Nail Changes and Nutrition: What Do We Know Now?

Our understanding of the role nutrition plays in health and disease states is rapidly expanding. The saying, “You are what you eat,” reflects the broad impact that an individual’s diet can have across all organ systems. A poor diet can cause direct damage to body tissues, harm metabolic processes, and make individuals more susceptible to infections and diseases.

The connection between nutrition and tissue growth has been noted since the early 20th century. Clark and Buxton (1938)¹ and Gilchrist (1939)² completed the earliest reliable studies examining the effect of nutrition on nail growth, showing that nail growth is slower and more variable in poorly nourished school children. To better understand the impact that nutritional deficiencies have on nails it is important to understand basics of nutrition and the roles that many nutrients play in biologic processes.

Nutrients from food broadly divide into 2 categories: macronutrients and micronutrients. Macronutrients are necessary in large quantities and supply all our energy. The main macronutrients include fat, protein, and carbohydrates. After undergoing digestion in the intestines, macronutrients break down into sugars (carbohydrates), amino acids (protein), fatty acids, and glycerol (fats). In addition to providing energy, the body utilizes these basic units as the building blocks for tissue growth, maintenance, and repair.

Micronutrients are essential nutrients that constitute a small amount of our diet. Essential nutrients cannot be synthesized in the body, yet they are required for normal physiologic function so essential micronutrients must be obtained from the diet.

Micronutrients include numerous vitamins and minerals that play essential biochemical and physiologic roles. Metabolic and cellular functions that micronutrients are involved in include metabolism, cellular protection, gene regulation, hormone perception, signal transduction and reproduction.³

Nail pathologies are very common, accounting for approximately 10% of all disorders of the integumentary system.⁴ Hard keratin, high glycine-tyrosine-rich matrix protein, water, lipids, and minerals including magnesium, calcium, iron, zinc, sodium, and copper all make up the nail plate.⁵ With these structural components of nails derived from one’s diet, as well as many micronutrients affecting processes of nail plate growth and repair, many nail pathologies result from, or are influenced by, nutritional deficiencies. In addition to affecting the nail plate, nutritional deficiencies can cause changes in a nail’s appearance by their impact on the nail matrix and nail bed. Nutritional deficiencies can lead to nails that are soft, brittle, thin, fissured, split, peeling, and separated from the bed. These changes can increase an individual’s susceptibility to secondary nail pathologies including trauma and infection.

Owing to the effect on people’s outward appearance, the impact that nutrition has on the health of skin and skin appendages has received considerable attention. In 2023, estimates placed the global skin and nail care nutritional supplement market at $3.55 billion.⁶

While nail changes resulting from nutritional deficiency tend to have limited pathologic effects, they can be an important indicator of nutritional status. Most nail changes are non-specific and can occur secondary to several deficiencies. Since podiatrists are uniquely positioned to identify and help act upon these findings, this article will review changes in the structure and appearance of nails associated with common macro- and micronutrient deficiencies.

Nail Plate Brittleness

Nail plate brittleness is a common nail disorder broadly associated with poor nutrition. It may result from one of many specific nutritional deficiencies. In this disorder, the lack of essential nutrients for nail growth, repair, and metabolism lead to structural alterations in the nail plate. The physical characteristics of nail plate brittleness include splitting, flaking, crumbling, soft, and/or stiff nails. Onychorrhexis (longitudinal nail plate fissures and furrows) and onychoschizia (lamellar peeling of the nail plate) are common clinical presentations of nail plate brittleness that result from protein-calorie malnutrition and other nutritional deficiencies.^7,8

Protein-calorie malnutrition is a state of inadequate food intake that can result in improper levels of all nutrients including protein, fat, carbohydrates, vitamins, and minerals. One of the most common causes of protein-calorie malnutrition is food insecurity, which is the lack of access or lack of guaranteed access to sufficient and quality food in amounts necessary to meet basic nutritional needs. Numerous factors can contribute to food insecurity, including race, low income, unemployment, high housing costs, limited transportation, and geographic distance from sources of fresh, healthy food.⁹ Many pathologies and several nail changes are associated with this nutritional disorder due to its broad effect across all essential nutrients. Additional causes of protein-calorie malnutrition include poor oral intake (common in elderly and chronically ill patients), eating disorders (anorexia nervosa, bulimia), periodontal disease, and malabsorption disorders.

