Nutritional Deficiencies Causing Metallic Taste
Zinc deficiency is the primary nutritional deficiency that causes metallic taste and altered taste perception, though vitamin B12 deficiency can also contribute to taste disturbances. 1
Zinc Deficiency as the Primary Cause
Zinc deficiency directly impairs taste function through multiple mechanisms affecting taste bud structure, nerve transmission, and central taste processing. 2 The clinical manifestations include:
- Dysgeusia (altered taste, including metallic taste) and hypogeusia (decreased taste sensation) are hallmark symptoms of zinc deficiency 1, 3
- Blunting of taste and smell occurs in severe zinc deficiency 1
- Taste changes specifically manifest as metallic taste perception in zinc-deficient patients 1
Diagnostic Considerations for Zinc
Measure serum or plasma zinc levels (normal range: 10.7-22.9 μmol/L or 70-150 μg/dL), but always check inflammatory markers (CRP) simultaneously, as inflammation falsely lowers zinc levels when CRP exceeds 20 mg/L. 1, 3
High-Risk Populations for Zinc Deficiency
Screen patients with metallic taste who have: 1, 3
- Bariatric surgery history (especially RYGB, BPD/DS, or sleeve gastrectomy)
- Gastrointestinal disorders (inflammatory bowel disease, chronic pancreatitis, malabsorption syndromes)
- Chronic alcohol use
- Elderly age (particularly those with poor protein intake)
- Pregnancy (increased requirements)
Vitamin B12 Deficiency
Vitamin B12 deficiency can cause taste disturbances, though metallic taste is less consistently reported than with zinc deficiency. 1
- B12 deficiency occurs commonly after bariatric surgery due to reduced intrinsic factor and hydrochloric acid production 1
- Neurological symptoms (numbness, tingling) often accompany the taste changes 1
- Deficiency can occur even when serum B12 levels are 300 pmol/L, requiring additional testing (methylmalonic acid, homocysteine, holotranscobalamin) for confirmation 1
Iron Deficiency
Iron deficiency causes hypogeusia (decreased taste) rather than metallic taste specifically. 4
- Seven of 25 patients with decreased taste sensation had iron deficiency as the identified cause 4
- Iron deficiency does not typically produce the metallic taste quality that zinc deficiency does 4
Other Nutritional Considerations
Copper deficiency should be considered if the patient has been taking high-dose zinc supplements (≥30 mg daily), as zinc-induced copper deficiency can cause additional neurological symptoms. 1
Clinical Pitfalls to Avoid
- Do not interpret low zinc levels during acute illness or inflammation as true deficiency—zinc redistributes to the liver during inflammatory responses, causing falsely low plasma values 1
- Do not assume normal serum zinc excludes deficiency in patients post-bariatric surgery—functional deficiency can exist despite borderline-normal levels 1
- Do not overlook medication-induced dysgeusia—many drugs cause metallic taste independent of nutritional status 5, 4
- Do not confuse burning mouth syndrome with nutritional deficiency—BMS patients report metallic taste but typically have normal laboratory values and represent a neuropathic pain disorder 5
Treatment Approach When Zinc Deficiency Confirmed
Administer 30-70 mg elemental zinc daily (0.5-1 mg/kg) for 3-4 months, using organic forms (zinc gluconate, zinc citrate, zinc glycinate) for better tolerability. 1, 6