Iron deficiency is the most common nutritional cause of ridges in fingernails, particularly vertical ridges that run from the base of the nail to the tip. Zinc deficiency is the primary nutritional cause of horizontal ridges. But before assuming a deficiency is to blame, it helps to know that the type of ridge matters, and the most common cause of vertical ridges isn’t a deficiency at all.
Vertical vs. Horizontal Ridges
Ridges in your nails fall into two distinct categories, and they signal very different things. Vertical ridges run lengthwise from the cuticle to the tip. Horizontal ridges, called Beau’s lines, run side to side across the nail. The direction tells you whether the nail’s structure is gradually changing over time (vertical) or whether something briefly interrupted nail growth at a specific point (horizontal).
This distinction matters because the causes are completely different. Vertical ridges tend to reflect long-term or chronic conditions. Horizontal ridges point to a temporary disruption, something that paused nail growth for a period before it resumed.
Iron Deficiency and Vertical Ridges
Iron deficiency is the nutrient most strongly linked to vertical nail ridges. Low iron affects how your body builds the protein that makes up the nail plate, leading to thin, ridged nails that may also become brittle. In more advanced cases, the nails can develop a concave, spoon-like shape known as koilonychia, where the center dips inward while the edges rise.
Central ridges running down the middle of the nail can also result from low iron, folic acid, or protein intake. Iron and folic acid both play roles in cell division, and your nail matrix (the tissue under your cuticle that produces the nail) is one of the faster-growing tissues in your body. When the raw materials run short, the nail plate it produces is uneven.
If your ridges appeared gradually alongside fatigue, pale skin, or cold hands, iron deficiency is worth investigating with a simple blood test.
Zinc Deficiency and Horizontal Ridges
Zinc deficiency is the nutrient deficiency most associated with horizontal ridges. These dents form when your body temporarily stops growing the nail, creating a visible groove that slowly moves forward as the nail grows out. Severe zinc deficiency or inadequate protein intake can trigger this pause. You may also notice white spots on the nails alongside the ridges.
Horizontal ridges aren’t always nutritional, though. High fevers from illnesses like COVID-19, pneumonia, or measles can cause them. So can chemotherapy, major physical stress, or injury to the nail itself. The common thread is that something significant disrupted normal nail production for a short window of time. Once the cause resolves, normal growth resumes and the ridge eventually grows out.
Protein and Amino Acid Deficiency
Your nails are made almost entirely of keratin, a protein held together by sulfur-containing amino acids, especially cystine. When protein intake drops significantly, the nail plate becomes thinner and more prone to ridging, splitting, and peeling into horizontal layers. This is less common in developed countries but can affect people with very restrictive diets, eating disorders, or conditions that impair nutrient absorption.
Nail hardness depends directly on these protein cross-links. Without enough of the right amino acids, the nail structure weakens from the inside out, producing visible surface changes that overlap with what deficiencies in iron or zinc can cause.
Thyroid Disease and Other Non-Nutritional Causes
Not every ridged nail points to a missing nutrient. Hypothyroidism (an underactive thyroid) commonly causes thick, brittle nails with vertical ridges. Eczema and chronically dry skin can produce similar changes. Peripheral vascular disease, which reduces blood flow to the extremities, can trigger horizontal ridges by starving the nail matrix of oxygen and nutrients even when your diet is adequate.
And the single most common cause of vertical ridges is simply aging. In one study of elderly patients, 85% had prominent longitudinal ridges on their nails. The nail matrix naturally becomes less uniform with age, producing slight variations in thickness that show up as fine lines running the length of the nail. If you’re over 50 and the ridges appeared gradually on most of your nails, aging is the likeliest explanation.
What About Biotin, Calcium, and Magnesium?
Biotin is the supplement you’ll see recommended most often for nail problems. Some research suggests it can help strengthen weak or brittle nails, but the evidence is limited and mostly applies to brittleness rather than ridging specifically. True biotin deficiency is rare in people eating a varied diet.
Calcium and magnesium deficiencies are frequently blamed for nail ridges in popular health content, but there is little rigorous scientific evidence linking either mineral directly to ridged nails. The nutrients with the strongest clinical connections to nail surface changes remain iron, zinc, protein, and folic acid.
How Long Ridges Take to Disappear
Fingernails grow at roughly 0.1 millimeters per day, or about 3 to 4 millimeters per month. A full fingernail takes approximately four to six months to grow from the cuticle to the tip. That means even after you correct a deficiency, existing ridges won’t vanish overnight. You’ll see smooth, healthy nail gradually emerging from the base while the ridged portion slowly moves toward the tip and is eventually trimmed away.
If horizontal Beau’s lines are present, you can roughly estimate when the disruption occurred by measuring how far the ridge is from your cuticle and dividing by 3.5 millimeters per month. A ridge sitting 7 millimeters from the cuticle likely formed about two months ago.
Identifying the Cause
The pattern of ridges across your nails offers useful clues. If only one or two nails are affected, local trauma or injury is more likely than a nutritional deficiency. If all or most nails show the same change, a systemic cause like a deficiency, thyroid problem, or recent illness is more probable.
Vertical ridges on their own, especially if they’ve appeared gradually and you’re over 40, are almost always a normal part of aging. Vertical ridges paired with spoon-shaped nails, unusual fatigue, or brittle texture point more strongly toward iron deficiency. Horizontal grooves across multiple nails suggest something temporarily halted growth, whether that was a zinc shortfall, a severe illness, or a period of major physical stress. A standard blood panel checking iron, ferritin, zinc, thyroid hormones, and folic acid can usually identify or rule out the most common nutritional causes.