Beau’s Lines

Beau’s lines appear as transverse grooves that run across the width of the nail plate. These nail changes result from temporary disruption of nail growth at the proximal nail matrix.^10–12 The appearance of Beau’s lines reflects the timing of the underlying causative disorder. The width of the groove in the nail plate indicates the timeframe during which the causative disorder occurred, the distance of the groove to the proximal nail fold gives an estimated time of when the insinuating event happened, and multiple lines reflect recurrence of the instigating disorder.^13,14

Beau’s lines are one of the most common nail plate abnormalities. This nail change is nonspecific and occurs with many disorders and disease states including general poor nutrition and specific nutritional deficiencies. Specifically, research has shown Beau’s lines to result from protein-calorie malnutrition, protein malnutrition, hypocalcemia, pellagra, and zinc deficiency.^13,15,16

Longitudinal Melanonychia

Changes in the nail bed can also affect the appearance and structure of the nail plate. Longitudinal melanonychia (melanonychia striata) is a linear, hyperpigmented streak extending along the long axis of the nail plate. This nail abnormality results from increased melanocyte activity and melanin production in the nail bed.¹⁷ As with many nail changes, longitudinal melanonychia is nonspecific and results from many factors including trauma, infection, medication, systemic disease and nutritional deficiencies.

Longitudinal melanonychia is most commonly associated with ethnicity, as this normal variant of the nail plate is visible in individuals with darker skin colors.¹⁷ Specific nutritional deficiencies associated with longitudinal melanonychia include protein-calorie malnutrition, vitamin D deficiency and vitamin B12 deficiency.^13,16,18 Longitudinal melanonychia resulting from vitamin B12 deficiency has a unique presentation, appearing diffusely blue with a reticular or net-like pattern. This nail abnormality results from reduced glutathione levels secondary to vitamin B12 deficiency leading to down regulation of tyrosinase, the only enzyme that inhibits melanin production.¹⁹

Most often longitudinal melanonychia is benign, but there is potential for it to present due to melanocytic hyperplasia secondary to premalignant and malignant pathologies. Characteristics that favor these linear hyperpigmented lesions being benign include age of onset less than 40 years, slow onset and growth, lighter discoloration, band width less than 3mm, no color variation, distinct borders, absence of associated nail plate changes, multiple lesions on multiple toes, uniform streak without proximal widening, absence of nail fold/border involvement and no personal or family history of skin cancer.^17,20 Nail bed and/or nail matrix biopsy is indicated for nail changes exhibiting malignant features.

Leukonychia

Leukonychia is a general term describing white discoloration of a nail. This nail disorder can be classified based on clinical appearance, with forms including total, partial, striate (transverse of longitudinal bands), and punctate.^21,22 Clinicians can also classify leukonychia based on the anatomic structure where the discoloration originates. Anatomic types of leukonychia include true leukonychia (changes in nail plate), apparent leukonychia (changes in subungual tissues), and pseudoleukonychia (changes in the superficial nail plate).^21,22 While leukonychia is typically benign, it can be an important indicator of underlying systemic disorders including nutritional deficiencies.

Muehrcke’s lines. Muehrcke’s lines are a form of apparent leukonychia that result from abnormal vasculature in the nail bed. These lines appear as paired, thin, white transverse bands that run parallel to the nail lunula. Since these lines arise from the nail bed vasculature, they resolve with pressure applied to the nail plate. Muehrcke’s lines are commonly associated with hypoalbuminemia.^16,21,22 Albumin, the most abundant plasma protein, has numerous physiologic roles and is an important marker of nutritional status.^23,24 Hypoalbuminemia can result from protein-calorie malnutrition and specific nutritional deficiencies. With malnutrition, an inadequate supply of amino acids leads to reduced albumin production in the liver.²⁵ Both iron and zinc deficiency are other causes of hypoalbuminemia, with iron deficiency leading to increased gastrointestinal loss of albumin and zinc deficiency leading to reduction in serum albumin from the binding of zinc to albumin for transport in the blood.^26,27 Muehrcke’s lines may resolve with albumin infusions and resolution of hypoalbuminemia.²⁸

Terry’s nails. Terry’s nails are another form of apparent leukonychia that present as white discoloration. This finding is described as ground glass opacification, is found in nearly the entire nail, and is edged by a thin band of normal appearing pink nail bed distally. These nail changes are believed to result from alterations in nail bed vascularity that is caused by an overgrowth of connective tissue.²⁹ Terry’s nails are most frequently associated with liver disease, but can also occur secondary to malnutrition, especially in the elderly. Ohta and colleagues found the presence of Terry’s nails to be associated with malnutrition and increased risk of mortality in older, hospitalized patients.³⁰

Transverse leukonychia. Transverse leukonychia appears as transverse, opaque white bands, typically present at the same location on several nails. This nail plate abnormality is a true leukonychia with the color change resulting from changes in the nail plate. Transverse leukonychia can result from nutritional deficiencies with hypocalcemia being the most common cause of this nail plate change. Both arteriolar spasm and disorganization of hard keratin formation have been proposed as mechanisms by which hypocalcemia leads to the development of transverse leukonychia.²¹ Calcium supplementation and the correction of the causative hypocalcemia are important treatment options for for transverse leukonychia.³¹ The distance of the white band from the proximal nail fold can help determine when the causative event occurred.

