingredient in the best-selling anti-dandruff shampoo in the world? Zinc pyrithione. Zinc. You put it on your head while your body lacks it inside.
3. 3
   Headachesmagnesium, B2Trial published in Neurology: 400 mg of B2 per day for 3 months, 59% of migraine sufferers halved their attacks, compared to 15% under placebo. And 77% of French women do not reach the recommended magnesium intake.
4. 4
   Constant fatigueB12, D, ironYour blood test can be "normal" and you can still lack iron. In 198 non-anemic women with ferritin below 50, 12 weeks of iron reduced fatigue by 48%. Ask for your ferritin, not just your hemoglobin.
5. 5
   WeaknessB1, D, magnesium80% of French adults are below the vitamin D threshold, and the risk of deficiency increases sevenfold between January and March. Muscle weakness is one of the first signs, long before the bones.
6. 6
   Hair lossbiotin, A, EStudy on 5,110 women: those who lose their hair more often have ferritin below 40. The body rations iron, vital organs first, hair last. That's why they fall out before you feel tired.
7. 7
   Brittle nailsbiotin, D, zinc2.5 mg of biotin per day: nail thickness +25% in a clinical study. But a nail takes 6 months to completely renew. What you see today is what you ate in the spring.
8. 8
   Dry skinC, E, omega 3Without vitamin C, your cells cannot assemble collagen: it is the mandatory cofactor of the enzyme. A collagen cream does not cross the skin. Vitamin C, on the other hand, arrives on the plate.
9. 9
   AcneA, zinc, E2024 study: blood zinc 79 µg/dL in people with acne compared to 105 in others, vitamin D 17 compared to 28. And the pill lowers zinc and B6. No one tells you when they prescribe it to you.
10. 10
    Mood swingsD, B6, magnesiumSerotonin is made from tryptophan, and the enzyme needs B6. PLOS One trial: 248 mg of magnesium per day, mood improved in 2 weeks, effect disappeared upon discontinuation. No ingredients, no serotonin.