A Slow Recording Of The Last Six Months

Six months of history, visible

A fingernail grows roughly three millimetres a month and takes about six months to replace itself entirely. A toenail takes twelve to eighteen. Which means the plate you are looking at was manufactured over the preceding half year, and anything that disrupted production is still recorded in it — slowly travelling outward.

That single fact explains why nails are the first place people notice a change after starting a supplement. New growth arrives as a visible boundary at the base, and you can literally point at where the change began. Skin replaces itself invisibly, everywhere, at once, which is why the same person swears their nails improved and cannot tell you anything about their face.

Changes that usually mean very little

• Vertical ridges running base to tip. Almost universal with age and almost always nothing. They are the equivalent of wrinkles on a nail.
• White flecks. Not calcium deficiency, whatever the folklore says. They are minor trauma to the nail matrix weeks earlier — a knock you have entirely forgotten.
• Peeling at the free edge. Usually water and detergent rather than nutrition. Repeated wetting and drying delaminates the plate.
• Slightly different growth rates between hands. Normal. The dominant hand grows faster.

Changes worth a second look

• Horizontal grooves across the whole nail. Beau’s lines. They record an event that halted growth — a serious illness, a high fever, chemotherapy. Measure how far up the nail the line sits and divide by three millimetres a month to date it, which is a genuinely useful piece of bedside arithmetic.
• Spoon-shaped nails, concave enough to hold a droplet. Koilonychia, classically associated with iron deficiency and worth a blood test.
• Persistently brittle, splitting nails in somebody whose hands are not constantly wet. This is the one place biotin has a genuine if mixed evidence base.
• Nails that lift away from the bed. Onycholysis, which has many causes including thyroid disease, psoriasis and fungal infection.

Changes that need an appointment

Also: nails clubbing outward and downward around swollen fingertips, which is associated with lung and heart conditions; a nail suddenly thickening, crumbling or changing colour, which is usually fungal but occasionally not; and any nail change accompanied by pain, swelling or discharge.

Where nutrition genuinely comes in

Nail plate is keratin, keratin is protein, and protein is built from amino acids. The nutrients involved in handling those amino acids are Biotin, Zinc and Vitamin B12, which is why they appear together on a panel aimed at nails.

The honest boundary is the same as everywhere else on this site. In genuine deficiency the nail changes are real and correcting the shortfall reverses them. In somebody eating normally the effect of extra is much smaller, and the two or three small older studies on high-dose biotin and brittle nails are the closest thing to positive evidence in the whole category — which is a modest claim, honestly stated.

Meanwhile the most effective thing most people can do for brittle nails costs nothing: wear gloves for washing up, stop using them as tools, and moisturise the nail fold. Water is the enemy of a nail plate and no supplement outruns a sink.