In a patient with a serum zinc level of 59 µg/dL and a brown longitudinal melanonychia, how much elemental zinc is provided by over‑the‑counter multivitamins such as Centrum Silver, and what nail abnormalities are typically seen in zinc deficiency?

Zinc Content in OTC Multivitamins and Nail Changes in Zinc Deficiency

Zinc Content in Centrum Silver

Standard over-the-counter multivitamins like Centrum Silver typically contain 15 mg of elemental zinc daily, which represents the routine daily maintenance dose recommended for adults. 1

• The 15 mg zinc content in standard multivitamins matches the recommended daily maintenance supplementation for adults according to bariatric surgery and micronutrient guidelines 1, 2
• This dose is designed for prevention rather than treatment of deficiency 1
• For comparison, therapeutic zinc supplementation for documented deficiency requires 0.5-1 mg/kg per day (approximately 30-60 mg daily for most adults) for 3-4 months 1, 3, 4

Nail Changes Associated with Zinc Deficiency

Zinc deficiency does not typically cause longitudinal melanonychia; the characteristic nail findings are leukonychia (white discoloration), paronychia, and brittle nails. 5, 6

Classic Nail Manifestations of Zinc Deficiency:

• Leukonychia (white nail discoloration) is the most recognized nail finding in zinc deficiency, which can present as longitudinal white bands 7
• Brittle, fragile nails that break easily 5, 6
• Paronychia (inflammation around the nail fold) 5, 6
• Slow nail growth and poor nail quality 6

Important Clinical Distinction:

• Brown longitudinal melanonychia is NOT a typical manifestation of zinc deficiency 5, 6
• Melanonychia suggests melanin deposition and warrants evaluation for other causes including benign melanocytic activation, subungual hematoma, or melanoma 6
• The serum zinc level of 59 µg/dL is below the normal range of 84-159 µg/dL, confirming zinc deficiency 8

Treatment Implications for This Patient

With documented zinc deficiency (59 µg/dL), the 15 mg in Centrum Silver is insufficient for repletion and therapeutic supplementation of 30-60 mg elemental zinc daily is required. 1, 3, 4

• Therapeutic dosing should be 0.5-1 mg/kg per day for 3-4 months 1, 4
• Zinc gluconate, zinc citrate, or zinc orotate are preferred over zinc sulfate due to better tolerability 3, 2
• Monitor copper levels concurrently, maintaining a zinc-to-copper ratio of 8-15:1 to prevent copper deficiency 3, 2
• Recheck zinc levels after 3 months of therapeutic supplementation 4
• The melanonychia requires separate dermatologic evaluation as it is not explained by zinc deficiency alone 6