Koilonychia

Koilonychia, or “spoon nails,” is a disorder where the normal nail plate curvature is reversed, creating a concave structure to the nail plate. The most common cause of koilonychia is iron deficiency anemia. Deficiency in sulfur-containing amino acids is a less frequent nutritional cause.³² Other potential etiologies of koilonychia include inflammatory arthropathy, repetitive occupational trauma and fungal infection.

Iron deficiency is the most common nutritional deficiency and can result from insufficient oral intake, decreased absorption and blood loss. Due to the essential role of iron in the production of hemoglobin, iron deficiency can lead to the development of iron deficiency anemia that appears microcytic and hypochromic on the peripheral blood smear.³² Iron deficiency anemia is the most common type of anemia, with premenopausal women and children being at the highest risk. Iron deficiency anemia occurs in an estimated 30% of the world’s population,³³ and reports contend that koilonychia occurs in 5.4% of these patients with iron deficiency anemia,³⁴ making koilonychia one of the most frequently observed nail abnormalities.

The pathophysiologic mechanism by which koilonychia develops is unknown. Potential etiologies include nail matrix changes that occur secondary to blood flow abnormalities, disruption of connection tissues below the nail plate, and a decrease in iron-containing enzymes in nail-forming epithelial cells.^35–38

Hapalonychia

Hapalonychia, or “eggshell nails,” is a nail disorder where the nail plate becomes abnormally thin and soft, causing them to easily bend, tear and break. The most common cause of hapalonychia is malnutrition, with specific deficiencies of calcium, vitamin A, vitamin B6, vitamin C and vitamin D cited as having a causative association.^13,16 Macronutrient deficiency may also contribute. Kwashiorkor is a disease state that results from severe protein deficiency with a relative excess of carbohydrates. Clinical findings in Kwashiorkor include muscular wasting, fatty liver, peripheral edema, and hapalonychia.³⁹ Hapalonychia that occurs secondary to the nutritional deficiencies listed above can resolve with treatment of the causative nutritional deficiency.⁴⁰

Nail Clubbing

Nail clubbing is a uniform bulbous swelling of the soft tissues surrounding the distal phalanx that causes flattening of the normal angle between the nail plate and the nail bed. The Lovibond angle is a measurement frequently used to identify nail clubbing. This angle, formed by the proximal nail fold and nail plate, is typically less than or equal to 160 degrees, but in clubbing increases to more than 180 degrees.^41,42

Nail clubbing has been classically associated with pulmonary disease, namely lung cancer, but has other etiologies, including nutritional deficiencies. Congenital iodine deficiency syndrome (CIDS), previously known as cretinism, is a disorder resulting from insufficient dietary iodine intake during pregnancy, which causes insufficient thyroid hormone production at birth. This disorder presents with severe impairments in physical and mental development. Dermatologic manifestations of CIDS include thick skin, hair loss, and clubbed nails. In addition to iodine deficiency, nail clubbing may also occur in association with Kwashiorkor (protein deficiency)⁴³ and vitamin D deficiency.⁴⁴

Splinter Hemorrhages

Splinter hemorrhages appear as red, splinter-like lesions below the nail plate. These nail changes are classically associated with bacterial endocarditis, but other causes include trauma and vitamin C deficiency.

Scurvy results from vitamin C deficiency and presents with variable symptoms including bleeding, arthralgias, skin discoloration, ecchymosis, and splinter hemorrhages.⁴⁵ Scurvy has been noted for centuries, but with supplementation and improved food availability, its incidence is now low. Cases that do occur are often seen with poor dietary habits including in those with alcoholism, advanced age, low income, or chronic illness. In cases of scurvy, vitamin C deficiency weakens both collagen structure and capillaries.

Splinter hemorrhages result from weakened capillaries, allowing the extravasation of blood into grooves on the underside of the nail plate.⁴⁶ Like many nail changes that result from nutritional deficiency, splinter hemorrhages resolve with treatment of the underlying nutritional deficiency and growth of the nail plate.

In Conclusion

It can be easy to dismiss nail changes as occurring secondary to trauma and fungal infection. This review highlights the importance of recognizing nail changes as they may be an important sign of underlying systemic disease. Despite the important role that nutrition plays in both health and disease states, nutrition education is often lacking in U.S. and European medical education programs.⁴⁷ Given the broad impact on our patient’s health, as well as the high number of skin and nail disorders that podiatric physicians encounter, it is extremely important to expand our basic knowledge of nutrition and the role that nutrition status plays in health and disease states that affect the foot and ankle.

Kristine Hoffman, DPM, FACFAS, is the Chief of Podiatry and Director of the Podiatric Medicine and Surgery Residency Program at Denver Health. She is an Associate Professor in the Department of Orthopedics at the University of Colorado School of Medicine.

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